The Gougeon Brothers on Boat Construction - WEST SYSTEM Epoxy

Chapter 11 – Laminating and Bonding Techniques 105
make good applicators, but they require time-consuming
loading and cleaning. While it may seem to be efficient
to use your finger to apply and smooth fillets, don’t do
it. A splinter in the joint may cut through your glove
and into your finger, and this can be quite painful.
To finish your joint, take a piece of thin stock a little
wider than the fillet itself and round off one end. Cut
the radius of this curve to match the desired radius
of your fillet when the stick is held so that it bisects
the joint. Because this dimension is very important in
controlling fillet size, round off several sticks and experiment
with them. <strong>The</strong> rounded end of an 804 Mixing
Stick creates a 3 ⁄8" (9mm) radius fillet. With a fillet stick
of any given radius, you can further control fillet size by
changing the angle of your passes. When you hold the
stick at a 10° angle to your joint, your fillet will be
flatter, while if you hold it at a larger angle, it will be
curved.
<strong>The</strong> experienced applicator can form a perfect fillet with
only one pass of the fillet stick over a properly applied
fillet mixture. It is not unusual, however, to need several
passes to form and smooth the fillet to the desired state.
Always make the final pass with the fillet stick with some
firmness so that the excess fillet mixture will be deposited
on either side of the fillet. <strong>The</strong> pressure on the fillet stick
is important because it creates a gap between the excess
material and the fillet so that you can clean away the
Plastic disc cut from a coffee can lid
and screwed to a scrap wood handle.
This tool was recommended to us and it
does a good job. <strong>The</strong> plastic discs can be
made to any radius and are easy to clean.
Figure 11-21 A simple plastic filleting tool that can be made
to the desired radius.
excess without disturbing the fillet. Figure 11-21 shows
a plastic-tipped filleting tool that has worked particularly
well to form very smooth surfaces on the fillet.
Clean up of the fillet begins with careful removal of
excess material. Usually a 1" (25mm) putty knife or the
beveled end of an 804 Mixing Stick is used in conjunction
with a paper cup or can. Carefully scrape away
the excess from either side of the fillet and then
deposit it in the container by wiping the side of the
knife on the container edge. Repeat this procedure
until all of the excess has been removed as shown in
Figure 11-20.
After the fillet has begun its cure and started to stiffen
(anywhere from 30 minutes to 2 hours depending on
fillet size, temperature, and hardener speed), you can
do some further smoothing of the fillet surface with
more passes of the fillet stick. A rough fillet surface
or protruding edges can be smoothed considerably,
especially if you catch the fillet at just the right stage
in the cure cycle. This saves a lot of sanding later on.
When the fillet has achieved a full cure, you can, of
course, sand it as smooth as desired, but this is hard
work, especially with a high-density fillet. Fortunately, a
properly installed fillet should need very little sanding
to achieve adequate smoothness. Usually we use handheld
80-grit sandpaper for smoothing fillets, being
careful not to damage any wood grain on either side of
the fillet. When the fillet is completed, we always apply
one coat of unthickened epoxy over the entire fillet
surface. You can do this when you apply a coat of
epoxy to the general area.
Figure 11-22 An alternative filleting tool can be made by
cutting an 808 Plastic Spreader with the desired fillet radius
and the adjoining sides at 75° angle. With an adequate amount
of thickened epoxy in the joint and by holding the tool at the
proper angle you can make a smooth fillet in one pass. <strong>The</strong>
sides of the tool will force all of the excess epoxy toward the
fillet and leave a clean margin on either side.