The Rot Doctor


Subject: CPES, House Rot, and Breathing Wood
Date: Fri, 02 Jul 1999

Hello Dr. Rot,

I have a four-family townhouse in a low lying area. Rainwater never quite comes up to the level up the wood itself, but the moisture is causing all the wood siding and corners to rot at the bottom.

Your CPES looks like an excellent solution for this problem. This is what I'm considering:

1) Remove and replace severely rotted wood.
2) Remove the existing paint at the bottom of the siding, to a level at least 6" above the height of the rot.
3) Brush on CPES liberally. Inject in thicker sections (like corners).
4) Use filler as needed.
5) Repaint.

Does this sound like an effective plan to you?

I mentioned this to a friend who has more knowledge about house repairs than I do. He had never heard of CPES, but he was concerned that the CPES might prevent the wood from breathing. Any moisture that gets behind the wood via other means, like condensation, would be trapped and might cause more rot at whatever level I stopped applying the CPES. To your knowledge, could this be a problem? If so, are there any additional steps you recommend to avoid it?

Thank you in advance, and I look forward to doing business with you.



Your plan sounds thorough and sound. It will work. Be sure that the wood is reasonably dry (i.e., you can't squeeze water out of it) before the application of the CPES. Pay particular attention to edges, seams and end-grain. Apply all that you can get the wood to accept. On any new wood going in be sure to also treat that with CPES after it is cut and trimmed but before installation. If you want to be obsessive about it, pre-drill nail holes and inject with CPES before hammering in the fastening.

Your friend's concern is genuine. It's a major issue in the boating industry, where epoxy resins are used generously. However, CPES is a very diluted resin (it's the solvents that allow it to penetrate so deeply) and so one or two coats do not stop the wood from breathing. If there are three or more coats then yes, the passage of air gets to be a problem. Also, generally speaking wood breathing doesn't become a major issue unless almost all of the wood is resin coated, i.e., it can still ventilate through uncoated portions of the plank or beam.

Get back to us if you have further questions, or there is any way we can be helpful.