Subject: The Epoxy on Wooden Boat Wars
Date: Sun, 18 Jun 2000
I've been reading up on the many forums and websites dedicated to wood constructed vessels and epoxy on wood hulls has its allies and its enemies..I'm about to purchase a 36' 1969 Trojan Sea Voyager(woody)..the hull is in good shape and ready for painting..I'm thinking about using your CPES to seal it before painting but I have a question..wood fibers naturally expand and contract as you take it to and from the water..wouldn't this process tend to separate your resin and make it useless?..I've read your previous responses and you point out that it has some elasticity but does it have enough?
Good question...and you're right about the wide variety of opinions
on using resins on wood hulls. Way back in the '70's when the resins
began to appear on the store shelves, old boat owners thought they might
be the final answer to those old leaking hulls. In most cases they
weren't and the hulls went to the bottom pretty fast.
We're much more sophisticated now and the resins, especially epoxy, are
widely used on wooden boats. The usual caution has to do with enclosing
the wood so that it can't "breathe", or if it can breathe it will expand
and contract under the resin sheathing and cause problems. These are
genuine concerns, but are somewhat dependent on the size and type of
hull. For large planked hulls it makes the use of resins almost
impossible unless the hull is hauled, seams reefed out, wood thoroughly
dried, and then a whole new hull basically constructed using the old
hull as a mold. Can be done, but is time-consuming and expensive. On
some of the smaller ply hulls the judicious use of resins and glass
sheathing has worked -- the ply is easier to dry and has much less expansion/contraction.
On particular areas being repaired on wooden hulls, these concerns are
generally not an issue. Epoxy can be used in local repairs and there is
enough of the wood left to allow the normal expansions and contractions
of the wood without affecting the areas that have the epoxy application.
Now, about CPES. CPES is a premium epoxy that is carried into the wood
by a mix of 14 different solvents, moisture displacers, sap dissolvers
and the like. When mixed it is as thin as diesel fuel. It penetrates
into any gaps in wood, concrete, fiberglass, etc., the carrier solvents
evaporate away, and the resin remains, binding things together and
forming a semi-waterproof barrier. Wood that has been treated with one
coat of CPES will still "breathe", although a bit more slowly than
untreated wood. Two coats of CPES will still allow air and moisture to
pass, although more slowly still. And three coats of CPES begin to seal
things up, although still not totally. So the bottom line here is that
CPES gets between and around the viable wood fibers (or inside the
damaged fibers), hardens things a bit, and prohibits the wood from
absorbing as much moisture as it normally would. It also creates an
epoxy surface environment that many fungi and bacteria would prefer not
to eat. When applied to the end-grain of wood, quite a lot of CPES can
be absorbed to very good effect, because it's here where wood
deterioration problems often get started.
So, CPES can be and is applied to good wood to give the thin protective
barrier that discourages the development of rot and bacterial
degradation and forms a very superior base-coat for subsequent coatings.
Because CPES is so thin, it does not "layer-over" the wood with a
waterproof resin, and so the wood can still expand and contract,
although as noted above a bit more slowly than un-treated wood. If
you've got a leaky old hull that you're going to re-launch, then it's
just going to take it a little longer to swell herself back up.
Our testing has shown that when paints/varnishes are applied over
CPES-treated surfaces the life of the paint/varnish is extended
substantially. We also know that when sealants, such as 3-M's 5200, are
applied to a CPES-treated hull before the CPES has completely cured
(between 20 and 60 minutes at 70F -- shorter if its hotter, longer if
its cooler) the bonding is stronger than it is to un-treated wood. In
the case of 5200 this bond is almost unbreakable. The same addition of
bonding strength applies to 4200, 101 and the polysulfides.
In your particular case, I would say that CPES applied above the
waterline would serve as a very good wood protector and primer for
subsequent paints. Below the waterline it might or might not be
beneficial, depending on whether the boat stays in the water or is
hauled. If it's hauled seasonally then The CPES would be very helpful.
Expansion and contraction of the hull will not be a problem. The coating
is elastic enough and thin enough that you'll have no worries. Many do
this, and many are happy.
This probably more than answers your question, but if you have
additional questions then come on back.