The Rot Doctor


Subject: CPES Cure Times & Capability
Date: Wed, 29 May 2002

Dr. Rot:

We write to you from San Diego, Ca. We are doing some repair work on a wooden Lightning (approximately 45 yrs. old) and have a couple of questions. Our project involves 1) replacing the deck with new 3/8 marine mahogany plywood, which we intend to CPES and varnish, and 2) repairs to the hull (we added a few splines) and some minor rib work (a couple show some rot), as to which we intend to treat all exposed wood where repairs have been made or new wood added with CPES and follow with paint. Here are the questions:

1) I can't recall what you recommended when I ordered the CPES a few weeks ago about when we should consider painting/varnishing after application of the CPES in order to achieve the best bond. In other words, how much cure time should we allow before painting and/or varnishing? Our daytime temp this week has been in the mid- to high-70's.

CPES will cure to a "tack free" state in about 1-3 hours at your temperatures and San Diego humidity. At this point you are free to apply the first coat of paint or varnish (un-diluted, full strength), and the epoxy will "lock in" the surface coating. You have a little spread here, and in the real world if you can get the first finish coat on within about 8 hours you will achieve the superior bond. If for some reason it goes longer and the epoxy cures, you will still get excellent's just a matter of degree.

2) We previously used the West System to glue in splines in doing hull repair work. Any concerns about incompatibility of CPES and the West System?

Nope, go ahead and use the West. It will bond with the CPES-treated surface.

I still have some of the West System materials and was inclined to use up what I had in a couple of patches (mostly filling some gaps) after applying CPES to the surrounding wood. Any concerns?

None at all.

Any different cure time (from your answer to question one above) for the CPES if I am following it with either the Lay-up and Laminating resin or West System?

Nope, all application procedures remain the same.

All you are really waiting for with the CPES is for it to evaporate away the carrier solvents, and the CPES "tack free" phase indicates that has happened. The reason is that you don't want the CPES carrier solvents diluting any subsequent epoxy or other finish that is applied on top.

3) I am trying to estimate whether I have enough CPES on hand currently. My project has expanded since I ordered originally, but I over-ordered some to begin with. I ordered two, two-quart kits so I have a gallon in total. Based on the scope of my repair, I plan to CPES the deck (both sides = approximately 80 sq. feet x 2, or 160 sq. feet in total), the outer sides of the hull (bow to stern) and approximately 25% of the interior of the hull (including ribs). Do you think I have enough? Also, is the coverage rate of CPES approximately 200 sq. ft per quart or per 2-quart kit.

The coverage rate of CPES for good wood is approximately 200-250 sq ft per gallon. In your application you will lose a little due to plywood cut-edge absorption, and some on the interior as it works its way into seams and joints. My quick mental math tells me that your gallon of CPES will not be quite enough.

Thanks for you help.

Chris B.

You're welcome, and come on back if you have further questions.