How do I remove antifouling paint from my boat?
My 30-foot fibreglass cruiser has several layers of old antifouling, and patches are starting to crack and flake. How should I strip it back, and do I need to remove the primer as well?
Answer
Remove failing antifouling with a vacuum-connected scraper, then tackle the remaining patches with controlled sanding and dust extraction or a suitable chemical stripper. On a fibreglass hull, stop at sound primer unless damage, corrosion or the requirements of your replacement coating system justify stripping further.
Check the existing coating
Wash off slime and fouling at the boatyard's designated washdown area, ideally immediately after lifting out. Dried growth makes scraping harder and hides cracks, blisters and loose paint.
Once the hull is dry, inspect several areas and scrape a small test patch. Establish whether just the surface is loose or thick layers are separating underneath. Keep any old paint records: primer and antifouling can be similar colours, so colour alone is an unreliable guide to where you should stop.
- Sound, compatible coating: clean and prepare it according to the next paint's instructions; complete removal may be unnecessary.
- Cracked or flaking coating: remove unstable layers, including thick build-up, back to a firmly bonded base, usually the primer.
- Rust on an iron keel or steel hull: expose affected metal so corrosion can be removed and the protective system rebuilt.
- Blisters or exposed laminate: investigate before repainting; confirmed osmosis may require specialist removal of coatings and affected gelcoat.
Self-polishing antifouling commonly needs complete removal after roughly 5 to 15 years, depending on application thickness and use. Hard antifouling builds up more persistently and generally needs sanding annually or every other year.
Scrape and collect the waste
For a typical fibreglass cruising boat, a carbide scraper connected to a suitable professional dust extractor is a practical first choice. A blade around 50 to 65 mm wide gives good control without making every stroke exhausting.
Wear a properly fitted P3 respirator, eye protection, gloves and disposable coveralls. Leave movement of props or cradle supports to the boatyard.
- Lay a tough tarpaulin beneath the working area, arranging the edges to retain flakes.
- Test the scraper on a small patch, holding the blade at a shallow angle.
- Pull with steady pressure, taking off paint in thin passes rather than digging under it.
- Ease pressure at hull curves, skin fittings and the edges of exposed primer.
- Vacuum loose material frequently and bag the collected waste.
Slightly rounding sharp blade corners helps prevent gouges. Do not use an angle grinder, aggressive sanding disc or wire wheel on a fibreglass hull: these can quickly cut through primer and gelcoat.