Re: Gelcoat Blisters - What To Do
for the stain, try hull & bottom cleaner which is oxalic acid. That stuff is inexpensive and works pretty well if you let it sit for 5-10 min then use a scrub pad with some elbow. A cheaper way may be MEK or xylene, or laquer thinner, depending on what the stain is and how it's on or in the gelcoat. If it's on the gelcoat and from algae growth then try the oxalic acid, if it's a mineral stain in the gelcoat then I'd use one of the solvents before trying the acid.
In any event, if you're going to paint it you'll want to sand it first anyway, then clean the surface with a solvent prior to priming or painting!
With the blisters, I have a 10' avon inflatable with a fiberglass bottom which has 50+ blisters, only 3 years old. But it sits in the water all the time. Will be epoxying that thing soon and bottom painting. I agree that If it has blisters now, it will continue to blister unless you do a major blister repair job... meaning the whole bottom basically.
It's really not that much more work. If you want a good paint job you have to prep the surface anyway. If it had good paint all you would've done was sand it lightly and solvent wash. To do an epoxy barrier coat you will have to sand/sandblast the bottom to remove all the paint, which will expose and open all the blisters. After that, putting on an epoxy barrier coat is not much more work than another coat of bottom paint.
