Subject: 43 GULFSTAR MKII (gelcoat blisters)
Date: Wed, 21 Jan 2004
HAVE BLISTERS ON BOTTOM OF POTENTIAL BOAT PURCHASE, SOME ARE LARGE SOFT SPOTS, MAJORITY ARE SMALL. NO REAL PATTERN. SOME BLISTERS GROUPED, AND THEN SPREAD OUT. I KNOW I HAVE TO REMOVE ALL THE PAINT COATINGS, CLEAN OUT THE SOFT AREAS AND THEN DRY. WHAT NEXT? LIKE YOUR WEB SITE. HAVE ALREADY LEARNED A LOT.
Gelcoat blisters. A really contentious topic. The standard repair is to grind out all damaged areas and start filling in the missing areas with epoxy resin and fiberglass cloth. Once these areas are filled in, the majority of people try and put a specialty barrier coat paint on to keep the moisture which will get into the fiberglass to a minimum.
There are several different theories among the "experts" as to why blisters
occur, but not much agreement. Since the conditions under which they occur vary,
it is hard to pin down. It can occur in some hulls from a specific manufacturer,
but not others from the same mold. It tends to occur more on boats in tropical
waters. In most cases, careful grinding, drying, patching, and barrier coating
seem able to prevent the reoccurrence of blisters. I would grind out the blisters,
dry thoroughly, then prime with our CPES™. Follow this with Fill-It™ Epoxy Filler
for the small blisters, and Layup & Laminating™ Resin and fiberglass cloth patches
for the larger blisters. Once everything is faired smooth, I would prime the whole
area with CPES and then put 2-3 coats of a barrier coat epoxy paint followed by
some topcoats of a high gloss polyurethane for the hull above the water, and a
good bottom paint for the hull below the water.
There have been cases where the blisters will reoccur despite the best efforts
to stop them. My understanding is that this is most likely to happen to hulls
which were manufactured with higher amounts of fillers in the polyester resin.
These fillers were used to stretch the resin and make to boat less expensive to
build. I mention this so that you will be aware that some blistering hulls can
be hard or impossible to permanently repair. One can take a small sample of the
fiberglass and have the sample tested to see if the manufacturer used cheap fillers
in the hull. These tests cost $150-200. And the current owner might not want you
grinding on the hull until after you have bought the boat.
Please get back to me if you have any further questions. I don't consider myself a blister expert, but I have read all the info that I can find, and could offer my opinion on any questions you might have.