Way OT - weatherproof coating for acrylic painted wood
 

We have some pieces of white pine cut out in fish shapes that we've painted with acrylic paint. We want to mount them on our outdoor shower enclosure so looking to make them more weatherproof. Can I simply put a few coats of water based urethane floor finish on them? Or is there a better way? They'll be taken down seasonally when we decommission the outdoor shower (about now) and put back up after frost in the spring.

A few coats of Krylon UV-Resistant Clear acrylic spray might be the easiest approach.

If you don't mind a slightly different color, any exterior housepaint will do about the best you can find. Clear finishes in bright sun don't survive as well, because the titanium dioxide and other solids in a colored paint are there partly to block the effects of UV and weather on the paint and on the wood itself. Just paint over the acrylic. As long as the acrylic was prepped right, your house paint (either oil or latex) will do just fine for you.

spar varnish. should be OK over acrylic. test before you do it but Lane is right about UV protection

I almost added an additional paragraph to discuss Falsie's suggestion. It will work but it won't last. Spar varnish will craze and darken within a year, and its ability to protect the wood or the finish underneath will be compromised. At that point, you'll need to paint over the varnish anyway to keep the color looking right. Ergo, just do the paint.

These are decorative fish, so the painting is representational rather than a solid color. It has to be some form of clear finish. I'm willing to re-apply annually. I'm using a water-based floor urethane product on some interior trim and it doesn't seem to yellow over time (I did all my wood window sills with this product) so that's my default if I don't find a better option.

Thank you all for responding to this really OOOT!

Lane, I was under the impression that crazing is happens b/c the substrate expands and contracts with changes in humidity while the varnish doesn't.

By painting the wood (I'm going to assume there's a layer of good primer beneath the paint) and then laying on the spar varnish in a few coats aren't you basically making the object waterproof thereby eliminating the potential for crazing.

I wood (pun intended) use a polyurethane that's formulated for outdoor use - that wood (ditto) ensure the poly has a proper UV protectant package.

Here's a sampling from Home Depot.

That certainly is happening, but the varnish itself is also failing due to UV damage. As also pointed out here, there are varnishes with UV additives, however it really depends on where this installation is located. Nothing saves a varnish (spar or polyurethane) when exposed to high UV. I varnished a wooden sailboat for years and learned all the hell that the OP here may be facing. But your points are good.

It looks to me that a water-based spar varnish may be the best option, with UV inhibitors and less likely to yellow than oil-based spar varnish. Does that make sense?

Got it. That makes sense.