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How to Laminate Fibreglass and Resin


Typical laminating projects: Canoe, Boat Hull, Replica Armour, Patio Furniture, Car Bodywork, Shower tray, Plants pots & Troughs, Cladding Panel and many more...

Preparing Resins for Casting or Laminating

All resins whether for casting or laminating, require the addition of catalyst (hardener) and accelerator if the resin is not pre-accelerated, to initiate the curing process.

Use a safety dispenser bottle to add 20ml of catalyst per 1kg of resin. Stir thoroughly - 30 mixes to the left and 30 mixes to right. The hardening process begins immediately, so only catalyze a working quantity, or your mixing containers will soon be full of solidified resin, work quickly once the catalyst has been added.

When Pigments are being used they should be stirred into the resin before adding the catalyst. On average add 10% of pigment paste depending on the colour required, black pigments will use 5% and other pigments can use up to 15% per weight. Please check colour charts for suggested percentage per colour to be used. To maintain consistent colour on a large project it is a good idea to pigment ALL the resin/gelcoat or poolcoat, and then decant working quantities to be catalysed as required.

Once catalysed, the resin gradually cures, taking on a jelly-like consistency in about 10 - 15 minutes, before becoming hard in about 30-40 minutes at room temperature (about 20°C). The curing process generates heat (known as "exotherm") within the resin. Too much catalyst or large volumes of resin increase this heat, so a thick laminate or a large casting should preferably be built up in stages. Overheating of the resin in the mould can warp and damage the mould.

Mixing Quantities - Polyester Resins & Catalyst

Liquid Catalyst
Add 2ml of catalyst per 100gm of resin, and stir thoroughly. Use as a guide as the temperature will vary on the catalyst ratio. Minimum of 1% and a maximum of 3% of catalyst addition. Less than 1% of catalyst addition could cause under-curing in the laminate not giving maximum strengthening properties and not more than 3% catalyst should be added as it will cause over-curing affecting the strengthening properties.

Resin Liquid Catalyst





















With general purpose resin (but NOT gelcoat) the rate of cure can be slowed down by using 1g liquid catalyst per 100gm resin - ie. Half the quantities shown above. This can be useful in very hot weather, when the resin might otherwise cure too quickly. Remember never use less then 1% of catalyst.

Laminating Technique

Preparing the mould

Unlike moulds made from "self-releasing" materials, such as polyester film, the GRP mould will need to be treated with release agents to ensure the laminate does not bond to the surface.

To prepare the GRP mould, first apply up to 6 coats of silicone-free wax release agent ( Ramwax –Run In ), buffing each coat to a high gloss and allowing it to harden for 1 hour before applying the next coat. Finally, a PVA release agent should be applied evenly over the entire mould surface.

For detailed information on mould release systems, contact Nivitex.


If the laminate is to be self-coloured, pigment the resin with a maximum of one part pigment to ten parts resin ( 5% of the weight of resin ). For economy, pigment the gelcoat only (10 to 15% pigment loading) – for best results pigment gelcoat and the resin.

Decant a working quantity of gelcoat into a mixing bucket and add 20ml of catalyst per 1kg of gelcoat. Stir thoroughly, then use a brush or polyester roller to cover the mould surface evenly with gelcoat. Wait for at least an hour, until the gelcoat becomes tacky (it will feel slightly sticky but will not actually adhere to the touch) and make sure there are no corners or crevices where the gelcoat is still wet. Then catalyse a working quantity of resin. Paint the Resin over the gelcoat.

Lay down a piece of glassfibre and push it gently into the wet resin with a brush. If the glassfibre material is Chopped Strand Mat, use a stippling action – do NOT "paint" to and fro, as this tends to separate the glass fibres. Make sure the glassfibre is thoroughly impregnated with resin (keep the brush well-loaded to add more resin if necessary).

Once completely "wetted-out", use a metal laminating roller to consolidate the layer and force out any air bubbles. This also forces through the fibres from beneath, which makes for better impregnation.

A further coat of resin and another layer of glassfibre can then be added, repeating the process. Any number of layers can be build up depending on the thickness and strength required. Do not apply more than two layers at a time as the quantity of resin will generate heat build-up and could damage your mould. Allow resin to cool down before applying more layers, then repeat process until required thickness is reached. For many jobs, two layers will be adequate. Remember that whilst a thicker laminate will be stronger, it will also be heavier, which can be a critical factor in some applications. A thin laminate can be made stronger or more rigid by adding ribs or box sections, easily laminated over formers of paper , rope, shaped foam or even cardboard.

You can also use glassfibre fabrics or woven rovings in conjunction with matt to give the required combination of strength and weight. If you are using a combination of materials, lay the mat first. Do not use two consecutive layers of fabric – always have an intervening layer of mat.

The exposed surface of a chopped strand mat laminate will be rather rough – this will not normally matter, but if necessary, it can be covered with a layer of surface tissue. Surface tissue is fine glassfibre material – it has a smooth side and a "hairy" side. Whilst the laminate is still set, apply the surface tissue, hairy side down, wetting out with more resin, and stipple down lightly. Surface tissue will give you a smoother finish and is also used on gelcoat before the matt is added to prevent print through of the chopped strand matt through the gelcoat.

During laminating, the resin on the brushes and tools will begin to solidify. Prevent this by washing them in brush cleaner (acetone) which will dissolve the resin. They must be wiped dry before reusing. Remember acetone is highly flammable – do not smoke or use naked lights anywhere near it! It is very volatile, and tends to evaporate, so keep it in a covered container.

When the required layers have been built up, leave the laminate to cure. It will soon reach the "green stage", when it becomes quite firm, at which point you can trim off rough edges with a trimming knife. Once fully hardened, you will have to use a hacksaw with a metal cutting blade. Cutting, sanding and drilling cured laminates (especially with power tools) produces harmful particles – to avoid these, you should wear a breathing mask and goggles. When fully cured, the laminate can be released from the mould. If this proves difficult, due to a complex mould or inadequate use of release agents, the moulding can sometimes be sprung out by striking the mould with the flat of the hand (or a rubber hammer) – do not use a metal hammer, as it will probably graze mould and moulding! A rubber mallet can be used, but requires some skill. Wooden or plastic (but not metal) wedges can be used to rise out the moulding, but take care not to scratch the surface.


Glassfibre, laminates and resin castings can be sawn, drilled, sanded or polished. Most tools intended for metal work (ie. Hacksaws) will be adequate for cutting or trimming laminates and castings, and further shaping can be done with rasps and files – tungsten carbide tools are particularly useful for this. Further finishing can be carried out with progressively finer grades of Wet and Dry paper, used wet, with GRP polishing compound being used for the final rubbing down. All of this work can be done by hand or with power tools. Grit and particles from both the glassfibre and the hardened resin can be injurious to eyes and lungs – it is therefore important to wear goggles and breathing masks during finishing. This is absolutely essential if power tools are used.

Painting GRP

Generally speaking, it is much easier simply to pigment the resin used in a laminate rather than paint the finished article. If it is necessary to paint a GRP item, first prepare the surface by sanding it lightly. Follow the paint manufacturer’s recommendations with regard to primers. The type of paint used depends on the type of item – a boat, for example, obviously needs extremely durable, weather-resistant paint, two-part polyurethanes being generally used. Some aerosol cellulose paints intended for bodywork should be avoided, as should any paint which has a chemical etching effect. Acrylics and enamels can be used on small items such as models.


A former is anything which provides shape or form to a GRP laminate. They are often used as the basis for stiffening ribs or box sections. A popular material for formers is paper rope, made of paper mound on a flexible wire core. This is laid on the GRP surface and is laminated over to product reinforcing ribs, which give added stiffness with little extra weight. The former itself provides none of the extra stiffness – this results entirely from the box section of the laminated rib. Wood, metal or plastic tubing, and folded cardboard can all be used successfully as formers. Another popular material is polyurethane foam sheet, which can be cut and shaped to any required form. It is often used as the basis for vehicle bodywork modifications, such as customized spoilers.

Bonding Fittings to GRP

It is often necessary to construct a GRP laminate so that various fittings can be added to it – typical examples are the drain pipe of a shower tray, the footrest of a canoe, the rowlocks of a dinghy, and so on.

Such items can often be incorporated directly into the laminate simply by placing them in the appropriate position during laminating. A few small strips of glassfibre can be laminated around the fitting to strengthen the join. Metal plates , strips of wood or even core matt buried at suitable points within a laminate will give additional strength to GRP items which need to take bolts or screws (eg, a “bolt-on” bodywork accessory such as a spoiler).

Adhesive for use with GRP

Since polyester resin is highly adhesive, it is the logical choice for bonding most material to GRP surfaces. A range of specially formulated Special bonding pastes can be obtained from Nivitex Fibreglass and Resins. Polyurethane-based jointing compounds, epoxy adhesives and most high-strength impact adhesives, “superglues” etc, can be used on GRP laminates. Most other adhesives will be incapable of bonding strongly to GRP and should not be used when maximum adhesion is essential.

Core Materials

Core material (eg. Coremat, polyurethane or PVC foam sheets) are used in sandwich construction-basically a laminate consisting of a core material between two or more glassfibre layers. This gives the laminate considerable added rigidity without greatly increased weight. Core materials are available which can be bent and folded to follow curved surfaces such as boat hulls. Core materials can be glued or stapled together then laminated over to produce simple box structures, such as storage tanks, without requiring a mould.

Storage and Handling

To ensure maximum stability and maintain optimum resin properties polyester resins should be stored in closed containers and maintained below 25°C and away from heat sources and sunlight. All storage should conform to local fire and building codes. Drum stock should be kept to a reasonable minimum with first-in, first-out stock rotation.

Standard Package

Non-returnable metal drums, kegs, plastic buckets.

Material Safety

A material safety data sheet is available from your Nivitex Fibreglass and Resins representative or call our offices. Make certain that you obtain a copy of this guide to the safe handling of unsaturated polyester resins and resin systems.



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The information included in this document is given in good faith and is intended to assist you the customer in determining the suitability of this product for your application. Due to the diverse applications and conditions in which many of our products may be used, we request that you, the user, test and inspect our product to satisfy yourself of its contents and suitability for your specific need. This document does not constitute any guarantee or warranty expressed or implied. The exclusive remedy for all proven claims is replacement of our product and under no circumstances shall we be liable for any special, consequential or incidental damages.

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