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What is Styrene?

Styrene is both the solvent and cross-linking agent in polyester resins - the resins will all contain a specific amount of styrene in the formulation to give the particular viscosity needed for the end use of the resin. It is possible to add more if you wanted to thin the resin down for any particular reason - generally you can add up to around 3 - 7% before you start to affect the properties of the resin. For instance, you can convert a brush gelcoat to one thin enough to spray by adding styrene, it is commonly used as a prime coat in some boat sheathing applications. Styrene has many other end uses - polystyrene for instance is polymerised styrene which can be used as a plastic sheet or foamed to make polystyrene cups and containers etc. It is a very good solvent for oils and greases etc so can be used to degrease GRP or metals etc before you bond to it.

How many coats of waxes should I apply to a GRP mould? I am producing mudguards.

Before you start waxing your mould, I would recommend post curing your mould: Effective post curing on this small scale can be done and is most effective after 24 hours from the laminate being completed. The catalyst remains active for 2-3 weeks after the parts are made so the post cure should be done before this; Ideally you build up the temperature gradually and leave it for 3-5 hours at the maximum post cure temperature you have chosen, as a general rule, 4 hours at 60°C then 2 hours at 80°C

.How do other manufacturers add Microban to their GRP resins and can I buy this?

Miroban is an anti-bacterial additive which can be added to a wide range of materials - it is supposed to kill bacteria and make the surface safer, but the manufacturers also state that it’s not a substitute for proper cleaning procedures. It can be added to a wide range of things - you see it in chopping boards for food and a whole range of other things. Scott Bader makes a range of gelcoats containing microban which tend to be used to make sanitary ware items - shower trays etc. By adding Microban you can use the Microban Logo etc on the finished item and in publicity, so it’s used as a selling aid. Crystic Microban Gelcoat 65PA - this is GC65PA plus microban additive Crystic Microban Gelcoat 48PA. Crystic Microban Gelcoat 96PA. Crystic Microban 47PA - topcoat with Microban. Hope this helps.

I have a question with regards to Methylene Chloride and fibreglass. I know that it is not recommended but do you know how severe/fast acting the reaction would be?

Cured polyester resins will not really dissolve in organic solvents like acetone or methylene chloride but will soften and swell after a time and eventually break up and crumble. Methylene chloride is a more aggressive solvent than acetone but would still take a few days to break the resin up if the resin was well cured. On the slightly inhibited back face of a laminate you would get an almost instant reaction as the solvent dissolved any wax and under cured resin but once this top layer was removed it would take some time for the solvent to damage the underlying resin.

What is the reason for using catalyst O for 491 pa resin?

A slower catalyst like our catalyst O or Butanox LA was originally used for getting lower residual volatiles for mouldings for food / drink storage as a more gradual cure was felt to give a more complete cure - some very rapid systems gave a short gel time and rapid hardening, but the cure did not carry on to completion so residual volatiles trapped in the laminate were higher. The more critical thing to get low residual volatiles is to carry out a proper post cure - 24hrs at ambient followed by 3 - 5 hours at 85 Deg C - this will need to be done whatever catalyst is used. Butanox M50 will be OK to use as long as you follow the post cure regime.


Can I make windowpanes out of fibreglass? I'm concerned that they will not let enough daylight through, can you please advise on what material to use and is this possible.

We had some broken windows of late and I personally made my own, materials that give most transparency were powder bound chopped strand matt, laminated with a translucent sheeting resin, this is not often at hand so I used the water clear casting resin and gave decent results, 2 layers of 450g matting should be strong enough for a decent size stone to rebound off!


How much GRP reinforcement does a boat bulkhead need?

Please always seek advice from a marine surveyor for any technical enquiries regarding sailing craft. But a general guide is usually 3 layers minimum starting from 4 inches, i.e., 1st matt 4 inches, 2nd 6 inches and 3rd 8 inches. This technique ensures maximum adhesion and is less likely to delaminate. Again, before any bonding takes place, please ensure surface is keyed, dry, and abraded with a wipe of acetone before starting work. Matting can be applied straight over, i.e., wet on wet, joints are to be overlapped at least 2 inches and staggered, for example, after the 1st strip of 4 inches is applied start the 2nd 5-inch strip a good 6 inches at least away from where you first started, then just add another piece to fill the start gap. This method will allow the laminating to be of an even thickness.

What is the best system for painting a speedboat?

What you would need is first use an epoxy primer undercoat then a 2-pack polyurethane paint. We do not stock these materials but as a distributor for Blake’s paints we are able to supply.

I have some fibreglass that has been on for years on my boat and i just want to lay a couple of layers of 450g chopped strand over to reinforce, what is the best method for maximum adhesion?

Whenever a fibreglass laminate has been on for a number of years you have to decide do you need to strip back as if it has not been applied correctly in the first place, it may be retaining water or a degree of delamination may be present, if it is in good shape and you do just want to reinforce you should abrade the existing with p40 glass paper, or a mechanical disc grinder with the same surface, when you are satisfied, then clear the surface of any dust present with acetone on a dry cotton cloth (read hazards), the acetone will bring an amount of tackiness back to the laminate which in turn will maximise the adhesion. Before you start the job, the fibreglass MUST be dry, never apply matting and resin on a wet surface, and always seek advice from a "friendly boat builder" if you can before undertaking any structural work.

How do I make a buoyancy chamber for my dinghy?

Polyurethane foam sheet can be bonded to suitable areas of the hull interior and laminated over to create buoyancy chambers. Alternatively, a hollow chamber can be produced in the same way as a moulded seat (indeed, the seat can be used as a buoyancy chamber!) then filled with polyurethane foam liquid mix. The liquid foam is supplied in two parts, which must be mixed together. You will need half a kilo of each part for each cubic foot to be filled. The foam mix should be used only in a very well-ventilated workshop or in open air. Before mixing the foam, mask around the open cavity – the foam mix is highly adhesive, and any overflow will be virtually impossible to remove once it had bonded to the surrounding area. Pour equal volumes of both liquids into a mixing container and stir thoroughly. The mixture will start to foam very quickly probably within 25 seconds. It must be poured into the cavity before this time has elapsed. The foam will reach its maximum rise in about two minutes. It will have expanded to between 20 and 25 times its original volume – the amount of expansion varies according to ambient temperature. At this stage, it is highly adhesive, bonding firmly to most materials – be very careful not to let it contact the eyes or skin, since it is almost impossible to remove. It sets hard within 30 minutes. During the foaming process, harmful fumes are given off so stand back from the cavity to avoid inhaling them. Leave to cure for two days, then seal the cavity with glassfibre laminate or with an upholstered seat or other suitable covering – the cover must be adequately sealed to prevent water entering the cavity (the foam is closed cell, but some water may penetrate and remain trapped). An alternative method is to line the cavity with polythene sheet, enabling the buoyancy material to be removed bodily (e.g., for repair work).


Is it possible to re-coat the gelcoat on my rowing boat? If so, is it just a roll on or paint brush applied job or more specialist? I would like to do this job myself in my garage. Can you help me with some info and supply the gear needed?

It is possible to do this with gelcoat, but it does require a lot of hard work to get a good finish. Gelcoats are very thixotropic and designed for in mould use so the back surface will never be as smooth as a paint film which then leads to a lot of rubbing down and compounding. If you want to attempt to do it you will need to coarsely abrade the rowing boat to get a good key, apply one coat of gelcoat by brush or roller and brush, leave to cure and then apply another coat of gelcoat with 2% solution MW wax addition. Leave to cure overnight and then abrade back to smooth out brush marks and then finer and finer grades to approx. 800 wet and dry paper followed by compounding with rotary buffer / polishing machine etc. It’s an awful lot of work - you may be better off abrading back the surface and applying a marine paint system.


What type of resin is best for coating the hull of my boat in carbon kevlar mat?

Polyester vs Epoxy? Polyester will be cheaper and can be used with Carbon / Kevlar as long as you use an isophthalic resin - you will get better adhesion with epoxy but if the substrate is well abraded and wiped lightly with acetone to give a good key you will get an acceptable bond with iso polyester. If you use Crystic 491PA you will need the usual tools - brush and metal roller for consolidation. If you want to use epoxy you will need a suitable laminating grade from West or similar and essentially the same tools and same surface preparation.


Can fibreglass be applied to sheath an aluminium boat, if so what preparation is needed?

Aluminium is not a very easy metal to bond to - the resin will cure against it without problem, but it may not give a permanent bond when the boat is put back into use. An epoxy resin is likely to give a better bond than polyester and the aluminium should be abraded and sheathed in a short a period as possible after surface abrasion.

I want to paint a GRP boat with a 2-pack paint, I have discovered that it is not recommended to paint this onto a new laminate as 'styrene leaching' can cause peeling and lift off the paint, at what point does the polyester resin 2-414pa stop leaching?

At normal workshop temperatures, 18 - 25°C the cure goes on for 2-3 weeks so it may be advisable to wait for 3 weeks before painting. The majority of the cure takes place in the first 48 hours but if you have the time, it would be worth leaving it longer before painting.

My boat has a GRP dark blue hull which has discoloured with a white bloom in places probably due to sea use. Polishing gets rid of some of the bloom, but around the stern areas it does not have a great effect. Can you recommend a course of action and products needed to restore the hull to its former glory (boat is 6yrs old)?

Some blue pigments will form a white bloom if water gradually permeates into the gelcoat - if the gelcoat isn't well cured it will do this after only a day or so outside in the rain. You can compound it out and repolish, but it may need light abrasion to remove - I would try using 800 grit wet and dry paper and then use a medium compound followed by a fine compound to restore the gloss. Protect the surface with a good quality wax polish applied every 3 months or so. If the bloom comes back after this, then you would need to consider painting with a marine grade two pack urethane paint.


What has the Lloyds approved resin got that many general-purpose polyester resins have not?

Lloyds set minimum values on cast resin and laminate properties which they recommend for marine structures. Cast resin properties include elongation to break, heat distortion point, water absorption and physical properties. Laminate properties include tensile strength, tensile modulus, flexural strength, and modulus etc. A lot of general-purpose resins would struggle to meet the minimum properties specified by Lloyds tending to be low on elongation, HDT and a range of other properties.


I have been on your website looking at the resin and gelcoats to do a repair on a boat. I've looked at all the tech sheets and they all say things like "workshop must be no colder than 15deg" or words to that effect... Now that's all good but how the heck am I meant to repair a boat out in the open and "maintain no less than 15 deg" without shipping it to California or something? Do you do resins made for "British weather"? Thanks for your help.

All polyester resins will be affected by temperature and water - rain, condensation etc whilst they are curing. If its too cold or the resin gets wet or covered with rain before it gels then you won’t get it to harden properly. For a lot of the year in the UK you will be at temperatures of 15 deg C or above so I dont think that sending the boat to California will be necessary ;-) It would be best to put some sort of temporary cover over the repair area if it looks like raining - plastic sheet etc. If you do need to work outside in the Winter months, then you will need some localised heating to make sure the repair area is done under reasonable temperatures - you could possibly drop to 10 deg C and still get an acceptable result but I would not go below 10 and preferably be 15 or above.


I need some advice on a boat project, there are two parts that I need a shopping list for and an idea of what to do. Inside of boat: - I need to cover the wood on the inside to waterproof the structure. Outside of the boat: - Again I need to add structure and waterproof the boat. I will be putting a stainless-steel plate across the rear to support the engine that will be hung on the transom. I would estimate the coverage area being 1m2 on each side of the hull.

We suggest you use WEST SYSTEM 105 resin and 205 fast or 206 slow hardeners as this system can be used to over coat the wood and laminate the reinforcements. Please ensure that the timber is dry before coating and proper surface preparation has been carried out. Our A pack of 1 kg of resin and .6kg hardener should be enough or if you have larger jobs the B pack at 6 kg. The resin covers 1msq per 100gms approx. on a non-porous surface. I attach a copy of our user manual. We would suggest that you remove any loose material from the join area abrade with 80 grit sandpaper degrease and fill the gap with a thickened epoxy mix. WEST SYSTEM 105 resin mixed with 205 hardeners then add 403 microfibers filler powder to achieve the desired consistency. Fill the gap flush with the hull. Please consult the WEST SYSTEM user manual if you are not familiar with using epoxy. We trust that this information meets your requirements and if you need any further information, please do not hesitate to contact us.


I am refurbishing the wooden deck of my Flying Fifteen. We have stripped all old varnish and rubbed down and moving on to the next step. We are contemplating using West System epoxy. West advice is to use 3 coatings of 105/207 system with 3 coats of two pack polyurethane varnish. All technical info suggests the use of 207 hardener to get clear finish, but if following up with the two-pack varnish would this be necessary, or could we get away with a cheaper hardener?

Yes, you could get away with using WEST SYSTEM 206 slow hardener and 105 resin and applying coat on coat while still tacky then apply the two-pack varnish. The difference between the 207 and 206 hardener is very slight the 207 just defines the clarity in the wood grain better.


I recently read an article in boat magazine regarding pouring resin around ballast ingots. I need to fill voids in a steel boat approximately 12'x12'x12' can you advise please?

You can cast around metal ballast, but to cut down on exotherm and shrinkage, with possibility of cracking I would suggest making up a mix of general-purpose polyester resin and filler at 1 part of each by weight, make sure you mix catalyst in thoroughly first. You could use calcium carbonate or alternative inert filler and at this addition level it would still remain pourable.


Why does it say on tech data for spray gelcoat "Only use white gelcoat below the waterline"?

White and clear gelcoats have the best resistance to osmosis - white is the only pigment that can be dispersed directly into the gelcoat so you are not adding any of the dispersion resins found in pigment pastes which can reduce water resistance.



I am a student, I am working on a project of making an electric car, where in a person can sit in. I wish to make the body of the car from fibre glass. I believe that your company have got all the materials that I will need for my project. Before using fibre glass, I would like to know how I will make my mould. will your company provide me all the material I need for making moulds. Do you suggest any books that you have to make a mould for a car on which I can put the fibre glass?

First of all, please read in the project information section on site about making fibreglass moulds, a good book to buy is the fibreglass handbook, my advice for you is to read this fully before embarking on your project, but please feel free to call us anytime and we will help you.


I am repairing an old fiberglass car. I have done most of the repair work required, except for a couple of cracks around the engine. Due to the repairs required and the very poor paint job, I had to take of all paint and the original gelcoat. Leaving only the bare fiberglass shell. What is the best way forward? I’m considering replacing the original gelcoat. Put a thin layer of surface tissue on top, slightly coloured to see the difference Use a layer of topcoat or flowcoat.

You could use a heat resistant resin for repairs near engines etc - there are a number you could pick from like C,474PA, C397PA would both be OK. Using gelcoat as a surfacing coat is possible but requires an enormous amount of work if you are doing it over large areas and want to get an automotive quality appearance. I think I would re surface with Crystic Primecoat or sprayable re surfacing polyester filler made by the same people who make car body fillers - U - POL and others. These are easy to rub back to a very smooth finish and a good surface to accept paints.


I am looking to make some carbon fibre copies of trims in my car engine bay. I have read the articles for making the moulds and i was wondering if you would be able to tell me what I would need to make the carbon fibre copies. The idea being, that my car will be the test bed and once i have learnt how to do it I would like to possibly look into starting a small buisness producing carbon fibre trims for cars as they are becoming very popular but are still quite hard to get hold of.

Carbon fibre parts are made by using vacuum bagging there are some great videos on you tube demonstrating this technique, the carbon can't be simply hand layed like most fibreglass as the fibres tend to spring back up and trap air, leaving the finished product riddled with pin holes and bubbles. To overcome this problem, you need a constant even amount of pressure on the laminate until it cures which is where the vac bagging comes into play. for smaller parts you can use a clamp moulding system where a male and female mould are created to sandwich the carbon and resin inside and using 'G' clamps to give the constant pressure. I would suggest to anyone thinking of trying the vac bagging system to do plenty of research first and then practice with some cheaper materials such as silver e-glass or black diolen. you can call us for advice on 0191 497 5134.


When using water clear casting resin what can I use for a mould?

We sell moulds in our craft section for water clear casting, but generally just use the ’Tuppa ware’ type of container / ice cube tray, it is always best to try a small sample first.


What materials and tools do I need to make small castings? I know that i need supplies of Polyester clear resin, hardener, various colourings and a re-usable mould. Can you please list the items that i need to make sure that i am ordering the correct chemicals.

Resins for casting can be found here in the Casting Resins section on our site, this will show the re-useable moulds too. Either water clear which is simply clear casting resin or standard which is a brown colour, both can be effectively pigmented with polyester colour pigments, for the water clear casting resin you can use one of the transparent pigments which give excellent effects, you need only put more than 0.5% upwards for the desired colour, you would not need more than 5%, for the opaque pigments you can add up to 10% by weight, dark colours like black/grey/brown usually only need between 5 - 7% whilst lighter colours like yellow/red need the full 10% pigmentation. There are also some re-useable moulds you can use to cast, on the standard casting resin you can cast any of our moulds in one hit, the water clears on the bigger variations it is advisable to stage in layers, sometimes the layers are visible in the casting.


I see you have "casting" materials. I want to cast a lead ballast for my model Marblehead sailing yacht (about 3Kg). Do you have a material I can use as a mould for this purpose please? What would you suggest? the resin needs to resist the boiling lead without exploding.

I don’t think a grp mould would explode if you poured in boiling lead - it might survive a one off but probably not for repeated use. Boiling lead is around 1740 deg C? If you put grp into a furnace and raise the temperature it will self-ignite at around 350 deg C . I would imagine that the lead would cool down rapidly so it may be OK, but I have not seen this done before so can’t say for sure. I know that low melting point alloys are cast into silicone rubber moulds to produce highly detailed toy soldiers etc.

I make figurines based on your videos. Immediately after polishing, the figurine looks great, but very quickly it acquires a dark coating and the product looks like cheap plastic. I polish the product again, but the tarnish appears again. Varnishing slows down the process of the appearance of the tarnish, but does not eliminate it.

As the powders are metal they will oxidize. Oxidation is a chemical process by which an ionic chemical reaction occurs at the surface of a metal when in the presence of oxygen. Lacquering the metal casts with a clear coat such as clear car lacquer will help prevent oxidization. 



Can I use less catalyst in warm or hot weather?

Never put any less than 1% catalyst in by volume, i.e., 10 ml per Kg as this will affect the curing cycle and you run the risk of an under-cured laminate. You can get a slower reactivity catalyst though and this would extend the geltime whilst you are working.



What is Hybrid Material?

A hybrid material is a reinforcement that contains more than one fibre type.


What is the difference between plain weave fabric and twill weave fabric?

Plain Each warp fibre passes alternatively under and over each weft fibre. (High crimp impacts lower mechanical properties). Twill One or more warp fibres alternatively weave over and under two or more weft fibres in a regular repeated manner. This produces diagonal rib. Superior wet out and drape, over plain, with only a small reduction in stability. Reduced crimp gives smoother surface and high mechanical properties.


What are multiaxial fabrics?

Multiaxial fabric is made up of two or more layers of unidirectional fibres stitched together with a polyester thread.


Common Problems

What is the Blister / bobble type things on my fibreglass moulded pool? Also, dark mouldy-looking patches. What is the problem, and can it be fixed?

This problem sounds like osmotic blistering which can be a problem with GRP pools - it can be virtually eliminated if the pools are made with an isophthalic resin or vinyl ester resin used with powder bonded csm on the initial layer behind the gelcoat. i.e., it’s easier to stop the problem occurring when the pools are made rather than to try and remedy the problem when it occurs. It’s cheaper however to use lower cost laminating resins so lots of pools are made with these - they can be prone to this sort of issue when water penetrates into the laminate, breaks down the resin and forms a weak acidic solution which smells like vinegar. Raised blisters formed which can be broken open to release a watery solution of acetic acid (vinegar smell) - this is the formed from the binder used in emulsion bound csm getting into contact with water. Be careful if you break the blister as the contents can shoot out with some force. The good news is that the strength of the laminate is generally unaffected unless the blistering is very severe, and the bad news is that the blisters will continue to grow and will eventually split open - they are very difficult to treat permanently to stop them coming back. The accepted treatment is the grind the blisters off and wash them out with clean water and allow to dry thoroughly before filling with a two-pack epoxy filler and then using an epoxy or two pack polyurethane paint. It’s a lot of work and there are no guarantees that it won’t come back. You could do a cheaper job using the same preparation and filling the voids with polyester gelcoat etc - again there is a good chance that this will not be a permanent solution. Hope this helps.


Hi, could you possibly give me a first impression regarding the gelcoat on my Sun 2000? It was blown off it trailer a year ago in severe winds and the mast was damaged by the crane driver lifting her back on and had to be replaced. Some superficial gel coat work was also completed. About 4 months after this work I noticed two areas of "crazing" on the hull. At the time I was told boats can develop these, but this was an immaculate boat and the more I look at it the more I feel it has been damaged then.

Cracking visible on the surface of the gelcoat can normally be attributed to two things: - Impact - distinctive pattern of cracks radiating away from the point of impact - can look a bit like a spider’s web.  Stress caused by the laminate flexing. It’s difficult to be completely sure from looking at the pictures but it looks more like the pattern you associate with stress cracking so presumably this section of the laminate has been subject to some movement during use or when it was blown off the trailer. It’s probably restricted to the gelcoat and first layer of laminate and as such will have little impact on the strength of the boat but is obviously unsightly and will over a long period of time allow water to permeate into the backing laminate. It’s not easy to repair - single cracks can be routed out and filled but there are too many present to do this in this case. You could abrade off the effected gelcoat and build up again with new gelcoat, abrade back to a smooth surface and re polish. This is quite a lot of work, and you may not achieve a good colour match to give an invisible repair. Alternatively, you could abrade the surface of the gelcoat over the whole of the area above the water line and re paint. It’s a matter of judgement really - the cracking probably will have little effect on the structural properties of the boat and will be difficult/expensive to repair successfully.


I read with interest your note on 'spotting' We have a three-year-old boat that has started to show lots of tiny blue spots in patches around the deck and cockpit. It looks like over spray from a spray gun, but they won't rub out. Is this the same and when you say 'fault' will it get worse and become a problem. At the moment it is unsightly and looks like the top surface is wearing thin in places.

This is the sort of thing you would really need to see - I can’t think of anything definite. Any weathering effects which look like spots where drops of water have been standing should be removable with a light compound like T cut or preferably one aimed at the GRP industry which are free of ammonia - one from the Farecla range or similar. You can sometimes get dark black /blue spots if GRP comes into contact with sodium hypochlorite ( bleach) which can be seen occasionally on swimming pools where chlorinated water can react with any free accelerator left in the gelcoat .It’s a compound formed between cobalt and chlorine which can be removed by washing with a weak acid - ascorbic acid is usually recommended which can be bought from chemists , you could also try citric acid. It seems a bit unlikely for a boat, but I suppose it could have come into contact with cleaning agents which contain chlorine. I hope this offers some help into your problem.


I have a crack on my mould, like a spider! What is this and what causes this?

This is normally due to some kind of impact on the reverse side of the mould, maybe you have not taken care of it, and it has sustained a knock which will immediately put pressure through the laminate and cause the gelcoat to crack. Best treatment is to carefully drill the ends of the crack just enough to go half way through the wall thickness of the mould, then grind out the crack with a small router tool, just work your way along each section of damage, wipe with acetone and fill with gelcoat, leave at least overnight and using wet and dry then polish make good, do not forget to treat your mould as new when finished. This I mean take care in applying enough waxes over treated area.


I have an RTV rubber skin mould that is helmet shaped and when the product is taken out from the mould the gelcoat is sticky. I am adding cat at 3% and after premixing i am transferring into another pot for final mixing, I have been told that the mould could be damp so i dried it out before applying the gelcoat but i still have the same problem.

This is a very common problem with silicone rubber moulds - they inhibit the cure of the resin which is in direct contact with them leaving a tacky surface. Some resins and gelcoats are affected more than others - the more flexible resins and gelcoats are worse so for example Scott Bader’s GC33PA is more affected than GC65PA etc. Some rubbers are worse than others - again the more flexible rubbers are worse, and the so-called styrene resistant rubbers are worse than the standard types. The tackiness should be confined to a very thin surface layer - under the tacky layer the resin should be normal. People who make filled castings which are painted can sometimes use this to advantage - they wash off the tacky layer which reveals more of the filler particles which allow the paint to adhere better. I don’t think you can totally resolve this type of effect but may be able to reduce it with certain resins and rubbers.


Core Materials

Can you use Rovicore to lay up by hand?

No, Rovicore contains a synthetic core to allow the resin to flow through which is used in closed mould applications, the core compresses depending on the mould cavity and comes in either 3mm or 5mm, various grade of glass are available to sandwich this core.

Can I use the polyurethane foam sheets to create a master mould? And also, how do I cut polyurethane foam sheet?

Yes, you can, best results are achieved by priming with catalysed polyester resin, let this cure and gently rub off all nibs with 240 grade wet and dry paper (use dry), after that it is best to coat with durabuild surface primer 2–3 coats, this is easily cut back and polished to give a very high sheen surface. Durabuild is expensive and so is not within everybody’s budget. Good results can be achieved with Flowcoat, this takes longer to obtain a good finish, it all depends upon the application the mould is being made for in the first place!


What is the expansion rate for Polyurethane foam liquid?

As a general rule, 1 Kg of polyurethane foam mix will create 1 cubic ft when expanded, this would be 500g of part 1 and 500g of part 2.


What nidaplast do you recommend for a boat deck?  

For a belt and braces approach to most boats we would recommend 20mm Nidaplast with 2 x layers of 600g csm either side applied with Lloyds approved resin. It is best to lay one side of the Nidaplast with the 2 layers of 600g and then install it ‘fibreglass side down’ onto beams that are fitted no more than 300mm apart for support. Bond them with a bonding paste suitable for GRP to wood such as freefix but be aware that this paste is rapid, so you have to be quick getting it down after mixing. Then secure with screws to the beams Once installed you can then lay-up the topside with 2 further layers of CSM using a board to kneel on so that you can disperse the weight and not risk breaking the Nidaplast or alternatively you can apply one layer to the topside prior to installation to protect it and once installed bandage the joins and add the second layer although this will show up taped joints throughout the deck. When everything is secure and cured you can apply your finish either a standard flowcoat or nonslip flowcoat.

If this is a high-performance boat or yacht and weight of a critical nature not allowing for the above belt and braces approach, we would recommend consulting a professional boat builder or someone experienced in composite engineering.



What is the best fibreglass to make motorcycle fairings?

Generally, 2 layers of 450g matting is all that is involved in construction, this would give you about 3 kg of weight per sq mt, you could put 2 layers 300g in but you may comprehend the strength. You may however want to sandwich 265g Diolen between 2 layers of 300g, this would increase the impact resistance but you would have to determine if rigidity was suitable, the approximate weight of this would be 2 kg per sq mt, from a personal point of view i would go with the second option, having worked with Diolen it has outstanding impact resistance at a fraction of the cost of other high profile cloths.



Can I use talc in gelcoat as a filler on my boat?

You could use talc to make a smooth paste for repair work but if it's going under water or in contact with water for prolonged periods then talc is probably not the best choice as it will increase the water uptake in the repaired areas. If you are using white gelcoat, then adding fillers like talc will throw the colour off so you won’t be able to get a colour match on the repair. Alternatives would glass bubbles, or you can thicken up the gelcoat with a thixotrope like cab-o–sil / Colloidal silica.


I have some fillers for various uses left over from an old project but i do not know what brand, can i use them and with what epoxy resin and hardener in the West range do you advise?

As you will see if you download a copy of the free WEST SYSTEM "User Manual and Product Catalogue" there is only one resin in the WEST SYSTEM epoxy range "105 resin - Standard" four hardeners "205 - Standard, 206 - Slow, 207 - Coating & 209 - Extra Slow", the hardener you are most likely to use is the "205 Hardener - Standard". This mix can be used for laminating and coating. There are six different fillers each with their own specific uses, 403 - Microfibres (general wood adhesive), 404 - High Density Filler (high load adhesive), 405 - Filleting blend (wood toned adhesive), 406 - Colloidal Silica (general structural adhesive), 407 - Low Density Filler (light structural fairing), 410 Microlight (lowest weight fairing). We do not suggest the use of other fillers as we cannot guarantee the effective use of them.



What filler is best for making a filleting paste with the West epoxy system?

Please refer to the WEST SYSTEM user manual present in each product listing for all the information you will need, it gives you very comprehensive and detailed application guides on all its products.



What is the difference between Flowcoat and Topcoat?

Both are just terms used to describe Gelcoat with addition of wax, this ensures the surface to remain tack free, a common use in flat roofing or pond builds.

What is the best way to apply non-slip flowcoat/topcoat to the deck of my boat?

Best way, and indeed advised way is by brush, apply too thick and you lose the effect as the granules become sunken in the Flowcoat, spread not to thin but spread evenly, this ensures the textured finish and is a really good finish too. I personally have applied a few times and it's impressive.

Can I thin down Flowcoat and can I apply more than one coat?

We do not recommend thinning Flowcoat and understandably can take no responsibility for any problems that may arise from altering our products. However, the product has been known to be thinned in various ways and if customers wish to experiment, we advise on trying this out on something non-critical first. Flowcoats are primarily designed to be applied as a ONE COAT product only and is at the right consistency to apply in one good liberal layer mainly for sealing the rough non cosmetic side of laminates to make a smoother, easy to clean, surface that seals the fibres from water, oil and dirt ingress. Flowcoat is not designed for high end aesthetic paint like finishes and second coats will not bond due to the wax content, any second layer applied no matter how well the first coat it is abraded, will most likely eventually start to flake and peel especially if the part is exposed to the outdoor elements. However, if thinning Flowcoat is something you wish to experiment with, Flowcoat can either be tinned with styrene at no more than 7% however this can slow cure times and effect the products performance if too much is added. Orit can be thinned with resin making sure that the resin is pigmented the same colour first so as not to dilute the Flowcoat’s original colour. Also ensure more MW wax is added to compensate for the addition of resin. i.e., add 20ml of MW wax for every 1kg of resin added to the flowcoat. If multiple layers are to be built up you can use gelcoat (same colour as the Flowcoat) as the first layer(s) and then use Flowcoat as the final layer, ensuring you have a good temperature-controlled area and that the product is curing at a reasonable rate. For example, if a second or third coat takes too long to cure it will start to dissolve and wrinkle the first layer, so you want the product to be curing off within approx. no less than 40 minutes Ideally. Again, we advise on experimenting on something non-critical first as it is not the usual way in which these products are used or designed for


How is Crystic Fireguard applied?

Crystic Fireguard is simply brushed onto the rear of a laminate as you would usually apply a flowcoat. It is usually applied in situations that conduct high heat like engine compartments.



Potable gel coat. I want to build a hopper for boiling water for about one hour without contamination from any of the resins. Can this be done with normal gelcoat and polyester resins or will vinylester or epoxy inner face be required?

Boiling water is surprisingly aggressive towards GRP and it’s not recommended to have it in permanent contact with it, but for short periods it should be OK. You would need a resin with good heat and water resistance.


Is Polyester Gelcoat compatible with Vinyl ester Resin?

Vinyl ester resins share the same cross-linking monomer (styrene) to polyester resins and Gelcoats so they are compatible with each other - you can actually mix the two together if you wanted to. Vinyl ester resins and blends of vinyl ester and polyester resins are often used as a blister resistant skin coat behind polyester gelcoats for boats etc.



I plan to build in a sequence of metal inserts into my laminate, what should the dimension of the base of the insert be?

As a general rule the base should be four times as wide as the insert is long, but in reality this is sometimes unachievable as space on the laminate surface sometimes does not allow this, as long as you prepare both surfaces you can get away with less base area, the insert should be abraded and wiped with acetone, please pay attention to the surface of the laminate also as this is critical for good adhesion, abrade and wipe with acetone also. Freefix 6470 is an effective bonding agent for this purpose, a better one is Scott Bader’s Crestomer Advantage 10, we have conducted tests and the Crestomer and it will take more load on its own than against the Freefix with two layers of chopped strand matting over base of insert. The Crestomer fixed insert will actually be stronger than the laminate itself and when breaking point is reached large pieces of fibreglass will attach itself to the back of the insert.



Is kevlar stronger than steel?

Comparing the fibre with steel is only true for certain grades and applies to the specific tensile strength only. Please call us with specific application and we will try to assist.


What is the difference between Kevlar and Aramid?

Aramid is a material formed by combining para-phenylenediamine and terephthaloyl chloride. This produces aromatic polyamide threads which are further refined to produce fibres. These fibres are woven into a very light, very strong cloth. When this cloth is combined with resin it produces a composite material which is 20 times stronger than steel with excellent torque and tensile strength, and excellent impact-resistant properties too. Kevlar is a brand name for a type of aramid made by the Du Pont company.



Can I laminate fibreglass into right angles?

Best not to, better to create at least a 5mm radius as the fibres in the glass matting will tend to spring away, if you must cut strips of matting say ½” wide and butt join into angle first or apply a layer of tissue matting in place.


Can corematt be used as a first layer on top of the gelcoat?

No, you must place a layer of chopped strand matting down 1st as the adhesion will not be as good and also there will be surface voids and maybe dry patches on the surface as Corematt absorbs a lot of resin. Best results are obtained by creating an equal laminate, i.e. 450g matt – Corematt – 450g matt.


What is The Green Stage?

This is a point reached by a GRP / Fibreglass laminate after the gel-time but before it is fully hardened. When 'green', the laminate is fairly firm but can be cut with a knife, making it easy to trim with a Stanley knife, care must be taken not to damage the mould.



How much resin do I need for 1 sq mt of chopped strand matting 300g, 450g, and 600g?

The easiest way to work it out is multiply the weight of your matting by 2.5, i.e., for 1kg of matt you would need 2.5 kg of resin. The usual resin: glass ratio varies from person to person, more competent operators will work at a 2:1 ratio as they have more experience working with the material and consolidating the layers correctly, it is not a good idea to go above 2.5:1 as this way you start to affect the properties of the laminate, i.e., by making it more brittle.


Mould making

I wish to produce a fibreglass mould for moulding concrete blocks, will I need a chemical resistant gelcoat for this, will the 14pa tooling gel coat you stock be suitable?

Due to the strong alkalinity in concrete, it is recommended to use a gelcoat with better resistance to caustic materials - you get a better resistance to caustic from an Iso Npg Gelcoat like Gelcoat 69PA rather than standard Iso like Gelcoat 65PA. You should also see a better result with a vinyl ester type like gel-coat14PA but i have never seen it used with concrete before - this has always been seen a very price sensitive application and historically it’s been difficult to get people to pay the extra for an Iso Npg type let alone a Vinylester!! We would suggest carry out a post cure procedure as its surprising how aggressive concrete can be when it sets.


How much will it cost me to make a grp mould from my car bonnet, then make a moulding from?

The cost would be dependent upon the specification you would like to make your mould and indeed your part from, choices range from general purpose resins to tooling resins for you mould, it would be more economical to manufacture your bonnet moulding from polyester resin and chopped matt, but you can make it lighter and stronger using epoxy resins and more exotic materials like aramid and carbon fibre.


How would I go about making a cavity between two fibreglass moulds?

Easiest way is to use the sheet wax we have in the mould making section, this has an adhesive back and can be laid into your female mould, warm it gently with a heat gun to soften if you need to bend over awkward shapes. If you need a cavity of, say 4mm, apply 2 layers of 2mm, stagger the 2nd layer, any gaps between the wax can be carefully filled with plasticine, if you are laying fibreglass to make your male tool apply a coating of PVA release agent over the wax as it sometimes can be difficult to part.


Have you heard of the Prestovac system for making closed mould panels? I have heard it is economical and does not involve any expensive equipment.

Yes, I have used this myself and can recommend it to anyone, it works simply on vacuum, on most parts you can get away with a single venturi pump. The resin is mixed the normal open mould way and simply poured into female tool, the male is then brought to match and using a seal to hold the pressure. Parts can be produced more economically without half the styrene emission and without the mess that contact moulding produces, please call us to discuss further.


I have a mould that has been gelcoated for a couple of weeks now, can I lay-up on top of it and will it be, ok? If it’s not ok how or what is the best way of removing it?

No, certainly not, the lamination must take place within a 24-hour cycle to obtain maximum adhesion, best technique of removing old gelcoat is gently apply air pressure to a peeled away section, the air will lift the gelcoat in the immediate area, and you can then use a soft PLASTIC wedge to remove it.


I have read your FAQ page on the subject of closed mould process, the 'Prestovac' system, what if i have an existing hand lay mould, can i use it to produce a female closed mould tool?

The simple answer is yes; without going into great technical detail, you can extend the flange on the female tool incorporating a pinch off section to enable closed mould production, from there you can then produce a male tool, call us for more detailed discussion.


How do i make a fibreglass mould? Thanks

You should first read our mould making section, then it would be a good idea to purchase The Glassfibre Handbook, but at any time please call us to discuss.


How do you make a GRP/Fibreglass mould? I'm a little confused with the male/female versions of mould-making.

Please see our project information section on making moulds, there you should find all of the information you need. Do call us if you need any more help.


What temperature should my workshop be before I start to gelcoat my mould?

Application and cure should not be carried out below 15°C, and care should be taken to make sure the material and also the mould are up to temperature too. Moulds that have become cold due to overnight workshop temperature take hours to warm up, so if you can see if you can attain a constant temperature or at least warm the workshop a few hours before starting work.



What is the difference between fibreglass - GRP and FRP, im new to this and am a little confused, oh and why do some people say glass fibre?

FRP stands for 1. Fibre reinforced plastic. GRP stands for 2. Glass reinforced plastic. Glassfibre is simply a preference to some people rather than fibreglass. Basically, all are just preferred terms used for description, FRP was used in the early days. Hope this helps ease the confusion!


What are the requirements for resins, gelcoats and mattings to meet Lloyds approval?

Lloyds set a range of minimum properties for gelcoat base resins and laminating resins - they also set limits on additions, like fillers and pigments. Manufacturers have to fully test the resins on a regular basis, and Lloyds can ask for evidence of the test results. Minimum properties for cast gelcoat resins Water absorption - 70mg max Elongation at maximum stress - 2.5% min Tensile strength at maximum stress - 40 N/ per square mm min Flexural Strength - 70N / per square mm Barcol - as specified for full cure Gelcoats must have a maximum inorganic content of 18% - this covers thixotropes , pigments and any fillers. Minimum properties of laminating resins when in cast form. Water absorption - 70 mg max Elongation at maximum stress - 2% min Tensile strength at maximum stress - 40 N / per square mm min Barcol - as specified for full cure Temperature of deflection under load - 55 deg C min Chopped strand mat laminate minimum requirements. The values change with glass content but for a typical glass content for chopped strand mat laminate (30% glass by weight) ,the following minimum values are specified. Tensile Strength - 90 MPa Tensile Modulus - 6.85 GPa Flexural Strength - 159MPa Flexural Modulus - 5.7GPa. Compressive strength - 117MPa Compressive Modulus - 6GPa Water absorption - 70mg max.


Why can't general lay-up resin be used for petrol tanks?

General purpose grades have never been suitable for storage of petrol as they do not have sufficient resistance to oils, diesel, petrol and other similar materials. Before unleaded petrol became the norm you could store it in an iso resin like our Crystic 491PA - this was actually sold by a company called Petseal for sealing rusty motorbike petrol tanks. Un leaded fuel currently used contains methanol which has made it more aggressive towards GRP so we now only recommend highly crosslinked iso resins like our Crystic 199 - this also needs post curing to develope sufficient resistance.


Do i need to register with the local authority my business of fibreglass moulding? Someone told me that if i was using so much resin/gelcoat i would need to, any advice would be appreciated.

Hmpi regulations say you need to register your process with them if you are polymerising 100 tonnes or more of styrene per year - assuming most polyester resins contain around 40% of styrene by wt then you can use about 250 tonnes of resin/year before needing to register. There are other guidance notes ref PG4/2 - secretary of state guidance notes for processes for the manufacture of fibre reinforced plastics which give details of how much styrene per tonne of product you are allowed to emit (maximum values allowable) Gelcoating - up to 200Kg of styrene per tonne of gelcoat Open moulding - including hand layup, spray laminating, filament winding etc - 60Kg per tonne of resin used. RTM, cold and hot press moulding - 20Kg per tonne of resin used. As a guide for normal hand lay up in open moulds you are likely to lose 5/10 % of the styrene content of the resin, this depends on surface area, temperature etc. This equates to around 21 - 42Kg of styrene per tonne of resin used, if you are using closed moulds where their styrene is contained then you will be emitting a small proportion of this figure.


Can you tell me if Bitumen can be put onto cured fiberglass laminate?

Applying hot bitumen to GRP will soften it until the Bitumen cools down but I don’t think it would do any damage to it long term.


Do you supply a hard-wearing fibreglass lacquer?

Scott Bader used to make a light stabilised clear acrylic lacquer called LS7 which could be applied to GRP sheeting to prolong its life but as this type of GRP sheeting was gradually replaced with acrylic or polycarbonate types as they were not selling enough to make it worthwhile. It was withdrawn some years ago and they would not now have the raw materials to make it.


How much variation in the glassfibre laminate can i expect when i am laying up parts?

You can expect variations in the resin content, good rolling is essential, you should consolidate the glass reinforcement without disturbing its distribution or breaking the fibreglass into strands. Draughts can cause under cure through styrene loss, temperature, inadequate mixing of catalyst can all lead to poor mouldings being made.



How much pigment do I need to add when casting with clear casting resin?

You really only need a very small amount, it depends on what depth of colour you require, best to add just a small amount on the end of a mixing stick, if it’s not enough added a little more, from 1-5% by weight


How much polyester pigment paste do i need to add to my gelcoat and resin?

Gelcoat is best to add 10% for most colours, slightly less for some darker colours, with the resin again you can get away with as little as 5% depending on colour, don’t forget always to stir pigment well before use.


Hi I am having a problem with a coloured gelcoat - applying with a brush is leaving lines and swirls as if particles of pigment are being dragged

Single pigment colours like white and black are generally free of all colour faults but where you have mixtures of pigments you always have the potential for separation, particularly if you allow the gelcoat to drain down the mould in huge sags and runs. Some colours are much more prone to this with greys giving the biggest issues as white pigment and black pigment are very different in terms of their density - white is a hard dense solid and black is a fluffy light powder. There are additives which are designed to hold the pigments together and we have what are called special pigments where this additive is milled into the pigment pastes prior to addition to the gelcoat. The additive influences the water resistance of the gelcoat and the special pigment colours are not generally recommended for permanent exposure to water - so OK for boat decks, colour bands and above the water line but not below the water line for boats spending all of their time in water. Spray gelcoats are probably less prone to colour faults but certainly not guaranteed to be free of all faults and again can be influenced a lot by the skill of the sprayer and difficulty in spraying certain shapes”.



Is pond construction better with a fibreglass/GRP liner than flexible paint?

Please see our detailed instructions for fibreglass pond construction here, which has details on layup. For layup we advise 2 layers of 450g chopped strand matting, followed by a tissue then a flowcoat. Click here to see our Pond packs and pond tool packs in various sizes for sale.


I am currently putting together a quote from you for enough fibreglass to cover an area of 325 square metres. the fibreglass would need to be marine safe when fully cured as it is for a Mariculture facility. Basically, the fiberglass would need to be totally non-toxic when cured and be able to withstand full strength sea water.

GelCoat 65PA or Flowcoat 65PA and Crystic 491PA will be food safe when fully cured - all polyester resins will retain a small amount of free styrene which can taint water or food when they are cured at room temperature and need a post cure treatment in order to make them fully cured and non-tainting. The post cure schedule should be 3hrs at 80 deg C - this may be difficult on such a large area, but some post cure will be required in order to make the laminate non tainting. GC65PA / Flowcoat 65PA and C.491PA will withstand sea water - for the best water resistance and resistance to blistering you should use a powder bonded csm behind the gelcoat /flowcoat.



I cannot separate my GRP mould from the plug. Please help, what have I done wrong?

Please bear in mind that this happens to all of us once if unlucky, or if careless, twice! When making moulds you must consider everything from temperature, humidity, draughts, what kind of release agent, how long did the gelcoat take to cure, the list goes on. Please take care and read our information pages on mould making or call us if you need any help. Carefully using plastic wedges part, the sides of your mould away, then pour some hot soapy water down, tapping very gently the sides of the mould (go very lightly or you will create star crazing on the mould). Leave for a while then repeat the process, using mole grips carefully clasp the side and lever up in short bursts of light pressure, if you need to pour more liquid down then do so and lever again. Hopefully releasing will take place, if not then the only alternative is breaking the master (plug) away. I can only suggest calling us as it all depends on what shape your mould is, what you are duplicating, is it a male or female mould etc.


I have finished the mould and polished it with a carnauba base polish, but when I applied the PVA release agent it appeared to separate leaving areas of the mould unprotected. Any ideas what is causing this and what do I do to the mould to ensure that the release agent covers the whole piece?

What has happened here is you are applying too heavy a coat. You must wax your mould as though you do not rely upon the PVA at all, then apply a very thin coat with a sponge in one continuous film as insurance for its release. Wipe off the existing PVA with warm water, apply another 2 - 3 waxes then LIGHTLY apply PVA, you should not be able to see any PVA on the mould when applied, it's that thin of a film. If you are spraying on, stand back a few feet and just mist it over the mould area, this allows a finer film, then again, a little heavier, put too much on and it will run and 'fisheye'. Follow this guide and it does work, done it hundreds of times myself.


Im trying to apply PVA release agent on my fiberglass mould, but it keeps draining into the bottom of the mould, where am i going wrong?

The PVA release agent is of very low viscosity and the solution will drain down vertical sections and accumulate in corners etc where drying time will be a lot longer, you have got to be very careful not to apply a gelcoat to soon before the solution has had time to dry, or you will find that your part will stick to the mould surface. If spraying the PVA put a fine mist on first, this allows any subsequent coats to adhere to the fine coat first and is less likely to run, if you are applying with sponge or brush just do not soak too much up at a time, hope this helps.


Is it possible to apply PVA release agent before wax to achieve a "sure thing" release?

Apply 3-4 layers of PVA blue gloss release agent. you need to let each coat dry, once the first coat is dry apply the second coat quite rapidly so that it does not have a chance to soften or dissolve the first coat and repeat for 3 coats of until you have a bold blue colour.

It is best to go for the blue gloss PVA release agent as this will give you a better finish and the blue will help you see each coat, you want to end up with a good bold blue finish, us a foam brush for best finish if you do not have access to a spray gun. If you are spraying then you need to just create a fine mist and let the mist settle on the part, do not spray like paint directly to the surface as this will be too heavy and may run. If spraying it will also take more just 3 coats to get then even bold blue layer, usually approx. 10 + passes with the spray gun. Once all coats are dry, lightly apply a coat of mould release wax and then very gently buff off the excess wax before applying your mould materials.


How do i repair my fibreglass panel?

We can certainly help you with this. However, it all depends upon the nature of the damage in first place and what the panel is used for, you will need to be a bit more specific, pictures help a lot, please email them though if possible.


Are SP handypacks and fiberglass mat suitable for repairing cracks on a shower panel?

No, sorry, cannot be recommended for this application, more suitable for repairs to polyester resins, epoxy resins and suitable marine woods. Information feedback from users who has tried similar job is variable success.


I need to repair some Gelcoat on my Jet-ski, do i need the wax additive or not, ie Flowcoat/Topcoat?

I’ve been repairing Gelcoat for 20 years + and I’ve never used wax as an advantage, basically you need to leave the repair for 24 hours before using wet and dry paper etc, by that time the tack is gone, it is best to leave for this time as the repair will shrink a little,( if you want this explained better call us), after 24 hours you are fairly safe to cut back, never rush a job, take your time, prepare and the results speak for themselves.

I wish to join ( or rather, bridge) a gap between two items of motorcycle plastic trim. The gap varies between 10 mm and 75 mm. I believe that both pieces of trim are thermoplastic. I will make a preliminary bridge out of clay and laminate onto that, overlapping onto both pieces of trim by approximately 20 mm. The "inside" will never be visible but the outside will be sanded smooth and painted.
The laminated area will be approximately 0.4 m2 and I want the finished laminate to be about 3mm thick. There is no mechanical stress on the finished item, it is simply cosmetic.

bonding to thermoplastics is quite difficult. Thermoplastic moulds are often used for resin castings as the resins easily release from the plastic often without the need for a release agent.  Even epoxies which tend to have the best mechanical bonding properties can struggle to stick to thermoplastics.   

To give yourself the best chance of a bond thoroughly sand the surface with 80 grit sandpaper and even score the surface with a knife at different angles to form a good key. You could even drill some small holes to create locking points for the resin. next you will need an epoxy with some flex as rigid epoxies are more likely to release as the plastic contracts and expands when exposed to different temperatures.  I’d recommend using west system G/flex as your best option as there have been some great results with this resin when used to bond ABS plastics 



Which resins should I use for a boat's Water Tank?

We would recommend an Isophthalic resin for potable water: Crystic 491pa has been used for this but the essential point is to post cure the tank to ensure the residual styrene content in the laminate is at extremely low levels. The recommended schedule is 24hrs at room temperature followed by 5 hrs at 80°C. Fill the tank up with hot water (60°C-80°C) containing a non-perfumed detergent, leave to stand for 2 hours and empty. The tank should be filled with clean hot water several times before use.


What resin should I use to cast chess pieces?

The standard casting resin (Green Label) is suitable and is also compatible with latex moulds. Fillers can be added to increase weight and to reduce brittleness.


Should I use Polyester resin or Epoxy resin to sheath my clinker dinghy?

Clinker boats 'move' in two directions and can kick off a hard coating. Epoxy is better than polyester and is therefore more expensive. Done correctly an epoxy sheathed boat will outlast you and me, not just last a few years. The secret is, is the boat worth it, and can it be done correctly?


Could you please tell me do you stock strand glassfibre products? What is resin A?

Yes, we do, as a distributor of Scott Bader materials we can supply a wide range of Strand products. Resin A is a term used for general purpose laminating resin, Resin B = gelcoat, Resin C = Clear cast resin, Resin E = low styrene emission resin, Resin F1 = fire retardant resin, Resin H = chemical resistant resin.


Hi, I am making a structure which will be used in building that would join two plywood boards together with reinforcement of two layer of fibreglass to make a joint, the joint will be in high tensile and compression force. Would you let me know which resin, catalyst and glass fibre of your product would suggest fulfilling my requirement. Please let me know how much resin is needed for one layer of fibreglass for 1 meter square.

For 1 square metre of 450g csm you will need approx. 1Kg of resin - this will give you a laminate just under 1mm thick. I don’t think i could recommend a laminate construction for the joint unless you know the actual loads it is expected to resist - we aren't really qualified to give structural and design advice and aren't insured if any recommendations fail. You really need to get advice from a structural engineer/consultant.


What is a phenolic resin?

Phenolic resins are used to make glass reinforced mouldings, like you would make using a polyester resin, but mouldings made from Phenolic resins have very low smoke emissions when they burn. They have been widely used for underground trains etc where low smoke emissions are critical.


Can you tell me if there is a harder wearing polyester which can stand up against osmosis?

The hardness of most conventional polyester resins all fall within a similar range 38 - 45 on a barcol hardness scale. There are two schools of thought on wear resistance - you either make it more flexible, more elastic like a urethane so it doesn’t cut or abrade cleanly or make it much harder by adding a hard abrasive filler like fine quartz powder. You can make polyester resins more flexible by using different raw materials to make them - you can increase the elongation to break from 2- 4 % up to over 100% by cooking in different glycols but this is usually at the expense of water and chemical resistance. You can blend in Crestomer 1080 - this is more expensive but has less influence on the water and chemical resistance. Adding 20% to the polyester resin will make a difference but you can add higher levels if necessary. Hard abrasive fillers can be added to an isophthalic resin like Scott Bader’s Crystic 491PA - you can add fine quartz powder, fine silver sand, alumina tri hydrate etc as long as the filler is dry and chemically inert. These fillers will have less influence on water resistance/osmosis than the more conventional calcium carbonate types. Hope this helps.


When using West resins how do i give myself more working time when applying?

The WEST SYSTEM resin and hardener react together in an exothermic chemical reaction which when mixed in large quantities can produce its own heat and exotherm, causing the mix to cure more quickly. The best way to describe this phenomenon is by comparing a 100g mass of epoxy in a paper cup or poured into a roller tray. The 100g mass of epoxy left to cure in the paper cup will cure in approximately 12 mins, become very hot, smoke & bubble (at this stage the container should be safely moved outside as the fumes given off are not particularly pleasant). The 100g mass of epoxy which was poured into the roller tray once mixed will become unusable in approximately 30 mins, not getting too warm & curing at a reasonable rate. Working in high temperatures can reduce the cure times. There are three ways which you can slow down the reaction: 1. Mix epoxy in smaller batches 2. Spread out larger quantities over a larger surface area to dissipate heat 3. Use a slower hardener such as 206 (slow) if working temp >16°C or 209 (extra slow) if working temp >18°C


I am making a relatively large buck for some bodywork out of Fibreglass, please could you advise me if your Chemical and Heat Resistant Resin be able to withstand a temperature of around 120 degrees C in an autoclave without any structural problems?

Our Crystic 199 has the highest heat deflection temperature, pls evaluate tech data sheet on product, and call me if you need any help.


I used Crystic 397pa resin to coat a bath with Bioside and it has started to break down, i have a feeling it has something to do with the method it was applied. Please find attached data sheets for the chemical used in the bath. The dilution is 50 to 1 with water. The resin was left until it felt dry before the bath was filled, approx. 6 hours.

The back face of a C.397PA laminate will be prone to chemical attack if the surface was not protected with a coat of resin with wax addition or a flowcoat of gelcoat with wax addition. In both cases 6hrs at ambient is insufficient for any application where chemical resistance is important. For aggressive chemicals you really need to fully cure the resin by post curing at elevated temperatures and even for non-aggressive chemicals you should still leave the laminate for a few days to develop a reasonable level of cure.

Please can you pls tell me why one would use a Vinyl Ester resin instead of polyester resin?

Vinyl ester resins generally have good resistance to heat, water and a wide range of aggressive chemicals so are used for chemical pipes and tanks and any applications requiring heat and chemical resistance. They have good blister resistance which can be caused by penetration of water into the laminate so can be used for boats (usually only in the first layers behind the gelcoat to save cost), spa baths etc.


Do you supply aluminium filled phenolic resin, is this a material familiar to you, and do scott bader supply this?

They have supplied phenolic resins in the past but no longer have any on the range. I have not seen any aluminium filled phenolic resins - the phenolics we used to sell used a strongly acidic hardener which might be an issue if filled with metal powders. You can get aluminium filled epoxy resins for mould making, this is to get better heat transfer in heated moulds. They tend to use a mix of aluminium powder and aluminium granules.


Do you supply a resin which can withstand temperatures of minus 80 up to atmospheric for dry ice container?

GRP has been used to make mouldings which operate at low temperatures - basically all of the structural properties go up except for elongation to break so they are stronger, stiffer but a little more brittle. I have some laminate properties down to minus 40 deg C - the elongation to break of the laminate drops from 2% at room temperature to 1.6% at minus 40 degree C. I have some impact figures for a csm laminate which was taken down to minus 72 deg C - the impact strength was actually higher than at room temperature as the laminate was stiffer at the lower temperature but would have presumably broken at a lower elongation to break . Generally speaking, it is possible to expose GRP to very low temperatures without doing any damage to the laminate.


Do you sell a suitable low shrinkage resin which can stand up to temperatures of 100°C?

The resins with the highest HDT's are usually the ones at the higher end of the shrinkage range - is this being used in a laminate or casting application.? Higher reactivity resins have the higher HDT's and also generate higher exotherms on cure so any casting jobs will be difficult unless highly filled. If it’s a laminating job, then C.474PA could be used - you can also fill with 25% filler - calcium carbonate or ATH to reduce shrinkage. Maximum HDT is one property that can only be achieved after a post cure schedule so you would need to cure at room temperature and after 24hrs gradually increase the temperature up to 80 deg C and hold for 3hrs.


What is the difference between unsaturated polyester resin and saturated polyester resin?

Scott Bader only makes unsaturated polyester resins which contain an unsaturated acid called Maleic acid/anhydride. They are liquid resins where the unsaturation in the Maleic forms crosslinks through the styrene monomer when you add the catalyst to form a three dimensional solid. Melinex is a polyester film based on a saturated polyester - they are solids so are not in the normal liquid form like unsaturated polyester resins dissolved in styrene monomer.


My Epoxy Resin is sludgy with bits in - What's wrong?!

Epoxy resins have a higher freezing point than water, and so can freeze or congeal during transit or storage in the winter months. This is easily remedied by heating the resin to about 50 degrees C until it returns to its normal state. For more info see this article and video: Crystallization in Epoxy Resins



What is the difference between Gelcoat and Resin?

A gelcoat would normally have about 3 times more thixotrope than a typical laminating resin. This increase in thixotropy means that the gelcoat can be applied to the recommended thickness of 0.4 - 0.6 mm in a single continuous film without drainage on vertical or inclined surfaces. The laminating resin could not do this, and obviously the gel coat would not wet out glass reinforcements as a laminating resin does.

Can you recommend a resin and a gel coat which is both resistant to petrol and heat up to 100°C?

Unleaded petrol is quite aggressive towards GRP - we only recommend Crystic 199 and full post cure. There is no readymade gelcoat based on C.199 although you can formulate one by blending C199 with Pregel 27 - it’s a bit long winded and you would also need to add the accelerator etc. You could use C.199 with a glass tissue instead of a gelcoat. Hopefully you need a resin which resists petrol and heat up to 100°C separately and not both at the same time - C199 will do both things but will not be resistant to petrol at 100°C. I doubt if any resin would resist petrol at 100°C. 


We were happy with the flexibility of the Crystic D8151 for our application once cured. If we stuck with neat Crystic D8151 base, could we still use Styrene as a thinner so we can apply it easier? We also still had a bit of tackiness on the cured surface once cured. ?(a day after application).In our mix we added ?3% of the base mass of D8151 in Solution MW – if we increase the percentage of Solution MW might this cure the tackiness ?

Like most flexible polyester resins C.8151 will cure with a very tacky back surface although I would have thought adding 3% MW would overcome this as it’s a higher addition level than usual. It would be possible to thin with styrene if they wanted a thinner resin - up to 5% shouldn't have too much influence on its properties. As MW is 95% styrene you are already adding some styrene so I would try 3% MW + 2% styrene and only add more MW if necessary. There are some other flexible grades but all smell of styrene - there is a much thinner, clearer resin called PD9295 used originally to inject between glass sheets for safety glass. It would be a good option if you can get it - it’s made quite regularly so could be worth a look, it would still need the MW to make it tack free. It’s a lot thinner so they wouldn't need to thin further."


We are currently using Scott Baders 1355pa fire retardant resin which has a class 1 rating.

From memory I think the 356pa had a similar rating and also had a class 1 or class 0 if backed up with a 65pa gelcoat.

Does the 1355pa have a rating when backed with 65pa or does it void any fire rating if backed with 65pa?   just it does not mention on the tech datasheet.

We have a class 2 certificate for GC65PA backed with 1355PA, so it drops from a class 1 to a class 2 - it’s a very old certificate dating back to 1982. As GC65PA contains no fire-retardant additives you need to restrict its thickness to the usual 500 microns or so as if much thicker than this you will almost certainly have some influence on the fire rating."



Can I apply fibreglass matting and resin over Aluminium?

A certain amount of adhesion will take place if you abrade the surface thoroughly with either P40 Glass paper or a disc grinder with the same grade surface, then immediately after you have prepared surface wash with Acetone and apply laminate, if you leave a while before laminating oxidisation will take place in turn adhesion will be greatly reduced. The same method applies to most metals, a coating of G4 will also help before the resin is applied.


I have a motorhome with an aluminium roof bonded to some kind of fibre board. It is painted in cellulose. The roof is made of three sections which are seam sealed. I would like to know if I could go over this seam with fibreglass matting and resin, as the seam has started to come away from itself, so that it would be waterproof again. Perhaps you could suggest the best way to go on this and if it is possible would the cellulose have to be removed for the resin to take. I would appreciate your help.

I have taken moulds off cars with the paints currently in use and there has been no reaction with the paint at all - I think these will be some type of urethane or acrylic base. I would not expect cellulose paints however to resist the styrene that polyester resins contain - this is the crosslinking monomer that takes part in the hardening process. I would expect the paint to partially dissolve and wrinkle under the resin so I think it would be best to remove it or at least try a small area first. I hope this helps.


Dear sirs, could you tell me what is the procedure to get the best bond onto Stirling board using polyester resin and fibreglass?

I've never tried to bond resins to Stirling Board - it’s made from wood pieces bonded together with a resin of some kind, so it depends on if this resin is compatible with polyester resin or does it inhibit the cure of the resin. I think it would be quite absorbent, so you probably don’t need to do any surface prep - just ensure its clean and dry. You should do a small test piece first then try to prise off the laminate and look for any under cure of the resin which has been in contact with the board - look for a sticky or tacky surface or smell of benzaldehyde (pear drop or almond odour). Hope this helps.