1. Osmotic Blistering
Osmosis- Movement of a solvent through a semi-permeable
membrane into a solution of higher solute concentration that tends
to equalize the concentrations of solute on the two sides of the
membrane.
On immersion in water all coatings absorb water, 0.1 to 3%. Water
seems to gather around interfaces in the coating, intercoats, pigment
binder, polymer metal, but especially at the polymer metal interface.
This Absorption causes swelling of the film which then expands locally
producing a loss in adhesion. This effect depends on water absorption,
film cohesion and adhesion. In this instance the blisters would
not be filled with water. The presence of retained solvent which
was hydrophobic at the film substrate interface is likely to enhance
this effect.
Blistering and Dis-bonding
Blisters are local defects in a a surface usually at the outer surface
interface formed by an accumulation of water or aqueous solution
together with a loss in adhesion and stretching of the outer layer.
Mechanisms of Blistering
There are a variety of way in which blistering might be thought
to initiate. Here are five possibilities which are not necessarily
mutually exclusive.
Subsequent Corrosion
In the absence of determining barrier effects, there is always sufficient
oxygen and water present within a blister for corrosion to proceed.
Furthermore, the water soon becomes conductive either because of
the presence of ions on the surface or by the leaching of conductive
material from the substrate itself. So we have in effect within
the same blister, reactive elements, electrolyte, oxygen and water.
Corrosion is therefore spontaneous and proceeds. Soon physical separation
of anodic and cathodic site takes place, with anodic sites predominating
at the center of the blister and cathodic site predominating at
the edge of the blister. The cathodic process generates alkali which
penetrates under the blister and allows it to expand and detach
the outer surface or film and the blister grows. Frequently the
single blister is the nucleating site for subsequent blisters which
nucleate at the edge of the dis-bonded front.
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2. gel-coat Repair Techniques
Many of the questions concerning the repair
of fiberglass boats seem to revolve around the techniques used when
applying polyester gel-coat to cover a repair made with WEST SYSTEM®
epoxy. There are several steps to a successful repair. It is important
that these steps are done in the proper order to assure a well matched
repair color.
One of the steps that is frequently left out is to apply a sealer
coat of epoxy to the repair area. This is necessary to fill any
porosity in the patch. Apply two or three very thin coats of epoxy,
extending each coat slightly beyond the previous one. Warm the area
with a heat lamp to speed the cure and to help the epoxy flow out
nicely.
When the sealer coat has cured, wash thoroughly with water and a
3M Scotch-brite pad to remove any amine blush. Any blush left on
the surface may inhibit the cure of the gel-coat This very important
step is often forgotten, and the result is usually an unsatisfactory
repair.
Sand the epoxy coated repair area with progressively finer grits
of sandpaper. Finish with 220 wet or dry.
De-wax an area twice as large as the diameter of the repair. Apply
tape around the perimeter of the de-waxed area. Use masking paper
to protect the boat from over-spray If there is a molded body line
or corner near the repair, you may want to extend the color patch
to that point. The same is true for a painted or vinyl stripe.
Sand the additional area out to the tape line with 320-grit paper.
This will be the total area to be gel-coated
Determine the gel-coat batch size for the size of the repair—approximately
80 square feet per gallon of gel-coat (20 sq. ft. per qt.).
Tint the batch of gel-coat to match the color of the boat. If the
boat is fairly new and the manufacturer is still in business, you
may be able to get gel-coat that will be a very close color match.
If this is not an option, you will need to get the gel-coat from
a FRP product supplier. Many marine distributors handle the gel-coats from various resin manufacturers. You will also need pigments
to tint the base color to obtain a good match. These pigments are
generally available from the gel-coat suppliers. Frequently, local
repair yards that do fiberglass repairs will sell these products
to the project user.
There are several gel-coat additives that, when used properly, make
matching a repair easier. These are clear, low-viscosity resins
which are not air inhibited. These products are mixed with the pigmented
gel-coat in place of a wax solution to provide a tack-free cured
surface. They also provide the added benefit of thinning the gel-coat without changing the color of the cured patch the way acetone
or styrene can. A few such products are Duratec Hi Gloss Clear product
number 904-001; Fast Patch by American Colors; and Cook Paint and
Varnish Company's number 970-X-900 Speed Patch Additive.
Matching the repair color to the color of the boat is probably the
hardest part of the entire job. You will find that most gel-coat
colors change as they cure. As you tint the gel-coat to match, apply
a small amount of un-catalyzed material to the sanded area surrounding
the repair. Use your gloved finger to spread this into a sample
the size of a quarter. Wait a couple of minutes for the solvents
to flash off. Any color variation will be evident. If the color
match is not acceptable, change the color by adding small amounts
of tinting pigments. As you adjust the gel-coat color, try to think
in terms of the basic colors, i.e.; the color needs to be blacker
or redder or bluer or greener... This will help you identify which
of the pigments to use. Use very small amounts of the pigments.
You may even need to dilute the pigment with white gel-coat to weaken
the effects. Apply an un-catalyzed smear with each change of color
no matter how small. Leave each of these smears on the surface until
you have the color as close to the boat color as you can get it.
When you are satisfied with the color match, wipe away all of the
test smears with acetone or lacquer thinner.
Divide the batch into a 2/3 portion and a 1/3 portion. Our technique
for using the patching additives is slightly different than the
recommended procedure. Mix the patching additive with equal parts
of the 2/3 portion of the matched gel-coat Catalyze following the
recommendations of the gel-coat supplier. Over or under catalization
may prevent the product from reaching a proper cure. Apply this
mixed gel-coat to the surface of the repair with a spray gun. Apply
several light coats, feathering each one farther from the repair
area. Allow the solvent to flash off between coats. You may need
to apply five or six coats to hide the shadow of the repair. Most
gel-coats colors will dry lighter in color if they are too thin.
Most manufacturers recommend a total film thickness of 15 to 20
mils. A common mistake is to apply two or three heavy coats, causing
solvent entrapment and improper curing. This may also have an effect
on the color of the cured repair.
Make another mixture with the 1/3 portion of gel-coat and patching
additive. This time use about three parts of patching additive with
one part gel-coat Spray the first coat of this mixture over the
previously sprayed area. Then apply two or three more coats of this
mixture over the entire area. Extend each coat farther than the
previous one, with the last coat out to the tape line. The semitransparent
film of lightly tinted clear patching additive will allow the original
gel-coat color to show through around the perimeter of the patch.
This will help blend any subtle color change into the original gel-coat
Once the gel-coat has reached a full cure, pull the tape and sand
the tape line smooth. Start with 320-grit wet or dry paper and work
up to 600-grit. Sand the surface of the repair if necessary.
Buff the surface with a white, medium-cut rubbing compound. Take
your time and do not overheat the surface while buffing. The excess
heat can cause a stain which will be very difficult to remove. Finish
with a fine compound and wax the area.
There are times when the repair will not match simply because the
original gel-coat color has faded. You may need to polish the entire
side of the boat to restore the original color.
Patience and experience are the two most important ingredients for
a well matched color repair. The mixing of the color is guaranteed
to teach patience. And since you may need to try more than once
for a proper match, the experience comes quickly. So get to it.
COPYRIGHT ©1991 Gougeon Brothers, Inc., PO
Box 908, Bay City, MI 48707, USA. WEST SYSTEM is a registered
trademark of Gougeon Brothers, Inc.
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3. Blistering Damage
The first sign of an osmosis, or more adequate
hydrolyze, process is that small blisters become visible on the
hull. Even if they don't appear to be anything but a cosmetic issue,
the underlying damage is quite severe.
When the "osmosis" blisters become visible, a complete layer of
the laminate has been severely affected.
Alkali residues from the hydrolyze will be spread inwards in the
fiber glass capillaries and cause an almost total loss of bond between
the fibers and the polyester!
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4. Chemotherapy for Rot
by Dave Carnell
Once rot gets a toehold in wood it is difficult
to cure completely—it is like a cancer. Digging out the rotted
wood will still leave spores and water in the sound wood. After
you fill in the cavity with something like epoxy, the rot continues
to flourish underneath. Products promoted to make rotted wood sound
and stop rot penetrate only until they meet water, with which they
do not mix. Under the solid repair rotting goes on. With one exception
(more later), the commercial products sold to treat dry wood to
prevent rot are completely ineffective against established rot in
wet wood because they are dissolved in petroleum solvents and oil
and water do not mix.
There are two commonly available inexpensive materials that will
kill rot in wood and prevent its recurrence. First, there are borates
(borax-boric acid mixtures) which have an established record in
preventing rot in new wood and in killing rot organisms and wood-destroying
insects in infested wood. Second, there is ethylene glycol, most
readily available as auto antifreeze-coolant. Glycol is toxic to
the whole spectrum of organisms from staphylococcus bacteria to
mammals. All of the published material on its effectiveness against
wood-destroying fungi and insects that I am aware of is the result
of my investigations over the past 15 years.
Both borate solutions and glycol penetrate dry and wet wood well
because they are water-soluble; in fact, penetration by glycol is
especially helped by its extreme hydroscopicity—its strong
attraction for water. For both, the fact that they are water-soluble
means they are not permanent solutions to rot in wood that is continually
exposed to water-below the waterline and in ground-where they will
eventually be extracted-dissolved out.
I first was interested in glycol as a wood-stabilizing agent, where
it is in many ways superior to polyethylene glycol (PEG), and it
was during this work that I realized the useful effect of glycol
on organisms, though I was pretty dense in interpreting the first
experiment.
The ladies immerse the stems of greenery such as magnolia branches
in glycerin to keep them green. Glycol is very similar to glycerin
in all its physical properties and much cheaper, so I stuck a magnolia
branch in antifreeze. The next day it was brown. After the third
attempt I tumbled to the fact that the glycol was killing the greenery.
This was the reason that glycol never replaced glycerin in applications
such as a humectant for tobacco and an ingredient of cosmetics and
pharmaceutical ointments, though it had all the desirable physical
properties.
I had two 2" thick slabs of a 14" diameter hickory tree that had
just been cut. I treated one with antifreeze and left one untreated.
I was looking at wood stabilization, not rot prevention. After about
six months stored inside my shop the untreated control was not only
cracked apart, but it was sporting a great fungal growth, while
the treated slab was clean.
The local history museum wanted to exhibit two "turpentine trees",
longleaf pines that had many years ago been gashed to harvest the
sap that made everything from turpentine to pine tar. The trees
delivered to us after cutting were infested with various beetles
and had some fungal growth. I treated them with antifreeze outside
under a plastic tarpaulin every few days for three weeks. They were
then free of insects and fungus and have remained so after being
moved inside and installed in an exhibit over four years ago.
I took three pieces from a rotting dock float that were covered
with a heavy growth of fungus, lichens, etc. I treated one with
antifreeze painted on with a brush, the second with a water solution
containing 23% borates (as B2O3), and left the third untreated as
a control. They were left exposed outdoors and were rained on the
first night. By the next morning the growth on the antifreeze-treated
piece was definitely browning and the borate-treated piece showed
slight browning. After two months exposure to the weather the growth
was dead on the antifreeze- and borate-treated pieces and flourishing
on the control.
I have a simple flat-bottomed skiff built of plywood and white pine,
which has little resistance to rot. After ten years some rot developed
in one of the frames. It may have begun in the exposed end grain.
It consumed the side frame, part of the bottom frame, and part of
a seat brace fastened to the side frame. The plywood gusset joining
the side frame to the bottom frame was not attacked. I excised the
rotted wood, saturated all with ethylene glycol antifreeze to kill
all the rot organisms, and there has been no further deterioration
in four more years afloat with wet bilges. I have not replaced any
pieces, as I am building another boat that can replace it; that
is more fun, anyway.
I have a 60+ year old case of the fungus infection known as "athlete's
foot". Many years ago it infected the toenails extensively. The
whole thing was pretty grotesque. My dermatologist and druggist
both assured me there is no known cure. About six years ago I started
using antifreeze applied under the nails with a medicine dropper
about every five days. The professionals are technically right.
I have not completely cured it, but the nails have grown out pink
and thinned almost to the ends and I never have any trouble with
blistering, peeling, or itching between the toes as I had had for
six decades. No drug company is going to have any interest in this
because the information has been in the public domain for so long
that there is no opportunity for any proprietary advantage. The
various wood-rotting organisms cannot be anywhere near as tough.
Glycol by itself has one big advantage over solutions of borates
in either water or glycol. Glycol penetrates rapidly through all
paint, varnish, and oil finishes (except epoxy and polyurethanes)
without lifting or damaging those finishes in any way. You can treat
all of the wood of your boat without removing any finish. The dyes
in glycol antifreeze are so weak that they do not discolor even
white woods. Once bare wood has been treated with glycol or the
borate solutions and become dry to the touch it can be finished
or glued. If a borate solution leaves white residues on the surface,
it will have to be washed off with water and the surface allowed
to dry.
This is my preferred process to treat rot. Once you find soft wood
or other evidence of rot, soak it with antifreeze even if you cannot
do anything else at the moment. Paint it on or spray it on with
a coarse spray. Avoid fine mist-like spraying because it increases
the likelihood that you will breathe in unhealthy amounts of glycol.
Put it on surfaces well away from the really damaged wood, too.
Use glycol lavishly on the suspect wood, which will readily absorb
10-20% of its weight of antifreeze.
Next dig out wood that is rotted enough to be weak. Add more glycol
to wet the exposed wood thoroughly. Then add the 25% borate solution
of the recipe below so long as it will soak in in no more than 2-3
hours. Then fill in the void with epoxy putty and/or a piece of
sound treated wood as required. The reasons I use borates at all
are: 1) it is a belt-and-suspenders approach to a virulent attack,
and 2) over a long period glycol will evaporate from the wood; especially,
in areas exposed directly to the sun and the high temperatures that
result.
If there is any question about water extracting the glycol or the
borates, you can retreat periodically with glycol on any surface,
painted or bare, and with borate solutions on bare wood.
Glycol's toxicity to humans is low enough that it has to be deliberately
ingested (about a half cup for a 150 lb. human); many millions of
gallons are used annually with few precautions and without incident.
It should not be left where children or pets can get at it, as smaller
doses would harm them, and they may be attracted by its reported
sweet taste that I have confirmed by accident. The lethal dose of
borates is smaller than of glycol, but the bitter taste makes accidental
consumption less likely.
For more visit www.boatbuilding.com
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