Primers & Undercoats

Our Primers & Undercoats range covers the preparation coats that go beneath antifouling, topcoat and varnish: epoxy primers for new or bare GRP, and undercoats that even out colour and improve adhesion before a final finish.

Primer is not an optional step to skip for speed – it’s what makes the final coat adhere properly and last. A new or bare GRP hull, or one stripped back to gelcoat, needs an epoxy primer before antifouling to seal the surface and give the antifouling something to grip, since antifouling itself isn’t designed to bond directly to bare gelcoat long-term. An undercoat serves a related but different purpose above the waterline: it evens out an uneven or dark existing colour so the topcoat goes on true, and improves adhesion on a surface that’s been sanded back.

Always follow the specific system’s recoat window – priming too far ahead of the final coat, or leaving too little time between coats, both reduce adhesion. If you’re unsure whether your hull needs priming before antifouling, it usually does unless you’re simply overcoating existing, sound antifouling.

Frequently asked questions

Do I need to prime a new GRP hull before antifouling?

Yes – an epoxy primer seals bare gelcoat and gives the antifouling a surface to bond to properly, which antifouling can’t do reliably applied directly to bare GRP.

When do I need an undercoat rather than going straight to topcoat?

When changing to a lighter colour over a darker existing one, or after sanding back to bare material – an undercoat evens out colour and improves adhesion.

How long should I leave between primer and the final coat?

Follow the specific product’s recoat window – too soon and adhesion suffers, too long and you may need to sand and re-key the surface before continuing.