PBO reader Mike Stanton thinks that his antifoul paint may be incompatible with his boat’s basecoat. Our antifoul expert has this advice…

Mike Stanton from the Isle of Man writes: “I wonder if you could help with a suspected incompatible antifoul issue on my 2011 Beneteau First 40 which I race and cruise in the Irish Sea and West of Scotland.

“I bought the boat in 2017 from the second owner who was based in Nieuport, Belgium. He’d bought it in 2014 from Sunsail in Port Solent where it had been part of their charter fleet.

“I’m having problems finding a compatible antifoul to the one that seems to be the base coat below the waterline. I’ve applied a cream-coloured layer of International Ultra 300 antifouling but that has not stuck well, despite extensive preparation and application of Primocon undercoat to large areas of the surface.

“There’s a brown layer applied by the yard in Belgium for the previous owner in 2017 and again this has had patchy success.

“Underneath the various flaking layers there is a dark blue paint that seems pretty solid. Sunsail are very kindly looking into their maintenance records for the boat to identify the product name of the blue layer so that I can determine a compatible brand.

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“But in the meantime any suggested next steps and products to use would be greatly appreciated. Failing that my final option is to strip back to gelcoat and start again, which seems a minefield.

“Again I’d be grateful for your thoughts on the ‘lesser of evils’ method of stripping (i.e. chemical, hand scraper or soda/sand blasting) to adopt.”

PBO antifoul expert Richard Jerram replies: ”I believe the blue antifouling applied by Sunsail may have been a Jotun product but I can’t be certain.

“However if the underwater area was thoroughly pressure washed with freshwater and the surface abraded wet with a 80- to 120-grade abrasive and a coat of International Primocon applied you should have been able to achieve reasonable adhesion.


Areas of osmosis uncovered by soda blasting will have to be filled and faired before antifouling

“Stripping back the antifouling to the gelcoat is an option and can be done by scraping or using a chemical stripper, although I appreciate this is a hard and time consuming job.

“The option of having the bottom professionally soda blasted is the easier choice but, inevitably of course, more expensive. However it will leave a good surface to apply an underwater primer before applying fresh antifouling.

“Soda blasting may find some very small areas of weak gelcoat which will require repairing before priming. These weak areas are likely to be very small indeed but might expose some glassfibre fibres which will need to be sealed back with two to three coats of solventless epoxy and filled with an epoxy filler.

“The underwater area should then be primed and a minimum two coats of antifouling applied.”

Got a question? Email: pbo@futurenet.com and we’ll put it to our panel of experts.

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This feature appeared in the August 2022 edition of Practical Boat Owner. For more articles like this, including DIY, money-saving advice, great boat projects, expert tips and ways to improve your boat’s performance, take out a magazine subscription to Britain’s best-selling boating magazine.

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