: I wrote Dr. Rot twice (the original question and one follow-up) yesterday and
: today to ask him about using CPES on my boat. I asked him how I deal with
: the "Blush" of CPES and what method he recommends for coating
: the inside of a kayak.

: I like his page, his products seem very good and he is sincere and helpful.
: Still his answers are a surprise. First that there is no "Blush"
: with CPES (he says NONE of his products have this). But most hard to
: figure out were his two (2) completely DIFFERENT recommendations
: reguarding the wait time necessary for the "Solvents" to
: "evaporate" BEFORE it is a good time for coating over the CPES
: with regular epoxy or "Clear Coat". I like him and think he is
: honest and knows what he talking about but I cannot understand how come
: his answers do not seem to "add up". Does anyone here have an
: opinion to help straighten me out on this???
: Both of his e-mail answers came today with in 1 hour of each other:
: "None of our resins blush, including CPES. That's just one of the
: advantages of using our wood-derived resins."

: Answer # 1 at approximatly noon: "On your boat, CPES would form the base
: coating for Clear Coat. You would apply one coating of CPES, allowing the
: wood to absorb all that it will, wait for a few days (or longer) so it can
: gas-off the carrier solvents, and then come back and apply the Clear Coat.
: The Epoxy in Clear Coat will bond strongly with the CPES-treated
: wood."

: Answer # 2 only ONE HOUR later: "So, you apply the CPES, wait until it
: has gassed-off the carrier solvents (2-3 hours) and you are free to then
: apply the Clear Coat. Basically, once the CPES-treated surface is
: "tacky", you can apply
: final coatings. The resin itself doesn't have to completely cure, since all
: epoxy resins cure in the absence of air."

Okay, here's the answer:

There is a "theoretical" point at which CPES has gassed off the solvents but the epoxy has not yet cured. I have been told by polymer experts (far more expert than I am in the finer workings of these mixes) that if you apply the final coating at the point where the CPES resin is still tacky, then it will bond to a greater degree with the final coating. This is, as far as I am concerned, theory, because for me -- and all the testing we have done shows this -- the bonding is very secure regardless of whether the CPES has cured or not. It would take some sophisticated testing and some delicate instrumentation to determine the differences, I suspect. Still, what the experts say makes sense, and our testing shows that the bonding does take place using the “tacky phase” method, and so from a practical point of view we will mention this in the interests of keeping the project moving more quickly.

We generally don't go into this "tacky phases" stuff much with our email responses. You guys (& gals?) are fairly sophisticated users of resins, so once we become aware of that then we are more apt to get into the finer points of application. Hence the two different answers. We try to be careful. Too many times raising these issues can confuse the person making the post, so we wait until we know that the person posting is among the more "enlightened" group. You just have to understand that we sell a lot of product to people who have no idea of what epoxy is, much less the finer points of its application.

Finally, I have to say that it is always important to apply coatings as close together as the particular compound will allow. This reduces greatly the possibility of air pollutants contaminating the surface. If more than a couple of weeks have passed since the initial coating was applied (assuming it was an epoxy), we recommend wiping down with lacquer thinner before subsequent coatings are applied. Acetone will work too, but lacquer thinner cuts through the surface junk more easily.

I hope this helps make the issue a little clearer.

Jim
--
The Rot Doctor
http://www.rotdoctor.com
E-mail: drrot@rotdoctor.com
Phone: 206 364 2155