How to prime plywood/epoxy for enamel painting?

[brownsoft]

Hi all, I've been rebuilding a 'Heron' sailboat(or is that Herron?) and I'm now ready to paint the hull. I've coated the ply with a couple of layers of epoxy and I'm thinking of finishing it with enamel paint (house or marine?) and the thing I really don't know is what sort of priming I need to do between the epoxy and the enamel? Does epoxy need a special primer or will a garden variety enamel primer do?
One final thought, does the paint need to specify that it has a UV inhibitor in it, or does all enamel paint have this already?

[mmd]

The choice between marine and exterior enamel is not too tough. Marine enamel will stay shiny longer and require repainting less often, but at a premium price. I am not familiar with the Heron design, but for most home-builds I reccommend ordinary exterior eanmel. If you do not like the performance of the paint, in a year or two you can repaint with marine enamel and not be out much money. The opposite is not so inexpensive. No special primers are necessary for epoxy, just one that is compatible with the topcoat paint you are applying.

[Scott Rosen]

A couple of things about painting over epoxy.

Some epoxies have amine blush when they cure. That leaves an invisible coating on the surface that will hinder paint adhesion. You can remove the blush by scrubbing with a ScotchBrite pad and cold water--no soap needed.

Some people report incompatability problems with some brands of paint and some brands of epoxy. It's best to do a small test area first just to make sure the paint and the epoxy are compatible.

Other than that, there's nothing special you need to do.

[JimD]

like Scott says, make sure you've scrubbed off any blush, primer never hurts but almost any paint will stick well straight over the epoxy.
jim

[JimConlin]

Adhesion issues aside, sanding epoxy to an acceptably fair surface can be a bit tedious. I've used Interlux 404/414. It's a two-part product. It smells awful and has probably made me (more) foolish, but it sands easily and both one-part and two-part (LPU) paints seem to adhere well.

[brownsoft]

Thanks for the advice. I remember reading about amine blush a while back but couldn't remember the solution. I think I'll go with primer and enamel.

Any comments regarding the UV issue?

[Scott Rosen]

Any decent hull and deck paint will have UV protection. It won't necessarily say so on the can.

[NormMessinger]

"I remember reading about amine blush a while back but couldn't remember the solution."

No solution, just plain water. You can wet sand and solve two problems with one application of elbow grease.

--Norm

[brownsoft]

Excellent stuff. Now the last question for now, how much elbow grease will I need to purchase and will standard elbow grease do, or do I need super powered.. tongue.gif

Just kidding, thanks for all the input.

[plimsol]

Just a variation on the scrub and wash. I scub with an amonia solution in water. It seems to lift the blush better. Use plain amonia, no soap. The blush is water soluable.
From what little I understand about epoxy chemistry, there is an unreacted part of the epoxy that bonds with the drier in the enamel and starves the enamel of the drier it needs to cure. Consequently, the enamel does not cure.
An additional step in the process is to wash down the scrubbed surface with paint drier, which is cobalt chloride in solution. This epoxy reacts with the drier wash rather than the drier in the enamel. For goodmeasure, put a little extra drier in the first coat of primer. Beware of Japan Drier, it does not seem to work. A caveat, this is just trial and error boatyard chemistry. It works for me.