Final Fairing & Finishing - WEST SYSTEM Epoxy

Final surface preparation
Preparation for the final finish is just as important as it is for re-coating with epoxy.
The object of the final sanding is to smooth flaws in the epoxy coating and provide the
appropriate “tooth” for the finish coating to key into. Allow the final epoxy coat to
cure thoroughly and sand it to a smooth finish by either dry or wet sanding. Wet sanding
will automatically remove the amine blush and it reduces sanding dust. If you prefer
dry sanding, remove the amine blush (as described above) before beginning to sand.
The amount of sanding required will depend on how smoothly you applied the final
epoxy coatings and which finish coating you choose. Since the epoxy is harder to sand
than wood or fairing compound, power sanders can save a lot of work over hand sanding.
An orbital or reciprocating sander with 80 or 100 grit paper works well for the initial
sanding if the surface has stipple, sags or other unevenness. When the surface has
reached an overall smoothness, switch to finer grits. Note that a dual-action (DA) orbital
sander with coarser grit (e.g. 80 grit) will produce the same degree of smoothness
as a reciprocating sander or hand sanding with a finer grit (e.g. 100 grit).
Complete the sanding with the appropriate grit for the type of coating to be applied. If
a high-build or filling primer is to be applied, 80–100 grit is usually sufficient. 120–180
grit paper may be adequate for primers and high-solids coatings. Sanding with
220–400 grit paper will result in a high gloss finish for most paints or varnishes. Grit
finer than this may not provide enough tooth. Keep in mind that light colored surfaces
do not show sanding scratches as easily as dark surfaces. Sand to a finer grit finish under
dark paints and clear finishes over dark wood. Always refer to the coating manufacturer’s
specifications for the surface finish recommended for a particular coating.
Refer to Appendix A for more information on sanding equipment and abrasives.
When you are satisfied with the smoothness, rinse the surface with fresh water. The
rinse water should sheet evenly without beading or fisheyeing, indicating that there is
no surface contamination. Dry the surface with plain white paper towels and allow to
air dry completely before coating. To reduce the possibility of contamination, it is a
good idea to apply the finish coating within 24 hours of the final sanding.
Finish coatings
Finishing 16
We’re using the term “finish coating” to distinguish it from the epoxy “barrier coating”
and to include all coating materials (pigmented and non-pigmented) that can be
applied over an epoxy barrier coat to form a protective system. Although modern linear
polyurethane coatings are chemically quite different than traditional coatings, the
term paint is generally used to refer to all pigmented coatings. The term varnish is often
used to refer to all clear coatings. However, manufacturers and others distinguish
between traditional varnishes and modern clear urethanes or clear polyurethanes.
Traditionally, paints and varnishes have been called on to protect structures from corrosion,
oxidation and other forms of deterioration from exposure to air, sunlight, and
water. However, paints and varnishes are not as effective for moisture protection as
epoxy.
If buried in the ground, used only on interior surfaces or on surfaces otherwise protected
from sunlight, an epoxy moisture barrier will remain effective indefinitely.
However, under prolonged exposure to sunlight, an epoxy coating, like many other
plastics, will chalk, turn yellow, and eventually break down. It is not intended to be an
exposed finish coating.
When applied over an epoxy barrier coat, the function of a finish coating like paint or
varnish 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