The Rot Doctor


Subject: A few questions about CPES
Date: Sun, 23 Sep 2007


A few questions:

1. I have to replace a foundation sill on my house. Contractors mention using pressure treated wood (a 6" x 6") and then PT plywood over the exposed studs. Should I have them treat the sill and plywood with CPES? Your website appears to say no, but I wanted to make sure. Seems like it would be an added layer of protection.

CPES will add protection to pressure-treated wood as long as the pressure-treating isn't fresh (greasy to the feel), in which case the pressure treating chemistry interferes with the ability of the CPES to penetrate the wood. So basically, you're right: CPES does add an additional layer of protection.

An important thing to remember is that once pressure-treated wood is cut or trimmed, untreated wood is exposed and is subject to rot. Even if you don't treat all of the wood, those areas that have been cut/trimmed should certainly be protected.

2. I have to reshingle the part of the house that is getting the new sill. If I use cedar shingles should I still use CPES?

CPES will protect and consolidate cedar shingles, particularly the bottom edges that are apt to absorb water. The new farm-raised cedar does not have the rot-preventing resins that the old original growth cedar had.

3. How long after using CPES can I paint the shingles?

This will depend somewhat on temperature and air movement, but the basic answer is that you can paint as soon as the surface is dry to the touch. This can be in as short a time as a couple of hours, or as long as 6-7 hours. Certainly you could CPES one day and paint the next.

CPES also serves as a primer for paint.

Thanks. Joe J. MA


You're welcome, and feel free to come back if you have additional questions.