The Gougeon Brothers on Boat Construction - WEST SYSTEM Epoxy

158 Core Boatbuilding Techniques
glossy or shiny and follow the directions given for fiberglass
preparation. Test the product in an inconspicuous
area to be sure that it will bond to epoxy. If any product
fails to dry within the period specified on its packaging,
try a different brand or use a primer.
Primers are sometimes used to make sanding quicker.
<strong>The</strong> theory is that they are easier to sand than epoxy;
while this may be true in some situations, you must
weigh the benefit against the time needed to apply the
paint and to achieve an even surface. Since primers are
difficult to apply evenly with a roller or brush—because
of the safety issues involved, we can automatically rule
out spraying primer paints—application time may well
exceed any extra epoxy sanding time. Primers definitely
do not flow as well as WEST SYSTEM epoxy, so you need
a good deal of sanding just to get the primer as smooth
as the original rough-sanded epoxy surface.
A colored base coat will facilitate final fairing by serving
as a guide to prevent oversanding and will also, to some
extent, reduce the number of coats of paint needed to
cover an unpainted surface. When we plan to paint a
hull, we therefore often add WEST SYSTEM pigment to
our final coat of epoxy and use this instead of primer
as a tracer coat.
Surface Glazing
While primers don’t significantly reduce finishing time,
glazing or surface compounds often do. <strong>The</strong>se commercially
available products are much thinner than standard
puttying fillers, so you can apply them quickly in a thin
film over large areas. We recommend using a wide
putty knife or squeegee to apply surfacer. This technique
results in a relatively smooth surface which is not difficult
to sand to a fine finish. Since small particles of dirt
can interfere with your finish, be sure your surface is
clean before applying these products.
Surfacing compounds have an advantage over primer
paints in that they are high solids materials and can be
used to mechanically force-fill small voids and depressions.
Imperfections in an overall cured epoxy surface
can be filled quickly and efficiently, assuming that they
are reasonably small or shallow. Often, the choice is
between sanding away small air holes and valleys or
filling them. <strong>The</strong> extra sanding takes time and may
involve the removal of more protective epoxy coating
than desirable, so surfacing compounds present an
attractive alternative.
All major paint companies market these compounds
with instructions for their use. Be sure to select compatible
surfacer and finishing systems since some finishes
use very active solvents which can lift surfacing materials.
Also check your instructions to be sure that you use
the recommended thinner when your compound is too
thick to apply in a controlled thin film.
Be particularly aware of the consistency of your glazing
compound as you apply it. If it is too thick, it will be
difficult to apply in a controlled film, and if it is too
thin, you will lose filling power. It’s better to err on the
thin side because you can always apply a second coat,
and this is much quicker than sanding away excess.
You may have to add thinner at regular intervals to
make up for its continual evaporation as you work.
Paints
Over the years, we have tried many different paints
manufactured by many different suppliers, but we
haven’t tried them all. Historically, some paints and
varnishes have not cured well over WEST SYSTEM epoxy.
207 Special Coating Hardener is an exception in that
Figure 15-6 Rolling on two-part linear polyurethane paint.