contamination. Instead, wet the surface with xylene, then blot-wipe
it using a single, short sweeping motion with a clean paper towel.
Use each paper towel only once, and use as many paper towels as
necessary. Test for silicone or wax contamination by misting the
surface with water. If it sheets away, the surface is clean. If it beads,
the surface requires additional cleaning.
Find out if the deck (or hull) around fastener holes is solid laminate
or some type of core material sandwiched between fiberglass skins.
If the spot where your hardware will be mounted is not solid fiberglass, depending entirely upon a flexible sealant to prevent water
from penetrating the core is a high-dollar sucker bet. If you drill the
fastener holes, examine the dust the drill brings out for a change in
color and/or texture. To evaluate existing holes, you need a bright
light and a straightened wire paper clip. Poke around at the inside
surface of the hole. Fiberglass will repel the wire, but it will burrow
into or flake soft core material. Nearly all fiberglass boats incorporate
core to stiffen decks and many also use core in the hull, so expect
to find core.
Where the deck is cored, you need to seal off the core around
penetrating holes to prevent water intrusion. One method is to
dig out the core material without enlarging the holes in the skins,
vacuum out the loose debris, and fill the cavity with epoxy. However,
bits of core may remain attached to the inside surfaces of the skins,
providing a wicking path for moisture when the holes are re-drilled.
An easier method, and the one I’ve come to prefer, is to drill the hole
1/8-inch oversize (Figure 2), fill it with epoxy, then re-drill the hole
through the center of the epoxy plug. Done with precision, this creates a 60-mm epoxy barrier between the hole and the core material,
and the epoxy bonds to surfaces perfected by the drill cut.
Of course, you can also dig out additional core to thicken the
barrier and reinforce the deck. Use a reaming tool made from a bent
nail or an amputated Allen wrench chucked into a variable-speed
drill to pulverize a soft core material like foam or balsa (Figure 3). If
the core is plywood, you’ll need a thin-shank cutter of some type in
a rotary tool. If you’re installing your hardware with screws into the
fiberglass, rarely a good idea, the epoxy barrier will need to be thick
enough to accommodate the cut of the threads.
Once the hole has been drilled and cleaned, close the bottom
of the hole with tape (putty or clay works well, too) and generously
mask the top surface to avoid additional cleaning and sanding. Fill
it a couple of