Over the years I have kept the hull of my sailboat pristine by coating it with clear linear polyurethane. Now I want to take it back down to gelcoat. I thought the only way to remove it was sanding it, but then I remembered airplanes are painted with this stuff and I doubt they get sanded. What do you think?
Don Casey responds:
At the Miami Boat Show I put your question to representatives from Interlux (Interthane) and US Paint (Awlgrip). Interthane recommended Interstrip 299E, which it claims will remove polyurethane, but not damage fiberglass, provided you don't leave the stripper on the fiberglass for eight hours. The US Paint rep, whom I found to be the more knowledgeable, said sand it off. He said that sandingoften in the form of blasting with a gentle medium, not sandhas become the norm even with airplanes. Because planes are mostly metal, strippers have been used in the past, but today the bigger problem is what to do with the toxic scrapings. Nose cones, which are fiberglass, are nearly always sanded, according to this rep.
If you use a stripper, do not leave it on one second longer than necessary to lift the paint, then get all residue off the fiberglass right away. There is very little chemical difference in gelcoat and paint, and I have firsthand experience with so-called safe strippers damaging the gelcoat. My own experience with the risk and mess of strippers leads me to recommend sanding as the better alternative.
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