[Paddlewise] Fiberglass/Gelcoat Repair Seminar Notes

On 20 Jul 2000, Patrick Maun asked about:

<<Subject: [Paddlewise] Need Resin Repair Tips
Hello all, I am doing some hull repair and touch-ups and would like some
tips.
First off, I'll be doing a bunch of gel-coat repair on the keel as
well as fixing up some scratches.>> <snip>

I thought my seminar hand-out might be useful. The actual visual
presentation covers a lot more, including "live" demonstrations, Q&A
periods, etc. My last seminar was well attended, with one major glitch.
The apartment above the Canoe/Kayak Club burst its hot water tank
sometime before I arrived early to set up my display. Nobody home. Water
gushed from the ceiling everywhere, so by the time I got it all settled
down, it was a mad rush to set-up the demo while participants sat
patiently waiting through the delay -- kind of rained on my parade, but
we did get through it, and I do thrive on pressure it seems. Let me know
if you have any suggestions or questions, as I'd like to expand the
notes for inclusion on a free website sometime, with pictures.

Also, I do a comparison of North American and British lay-ups. It is
very dramatic, as I pound a round cut-out vacume-bagged piece as hard as
I can with a hammer, with no damage; but, an awl goes through it
instantly. On the Brit boat cut-out, nothing  penetrates, but it is 40%
heavier or so. Lots of interesting info I could share, but too long for
PW. As it is, thecore notes below are very long, so delete or scroll
down if not interested. Thanks for your time. It may be a few days
before I can answer back.

-------------------

© Doug Lloyd – Maintenance and Repair of Fiberglass Kayaks

Fiberglass Kayak Construction
The modern fiberglass kayak employees a number of products in its
construction. While epoxy or vinylester resin can provide a superior
lay-up if done correctly, the majority of boats are made from a
combination of glass fiber reinforcing material and quality, polyester
resin. Fiberglass refers to the actual thin fibers or glass filaments,
but is also used to describe the reinforcing fabrics made from these
fibers and generally, the entire finished product of glass fibers bound
in the cured resin. Other non-glass fabrics such as carbon fiber,
Kevlar, Dynel and Vectra can also form part of a “fiberglass”
lamination.

Chemical boatbuilding varies with each manufacturer with respect to the
actual material composite (mat, cloth, woven roving, etc), placement and
arrangement, thickness, skill and technology of fabrication and assembly
methods, and method of lay-up (hand-laid vs. vacuumed bagged). The
objective mechanical properties of a fiberglass laminate requiring
consideration include tensile, flexural, compression, and impact
strength -- which can vary depending upon the type of reinforcing
materials used. Other considerations include intended use and market
place norms for acceptable strength-to-weight ratios. With only moderate
abrasion resistance, cosmetic repairs are inevitable.

Understanding Resins
Polyester resin is a thermosetting plastic, made from oil products, and
cured by chemically applied heat from within the resin during the
chemical reaction (exothermic heat) -- ideally hardening at room
temperature.  This heat is the setting agent that takes molecules in the
liquid resin, and cross-links them (polymerization) into a solid plastic
(that cannot be re-liquefied). An accelerator (usually cobalt
naphthanate) has been formulated into most resins, so only a catalyst is
required to start the reaction – usually methyl-ethyl-ketone (MEK)
peroxide. Polyester resin eventually cures, even in its airtight
container, so ensure you purchase and use new product.

A number of different types of resins are commonly available, and this
can cause some confusion in choosing a correct product for the intended
use. Resins generally fall into two categories: laminating resin and
finishing resin.  Laminating resin is also known as molding, lay-up,
bonding, or unwaxed resin. It is air-inhibited, meaning that it will not
cure properly in the presence of oxygen – remaining tacky and difficult
to sand as no wax rises to the surface to seal the curing process. The
properties of laminating resin allow gel coat to bond to laminations and
successive laminations when molding.

Finishing resin on the other hand contains a wax additive that will rise
to the exposed surface, sealing it to allow complete curing and
subsequent sanding. It is nonair-inhibited, and is also called a waxed
resin. This waxy surface can prevent subsequent bonding of additional
layers, unless well sanded and prepped with acetone. Laminating resin
can be converted to finishing resin with the simple addition of a
special wax (air-dry) to the laminating resin, or you can attempt to
cover the exposed surface with a cellophane type membrane. A
general-purpose resin is also available that can be used for either air-
or nonair-inhibited requirements, but may not provide optimal
performance.

Special Resins
Polyester resin can be purchased in regular and higher viscosity
formulas. Gelled resin is available off the shelf, and would be
indicated for use on more vertical surfaces, where avoidance of sagging
and running is required. Given the ease, of which a kayak can be
positioned, it is unlikely a higher viscosity resin will be needed.
Thickening agents such as thixotropic powder can be added to regular
resin to create higher viscosities.

Gel coat polyester resin is one of the specialty resins that kayak
manufactures use to protect the underlying fiberglass structure, provide
a reasonably durable wear surface and waterproof barrier, and form
vibrant, outside color surfaces. Base formulas are clear to which color
pigments are added. Reductions in the use of lead over the last few
years has lead to increasing difficulty matching older gel coat
finishes, and changed the look of some old favorites. Gel coatings are
air-inhibited, so ensure an air-dry agent is added if the gel coat is to
be applied topically, unless the supplier has already added the waxed
dryer. Gel coat is typically kept from building too thickly in areas
where there is greater flexibility. It cures to a brittle finish and can
easily crack.

Epoxy resin is another thermosetting plastic resin that sets by applied
heat, either exothermic or externally, or a combination of the two.
Epoxies come in a variety of viscosities, and use between 30% to 50%
hardener as part of the added mix to create a reaction (compared to 1%
to 2% catalyzed additive with polyester resin). Epoxy resin costs twice
as much as polyester resin, but exhibits superior adhesion, greater
strength, and bonds to a greater variety of materials. It also shrinks
less and offers the ultimate in waterproofness. It is important to use
quality brands.

Safety and Handling
Concerns fall into two main categories: pre- and post-cure handling.
Prior to working with cured products, health hazards are very high. The
consequences of vapor inhalation range from mild irritation to
increasing sensitization – epoxies being the worst. Skin irritation is a
real possibility, and dermatitis may occur with skin contact from any
resin. Powders and fillers are easily and accidentally breathed in or
“puffed” up into one’s face during the mixing phase, so proper
precautions must be taken. Strands of fiberglass and milled fibers are
at the least, very annoying if they get onto your skin. Fully cured
epoxy is physiologically innocuous, but skin contact must be avoided
while it is in the viscous and/or gelled state. Liquid chemicals are all
too easily splashed about while being mixed and applied. Catalysts, such
as MEK, are known to have instantaneous and grave consequences if
splashed into your eyes.

Working with cured fiberglass still requires caution. Sanding and
cutting hardened fiberglass can raise a lot of dust particles, which in
reality, are shredded pieces of glass strand. Any use of power sanding
equipment demands even more caution. Though chemically inert for the
most part, cured fiberglass retains the ability to severely irritate
your lungs. The edges of hardened fiberglass can be relatively sharp, as
is the edge after cutting. A single strand of fiberglass, coated in
cured with transparent resin, can inflict injuries similar to that of a
long wooden sliver.

The need for protective clothing and safety equipment will depend upon
the size of the job, individual sensitivities, and duration of exposure.
Clothing that provides as much skin coverage as possible is recommended,
both as a layer of defense from minor splashes that could result in a
chemical burn, and to keep air-born particles and glass strands away
from your skin. Wearing a quality respirator best prevents respiratory
irritations and ailments. Disposable dust masks may be adequate for
small repair work, but a properly fitted mask is required for power
sanding. Wearing an approved respirator with suitable cartridges for the
type of chemicals being used is mandatory, especially if working inside
a kayak (such as with inside seam work).

By working in a well-ventilated area and using common sense, you should
be able to avoid dangerous vapors, fumes, and other harmful substances.
Always wear eye protection in the form of goggles or a full-face shield,
during mixing, poring, or other handling procedures with pre-cured
products -- including any and all solvents. Protect your eyes from
post-cured particles and dust. Use disposable polyethylene gloves where
possible. For back-up protection and even initial protection for small
repair work, a barrier hand protectant cream can be applied, allowing
easy clean up with soap and water. Use multiple coats, and ensure the
barrier cream is intended for fiberglass protection. Avoid using acetone
solvents to clean hands and skin, especially with epoxy, which only
further dilutes and penetrates more readily into your skin. Common table
vinegar is an ideal substitute.

Other Rules and Procedures
Never smoke or use open flamed heaters in the work area. Keep chemicals
away from flame or fire. Keep children and pets out of the work area.
Know the emergency steps for chemical burns to skin and eyes and
possible ingestion. Read, understand, and follow all directions and
precautions recommended by the manufacturer of the product being used.
Certain solvents, epoxies, and curing agents are highly flammable and
even explosive. Handle these products with care and keep them away from
any source of high temperature. Dispose of saturated rags as soon as
possible, by burning them away from the work area in an open-air
incinerator, or placement in a fireproof metal bucket for future
disposal. Store chemicals in a safe, cool, and dry place. Do not store
MEK in a metal container as a spontaneous explosion could occur with
prolonged reaction.

Do not mix products together unless specifically recommended, and in the
proportions indicated in the directions. Work in an organized fashion,
avoiding haphazard placement of chemical containers near the edge of
benches, etc. Ensure adequate lighting is available, but avoid working
in direct sunlight if possible. Clean up spills immediately. Do not use
sawdust as an absorbent, nor should you dispose resins and hardeners
into trash that contains sawdust due to the possibility of spontaneous
combustion. Dispose of discarded containers by puncturing a corner of
the can and draining the residual out. You can add hardener or resin as
appropriate. This will procure an inert mass, which can then be safely
discarded once fully cured. Curing resin can get hot enough in the
mixing pot to actually ignite surrounding materials if there is enough
combustibility. Remove the pot to somewhere safe and well ventilated
until the hot gel has fully cured for disposal.

Exterior Fiberglass Maintenance
In order to get the longest life from your kayak and keep it looking
good, some kind of maintenance schedule should be adhered to.  Remove
stains as they occur. A small amount of acetone rubbed on judiciously
with a clean, white rag will remove all but the most stubborn stain.
Regular applications of a quality, UV inhibiting wax will help keep the
gelcoat from becoming dull and porous. Store your kayak out of the
elements if possible, and out of direct sunlight when not in use.
Oxidation of the kayak’s exterior surface will inevitably happen over
the years, leaving the gelcoat pitted at a microscopic level.  Once the
process is allowed to go unchecked, rapid chalking will occur and may be
irreversible to the point where even wet sanding and cut polish buffing
will only temporarily restore luster. Commercial boat yards can gelcoat
resurface or paint your kayak, but expect to pay a premium price for
this type of full restoration.

Gelcoat Scratches
Scratches are going to be inevitable, especially along the hull. Some
scratches are superficial; others may be more serious. Deeper scratches
will require proper repair with new gelcoat or some other filler. For
light gelcoat scratches, you can use wet/dry sandpaper. With a good
sanding block, start with 320 grit, moving incrementally up to 600 and
on to 1200 if you wish. Do not sand in the same direction as the
scratch; rather move at an angle in various directions and contain the
area of sanding to as small a spot as possible. A power-buffer with
polishing compound should restore the gelcoat to almost like new. Be
careful not to sand through the gelcoat, or you will be facing a more
elaborate repair job. Polishing to factory luster is not always
possible.

Repairing Damaged Gelcoat
Deeper cuts, gelcoat gouges, nicks n’ chips, stress cracks, and opened
voids require proper preparation and use of a marine gelcoat filler or
equivalent. A second stage cosmetic restoration may also be required. It
is best not to let this type of damage go untreated, as water may
penetrate into the fiberglass reinforcing below the gelcoat surface. The
area to be repaired must be clean and free of debris and anything that
might break free, especially around the damaged perimeter. For deep
repair work, ensure that any glass fibers protruding above the surface
of the gelcoat area are appropriately cut back or sanded off. If a void
has opened up somewhere (it will look like an air pocket with an “egg
shell” edge), make sure the shinny inside surface is sufficiently
roughened up to allow adhesion of a filler. You can use a Dremel tool
with a burr-bit to prep gouges, etc, or often times a piece of 120-grit
sandpaper can be folded in half on edge, and then the “V” portion used
to sand the inside of the longitudinal cavity. The repair area must be
thoroughly dry, vacuumed for dust, and wiped down with acetone.
.
Stress cracks are a little harder to diagnose severity. Surface “spider”
patterns indicate either a manufacturing defect (which may only be a
cosmetic problem) or an ongoing stress fracture indicating inappropriate
flexing. A broken, concentric ring pattern may indicate a one-time
impact, which may require fixing if deep enough. Once underlying
structural problems have been rectified or a one-time-only-category has
been determined, you will need to excavate the crack to the fiberglass
below, and then back-fill with filler.

Choice of filler is a matter of personal preference, available product,
and desired cosmetic outcome. Color-matched pigmented gelcoat is perhaps
the easiest product to work with and achieve a good result. Retail kayak
outlets should be able to supply you with hopefully, just the right
color of gelcoat for the boat you purchased through them. Polyester
gelcoat is typically of high viscosity, and normally has had the air-dry
agent added by the dealer (double-check). You will need to purchase some
MEK catalyst. Do not use old catalyst you may have had around for a
while. Remember to treat MEK with extreme caution – wear eye protection.
You can add filler if you wish to thicken it up, especially if you need
to build up a vertical area such as near the end of the stern keel line.
However, the less additives you use, the greater the bond in smaller
gouges. You can use a small artist brush or simply a match stick (cut
end off first) to drip the mixed gelcoat into the cavities. As gelcoat
will shrink, you need to leave it “proud”. Make sure you work the
gelcoat in by “tapping” it in place. Use a sectioned cutter blade or
razor blade to cut to the level surface, once the gelcoat has hardened a
bit, but not before it has fully hardened. It should be like Jell-O when
it is ready to “cut”. A second filling is sometimes required. Polish
when cured.

Alternatively, you can also use epoxy resin -- either “Cold Cure” or the
exothermic “West Epoxy” system. Cold Cure will not be compatible with
any subsequent gelcoat layers. Thickeners can be added, or even a
coloring agent. The match will not be the same as pigmented gelcoat, in
most circumstances. Epoxy will yield a longer lasting repair. It is
appropriate for larger damaged areas and the deeper gouges, and has less
viscosity for filling smaller voids/scratches. MarineTex is a pre-made
epoxy filler, that comes in gray or white, and in excellent, but costly.

You can also use polyester “Bondo”. It can be purchased in a marine
grade, light-grey, with a white paste catalyst. This is a very easy
product to use, but being of a putty consistency, it will have to be
squeeged into the damaged portion of the gelcoat. Care must be exercised
not to leave any on the surrounding, undamaged area (this holds true for
any of the thickened resins described above).  Regular polyester
autobody filler can also be used, but the darker the filler/catalyst,
the more the cavity will contrast with the surrounding area. You can
gelcoat over any polyester filler, but subsequent scratches show up the
least if the filler matches the original gelcoat more closely. As with
the gelcoat filler, you can cut back the filler to surface level with a
razor blade just prior to the filler hardening.

If you wish to sand your choice of filler, rather than cut it back level
with a blade, you will need some quality masking tape. The procedure is
to apply a suitable length of tape along each side of the gouge, then
apply a second strip over each of the first layers. You can then trowel
on your filler, level with the top 2 mil layer of tape, then immediately
pull off the top layer of masking tape, which will remove the excess
filler. Wait until the filler material hardens up a bit, then rough sand
the compound level with the remaining tape, being careful not to sand
any of the surrounding area and not below the level of the tape. Peel
off the remaining tape and let cure for a day. You can then wet sand the
repaired area, sanding carefully at an angle to the length of the repair
and finishing with polish and wax.

Fiberglass Repairs
Major damage, such as severe cracks to the reinforcing layers or even
punching a hole right through the hull, can be adequately fixed by the
do-it-yourselfer. The cosmetic finish may or may not be as adequate.
Typically cloth tape is used for repair work of this nature. Much of the
success of the repair is determined by good preparation. Inside surfaces
must be sanded and cleaned, and outside gelcoat surfaces must be
thoroughly sanded with coarse grit paper to allow sufficient adhesion
and bonding. It is best to keep the cloth (or mat) from becoming overly
saturated with resin, which will produce a brittle repair. A number of
layers may be required, with inside and out overlapping  -- depending
upon the severity of damage and size. You will need to spread the repair
out a bit, so as to taper the repair site. Often, the visible outside
surface can be sanded flush, then covered with matching gelcoat and
buffed out, leaving a relatively unnoticeable repair. Rather than using
finishing resin or epoxy resin, you can in the case of hull repairs, use
white gelcoat, saturated directly into the fiberglass fabric. Any
subsequent gouges would then show up as almost white. If you wish to
ensure optimum results, both aesthetically and from the point of safety,
it is often best to seek out a professional boat yard for this type of
work.

Custom Fiberglassing
You can create your own additions, alterations, and accessories for you
kayak out of fiberglass, including new bulkheads, thigh supports, and
even new hatch openings. It is best to make the parts from fiberglass
and then use epoxy and cloth tape to “glass” things in place. Epoxy
holds better to older fiberglass. Fiberglass bonds to itself well
enough, but subsequent items are usually added at the time the kayak is
made, while it is still “green”. Epoxy’s tenacious bond is more reliable
once the kayak leaves the factory. You will need various supplies
depending on what you wish to accomplish. You may need to make a small
mold, purchase mold wax and release agents (hair spray works great!).
Wax paper is handy for flat or slightly curved surfaces, eliminating the
need for special release substances.  Minicell foam can be carved to
provide a molding form, or you can use quick-setting dental plaster to
reproduce items.


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