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Frequently Asked Questions

GRP (glass reinforced plastic) roofing is a popular roofing material used for low-slope and flat roofs. Here are some frequently asked questions about GRP roofing:

Q: What is GRP roofing?

A: GRP roofing is made of layers of reinforced fiberglass and a resin coating. It is a lightweight, durable, and waterproof material that is commonly used in flat roofs.

Q: How long does GRP roofing last?

A: GRP roofing can last up to 25 years or more with proper installation and maintenance. The lifespan of GRP roofing depends on various factors such as the quality of materials used, the installation process, and the level of maintenance.

Q: How is GRP roofing installed?

A: GRP roofing is installed in several steps, including surface preparation, laying out the fiberglass matting, mixing and applying the resin and catalyst, and adding a final layer of topcoat for added protection.

Q: Can GRP roofing be repaired?

A: Yes, GRP roofing can be repaired if there is damage or a leak. The repair process typically involves cleaning the damaged area, applying a resin patch, and adding a topcoat for protection.

Q: Is GRP roofing eco-friendly?

A: GRP roofing is considered eco-friendly as it is a low-energy material that can be recycled at the end of its lifespan.

Q: Is GRP roofing expensive?

A: The cost of GRP roofing depends on various factors such as the size of the roof, the quality of materials used

Select our most frequently asked questions below. If you have any other queries – please contact us using our contact form and we will get back to you as soon as possible

Thorough mixing of catalysts into resins and gel coat is very important. Also, the correct additions should be observed to maintain good results. Dispensers are advised for accuracy.
The details below gives the correct ratios of catalyst to resin and gelcoat by weight. 1% is considered a slow mix, 2% is ideal, 3% is a fast mix. Additions outside these bands in not advisable for proper curing, in fact adding more than 4% may result in a failure to cure. The pot life of these mixes is also determined by temperature. The higher the temperature the faster the cure.
As a general guide 2% addition at 20ÂşC gives 15-20 minutes pot life. The resin will always cure quicker if left in a mass such as the mixing bucket or in castings. Never mixed gelcoat or topcoat above 2% it is best to mix smaller amounts frequently.
Follow the basic principles based on weight for example 10kg will use 200ml at 2%

  • 1kg @ 1% is 10ml
  • 1kg @ 2% is 20ml
  • 1kg @ 3% is 30ml
  • 1kg @ 4% is 40ml

Orders required to be delivered on the next working day must be placed before 1pm. All orders placed after 1pm are likely to be despatched on the following working day.
Allow 1-3 working day to avoid on site delays

YES YES YES Never use Resin or related products unless its dry

If your boards are wet please ensure they are dry prior to GRP application. Acetone will evaporate water on cured laminate prior to topcoat.

Yes of course providing you lightly sand the laminated areas then wipe down with acetone solution.

Using the woven tape can be a little tricky for a novice.
Potential problems

  • Snagging
  • Creasing


  • Cut shorter strips
  • Apply the main roof CSM over the woven during the laminating process
  • Use strips of CSM matting instead of the Woven bandage cut into Max 2m lenghs (Roll up before laying for ease of application)

White Laminating buckets. Our white buckets are 5.6Litres they do have a line visible on the inside, this mark is the Maximum 5.6L mark. Note some larger kits have 11 Litre buckets. TIP:

  • Peal away cured Resin and re-use the bucket again
  • 5 Litre buckets hold approx 5kg in weight (example 1 lItre = 1kg approx)

Cleaning tools
Potential Problems

  • Roller is going hard while im using it
  • Barrol head jammed
  • Roller is Rock solid


  • Have a litre of acetone in a tub for cleaning during the Process of laminating
  • Unscrew the barrol head between sessions allowing the frame to soak clean
  • Unscrew the barrow head and wire brush clean & Soak overnight in a well vented area.

Repairing a GRP roof If the roof surface becomes damaged by impact or has to be cut for any reason it can be easily repaired using the following procedure:

  1. Clean off the damaged area with solvent and abrade the GRP surface with a hand grinder for a distance of 100mm from the damaged area or edge to be joined.
  2. Cut the 450/600gm2 glass to the correct size to cover the affected area and mix sufficient resin with catalyst as previously described.
  3. Brush resin onto the area to be laminated at the rate of 1 kilo per square metre. Place the glass over the area, wet out the glass with resin at the rate of 0.5 kilos per square metre. Stipple well with the brush or use a paddle wheel roller for larger areas.
  4. Ensure that the laminate is free from air and completely consolidated and allow to cure.
  5. Mix the Topcoat with catalyst as previously described and apply with a brush at the rate of 0.5 kilos per square metre.
  6. Allow to cure. This procedure will ensure that the patch or joining piece applied will bond to the original laminate and form a weatherproof patch over the damaged or cut laminate.

Advice when using GRP during Winter months

  • Always check the local weather forecast (See Commercial Manual for details on how to obtain an accurate forecast.) • During the Winter, avoid topcoating a roof after 2-3pm unless it is a clear bright day and not too cold. The heat from the sun contributes a great deal towards the curing of the laminate during colder months. After the sun has set, it is unlikely that the topcoat will cure over night. If left uncured, the topcoat may cure with debris and leaves stuck to the surface, or with an undesirable finish if it rains. • Ensure that the surface temperature of the boards is checked before laying the resin or topcoat.
  • Ensure that the resin is warmed before use if the ambient temperature is below 10ÂşC.
  • Always ensure that the resin remains indoors the night before it is used.
  • Do not use resin or topcoat in temperatures below 5ÂşC.
  • If it begins to rain, cover the roof with a visqueen sheet.
  • If you are unable to laminate over a prepared deck, then coat the decking with catalysed resin and cover any exposed edges. This will seal the deck and prevent moisture uptake until the laminate can be applied. Always cover the edges of the roof and uncoated boards with a polyethylene sheet.
  • Always ensure the deck or substrate to be laid onto is completely dry before laying the laminate. Sweep off any excess water and mop up the excess with dry cloths before allowing the roof to dry naturally. Wiping the surface with acetone can speed up this process.
  • Do not start to lay a roof if a period of rain is forecast. Advice when using GRP during Summer months • Always check the local weather forecast (See Commercial Manual for details on how to get an accurate forecast online and useful telephone numbers.) • Do not use roofing resin or topcoat in temperatures above 35o C.
  • Always mix smaller batches of resin then you normally would to give adequate time to apply it before it starts to catalyse. • Always use LPT catalyst in hotter weather if the resin starts to cure too quickly.
  • Always apply the laminate in the shortest runs possible across a roof. The shorter the length of laminate, the less likely it is that the resin will catalyse before it can be consolidated into the laminate.
  • Use a temperature sensore to measure the surface temperature of the laminate before applying the topcoat. If topcoat is applied to surfaces above 50o C, the wax component of the topcoat will melt and the topcoat will remain tacky to the touch, this will usually mean that any loose debris will stick to the roof and the colour of the topcoat will also be impaired.
  • If possible, topcoat the roof out of direct sunlight or wait until later in the day before applying it, it may mean that the roof will take you longer but it will save you time spent returning to the roof to re-topcoat it at a later date. Safe working practices It is always the installer’s responsibility to ensure safe working practices for themselves and their employees and always pay attention to the risks for other members of the public that may be nearby at the time. The following notes are designed to help you ensure a safe working environment, but they are by no means comprehensive and any installers should always assess any potential risks when working on a contract and make sufficient means to address them. In addition to these notes, the installer should also be aware of the health and safety information that applies to most materials (see Health and Safety Manual.) 20 G

1) Failure of resin to cure/harden Decription of problem Laminate is still wet and resin is uncured with no other symptoms. Possible cause Remedial action

  • Resin may have been inadequately mixed.
  • Unsuitable catalyst may have been used (e.g. LPT or summer catalyst used in winter.)
  • Not enough catalyst may have been used for the temperature.

Remedial action

  • Catalyse another batch of resin, ensuring that you use the correct catalyst. Always add extra catalyst (doubling up if necessary) and roll vigorously into the resin.
  • Larger laminates or laminates that have been left for a long time or contaminated by dirt, debris or water etc. will need replacing completely.
  • Always check the ambient temperature before mixing batches of resin and consult the catalyst chart for guidance if unsure.

2) Resin cures too fast Description of problem Resin cures before it can be properly applied and consolidated into the CSM.

Possible cause Remedial action

  • Unsuitable catalyst may have been used (e.g. Winter catalyst used in Summer.)
  • Weather may be too hot for Summer catalyst

Remedial action

  • If the ambient temperature is very hot or there is a lot of direct sunlight, use summer catalyst.
  • Reduce the size of the batches mixed.
  • Always ensure that you are laying the shortest possible runs across a roof to give you adequate time to properly consolidate the laminate.

3) It begins to rain while laminating/topcoating

Roof has not yet cured and it begins to rain.

Remedial action

  • STOP! Cover the roof with a non-woven polyethylene sheet and try to ensure that non of the laminate gets any moisture onto it. • Always ensure that you check the local weather forecast before you start a roof.
  • Always have enough polyethylene sheets with you to cover the roof. Resin contaminated with water will not cure and require a re-skin (see below.)

4) Failure of topcoat to cure

Topcoat is still wet and has not cured.

  • Topcoat has not been sufficiently mixed or not enough catalyst has been mixed in.
  • Topcoat might be contaminated by water

Remedial action

  • After water has evaporated apply another very thin layer of topcoat, ensuring that it is vigorously and thoroughly rolled in to the uncured layer.
  • Always add more catalyst to the second batch, up to double if necessary.

Delamination of the laminate from the boards

This will not cause the roof to leak.

This is caused by poor adhesion of the laminate to the boards and is more likely to happen with plywood rather than OSB.

Remedial action

The laminate can be completely removed and reapplied after priming the boards with G4 or Resin (to ensure no further delamination occurs.)

Delamination of topcoat

This will not cause the roof to leak, but will spoil its appearance.

Application of the topcoat to a contaminated surface (usually wet).
Application of the topcoat to a hot laminate may also cause this to happen.
Whenever the adhesion of the topcoat is poor, some topcoat delamination may occur.

Remedial action

The topcoat cannot just be reapplied on top of existing topcoat.
Generally, the best solution is to clean and abrade the surface, removing all of the flaking top coat, then re-laminate the entire roof surface and reapply the top coat.

Cracking of the topcoat

This is usually caused by the topcoat being applied too thickly, topcoat should never be applied thicker then 0.5mm.

Remedial action

The only solution is to relaminate over the cracked area after careful surface preparation.

Cracking of laminate

Could cause the roof to fail if cracking is severe enough.

The roof is over 50m2 and an expansion joint has not been incorporated into the roof

Remedial action

Grind down and laminate over the crack with two layers of 450g/m2 CSM.
It may be necessary to cut out a section and laminate in an expansion joint at 50m2 intervals.
Always check the board fixings, these may need to be re-fixed if they have been pulled away from the joists.

Tacky topcoat

Topcoat has suitable catalyst and has been adequately mixed but is still tacky. This problem usually manifests itself in very hot conditions.

This is usually caused by application of the top coat in hot, sunny conditions, so that the waxy surface layer cannot properly form.

Remedial action

Clean down with acetone and re-apply in cooler conditions.
Tacky topcoat usually occurs at approximately 55o C and this is usually caused by very hot conditions and direct sunlight.

Board swelling (’tile’ outline on the roof)

This will cause a ‘tile’ effect to appear on the roof as the outlines of the boards appear as ridges on the roofs surface. The roof is unlikely to leak, but in very bad cases, some cracking may occur at the joints.

This is caused by moisture uptake in the boards. It may be due to excessive condensation, but is more likely to be a result of some porosity in the laminate, allowing water to seep into the boards.
The problem is made worse by poor board fixing, allowing the boards to move and rise up off the roof timbers. • Insufficient expansion gaps have been left between the boards if over 50m2 .

Remedial action

The roof must be cleaned and all of the ridges ground down.
New expansion joints must be fitted to the roof using E280 trims and the entire roof surface must be relaminated.

In very bad cases, it may be necessary to fix new boards over the existing roof and relaminate, ensuring adequate provision for board expansion with expansion joints on larger roofs.