The Rot Doctor


Subject: Wood Preservation
Date: Wed, 18 Aug 1999

Thank you for your website and especially your articles about CPES. I am considering the purchase of a large (54 foot) wooden (juniper over cypress) boat. The hull is in excellent shape but I have been warned and warned by various friends about wooden boats , so I am trying to gather all the information I can before taking the plunge.

My question concerns the use of CPES as a preventive measure on hulls which have no perceptible rot. Your articles seem to indicate this would be advisable, but I am wondering how the product penetrates a solid mass of dense wood. Balsa and rotten pieces of other species, yes, but isn`t healthy wood too dense for penetration to occur and isnt penetration necessary for the beneficial effect to occur?

CPES will penetrate good flat wood a millimeter or so. It gets a good grip in the tiny spaces between the wood fibers, which is why it makes such an excellent paint/varnish base. Even this small amount of penetration gives the wood some protection -- not absolute protection, but some protection -- by creating a surface environment that fungi and bacteria are not interested in.

More importantly, though, it penetrates deeply into seams, cracks, butt-joints, where it can enter the end-grain and penetrate quite a ways -- depending on how porous the wood is. It's at these locations that rot usually starts, and because they are now protected with epoxy the rot never has a chance. This is why people, including a lot of boat rebuilders, use CPES on every piece of wood they can get at.

On used boats the wood is never in pristine condition and is more absorbent, so the use of CPES becomes an even greater protective factor.

Also, is it possible that the product, if it seals the surface, would prevent the wood from breathing and actually be harmful to healthy wood?

One coat of CPES does NOT seal the surface. The wood can still breathe, not as freely, but good enough to all normal expansion/contraction procedures. With 2 coats the wood will still breathe somewhat, and with 3 coats you have effectively sealed it off. CPES on wood does not appear as a coating, as a normal resin does, but as a kind of sheen. This is because it is diffused among the wood fibers. it's kind of a Gor-Tex effect: the wood will shed water but still breathe.

Thanks again for your products and information.

Phil B.


Come on back if you have additional questions. Most of us buy old wood boats because that's what we can afford. If I were rich I would have one constructed from aluminum, insulated hull, and completely lined with beautiful wood. But I'm not rich, so we have the old Canadian tug, and the maintenance is constant. But i have fun and I'm on the water, which in the end is what matters.

It was messing around with wood boats that got us started with CPES and made us believers. It wasn't until years later that we decided to market it nationally.