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How many top coats do you need on a fibreglass roof
About to tackle a small GRP roof and not sure if one top coat is enough or if I should be doing two. What’s the usual?
Expert Trade Answers
"For a GRP fibreglass flat roof, the number of top coats required depends on the manufacturer's specification, the quality of the system being installed and the finish required. In most professional installations, the roof is normally finished with one properly applied GRP top coat, provided the underlying laminate layers have been installed correctly and the top coat has been applied at the correct coverage rate.
The top coat is not there to provide the main waterproofing — the waterproofing comes from the correctly installed fibreglass laminate system underneath. The top coat provides the final weatherproof, UV-resistant finish and protects the laminate from the elements.
Applying extra coats does not automatically make a roof better. The important factors are correct preparation, a properly prepared roof deck, correct resin and mat application, good detailing around edges and upstands, and following the manufacturer's installation guidelines.
A professional GRP roof system should include all necessary trims, edge details, drainage falls and finishing work to ensure a long-lasting watertight installation.
My advice is to always follow the specification of the GRP system being used rather than adding extra layers unnecessarily. With fibreglass roofing, correct preparation and workmanship are what determine the lifespan of the roof."
The top coat is not there to provide the main waterproofing — the waterproofing comes from the correctly installed fibreglass laminate system underneath. The top coat provides the final weatherproof, UV-resistant finish and protects the laminate from the elements.
Applying extra coats does not automatically make a roof better. The important factors are correct preparation, a properly prepared roof deck, correct resin and mat application, good detailing around edges and upstands, and following the manufacturer's installation guidelines.
A professional GRP roof system should include all necessary trims, edge details, drainage falls and finishing work to ensure a long-lasting watertight installation.
My advice is to always follow the specification of the GRP system being used rather than adding extra layers unnecessarily. With fibreglass roofing, correct preparation and workmanship are what determine the lifespan of the roof."
Answered on 22nd Jul 2026 - Member since Jul 2026 -
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"Two top coats is better to be on safe side no problems after that"
Answered on 26th Sep 2025 - Member since May 2025 -
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"You only need one top coat on a fibreglass roof, but we generally give it 2 coats just to be on the safe side."
Answered on 20th Sep 2025 - Member since Sep 2025 -
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"strip off the old roof covering and boards, fix new boards , apply resin to board ,new matting with more resin until it goes transparent with metal roller,leave to dry then roller 1 solar topcoat to finish"
Answered on 10th Mar 2026 - Member since Mar 2026 -
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