Accounting for humidity?

[Pirate]

So, if your shop is typically at 80% humidity and house, where finished project will live is typically 40 - 55% humidity, how do you adjust for this?
Built this turntable for tv, out of rough 3/4' ply. (To match rustic cabinet)
Ply was in shop for years.
After bring in house, the edge of the ply has a warp, even though the upright screwed to it is only 4" from edge. Bottom blue piece also warped.
If I had acclimated the wood in the house and it warped, being it was plywood, not sure what I could have done.

[Pirate]

Sorry about pic size.

[jteneyck]

Plywood doesn't expand/contract with changes in humidity like solid wood does, but it can still warp if there is a moisture imbalance, as your photo proves.  But you can greatly reduce the chances of that happening if you can allow air to freely circulate around all the surfaces of the piece when you bring it into your house.   But that couldn't happen when you stacked up the parts so they warped.  They may still flatten out again once the moisture content in them equilibrates but of course it would be better had it not happened to begin with. So rather then stack them up like you have them, it would be better to separate them so that air can get to all the surfaces equally.  Hopefully, these pieces will flatten back out again.  Taking this precaution with future projects should prevent the problem from happening.  How long, you ask?  I'd guess at least 2 weeks for anything with finish on it.  

John

[ianab]

I agree with John. The top surface is exposed to the 40% house air, the bottom surface isn't. So the top is going to dry faster. and shrink a small amount. Even though the plywood is generally pretty stable, and painted to slow the moisture changes, there can still be enough movement to notice if it's unbalanced like that. 

I'd sit it on some blocks of wood so air can circulate more evenly and wait for a week or 2 and see what happens.

[AHill]

Typically, if ply warps, it's because one side had more moisture than the other. Store upright or sticker to equalize both sides before working with it. As mentioned before, humidity won't make it expand and contract like solid wood.

[Pirate]

I would have thought the 3/16 (+/-) air gap would have been enough for equal drying.

[jteneyck]

I would have thought the 3/16 (+/-) air gap would have been enough for equal drying.

That's not much of a gap for air to circulate through considering how large the parts are.   Stickers are typically 3/4" thick for a reason.  

John

[ianab]

Plus when you are stickering wood in a stack, both sides have the same moisture, and hopefully dry down the same. All that's happened here I guess is that the exposed top has dried down 10X faster than the enclosed lower surface. If you want to see this happen, lay a sheet on a green lawn in the sun. top will dry, bottom will absorb moisture from the grass. It will banana in a couple of hours.