The Rot Doctor


Subject: CPES with paint and varnish
Date: Sun, 10 Sep 2000

On one of your Q&As dated Jul 20 you recomended CPES over wood and followed by paint in 15 to 45 minutes to improve adhesion. On another Q&A dated Jan 31 you recomended CPES on teak and followed by varnish in 2 to 3 days. Wouldn't you also get better adhesion of varnish to CPES if you only waited 15 to 45 minutes?

Yes, you're basically correct. The whole issue gets a little tricky, because to apply a finish coat too soon will not work -- the still-evaporating carrier solvents will not let the finish coat bond securely. How long you wait will depend on temperature, wood density, and air movement. It might be 15 minutes on a sunny, dry day in Miami, but it would also be more like 45 minutes (or longer) on a cloudy, still day in Seattle.

The best way to proceed is to 1) stick your nose next to the surface and see if the carrier solvent fumes are strong-smelling, and 2) touch the surface and see if it's just tacky. No strong fumes and a tacky feel will mean it's okay to go ahead with the first coat of the finish, paint or varnish.

If the wood is deteriorated and there is deep (more than 1/8") absorption of the CPES, then one is better off letting it fully cure. If if the CPES is fully cured, there is still superior bonding with the finish coat.