Subject: CPES, Breathing (wood) and sealants
Date: Wed, 25 Oct 2000
I am truly confused. I am restoring a 14' Stauter. I am almost finished removing all the old paint. You suggested 2 gallons of CPES for the boat. In one of your articles a person who had leaking seams on their sailboat was told to seal the outside with CPES but not to seal the inside so the boat could breath. Do I need to use CPES on the inside and outside of my boat?
The second question is do I need to seal all the seams/crack, for example where the mahogany ribs meet the light ply or where two pieces of light ply meet, where two pieces of wood come together. I observed that some of the seams/cracks had some type of sealant while others similar seams didn't. I don't know if I should seal them or what product to use.
The third question is what does breathing mean?
Thank you for your time and your advice.
You're confused because it's a somewhat confusing issue. With wood,
"breathing" refers to the ability of the wood to pass air and moisture
in and out, as temperature and moisture and humidity change. This is why
a wood boat that generally sits in the water will open up her seams when
she is hauled and left dry for a few weeks or longer. She'll soak up
again when put back in the water and the wood re-absorbs moisture, but
not without leaking during the process. This is a bigger problem with
planked boats than ply boats (more seams), and with larger boats than
smaller boats (more wood to shrink/expand).
So, if you have a large planked boat and you wish to protect the wood,
it is generally best to seal only the outside, leaving the inside wood
bare so it will "breathe". However, unlike most epoxy resin coatings,
CPES is so thin that it soaks into the wood (rather than sitting on top
of it) and doesn't stop the "breathing". It does inhibit it somewhat,
but doesn't prevent it altogether. Two coats of CPES inhibit the
breathing more so, and three coats just about close off the wood, as a
normal coating of thick epoxy will. Depending on the boat, its size,
method of construction, intended use, etc. we will sometimes suggest
that the CPES and other epoxies be kept off the inside. On other boats,
ones that are smaller, kept on trailers or ashore, we will generally
suggest that a coat of CPES on the inside will be a good thing.
Now, if there is wood deterioration/rot then all these considerations go
out the window for that particular area. If you want to leave the wood
in place and return it to useful service, then epoxy saturation with
CPES and possibly Layup & Laminating Resin becomes essential. After this
is completed, what is repaired for all intents and purposes is not wood
any longer but epoxy resin absorbed into and around an old wood matrix.
You can see a demonstration of this in our "What's New" section where we
combined CPES and L&L Resin with sawdust and balsa wood. It ends up
being quite strong.
To answer your particular question, you can use CPES on the outside of
your boat and if you wish you can safely use one coat on the inside. You
boat is ply covered, so there will be less swelling/shrinking of the
wood and "breathing" is less of an issue. However, if the inside shows
no sign of being punky or soft, then the CPES is optional. By the way,
all ordinary oil or latex based paints will allow the passage of air and
water, so they do not stop wood from breathing. They can be applied over
a coating of CPES very effectively.
Seams are sealed if you want to keep water out...otherwise, no, don't
seal them. On your boat the seams between the frames and the ply should
not be sealed, because this will allow the wood to breathe. Wood that
breathes cannot hold absorbed water (it evaporates away), and so it
prevents the moisture level from being sustained at levels high enough
to support the activity of fungi and bacteria. On areas where you want
to keep the water out, generally on the exterior of the hull, then
caulking/sealing is required. If the seam to be closed is on the hull
itself, such as between hull pieces, which will be sanded and painted,
it is generally best to use a hard, permanent seal, such as our Fill-It
Epoxy Filler. If the seams are in places such as the hull/deck seams,
then you will probably want to use a flexible sealant.
There are a bunch of sealants, and of these we believe the polyurethanes
are the best. In the boating world, these are best represented by 3-M's
5200 and 4200. The 5200 is a sealant/adhesive, and gives good bonding
but less flexibility. The 4200 also gives decent bonding, and much
better flexibility. Both of these adhere very strongly to CPES-treated
wood. Never, ever use a silicone sealant! We don't like them used
anywhere, and on wood they are terrible because they contaminate the
wood and prevent the bonding of epoxies and many paints, even after they
have been scraped away.
Okay? This is a long answer, I know, but the questions you raise are
good ones for the novice wood boat owner, and I wanted to be clear. Come
on back if you need clarification or have other questions.