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Blisters And Fiberglass Delamination
Understand Fiberglass Delamination
by
In
the early days of fiberglass boat construction the durability and strength of
the material was underestimated.
Builders
formed thick hulls with integrated tubular ribs and stringers.
Since
this was the time before computer aided design tools, builders in the North
Western United States built using the old default method of more is better.
In
1956, when the first fiberglass boat was
built, the material was very new but already found acceptance in aviation and
automotive industries.
The
only way to build at that time used layers of fiberglass impregnated with
acrylic resin that hardened when cured.
Large
molds allowed entire hulls to be made as one piece with no seams.
Some
wooden structure was added inside the hull for rigidity and it was bonded in
with more fiberglass material.
No
precautions were taken to compress the curing hull or eliminate air bubbles in
the structure as is done today. We know this method as solid core construction.
Fiberglass
materials remained expensive, and as demand for these new boats increased,
manufactures began cutting costs to compete in the marketplace.
Soon
a layer of wood was added to lighten and strengthen the hulls and decks.
The
fiberglass and wood sandwich was a great combination until one of the outer
surfaces of the fiberglass was breached. This is called wood core construction.
It
didn’t take a crash on the rocks to let water into the wood layer. Small cracks
allowed the wood to become soaked and it swelled, and then rotted.
Soon
the inner and outer fiberglass layers couldn’t do their job and broke down from
repeated flexing.
This
was the first type of fiberglass delamination and the failures damaged the boat
building industry badly since many manufacturers had transitioned to all
fiberglass construction, leaving more traditional materials behind.
Fiberglass
construction was quickly becoming known as poor quality because of delamination
issues.
Two
Types of Delamination
The
first type of delamination, where a wood core either separates or
disintegrates, is very difficult to repair.
One
of the fiberglass surfaces needs to be removed to access the core. It’s usually
the inner skin that’s removed because it’s less visible so finish quality is
not as important.
The
process is expensive and requires skilled labor; many boats were scrapped
because of the cost of repair. Even with today’s modern materials and processes
this kind of repair is difficult.
Another
type of delamination is similar but without the wooden layer. In these cases
tiny flaws in the fiberglass itself allow air to be trapped.
If
the hull is cared for badly, water can enter through microscopic channels and
enter these voids filled with air.
Expansion and
contraction of these tiny bits of water will make the voids
grow horizontally along the layers of fiberglass cloth and resin binder.
Temperature
fluctuation causes the expansion and contraction of the water and if freezing
and thawing are encountered the voids will grow quickly.
Small
bumps soon become visible in the smooth finish. These bumps are called blisters
and it’s a serious condition.
Blister
Repair
The
only way to repair this damage is to remove the outer gel coat and underlying fiberglass
material to access the damage. It is then filled with new resin and the gel
coat is patched.
It
sounds easy, but unless you have considerable experience working with composites it’s easy to make the situation
worse.
If
the boat is going to get a new coat of paint the problem of color matching
isn’t an issue.
Blending
a patch into existing paint is an art form and lighter colors are much easier to
match than bright or dark paints.
Mechanical
bonding is the larger issue since the new patch is only connected to the hull
through adhesive properties.
The
same vibrations that formed tiny cracks will cause the boundary of the patch to
loosen. Some blister repair involves drilling a few very small holes and
injecting an epoxy compound.
The
blister is then compressed while the epoxy cures. This allows the patch to
become a more integrated part of the hull.
Causes
of Blisters
Marine
growth can penetrate the gel coat and allow water into the structural area.
Keeping a clean bottom and using an anti-fouling paint is the most important
step.
Abuse
is another way tiny cracks form and allow the entry of water. Some boats are
exposed to these conditions as a normal course of wear.
Other
boats are needlessly used in a careless way and this causes hull problems.
Never
allow someone to load heavy objects on the cabin top or jump onto the deck from
the dock. Not only is it dangerous, but it can lead to delamination in these
areas which will grow with further vibration from normal use.
Poor
storage practices like leaving water in the bilge can lead to severe
delamination.
Even
in tropical climates the expansion and contraction of water trapped between
layers of fiberglass can raise blisters.
In
climates which freeze and thaw often it’s possible a small blister can turn
into a “pop” where the outer surface is torn away by the pressure of internal
ice.
Pops
can be fixed with the same processes as a blister but the extent of the damage
is unknown and the hull is permanently compromised.
Sonic
survey can reveal some of the damage but prevention is far easier.
Paul Bruno
United States Coast Guard licensed Ship Master with
Passenger Certification.
A marine contractor familiar with all ship systems
who has worked in the industry for more than 20 years.
Has a USCG Master's License and a degree
in Creative Nonfiction and Technical Writing, from the University of
Wisconsin.
Experience
Paul Bruno is a former writer for ThoughtCo who
contributed work for over five years on the maritime industry. He has worked
with a variety of vessels throughout his maritime career, including various
commercial ships as well as the Great Lakes schooner reproduction "Dennis
Sullivan." As a marine contractor, Paul is familiar with all ship systems,
and his lifelong passion for electronics has led to a focus on marine hardware
and software development. When he is not working, Paul's favorite hobby is knot
work, keeping busy with the nearly 4,000 documented knots, splices, and eyes.
Education
USCG Master's License, 1993
Creative Nonfiction and Technical Writing,
University of Wisconsin, Milwaukee and University of Waikato, Hamilton NZ
Paul Bruno
ThoughtCo and Dotdash
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