Polyurthane over epoxy ?

West System advises using a coat of polyurthane over clear coat epoxy as a UV inhibitor. If the boat will have long exposure to the sun.

I just finished the bottom of one canoe that won’t have that exposure, so I won’t use it on that, but now I am doing the bottom of my ultralight Jensen Kevlar and that will have a lot of sun exposure to the hull.

I am thinking of doing it to it.

Has anyone used polyurthane over a new coat of epoxy and how did it come out ?

Jack L

Fine, as long as the epoxy is cleaned
of any amine blush and perhaps lightly sanded.

Use Interlux Goldspar 95
dries faster than regular varnish and is harder

I’ve used automotive clear coat
spray on a carbon/kevlar paddle and that looked shiny and nice. Not much abrasion resistance as boat bottoms go, I’m afraid. And I have no idea about the actual UV protecting properties of the thing… Easy to spray on, dries fast (15 minutes b/w coats). Not sure if regular polyurethane is much different.

I would use a voc 2k spar varnish …

– Last Updated: Sep-27-10 12:28 AM EST –

...... spar is more than a UV inhibitor , it is suppose to be formulated for high flexabilty and have greater expansion-contraction ability (marine grade varnish) . A 2k spar varnish will excell in all performance criteria by a large margin over a 1k product (especially abrassion resisitence)

A 2k "marine grade" polyurethane is suppose to be equal in those performance criteria . I personally wouldn't use any water base product for a marine application/enviroment use .


Use 202 and 2333N (apply min. 4 coats / cut by 10% (or less) as desired) .


Linked products are not inexpensive , so don't fool around with other standard store shelf reducer , cleaner agents as alternates ... use recommended cleaner and solvent if you chose the Interlux Perfection product .

This 2k stuff is much tuffer than standard 1k Interlux Topside urethane or a Minnwax spar ... therfore focus on prep. , temp. and application should be taken seriously for optimal results .

You may not care to go through the focus on prep./application and cost required with the Interlux 2k product ... for simpler and least cost you might use the Minnwax spar (or similar) applied once/year or as needed/desired .

It is important to let the epoxy cure,
a month or so, depending on the brand of epoxy.

Then, wash the hull down with a good detergent, to remove any possible amine blush, and rinse well.

If there is a question of whether it cured enough, if you epoxy-coated a test piece when you epoxied the boat, you can first varnish the test piece. If the varnish doesn’t dry, doesn’t look right - especially if it remains tacky - then you will need to wait longer for the epoxy on the hull to cure.

A good marine-grade spar urethane is the standard. Sand between coats with 220 (opinions and some varnish manufacturers differ a little on what coarseness to use). Three to four coats are typically recommended for decent UV protection.

There are also opinions about application. This stuff gets tacky almost as soon as you apply it, so keeping a wet edge and using minimal strokes over the same area is best. Pygmy Boats recommends using a very thin nap roller (~4" wide) for application, closely followed by a foam brush to smooth it out. I roll with my left hand and brush with my right, doing only a square foot, or so, at a time.

Good ventilation is essential. I am in the process of finishing varnishing my wife’s boat (finally!) and strung up overhead tarps to do it in the yard. Early morning, Spring or Fall, is a good time to do this (as long as humidity is not too high).

The purists will tell you to only varnish inside, in a practically sterile, totally dust-free environment, after misting the floor to hold down dust. I did the first one that way and the one outside is coming out better, probably due to the learning curve. I’ve done a fair amount of woodwork in my life, but I find varnishing boats to be quite challenging (translate, not fun).

BTW, Pygmy recommends paddling the boat awhile between epoxying and varnishing - then there will be no question of the epoxy being cured. We paddled our Terns over a year before starting varnishing - but they do need to be varnished, eventually.

Good luck.

Follow Pilotwingz advice.

Thanks all, especially all the details
from pilotwingz, but when I see the cost of that stuff, it comes to more expense then the West Systems Epoxy, and the six to seven coats is way more time then I want to spend

If I were building a boat from scratch, I would go that route, but I am just looking for UV protection on the hull when the boat is on the roof of my vehicle.

I will probably just opt for a home made cover.

Good education here though so thanks again.

jack L