We received the following email a few weeks ago:
From:Philippe Sandel
To:linandlarry
Subject: Epoxy Question
Hello,
I have been reading your books time and again
in preparation for some extended offshore cruising.
Your views greatly help to keep some common
sense amongst all the hype being offered.
As I am entering the final planning phase,
can I ask you a short question on hull construction
materials? In your book on Details of Classic
Boat Construction(edition 1999) you make a case
against the use of epoxies in combination with
wood. Is this position still valid in 2007 or
has there been an evolution in current epoxy-products
which would allow for a dependable, long-lasting
woodcore-epoxy type construction (the design
I am looking at is found on www.chantiermer.com/presselordjim.htm
Could you maybe address this epoxy-issue briefly
in an upcoming cruising tip on your site?
Sincerely,
Philippe Sandel, Belgium
Our answer is, unfortunately, little has changed
since Larry wrote the appendix to Details of Classic
Boat Construction for the 1999 edition. It showed
why we are uncomfortable about using epoxy adhesives
for any structural members of a wooden boat or for
any wood to wood gluing where the joint will be
subjected to either heat, regular soaking in water,
and what is called deep cycling, i.e. being wet
then dry, time and again, or exposure to UV light.
None of the epoxies we see being sold for boatbuilding
purposes are rated waterproof, all have low Heat
Deflection Temperatures. HTD is the temperature
at which any plastic (epoxy is a plastic) will soften
enough to loose 30% of its strength. With each degree
rise in temperature more strength is lost. You can
look for yourself at www.westsystem.com under product
information, typical physical properties. There
you will see the epoxy distributed by West System
has HTD's ranging from as low as 116°F to a
top value of 123°F. Products from other companies
such as System Three, Poly-shield etc. are little
different.
The one thing that has changed is, since we began
writing about the problems with epoxy adhesives
for boat building, the distributors and marketers
have become much more careful with advertising
and information pamphlets than they were even
eight or ten years ago. If you read carefully
you will see these products are called "water
resistant" not water proof. Furthermore,
if you search through the information you can
find on most of their sites or by ordering instructional
booklets, there are warnings that using these
epoxies in temperatures below 65°F will result
in less than optimal results (this is couched
in terms such as - will loose physical properties.)
To our knowledge, there is still only one adhesive
that can be advertised as waterproof, for extreme
exposure exterior use and that is resorcinol glue.
Many wonderful, long lasting laminated boats have
been built using this adhesive. Take a look at
John Guzzwell's Treasure to see a fine example
as are the Luder 16's and Sparkman Stephens boats
built in the 50's and 60's. Those built using
dark purple adhesives - resorcinol, are still
in fine shape today.
An interesting aside, when the second edition
of Details of Classic Boat Construction came out
with the appendix on problems with epoxy adhesives,
the attorney for West System called and said her
office was reviewing our appendix. The upshot
was a request that in future we capitalize the
name West System and if possible use the trademark
symbol. I.e. they could not refute any of the
problems we stated.
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