The Gougeon Brothers on Boat Construction - WEST SYSTEM Epoxy

Chapter 13 – Synthetic Fibers and WEST SYSTEM ® Epoxy 127
Applying Unidirectional Graphite Fibers
WEST SYSTEM Unidirectional Carbon Tapes are useful
in masts, rudders, centerboards, and other applications
where high strength and stiffness are necessary but
space is limited. <strong>The</strong> fibers, each one less than the
diameter of a human hair, are arranged in bundles
of about 12,000 fibers each (12K). <strong>The</strong> bundles are
stitched together, 12 bundles to an inch, for a total
of 144,000 fibers per inch of width. <strong>The</strong> fibers are
arranged and held together with stitching to make
application easier.
To prepare a surface for graphite fibers, check to see that
it is clean and apply an initial coating of WEST SYSTEM
epoxy, following instructions in Chapter 15. Before the
coating begins to cure, fill surface voids with a putty-like
mixture of epoxy and 406 Colloidal Silica and allow this
to cure. Sand filled areas flush with the surface and then
lightly sand the entire substrate. Remove the dust with
a damp cloth and rinse the rag with clean water to
guarantee that no contaminants remain to affect
adhesion. Before applying graphite to aluminum, use
a WEST SYSTEM 860 Aluminum Etch kit to prepare the
substrate. Defects and holes in aluminum may be filled
with a mixture of epoxy and 406 Colloidal Silica and
sanded, but an initial coating of epoxy is unnecessary.
Apply a liberal coating of unthickened epoxy to the
surface. This should be thick enough so that the graphite
fibers will be partially saturated when they are laid out.
Place the fibers as desired in the wet epoxy. If you are
dealing with long pieces of graphite, use a dowel as an
axle through the reel, unrolling with one hand and
positioning with the other. Apply more epoxy and lightly
work it into the fibers with a plastic spreader. Tap epoxy
in between the filaments with a stiff-bristled brush. This
process is easier if you warm the epoxy with a hair
dryer as you work, especially when working in cool
temperatures. When the graphite seems to be thoroughly
saturated, carefully inspect it, probing with a corner of
a spreader and moving the fibers very slightly.
Use a modification of this technique to bond graphite to
vertical and overhead areas. After coating, filling, and
sanding as usual, apply a second, light coat of epoxy to
the surface. Before applying the graphite tape to the
surface, wet out the fibers on a protected work surface.
Press the epoxy-covered tape into place on the surface
and run your gloved hand or a plastic spreader along
the tape with even pressure. Apply more epoxy to
thoroughly coat the tape. For additional strength, it’s
possible to apply several layers of tape on top of each
other. In this situation, it’s best to step-taper the layers
of tape like a leaf spring, applying the longest piece first
and then successively shorter pieces. This way, you can
feather each layer when you sand it and avoid cutting
through full-length fibers.