The Rot Doctor


Subject: Window question (preventing rot)
Date: Thu, 27 Jul 2000

While most of my windows don't show any rot, I am thinking about using CPES to 'prevent' future problems. I am stripping paint to prep for new paint anyway, would this be a good preventative procedure??

Does CPES keep water from penetrating? And if so, I presume if it keeps water 'out' it will also keep water 'in'. So, my next question; If I only use CPES for the lower portion of the window(s) (say the sill and lower portions of the brick molding) if water were to penetrate the wood at the top of the window, would there be a problem?

Thanks in advance,



One coating of CPES partially waterproofs wood. What it does in effect is prevent the wood from being able to absorb enough water to reach levels that will support biological activity, i.e., rot fungi and bacteria. This is of some importance on the flat surfaces, but of great importance on end-grain and enclosed areas, such as cracks and seams. That's usually where the rot gets started.

Several coats of CPES will waterproof wood.

So, to answer your questions, Yes, a CPES treatment on the bare wood will go a long way toward preventing future rot. It will also serve as a superior paint prime coat and will extent the life of the paint by a significant margin.

On the upper portions of windows the rot is not usually a problem because the moisture always descends, so the upper portions usually don't retain enough water over an extended period of time to support the rot fungi. Naturally, it's always best to treat all the wood, but that's a lot of work. Your plan makes sense, and it won't take a whole lot of CPES to treat basically good wood, although you will want to allow it to be absorbed into all cracks and seams.

For estimating the amount of CPES required, you can figure you'd use about 1 gallon per 150 sq ft.

Come on back if you have additional questions.