The Gougeon Brothers on Boat Construction - WEST SYSTEM Epoxy

Chapter 15 – Coating and Finishing 153
coating operations at 70°F (21°C) or less and 206 Slow
Hardener in hotter weather. 209 Extra Slow Hardener is
available for general coating and bonding applications
in temperatures above 80°F (27°C). We recommend
207 Special Coating Hardener for clear finish projects.
It resists blush formation and is formulated for
maintaining clarity. Under normal conditions, you can
sand epoxy coatings in 24 to 48 hours after application,
depending on ambient temperature and hardener.
Use epoxy without fillers or additives for most coating
jobs. When you need a mixture that will not run easily,
add small amounts of 406 Colloidal Silica. Don’t thin
WEST SYSTEM epoxy with solvents because doing this
may compromise the moisture resistance and physical
properties of the epoxy.
<strong>The</strong> most practical way to apply a WEST SYSTEM epoxy
coating usually is to roll it on with a high-density
urethane foam roller. After a good deal of experimenting,
we have settled on WEST SYSTEM 800 Roller Covers,
which have 1 ⁄8" thick foam on a stiff backing. Covers
with porous, low-density foam or with foam thickness
greater than 3 ⁄16" will add an undesirable amount of air
to epoxy during application and reduce control of
coating thickness. We therefore advise against using
them. Roller covers are inexpensive and almost impossible
to clean, so we always discard them after use.
We have weighed our roller covers before and after
using them and have found that they sometimes absorb
over 2 oz (60g) of epoxy. Two ounces can be a significant
waste factor in small jobs, so organize your work and
try to coat a number of components at one time with
one roller cover. Foam will deteriorate as epoxy begins
to cure because increasing epoxy viscosity causes
increased drag. To extend the life of your roller cover,
mix small batches of epoxy and roll your cover dry
before adding additional epoxy to your roller pan. Mix
about 4 oz (110g) of epoxy at a time and add more
small batches to it in the roller pan as needed.
<strong>The</strong>re are many areas in a boat that can’t be reached
with a standard 7" (180mm) wide roller. One of our
solutions to this problem is to saw roller covers into
shorter widths and mount them on an adjustable 801
Roller Frame. In other tight situations, we use small,
Roller segment
Wood handle
Saw slot
Figure 15-2 Cutting a roller cover into segments to make
foam brushes.
cheap, bristle brushes for coating. For firmer action
and greater control, we usually cut the bristles on our
brushes short.
WEST SYSTEM epoxy is a dense material which requires
a good deal of roller pressure. This pressure, combined
with vigorous rolling action, leads to an even surface
coating over a large area, but it also often produces a
surface stipple of air bubbles. Remove this stipple
before the epoxy cures so that the surface is smooth;
sanding and finishing will be easier. Factory-made foam
brushes can be used to eliminate stipple, but they are
expensive and a little too flexible to be ideal.
We make our own, cheaper, brush-like foam tools from
WEST SYSTEM 800 Roller Covers. Cut a roller cover in
half crossways, and then slice each half longitudinally
into three pieces. <strong>The</strong>se cuts will serve as brushing
edges, so they must be straight and clean. Make a
handle by sawing a slot in a stick and insert a segment
of roller into it, as shown in Figure 15-2.
We sometimes use bristle brushes to smooth out and
touch up epoxy coatings, although, as a rule, they are
not particularly effective for applying epoxy and they
cost a lot more than rollers. It’s hard to brush an even
and consistent coating over a large area and, once the job
is done, harder still to clean the brush. WEST SYSTEM
epoxy can be cleaned from bristles, but because epoxy
continues to cure even after drastic reduction with
thinners, this procedure is much more time-consuming
than standard paint cleaning. If you use brushes, store
them in a covered coffee can full of solvent.