plywood question

[Alan Schell]

I'm building a set of cabinets for the shop. I cut the panels for the doors and laid them flat on the floor for a couple weeks while working on other parts of the cabinet and they have warped. Can this be fixed, and will they warp again once installed?

[Prashun Patel]

You can try to flatten them by wetting the surface of the convex side and letting it dry by itself. Water causes the cells to expand. The glued underlying veneers will act as 'clamps' that prevent the wood from expanding outward . The cells will instead compress inward. Then when the water evaporates, the cells will shrink, but retain their compression, causing the piece warp to correct itself.

That's how I understood from Flexner's book.

I've tried it before on plywood shelves. Once it worked; once it didn't. In both times, I was able to muscle the piece into compliance with cleats and edge bands.

Are you using BORG plywood? I've had 'cabinet grade' BORGply warp up on me like a Venus flytrap as soon as i ripped it.

[Jerry Olexa]

Humidity could also be a factor esp if in lower level basement. Put some weight on them for a few days. Can be frustrating...

[Jeffrey Makiel]

I believe you will always have a problem. Using a waterbased finish will exacerbate the situation. To aggrevate matters worse, I'm finding that modern hardwood plywood (whether from a large retailer or local hardwood lumber supplier) is generally more unstable today than it was 20 years ago. I do not know why, but I'm guessing it has to do with the substrate material.

I may get a spanking for this, but hardwood veneer sheet goods with an MDF core are the most stable but difficult, if not impossible, to find at the retail hobbyist level. A small mom and pop cabinet retailer that has been in business in my area for decades has proved this to me.

Making your own MDF core sheet goods for a cabinetry project would be very time consuming and only worth it if you are working with highly figured or exotic wood. I noticed that episodes of Woodworks with David J. Marks, he used and MDF core on many of his veneering projects. However, there will also need to be some investment in tooling.

-Jeff

[John Schreiber]

If they were flat on the floor (especially a cement) floor, one side of the wood was exposed to room air and the other to no circulation and perhaps a bit of moisture. That's about guaranteed to create wood movement.

Just moving them off the floor and arranging them for good ventilation may solve the problem. A huge amount of furniture design is controlling and allowing for wood movement. Generaly, anything I'm working on that I don't plan to use right away gets stacked flat with stickers (narrow pieces of wood between each piece) for ventilation.

[Howard Acheson]

Well, you've found out never to lay panels on a surface that prevents air from getting easily to both sides. It is particularly bad to lay them on a concrete floor. Concrete is very moisture porous and will impart moisture to any wood laying on it.

You may be able to get the panels flat by stacking and stickering them with weight on the top and putting them were there is some small air movement. Don't have a fan blowing full force. Try this before wetting the panels or putting them outdoors.

[Peter Quinn]

As far as future storage I was taught (in a cabinet shop where I worked) to cut parts as close to final assembly as possible. No reason to produce parts from sheet goods far in advance, although in a home shop or small shop sheet goods must often be broken down for storage quickly due to space constraints. It might be better to source your plywood when you are ready to use it if possible.

Once parts, plywood or solid lumber, are cut to final dimension they should either be given complete and equal air circulation (assuming they have acclimated to your shop's environment and that your shops environment is stable) or be wrapped in cellophane shrink wrap tightly to slow or eliminate contact with environmental moisture. You can get shrink wrap in most hard ware stores or from office supply stores. I keep a 6" roll and an 18" roll handy to keep parts in line.

In any case avoid storing parts close to the floor, concrete or otherwise. Perhaps stickering your panels for a few days or a week might allow them to dry which may cause them to flatten. I have used borg plywood that was too wet and once cut it warped as it dried to my shops humidity level. I have no reliable fix for this other than to source better plywood and remake the parts.

[Chris Padilla]

Everyone has it pretty much covered. I understand they are already cut to size but if you are still have issues, you might try edgebanding two edges (in the direction to force the plywood flat again) with some hardwood but cut the plywood down a little bit to allow for the hardwood edging. You'll need to flatten the plywood as best you can before gluing on the edgebanding.

However, this may be more trouble than it is worth and it could be cheaper/easier/faster to simply get another sheet of plywood and recut.

[Alan Schell]

Thanks. I have stickered and will wait.