Dealing with warped plywood.

The dreaded humidity monster bit me and warped the 6 sheets of ply. Was about to cut a few patterns this morning for my Brockway Skiff. I have the sheets laying flat now with weights on them.

I was wondering what everyone else does when this happens.

 

The frames should get the plywood to take the proper shape. What kind of plywood are you using?

 

If the sheets have curled a bit, from humidity or being wet. Let them dry flat and if still cupped or curled, stand them up and wet the side you want them to curl toward, then let them dry again. They will curl toward the wet side, each time they dry. As to how much, well, this is a crap shoot, but mostly they'll curl about as much as they did previously. The species type, the plywood grade and panel construction will really be the determining factors, but it's better than nothing. What type of plywood (grade and species) is it? How was it stored, when it curled?

 

I've usually found most timber will curl a bit (ply included) even if perfectly q/sawn and nil run out. Mostly this is from being laid down so one face gets a temeprature and humidity change. Mostly as PAR says if you even it up on both sides it will go back pretty flat. Generally this why ply is stored on edge. The better the quality, the less curl, and the flatter it will return to.

Stuff like 18-20mm thick three ply solid oak flooring tiles will exhibit this trait too, prior to being fixed to the floor. I've had to advise the flooring guys (who should have known better) how to get it flat prior to laying.

 

They are Georgia Pacific......... BC grade panels. (1/2" & 3/4")

I have always laid the panels flat (with weights) in the past and dealt with a little cupping or bowing.

I am throwing together a 14' Brockway for the grand kids to beat on for a few years. The stem post, chine, transom, and bottom panels will take a lot of the distortion out when they are glued and screwed together. It just makes things a little cumbersome.

I posted more out of curiosity than anything else, to see how others deal with it.

Thank you for the responses guys.

Merry Christmas!

 

On those BS sheets, does it say "Exterior" or "Exposure 1" (sometimes with the addition of exterior on exposure 1). A critical difference between the two. Exterior will tolerate continuous emersion, while Exposure 1 only tolerates intermittent contact.

A little curling isn't going to hurt anything, so work with the curves as you cut out the pieces, so they'll flow with the boat's requirements.