Varnish over epoxy

[Saint]

I did a quick varnish over the epoxy/fiberglass sheithing inside my daysailer. I don't know if i have more than two coats, the first of which was thinned with turps. This year I had my boat sitting outside in the sun for about three / four weeks and my varnish is peeling off. I am not very surprised that my thin coating didn't last very long, I'm just surprised that it is peeling. Is this the normal way varnish fails on top of epoxy? Or is the fact that it is peeling indicating that the surface wasn't prepped correctly?

Saint

[Bob Perkins]

If the epoxy you varnished over had not been cleaned of blush (waxy stuff that comes to the surface) or more importantly - not scratched up with sandpaper. Then you are correct that surface prep is probably the issue.

The smooth epoxy gives very little surface for the varnish to attach too..

[Ian McColgin]

Another thought: I am a great fan of using one of the newer water based "varnishes" (CTOL etc) over an epoxy primer. Both are vapor permiable and any moisture in the wood will pass out though both under the hot sun. If you use traditional varnish, the vapor will push through the epoxy against the varnish, leading to failure even if you've correctly prepped the surface.

This approach is especially wonderful in problem areas like cap rails and toe rails on older boats.

G'luck

[Mick Herron]

I need to echo and expand on what Bob said about preparation. I agree that sanding will improve the surface for varnish adhesion (and paint) however sanding alone will not solve the amine blush issue.

Wash the cured epoxy surface with detergent and a scotch brite pad, then rinse well. Usually amine cantamination will cause the coating (paint or varnish) to cure very slowly or not at all. I have found from my own experience that sanding does not eliminate the waxy coating and can lead to a soft finish that can be scraped off with finger nail or tying rope.

I can't comment on water based coatings, I have had no experience with them.

[ddeaton]

Dishwashing soap also helps remove the blush, or oily substance, that winds up on the surface after curing. Someone told me once only to use Dawn liquid. I cant believe alcohol or stronger solvent wouldnt work as well. This with the surface sanding is what I have heard. I havent any first hand yet, as I am just getting ready to lay varnish myself.

[chuckm]

the 2nd and 3th epoxy coats over say the hull? Correct?? One needs to wash and scuff prior to expoxying the additional coats. I have'nt done yet, just my understanding. Correct me if I'm wrong.

[ddeaton]

Chuck,
I layed 2 coats of thin System 3 on most my ply pieces and scuffed but did not clean with soap. I just wiped down with alcohol. So far so good. I havent varnished yet or been in the weather.

[Roy Morford]

I have varnished over epoxy on several strip built kayaks with no problems, even after several years use. Preparation is the key. I've read that the amine blush is water soluble so washing with a SMALL amount of dishwashing liquid, followed by sanding is the way to go.