[MGSailor]

I have a 37' sailboat with ablative bottom paint. The paint flaked off down to the gel coat in several areas after the post haul-out power wash. The boat was new in 2012. It was first painted in 2012 and a second coat was applied in spring 2013.

How should I best address this issue? Is it possible to locally prime / sand the affected areas to obtain a smooth surface? I am concerned about damaging the gel coat and obviously want to avoid stripping the entire bottom and starting over.

I am hoping that the combined experience of the Sailnet community can point me in the right direction.

 

[MarkSF]

How big are the areas? For some reason the adhesion was bad between the original paint and gelcoat (not clean enough? Some mould-release agent left on the surface?) Anyway, you are right the most reasonable approach seems to be to prepare the areas with bad adhesion, and re-paint.

 

[TQA]

Scrape sand prime antifoul,

Repeat as required.

Having a bottom that is not perfectly smooth is not a big deal unless you race.

 

[zz4gta]

Since we don't know what caused it to come off, the only right answer is to strip it to gelcoat, sand, prime, and re-paint. Anything else, no one will promise anything.

If it was me, on a large boat, I'd just fix the spots until it got bad elsewhere. A small boat, it's not that much work, and is a more DIY project.

 

[TakeFive]

Be wary of taking advice from owners of 30+ year old boats. FRP chemistry has changed a lot since then. Your 2-year-old boat is different from theirs.

Sometime in the 1990s, most boat manufacturers changed their FRP chemistry from polyester to vinyl ester. This greatly reduced the occurrence of osmotic blisters, which may make the application of a barrier coat unnecessary. Did your dealer apply a barrier coat?

My advice: DO NOT SAND until you've checked your hull warranty. For a 2012 boat, you are probably still under warranty, and sanding may void your warranty. If sanding voids your warranty, you would want to apply a sandless primer. I use the Interlux sandless primer. Read the instructions carefully - you need to apply the bottom paint while the primer is tacky. Also, NEVER SPRAY SANDLESS PRIMER. Airborne isocyanates will kill you.

I'd suggest a spot repair of the bare spots. De-wax with solvent, apply sandless primer per instructions, apply bottom paint while the primer is tacky. Each year you'll have less bare spots as the sandless primer fixes the adhesion problems. Unless you race, the uneven spots in your bottom paint will have no noticeable effect.

 

[MGSailor]

Great advice. Thanks everyone!

 

[celenoglu]

It is generally due to remaining mould release agents left on the hull during production. Sanding might or might not work. Sanding will carry the leftovers fromone point to the other. Clean the remaining flked paint and use solvents to cleanthe remaning mold release, then you can sand, prime and paint. This is very common on new boats. Normally the remaining mold release should be cleaned with solvents before applying the first paint which nearly none of the producers handlers are doing.