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I managed to rescue some 3/8 interior grade birch plywood I had sitting outside from a surprise rain storm last night but not before it took some water. I had been planning on staining the pieces today.

Around here 12-18% emc is about normal. It is hard to tell if the wood is damp by feel because it is cool and humid today, but the edges exposed to the rain are at about 45%.

My question is: Do I care? The surface appears dry by look. Should I wait for this to all dry out another day or two or can I just go for staining it and trust it? I really want to get this done today.

Its a Minwax oil based stain, water seems to bead up on it while it's drying, so I guess has at least some sort of moisture trapping effect, could staining it while it's damp also affect the longevity? I plan on finishing it with helmsman spar urethane after staining.

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    I'd wait. First there is the issue of water and oil not mixing. Then there is the almost certain fact that the surface is not uniformly dry since it was most likely not uniformly wet. Staining it now (even with a water-based stain) would likely lead to a splotchy result. Then consider that staining birch plywood has a reputation for producing splotchy results - so, find something else to do today.:)
    – Ast Pace
    Sep 24 '16 at 15:29
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    I would strongly recommend you wait also. If it was waterbased stain you could be fine (many stain guides suggest pre-wetting before staining!) but not with oil-based. It might work fine, but is it worth taking the chance it'll take the stain very irregularly?
    – Graphus
    Sep 25 '16 at 9:59
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    I would think oil-based stain would really trap water in there. Wonder how it may look on the inside. Maybe even rot??
    – Ljk2000
    Sep 27 '16 at 3:01
  • @AstPace Sounds like an answer to me.
    – Matt
    Sep 30 '16 at 3:01
  • @Graphus Sounds like an answer to me.
    – Matt
    Sep 30 '16 at 3:01
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While waiting is better, yes, you can apply oil based finishes (as well as water based finishes) to wet wood. Some folks like to wet wood for applying water based stains for evenness of application. Finishes are a moisture barrier which slows the movement of moisture but will not 'trap' the moisture in the wood forever. Since you are discussing plywood, the issue of swelling and shrinking due to moisture is minimized as well due to the cross grain construction of plies.

Folks use heat and increased air flow to aid drying as well. You can use even volatile solvents to slightly accelerate the evaporation of moisture. (Please use common sense and reasonable safety measures.)

Having said that, I will note that the harder the finish, the more likely side effects like slight crazing or a few cracks due to shrinking/swelling. Also note, that wood stored outside will have a higher moisture content in any case than wood stored inside. Another issue, is make sure the wood is clean; dirt and gunk of all sorts will lead to heartache when trapped under a finish.

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  • Although I wouldn't see a definite issue with damp wood and water stains I think there's a very good chance the user would experience big problems with 'hold out' applying an oil stain to a wet surface.
    – Graphus
    Dec 8 '16 at 8:52
  • Duly noted and for completeness I should say that lacquer and shellac will turn milky white if there is too much moisture. I would also recommend Bob Flexner's books (I like Understanding Wood Finishing: How to Select and Apply the Right Finish) and blogs (to start, given this question popularwoodworking.com/article/… ).
    – ewm
    Dec 8 '16 at 12:58

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