weathered wood finish

[kenneth kayser]

My wife bought a work of art painted on old barn boards. We want to put it on an open porch, so it has to be finished to protect it from the weather. What can I put on first so that subsequent coats of exterior poly do not darken the wood. So far, I have tried clear acrylic with a VERY thin mist coat. That did not discolor the wood, but the coat is extremely thin and I do not know if I can apply it uniformly. Slightly thicker coats darken the wood. Would shellac work?

[Scott Holmes]

Blonde de-waxed will work. Zinsser seal caot is dewaxed blonde shellac. Another option would be Zinsser's aerosol shellac.

Shellac is color fast; as long as it's on a covered porch it should be fine.

Which acrylic brand and type did you use?

[Howard Acheson]

Some things to keep in mind. Any oil based clear finish will be amber to some degree which will affect the "look" of any colors underneath. Finishes intended for outdoor applications are the most amber. Poly is not a good choice outdoors even if shaded from direct sunlight. Reflected sunlight still contains some UV. UV rapidly deteriorates urethane and within a year or two, the finish will get cloudy, begin to peal and eventually totally fail.

A better product would be a true marine exterior varnish. You can't get this at a big box or local paint store. Go to a marine supplier and look for brands like Interlux, Pettit, Wolsey or, best of all, Epifanes. It's expensive but lasts for a few more years.

The best way to deal with it is to have some UV blocking covers made that could be used and then removed when you want the art to be visible.

[Gary Max]

You have already started by--"So far, I have tried clear acrylic with a VERY thin mist coat."
Most of the time mixing finishs with different bases is not a good ideal.
I would stay with the Acrylic.

[kenneth kayser]

This will not be in direct sunlight, so UV blocking is not paramount. I want to protect it from humidity and some rain. It will not be in direct rain, but with high winds some water will get on it. The darkening I am concerned with is not from yellowing; it is the immediate darkening from the finish penetrating the wood. Weathered wood is very porous. It may not be possible to coat it without changing the appearance of the wood. I bought some spray shellac. My idea is to give it a very thin coat to seal the wood without changing the appearance. Then go over it with something to take the weather. I'll post how the shellac worked. I am experimenting on the back side.

[kenneth kayser]

Tried the shellac. Darkens the wood as much as anything. Also, the acrylic (Krylon, "crystal clear") was too thin and did not keep other finishes out. I am beginning to think that weathered wood may have a surface that will darken no matter what is applied.

[Howard Acheson]

Minwax Polycrylic is waterborne acrylic finish. It will be water clear when it dries. It comes in spray cans or in cans for brushing. Minwax also makes an exterior waterborne acrylic finish:

Minwax® Water Based Helmsman® Spar Urethane
A crystal-clear, non-ambering finish specially formulated to provide long-lasting beauty and tough protection for your wood, indoors and out

I've not used the product but it should be a somewhat better product for outdoor conditions.