Particleboard Warping in Cold Weather

Dry shop air can cause some materials to dry out and warp. August 12, 2014

So per usual it gets cold outside, my 3/4" 4x8 pb I have in the shop starts warping. I keep the shop at 65 at all times including when we are not here during the work week. I turn the heat down to 60 when we are not here. The top 4x8 sheet warps the width, and length dimensions. After I cut panels out of full sheets each panel has a warp in it. I donít have a problem with any melamine products.

Forum Responses
(Cabinetmaking Forum)
From contributor L:
The relative humidity in your shop is below the equilibrium level for the particle board. If the board is exposed to the dry shop air, the top of it will dry more than the underside creating the warp. Hot air blowing on it from a furnace will make it worse. The ideal solution is to humidify your shop. Melamine is less prone because the surface has a water resistant resin keeping the moisture in. Try covering the particle board with a sheet of melamine board or plastic for a short term solution.

From Contributor O:
Contributor L is right. Another way to deal with it is to have a sheet of 1/4" or 1/2" as a cover sheet for your PB stack. It will moderate the differences (in EMC) between the stock and your shop. As panels in process are left overnight, ensure that no hot air blows on them by a cover sheet of cardboard, or that air can get to both sides of any panel. This should keep it all flat. If you are laminating or veneering, make sure all those materials also get the same treatment, or else your completed panels are at risk of warping or seams opening up. Iíve been there.

Years ago, I took over a shop that did a lot of pre-hanging of W Pine 6 panel residential doors. Once the weather cooled off in late fall, the shop guys would reject 20-25 doors per day as warped to return to the manufacturer. As I looked at the problem I could see that every door would warp (ends of the door would rise off the stack in the racks) in the unheated and damp warehouse. Flip it over, and the next day it warped the same as the others. The exposed faces were dying out, shrinking, pulling the doors out of flat. We put 1/4" cover sheets on the stacks and they stayed perfectly flat. The reject rate went from 25% to once the doors were pre-hung and air could get to all sides, they stayed flat. Even on the jobsite, we could minimize returns from the jobsite by insuring the doors were stored properly.

From contributor G:
We had the same problem. Our solid wood was being affected also. We added a couple hanging humidifiers that have their own 1/4" water lines supplying them - problem solved.