PBO reader Antony Cole wants to know how to remove gelcoat from his boat. Our paint and antifouling expert Richard Jerram has this advice…

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Antony Cole writes: “I have 50-year-old GRP trimaran with damaged gel coat undersides.

“The gelcoat was left rough and pitted by grit blasting to remove the old antifouling and in many places the fibreglass laminate has been exposed, while in others the gel coat has many cracks.

“Luckily the GRP looks to be in good condition with no signs of osmosis. I want to repair and make ready for Coppercoat antifouling and need advice on the best way to do this.

“My plan is to remove damaged gelcoat by sanding with 40-grit or even coarser discs with an orbital sander or angle grinder, then fill and fair with epoxy filler using glass bubbles.

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“Finally I’d apply multiple coats of a high build epoxy primer before antifouling.

“I’ve been advised that I should use a solvent-free epoxy primer but don’t know what the difference is between epoxy primers, apart from the cost.”

PBO paint and antifouling expert Richard Jerram replies: “You’re right, surface should first be well sanded with a 40-grit abrasive.

“The safest way to do this would be to use an orbital sander rather than an angle grinder as a grinder might gouge the surface and expose more bare laminate.

“Areas of bare laminate will need to be coated with a solvent-free epoxy and then filled using an epoxy filler.

“Solvent-free epoxies are ultimately more durable than those that have been thinned with solvents.

“When cured abrade the filler smooth and seal with a second coat of solvent free epoxy.

“Ensure all sanding debris has been removed and the surface is free of all contaminates.

“Coppercoat can then be applied in accordance with the manufacturer’s instructions.”


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This feature appeared in the April 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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