The Gougeon Brothers on Boat Construction - WEST SYSTEM Epoxy

Chapter 26 – Interior Construction 327
Foam
Filleting on all plywood
joints to ease cleaning
Plywood box
Figure 26-21 Cutaway of inner icebox construction.
Begin by building the inner box. Since a major goal is
to build a box that has a rounded, smooth interior with
no difficult-to-clean sharp corners, we like to use large
low-density fillets on the inside corners to join side and
bottom panels. It’s most efficient to locate the opening
on the top of the box and try to make it as small as
practical for easy access. When the interior box is
finished, but before assembling its top, apply a
minimum of four coats of WEST SYSTEM epoxy to its
interior surfaces. We often add a layer of 6 oz (200g/m2 )
fiberglass cloth to the interior for abrasion resistance.
Add white pigment to the final epoxy coatings to facilitate
future cleaning: the white makes it easy to tell
when you’ve got the icebox clean. Sand thoroughly by
the third coat so that the final coat will be smooth.
When you have coated the box interior and the underside
of the icebox top, attach the top.
Fit a neck around the perimeter of the top opening. This
should be at least as high above the box ceiling as the
thickness of the insulation you plan to use. To be sure
that you will have adequate bonding area, make the
neck from 1 ⁄2" (12mm) or thicker stock or plywood. Give
the exterior of the inner box a coating of epoxy and
allow it to become tacky before bonding precut pieces
of foam in place. <strong>The</strong>n use a thick mixture of epoxy and
low-density filler to carefully bond the insulation to all
exterior surfaces of the inner box, leaving only the top
opening uncovered. An adhesive mixture that is sufficiently
thick will act as contact cement, holding the foam
in place without clamps. If difficulties arise, use tape or
string to hold the foam in place.
When the interior box is finished, position it on a preconstructed
base that will hold it at its proper height.
Bond the foam on the bottom of the inner box to this
base, using the same thick adhesive. Install front and
side panels around the foam perimeter. Although the
panels don’t have to touch the foam, it’s ideal if it works
out that they do.
If the icebox is located against the hull, leave a gap
between the foam and the planking and don’t try to fit
it snug. Doing it this way requires less fitting and is
therefore easier; having the foam tight against the hull
serves little structural purpose. Make the lid for the
icebox the same thickness of insulating foam as the base
and bond plywood as thick as that used on the inner
and outer boxes to its inner and outer surfaces. When
the lid fits, install a lip around the perimeter of the box
and add a handle to complete the job.
Tanks
<strong>The</strong> tank building methods described in this section
have been used with WEST SYSTEM epoxy since the early
1970s to successfully construct tanks for potable water,
sewage, gray water, ballast, diesel fuel, and a limited
number of gasoline tanks. Since then, the regulatory
environment and insurance considerations have evolved
and placed safety restrictions on various aspects of tank
building, specifically potable water and gasoline. Some
gasoline formulations available today soften epoxy. For
these reasons, we do not recommend building potable
water or gasoline tanks with WEST SYSTEM epoxy. WEST
SYSTEM epoxy continues to hold up well against diesel
fuel, sewage, and gray water.
Tank Regulations
U. S. Coast Guard (USCG) regulations, Food and Drug
Administration (FDA) regulations, American Boat &
Yacht Council (ABYC) standards, and insurance restrictions
should be carefully considered by anyone,
professional and homebuilder alike, planning to build a
composite tank. Tank construction material and
construction processes have been investigated
thoroughly over the years, and the lowest grief option is
choosing a certified tank from a manufacturer. Certified