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From: (no name) (no email)
Date: Thu Aug 02 2007 - 09:45:49 EDT
First, let me qualify the following blister repair procedure by stating that
blisters are mostly cosmetic. Except in unusual cases there is little real
evidence that osmotic blisters significantly weaken a hull. Boats can go for
years without blister repair. There is a dearth of documented cases where failure
to repair blisters actually sank a boat. However, blisters seriously affect
the resale price of a boat. Few shoppers will consider a boat riddled with
blisters reasoning that if the blisters have not been repaired, what other types of
maintenance has the owner neglected?
A while ago I posted a quick technique for blister repair which restores the
strength of an area covered with blisters although it does little to improve
the appearance. The method was vetted by Gougeon Bros. engineers. If you are
worried about blisters in a stress area, give it a try. It might alleviate some
anxiety.
Gel coat blisters are of little concern. They are small bubbles between the
gel coat and the first layer of FRP. Gelcoat blisters usually are quarter sized
or smaller and have well defined edges. Simply sand them off and recover the
area with a matching layer of gelcoat. If below the waterline, simply give the
exposed FRP a covering of epoxy and repaint.
Deep fiberglass blisters are another story. These are pockets of fluid within
the fiberglass layers. Osmotic pressure causes the fluid to accumulate to the
point where they force the layers of fiberglass apart. They are usually
bigger than gelcoat blisters and the edges are poorly defined. They can best be
seen by looking at the suspect area of the hull from a grazing angle just after
the boat is hauled.
After the blisters are identified and marked, drill a 1/8" hole near the
bottom of the blister at an acute angle. You want to penetrate the fiberglass to
the level of the osmotic fluid pocket. Drill a similar hole near the top of the
blister. The fluid will drain out. After a day of drainage, using an epoxy
injection syringe, irrigate the interior cavity 4 or 5 times with alcohol.
Rubbing alcohol or cook stove alcohol works fine. Let drain thoroughly between
irrigations. This will wash out the residual gunk from the interior of the
blister. Let dry a couple of days.
When dry, mix up a batch of thin epoxy resin. Ordinary resin can be thinned
with a very small amount of acetone. Fill an epoxy injection syringe and inject
into the bottom hole until epoxy begins to flow from the top hole. Cover the
bottom and top holes with masking tape to hold the epoxy in place. The epoxy
will saturate the fiberglass strands in the interior of the blister and fuse
everything into a solid mass. It will be as strong as new. Repeat for all
blisters. Fair and repaint.
The blister will still bulge but future buyers may be mollified if you
carefully describe the procedure and document it with pictures. The boat won't bring
as much as if it had a pristine hull but it probably won't be discounted as
badly. As far as performance goes, the presence of a few blister bulges won't
slow down an 8 knot trawler.
Larry Z
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