Proper finishing techniques will not only add beauty to
your efforts, but will also protect your work from ultraviolet light, which will break
down epoxy over time. The most common methods of finishing are painting or varnishing.
These coating systems protect the epoxy from ultraviolet light and require proper
preparation of the surface before application.
Preparation for the final finish is just as important as it
is for recoating with epoxy. The surface must first be clean, dry and sanded.
1. Allow the final epoxy coat to cure thoroughly.
2. Wash the surface with a Scotch-brite(TM) pad and water to remove amine blush. Dry with
3. Sand to a smooth finish (Figure 32). If there are runs or sags, begin sanding with
80-grit paper to remove the highest areas. Sand until the surface feels and looks fair.
Complete sanding with the appropriate grit for the type of coating to be applied-check
coating instructions. Paint adhesion relies on the mechanical grip of the paint keying
into the sanding scratches in the epoxy's surface. If a high-build or filling primer is to
be applied, 80-100 grit is usually sufficient. 120-180 grit may be adequate for primers
and high-solids coatings. Finishing with 220-400 grit paper will result in a high-gloss
finish for most paints or varnishes. Grits finer than this may not provide enough tooth
for good adhesion. Many people prefer wet sanding because it reduces sanding dust and it
will allow you to skip Step 2.
4. After you are satisfied with the texture and fairness of the surface, rinse the surface
with fresh water. Rinse water should sheet evenly without beading or fisheyeing. If rinse
water beads up (a sign of contamination), wipe the area with solvent and dry with a paper
towel, then wet sand again until beading is eliminated.
Proceed with your final coating after the surface has dried
thoroughly. To reduce the possibility of contamination, it is a good idea to begin coating
within 24 hours of the final sanding. Follow all of the instructions from the coating
system's manufacturer. A good trick used by professionals, is to make a test
panel to evaluate the degree of surface preparation required and the compatibility of the
The function of a finish coating like paint or varnish over
an epoxy barrier coat, is to decorate the surface and protect the epoxy from sunlight. In
doing so, the finish coating extends the life of the epoxy moisture barrier, which, in
turn provides a stable base that extends the life of the finish coating. Together the two
form a protective system far more durable than either coating by itself.
Protection from sunlight is a primary consideration in the selection of a finish coating.
Long term UV (ultraviolet) protection of the barrier coat depends on how well the finish
coating itself resists UV and keeps its pigments, or its shield of UV filters on the
surface of the epoxy barrier coat. A high gloss finish reflects a higher proportion of the
light hitting the surface than a dull surface. All other thing being equal, a white
(especially a glossy white) coating will last the longest.
Most types of coatings are compatible with epoxy.
Thoroughly cured epoxy is an almost completely inert hard plastic. This means most paint
solvents will not soften, swell or react with it. However, it is still a good idea to
build a test panel to assure coating compatibility.
Latex paints are compatible with epoxy and
they do an adequate job of protecting the epoxy barrier from UV radiation. In many
architectural applications latex paint may be the most suitable coating to use. Their
durability is limited.
Alkyd finishes-enamel, alkyd enamel,
marine enamel, acrylic enamel, alkyd modified epoxy, traditional varnish and spar
varnish-offer ease of application, low cost, low toxicity, and easy availability. Their
disadvantages are low UV resistance and low abrasion resistance.
One-part polyurethanes offer easy
application, cleanup and better properties than alkyds. They are also more expensive and
some may be incompatible with amine cure epoxy systems such as WEST SYSTEM epoxy, although
207 Hardener may offer better compatibility. Test first.
Epoxy paints are available in one-part and
two-part versions. Two-part epoxies offer many characteristics similar to the higher
performance polyurethanes. They are durable and chemical resistant, but offer limited UV
protection compared to the linear polyurethanes.
Two-part linear polyurethane (LP) paints
offer the most durable protection available. LP's are available as pigmented or clear
coatings and offer excellent UV protection, gloss retention, abrasion resistance, plus
compatibility with epoxy. However, compared to other types of coatings, they are
expensive, require more skill to apply and present a greater health hazard, especially
Bottom paints are available in a variety
of formulations. Most bottom paint systems are compatible with epoxy and can be applied
directly over a prepared epoxy barrier coat. If you are unsure of compatibility or have
curing or adhesion problems with a specific bottom paint, use only a primer recommended
for that bottom paint over the barrier coat. Follow the recommendations given for
preparation of fiberglass surfaces. Other paints, including marine LP's and primers, are
not recommended for use below the waterline.
Primers are usually not needed to help a
paint film bond to epoxy, although interfacing primers may be required with some
specialized bottom paints and high-build primers are useful for hiding scratches or flaws
in the substrate. If the instructions on your paint or varnish recommend a specially
primed surface, follow the recommendations given for fiberglass preparation. Self-etching
primers do not work well on an epoxy coating because of epoxy's chemical resistance.
Polyester gelcoat is a pigmented version
of the resin used to build fiberglass boats and other products. Gelcoat is sprayed into a
mold before the glass fabric and resin are applied to provide a smooth pre-finished
surface when the part is removed from the mold. It is not often used as a post-production
finish coating, but it can be applied over epoxy and is useful in some repair situations.
Refer to 002-550 Fiberglass Boat
Repair and Maintenance, published by Gougeon Brothers, for detailed
information on patching gelcoat over an epoxy repair.
Follow all instructions from the coating systems
manufacturer. It is a good idea to make a test panel to evaluate the degree of surface
preparation required, and the compatibility and handling characteristics of the finish
For detailed instruction on the application of these techniques in repair and
construction, refer to specific WEST SYSTEM instructional
publications and videos.
For complete descriptions of all WEST SYSTEM products, including selection and coverage
guides, go to the Product Guide.
To help you identify and prevent potential problems associated with using epoxy, go to the
For complete information on the hazards associated with epoxy and the precautions you can
take to avoid them, go to Health & Safety.
To see how these techniques have been put to use in a wide range of repair and
construction applications go to the Projects