The Gougeon Brothers on Boat Construction - WEST SYSTEM Epoxy

Chapter 11 – Laminating and Bonding Techniques 97
Figure 11-10 A DN-class iceboat hull bottom showing
honeycomb core material between frames. <strong>The</strong> outer
plywood skin has not yet been bonded to this panel.
little additional weight, into parts that have a lot of
surface area. It may be used on cockpit floors, bunk
bottoms, bulkheads, partitions, decks, cabin tops, and
even hulls.
Many materials have good panel stiffness, but they are
also relatively heavy by the square foot. A core must be
lightweight, and it must have adequate crush and shear
strengths. We’ve found three core materials that bond
well with epoxy and produce good results when laminated
between wood skins: lightweight wood, such as
balsa, in both flat and end-grain dimensions; various
types of foam; and manufactured honeycomb materials,
especially resin-impregnated honeycomb paper.
Balsa is one of the better core materials. When used in
its end-grain dimension, it makes a core with excellent
crush resistance. We’ve also tried balsa in flat grain, using
it both as a core and to improve structural strength by
contributing to the overall stiffness and strength of a
panel. End-grain balsa is available with a special surface
treatment that is designed to reduce resin absorption
into the core. It is also available in an untreated form.
When using the untreated type, there is a possibility
of epoxy starvation to the glue joint of the layer glued
over it. We have seen epoxy drain completely through 1 ⁄2"
(12mm) thick end-grain balsa, so be sure to experiment
with gluing technique if you are using the
unsealed type.
We have often used other lightweight woods in flat
grain dimension as cores in some framework laminations.
Laminated deck beams are good examples of
how to save weight higher up in a hull by combining
proper proportions of a low-density wood, say, cedar,
with a high-density wood, Douglas fir or mahogany.
<strong>The</strong> resulting lamination has adequate stiffness and
strength and is much lighter than one made entirely
of high-density wood.
Resin-impregnated honeycomb paper is the cheapest
of the various honeycombs available, and it is easy to
bond and apply. Prices vary by cell size, resin content,
and thickness. We used paper honeycomb for years
and found its light weight and good crush and shear
strengths perfectly adequate in many applications.
Honeycomb paper is helpful on both flat and curved
surfaces. It can be applied to slightly compounded
areas, such as decks and cabin tops, because its cells
are able to bend slightly and deform. Honeycombs
are available in a wide variety of materials, from paper
to titanium. Metallic honeycombs are among the most
expensive core materials.
Foam cores have become a reasonable alternative to
balsa and honeycombs. Foams cover a wide range in
price and density, but they are generally more expensive
than balsa and paper honeycombs. <strong>The</strong>y are better
insulators than other core materials. WEST SYSTEM epoxy
will not chemically react in a destructive way with
foams. But, because of the insulating properties of foam,