One pack polyurethane over epoxy

Submitted byBrian White onWed, 08/15/2018 - 20:27
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Kayak Building

I built a stitch and glue kayak 10 years ago using a non blushing epoxy and covered the epoxy with an expensive water based cross linked polyurethane designed to be applied over epoxy and protect it from UV damage.  After 10 years without maintenance the deck has some damage to the epoxy.  I have sanded the deck and recoated it with epoxy.  As there are now some one pack polyurethanes with very good UV resistant ingredients at a third of the price of the two pack products, I though that this time I would apply a one pack polyurethane over the epoxy.  My problem is that the one pack products are designed to be applied over bare wood.  I am hoping that after thorough sanding of the new epoxy to remove the gloss, the one pack polyurethane with bond well with the epoxy and give long term protection.  Has anyone had any first hand experience of applying one pack polyurethane over epoxy?  Reports of good or bad experiences are equally valuable.

JayBabina

Thu, 08/16/2018 - 07:54

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I assume your concern is about a good brand of one-part water-based poly that will bond to the epoxy.

Generally water based polys, have great bonding power with most surfaces other than oil. I have used a quality water based poly on one boat (Benjamin Moore) which is thicker than the thin MinWax types but was disappointed with the ability of it to lay out nice and flat like oil polys do. Probably drying time is too fast? I am interested in what brands if any worked out well from any builders. I am referring to brush application.

I used some Varathane brand marine water based poly just a couple of months ago and it would turn white when it got wet so water was obviously getting throught, it would dry clear again.  After about a month I sanded it with 800 grit and sprayed a 2 part clear coat on it.  The Varathane did not level well when it was hot but when it was below 80 degrees it leveled pretty  well.  I like that it is clear and I used some about 4 or 5 years ago and it seemed to work ok. 

I have used a lot of one pack oil based polyurethane over the years and have been happy with the results.  I had not thought of using a one pack clear water based varnish.  The only one that I can find readily available in Australia is a Dulux Intergrain Ultraclear.  I cannot find out if it is a polyurethane or acrylic.  All of the clear finish products specify use over wood only.

I have used 1 K for manys year on nonblushing /no wax  epoxies and it turned out very very mostly Rylard varnish. But now I use 2 K  laying 3-4 coats as it has better UV and wear resistance but then I top it with 1 k ,2 -3 layers and also have it for repair as its much easier with the 1 k-

The 2 K is nowadays easy to apply just rollon it streches itself and looks like a spraycoat.