Fiberglass
(FRP or "fiber reinforced plastic") was once considered an
almost "maintenance-free" hull material. Wooden boats are
subject to rot and decay, steel boats are susceptible to rust, and aluminum
hulls can be laid waste by electrolysis. The fiberglass alternative
was thought to be a "wash and wear" material, requiring nothing
more than a regular scrubbing and an occasional paste wax. As the original
FRP vessels began to age and the industry began building mass-produced
pleasure boats almost exclusively from fiberglass, we discovered that
the material was, indeed, remarkably exempt from rot, rust and electrolysis.
However, we encountered a few "new" problems generally unique
to FRP boats.
Fiberglass hulls can develop osmotic blisters. The condition is often
referred to as "the pox" and has become increasingly common
during the last few decades. Osmosis occurs when water passes through
semi-permeable membranes (such as the colored resin or gelcoat layer
of a FRP hull) in an attempt to achieve chemical balance between the
solutions on either side. The water usually does not penetrate far beyond
the first layer of laminate or two beneath the gelcoat. As water permeates
the gelcoat, it encounters and reacts with water-soluble materials at
the laminate layer. The chemical by-products create a gas pressure that
can deform, or "blister," the gelcoat. Tiny drops of high-pH
material created by the interaction of water and the soluble materials
can compromise the resin content in laminate immediately surrounding
the blister. The acid typically weakens the bond between the laminate
and the gelcoat, promoting the continuous spread of the blistered area.
During
the last few years, more mass production builders
switched to vinylester laminates in the outer layers of
their hull lay-ups to help control blistering.
Osmotic blisters alone will almost never weaken a hull to a point where
it becomes unsafe or unseaworthy. Left unchecked, the process has been
known to progress to a point where the hydrolysis from acidic blisters
will penetrate far beyond the top layers of roving and resin and promote
serious delamination. Dockside philosophers and theorists by the score
have speculated about the possible causes behind the general increase
in osmotic blistering.
Arguments about the chemical composition of modern resins, the lay-up
procedures in modern manufacturing facilities, EPA regulations and other
possible causes rage on year after year. One aspect of osmotic blistering
that doesn't seem subject to a lot of debate is that blisters are undesirable
on a hull and can have a very negative impact on resale value.
While the hypothetical discussions about
the causes of blistering continue, owners of FRP vessels are more presently
interested in finding somebody capable of solving the very real problem
on their specific boats. We spoke to Phil Riise, owner of Seaview East
Boatyard in Seattle and Bellingham. Seaview has earned a good reputation
for effective blister repair, and Phil agreed to share some experienced
insights with our readership.
Phil included a general disclaimer: "We've
been doing blister repair since 1979. Some of the things we have learned
along the way might be at odds with the opinions expressed by some of
the so-called experts in the field. I don't want to claim to be the
unquestionable and absolute final authority on blisters, but we have
developed a repair process that works very well and our customers are
happy with the results."
Phil said that many inquiries about blisters come from boat owners who
are thinking of selling a boat and are concerned that potential buyers
will either reject the boat entirely or expect a steep discount due
to a blistered hull. "Sometimes," said Phil, "we hear
from a guy who has just purchased a boat and knows that he has a problem.
Other times, we get inquiries from people who have had blisters repaired
someplace in the past and need somebody to redo the job because the
cure wasn't permanent."
According to Phil Riise, Seaview tries
to avoid quoting a standard dollar-per-foot rate for sight-unseen blister
jobs. "If a boater knows he has a problem, we'll haul the boat
for free to help evaluate the severity. In some cases, all a boater
really has to do is keep an eye on the situation to make sure it doesn't
increase. When a repair is really needed, it will vary between a minor
spot job all the way up to a total peel process. The right solution
will be different on different boats."
Left
unchecked, the process has been known to progress to a point where the
hydrolysis from acidic blisters will penetrate far beyond the top layers
of roving and resin and promote serious delamination.
Phil pointed out a Hatteras in the Seaview yard, with a chunk of gelcoat
and laminate removed. "With a boater's permission," said Phil,
"we'll go ahead and do a test peel. 'Peeler' is just a fancy name
for grinder. We start by peeling off the gelcoat in a blistered area,
and then we visually examine the top layer of laminate below that. The
damage to the outer layers of the hull is very evident to the eye. We
also use a moisture meter to help us determine whether we need to peel
away additional layers below the gelcoat."
Seaview's test peel on the Hatteras hull
was a rectangular area with gelcoat and laminate stripped away to different
depths. The first pass of the peeler had removed the gelcoat, and the
"roots" of the blisters were evident in the hull below. The
high-pH material in the blister had left star-like dimples in the top
layer of laminate.
Some blister repair philosophies emphasize
hauling a boat for several months and placing it in a warm, dry area
to reduce the moisture content of the hull. "Drying a boat is not
a good substitute for replacing the laminate," said Phil. "This
laminate has been water soaked and is resin-starved, and simply putting
fresh gelcoat over damaged, resin-starved material will not result in
a permanent solution. Water will pass though the gelcoat again, and
the process will simply continue."
The peeler's second pass, parallel to the first, had removed the gelcoat
and the first layer of laminate. The second layer of laminate was visible,
and there were faint signs of blister roots at the second level. The
third pass of the peeler revealed the third and unblemished layer. The
third layer also passed the moisture meter test.
"Curing blisters on a boat is somewhat
similar to getting rid of wood rot," observed Phil. "You don't
just cut out the most obviously rotten part and then patch in a piece
of new wood. To do a proper job, you have to get rid of all the bad
materials and go a little ways into the good material to be sure that
all the rot and decay has been eliminated. Some people just grind and
fill blisters, but that's a lot like shooting Git Rot into a chunk of
decayed wood and pretending that the problem is solved. When you grind
out a blister and fill the void with epoxy, there will almost always
be some of the high-pH chemical around the edges of the repair. Epoxy
doesn't do well in a high-pH environment, and such a repair is very
likely to fail."
After determining the depth of the problem,
Seaview will advise a boater whether a spot repair or a total peel would
be the best way to proceed. "We will often suggest a spot repair
in cases where there aren't more than about twenty small blisters or
so," remarked Phil, "but in cases where the blistering is
very widespread the best results will be achieved by getting rid of
the top layers of laminate and beginning the repairs at that point.
When there are a lot of blisters, you sort of have to connect the dots
and assume that high-pH material has worked its way out from the areas
directly under the raised gelcoat. Too many spot repairs and you wind
up with a total peel job anyway."
After Seaview has removed the gelcoat and compromised laminate, the
laminate thickness is restored with vinylester mat and resins. "We've
been using the vinylester material since 1988," said Phil. "We
were one of the first to use this material, and in the beginning it
was hard to find. Vinylester has been very successful. We warranty our
blister repairs for five years. While some of our early epoxy-based
repair jobs had to be redone under warranty, we haven't had to redo
a single vinylester job yet."
"Our original vinylester repairs
used a thixotropic resin," remarked Phil. "Now we have products
available to us so that we can use vinylester-based products for the
entire repair job. This means that the job will cure evenly and remain
stable in the post-cure, too."
Seaview's long and successful history
using vinylester resins should be encouraging for many boaters. During
the last few years, more mass production builders switched to vinylester
laminates in the outer layers of their hull lay-ups to help control
blistering. Even so, Phil Riise does not seem to anticipate an eventual
end to blister problems in the Puget Sound area.
"Many of the boats in Seattle live
in freshwater, but play in salt," remarked Phil. "And that's
good from the standpoint that moving back and forth between fresh- and
salt-water helps keep the bottom clean. The practice affects blistering,
however, because boats that need bottom paint less often don't get hauled
out as frequently. If blistering is in the beginning stages, it may
not be noticed right away. The relatively warm freshwater inside the
locks also speeds up the chemical reactions that promote blisters." 
