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We have been in business as manufacturers and suppliers to composites manufacturers for over 50 years, so our experts have a great deal of experience in this area. This is a selection of genuine questions from our customers. If you cannot find the information you require here, please contact us or call on 0191 497 5134, we are pleased to help.


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 effect 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.

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.

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 its 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 make 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 its 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.

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 undercured resin but once this top layer was removed it would take some time for the solvent to damage the underlying resin.

A slower catalyst like our catalyst O or Butanox LA was originaly 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 geltime 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.


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!


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. off!

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.

Whenever a fibreglass laminate has beed 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 hazzards), 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.

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).

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 brushmarks and then finer and finer grades to approx 800 wet and dry paper followed by compounding with rotary buffer / polishing machine etc. Its an awful lot of work - you may be better off abrading back the surface and applying a marine paint system.

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.

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.

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.

Some blue pigments will form a white bloom if water gradully 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.

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.

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 wont 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 out side 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.

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 hardener 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.

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.

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.


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.

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


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

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 browny 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 clear on the bigger variations it is advisable to stage in layers, sometimes the layers are visible in the casting.

I dont 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 cant say for sure. I know that low melting point alloys are cast into silicone rubber moulds to produce highly detailed toy soldiers etc.


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.


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

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.

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

Common Problems

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 its easier to stop the problem occurring when the pools are made rather than to try and remedy the problem when it occurrs. Its 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 thouroughly before filling with a two pack epoxy filler and then using an epoxy or two pack polyurethane paint.Its a lot of work and there are no guarantees that it wont come back. You could do a cheaper job using the same preparation and filling the voids with polyster gelcoat etc - again there is a good chance that this will not be a permanent solution. Hope this helps.

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 spiders web. Stress - caused by the laminate flexing . Its 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. Its 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. Its 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. Its a matter of judgement really - the cracking probably will have little effect on the structural properties of the boat and will be difficut/expensive to repair successfully.

This is the sort of thing you would really need to see - I cant 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 .Its 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.

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 routering 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.

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 Baders 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 dont think you can totally resolve this type of effect but may be able to reduce it with certain resins and rubbers.

Core Materials

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.

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!

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 may however want to sandwich 265g Diolen beetween 2 layers of 300g, this would increase the impact resisitance 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.


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.

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.


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 it’s products


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.

Best way, and indeed advised way is by brush, apply too thick and you lose the effect as the granuales 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 personaly have applied a few times and it's impressive.

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 would 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

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.


Boiling water is surprisingly aggressive towards GRP and its 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.

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.


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 Cresomer and it will take more load on it’s 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.


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.

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.


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.

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.

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.


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.


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 its 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.

The cost would be dependant 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 fiber.

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.

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.

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.

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.

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.

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.

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.


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 prefered terms used for description, FRP was used in the early days. Hope this helps ease the confusion!

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.

General purpose grades have never been suitable for storage of petrol as they do not have sufficient resistace to oils, diesel , petrol and other similar materials. Before un leaded 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.

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 lay up, spray laminating, filament winding etc - 60Kg per tonne of rsin used. RTM,cold and hot press moulding - 20Kg per tonn 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 there styrene is contained then you will be emitting a small proportion of this figure.

Applying hot bitumen to GRP will soften it untill the Bitumen cools down but I dont think it would do any damage to it long term.

Scott Bader used to make a light stabilised clear acrylic laquer 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.

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


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 add a little more, from 1-5% by weight

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, dont forget always to stir pigment well before use.

"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 "


Please see our detailed instructions for fibreglass pond construction here, which has details on lay up. For lay up 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.

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.


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 to call us as it all depends on what shape your mould is, what you are duplicating, is it a male or female mould etc.

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 it's 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 to much on and it will run and 'fish eye'. Follow this guide and it does work, done it hundreds of times myself.

The PVA release agent is of very low viscosity and the solution will drain down vertical sections and accumulate in corners ect 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.

"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."


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.

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.

Ive been repairing Gelcoat for 20 years + and ive never used wax as an advantage, basically you need to leave the repair for 24 hours before using wet and dry paper ect, 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.


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.

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.

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 out last you and me, not just last a few years. The secret is, is the boat worth it, and can it be done correctly?

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 retardent resin, Resin H = chemical reistant resin.

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 dont 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.

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 emmissions when they burn. They have been widely used for underground trains etc where low smoke emissions are critical.

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 doesnt 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 necessay. Hard abrasive fillers can be added to an isophthalic resin like Scott Baders 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.

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

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.

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.

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.

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 strenth 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.

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 its 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.

Scott Bader only make 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.

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

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.

Unleaded petrol is quite aggressive towards GRP - we only recommend Crystic 199 and full post cure .There is no ready made gelcoat based on C.199 although you can formulate one by blending C199 with Pregel 27 - its 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.

"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 its 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 - its made quite regularly so could be worth a look , it would still need the MW to make it tack free.Its a lot thinner so they wouldn't need to thin further."

"We have a class 2 certificate for GC65PA backed with 1355PA so it drops from a class 1 to a class 2 - its 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 ."


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 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.

I've never tried to bond resins to Stirling Board - its 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 dont 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 undercure 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.