P40 grit sandpaper is the recommended grade for preparing cured GRP laminate prior to topcoating. Its coarse abrasive quickly removes sharp glass fibres, trims down resin ridges and creates the mechanical key needed for strong topcoat adhesion.
Correct sanding at this stage is essential to achieving a smooth, professional GRP roof finish and preventing future coating issues.
Why P40 grit is ideal for GRP preparation
• Quickly removes sharp glass fibre spikes after lamination
• Flattens overlaps, resin build-up and high spots
• Creates a strong mechanical key for topcoat adhesion
• Helps prevent pinholes and capillary water ingress
• Speeds up preparation of large and detailed areas
Important sanding guidance
Always ensure the laminate is fully cured before sanding.
If the laminate is still “green” in the curing cycle, the resin will soften and clog the sandpaper, making sanding difficult and less effective.
Once fully cured:
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Sand the entire laminate surface using P40 grit
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Remove dust thoroughly
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Wipe down with acetone
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Apply GRP topcoat
Using the correct grit at the correct stage is key to achieving a durable, long-lasting GRP roofing system.