Under Bottom Paint

[Jay B.]

Steve, my CD25 has exactly this condition...tiny blisters between the gel coat and barrier coat. I have popped a few of the blisters...and plan on sanding and feathering. Do you fill the spot left by the sanding or just bottom paint over it? What do you use to sand, a dremel tool or a power sander of some type?

Thanks!

Jay

To treat these blisters I sand through them and feather back to the gel coat. I suspect that I will eventually remove all of the expensive and time consuming barrier coat that I once applied. None of the areas of bare gel coat have caused any problems.

[dawnhoward]

We have just peeled the gel coat off. There were so many little & some bigger blisters under the gel coat. It is currently drying. She has to be washed every three days to get the vinegar smell out of the Fiberglass. She should be ready for a new resin coat, next week. Then will come 4 coats of barrier paint a 5th at the water line, 2 coats of ablative. Thank you God my Besties brother is 1 of 2 guys in Florida that peel the gel coat & reapply. So she will be good for another 35 years.

[Steve Laume]

Steve, my CD25 has exactly this condition...tiny blisters between the gel coat and barrier coat. I have popped a few of the blisters...and plan on sanding and feathering. Do you fill the spot left by the sanding or just bottom paint over it? What do you use to sand, a dremel tool or a power sander of some type?

Thanks!

Jay

To treat these blisters I sand through them and feather back to the gel coat. I suspect that I will eventually remove all of the expensive and time consuming barrier coat that I once applied. None of the areas of bare gel coat have caused any problems.

If you have a brother with a striping (gel coat) business you might have him peel it and start over.

I use a Porter Cable random orbit sander for bottom work. If you take off the little dust collection canister you can duct tape a shop vac to the outlet and have a fairly dust free sanding situation.

I never could understand the fascination with Dremel tools. Trying to sand out all the little blisters would be like bailing with a thimble, Steve.

[Matt Cawthorne]

With respect to any adhesive system, you need to get the prep right. Not all barrier coats are the same. The year that I bought my boat (1993) the boat had a bunch of blisters. I ground them out, faired, and barrier coated with West epoxy and barrier coat additive. In the years since, I have had some blisters, but it has never been a failure to adhere to the gelcoat. So you have to sand the surface of the gelcoat, wipe clean and do a proper job of dealing with the epoxy. All of the blisters since were either above the barrier coat or between two layers of gelcoat. The boat sits a couple of inches below the originally painted water line. I have since moved the barrier coat up. As for being between two layers of gelcoat there is no excuse. The gelcoat in these areas splits in half (thickness wise) with a scraper. I think that there was some problem with their gelcoat application system. I don't even think that there was supposed to be 2 layers of gelcoat. It is mighty thick. Since I have spotted the problem, the order of the day is to remove all gelcoat in the area of the blister (down to the dark fiberglass), build back to the thickness of the gelcoat with fiberglass cloth and epoxy and then barrier coat. None of these repairs has ever had a problem. If I had free time on my hands I would just remove all of the gelcoat on the boat, add a few layers of glass and barrier coat over that. My recommendation to anyone who is going to remove all the paint, is to remove all of the gelcoat as well.

Chemically speaking, polyester resin is a sponge. It can hold almost 10% of it's weight in water. It is a moisture highway. Gelcoat is not great either. Epoxy barrier coat is much better, but it is a moisture limiter and does not stop ingress.