The Gougeon Brothers on Boat Construction - WEST SYSTEM Epoxy

Chapter 14 – Hardware Bonding 137
Figure 14-10 Use a syringe to fill oversized holes.
voids which can result when the wood absorbs so
much epoxy that little is left for bonding the fastener.
Other typical problems, shown in Figure 14-7, caused
by air bubbles from the epoxy mixture and air pockets
in the oversize hole, can be eliminated with efficient
work habits. Stir the epoxy mixture carefully, getting as
little air as possible into it, and always begin filling an
oversize hole at its bottom and work up.
It’s more difficult to install fasteners in oversize holes on
vertical surfaces. Here, a two-step application procedure
works well. First, use a pipe cleaner to wet out the hole
with unthickened epoxy. Wait a few minutes and then
use a syringe to fill the hole with a thick mixture of
epoxy and WEST SYSTEM 404 High-Density Filler. <strong>The</strong>
Bubbles from the
mixture.
Void from epoxy soaking
into wood.
Air pockets in
thickened mixture.
Figure 14-11 Potential problems with bonded fasteners.
adhesive should be thick enough to stay in the hole
without running, but not so thick that it cannot be
administered with the syringe. To load it into the
syringe, remove the plunger and force the epoxy
mixture down into the barrel with a paddle. Begin
injecting the epoxy into the bottom of the hole and
work up. Try to avoid trapping air in the cavity as
you proceed.
In situations where a screw hole—standard or
oversize—is horizontal or extremely deep and the
syringe is not long enough to reach to the bottom of
the hole, slide a thin drinking straw over its tip. Insert
the straw into the hole and, starting at the bottom
and working up, inject unthickened epoxy. Let this
penetrate for a few minutes and then use the same
tool and technique to inject a mixture of 404 High-
Density Filler and epoxy.
Before inserting the fastener into the epoxy-filled hole,
coat it liberally with the thickened epoxy mixture to
mechanically fill all its threads. If an uncoated fastener
is inserted in the hole, its threads may not completely
fill with adhesive and the quality of the bond may be
reduced. An advantage of the two-step process is that
adhesive which oozes from the hole doesn’t run and can
be removed with a putty knife.
Procedures for Bonding
Hardware (Fittings)
Hardware bonding has one disadvantage. In most cases,
it requires more time than normal hardware installation
methods because of the added steps required. After you
have gained some experience with hardware bonding,
however, the extra time required will not be substantial,
and we assure you that the results will be worthwhile.
For example, chain plates are usually very heavily
loaded, and their fasteners are usually loaded in perfect
shear. Chain plate movement has always been a
common problem with wooden boats, but it is easily
solved with hardware bonding. Design criteria for chain
plates should include maximizing bonding surface area
of the chain plate strap for maximum load distribution.
Bonding hardware in place is much easier if you do it
before the boat receives its final paint job, but then the
painting job is made more difficult because you must
protect the installed items and paint around them. <strong>The</strong>