Warpage, is defined as any deviation of a panel product from a flat plane. While other factors may contribute, this section addresses only moisture related warpage. Because moisture loss and gain will make wood contract or expand, it is important that all components in a plywood assembly have essentially the same mc. It is difficult to achieve identical mc’s for every component, but if the difference is substantial, the components with the higher mc will contract more as that component reaches equilibrium with the rest of the panel. This will create an uneven distribution of stress in the panel, and warpage will almost surely occur.

Warpage can, and often does, result when moisture leaves on surface of a panel at a different rate from the opposite surface. A cabinet door, for example, may exhibit warpage during cold weather since the face side of the panel is usually exposed to the outside of the room where it is in direct contract with heated air. Both sides may give off moisture, but the exposed side will do so at a faster rate. The veneer surface will contract, the panel will undergo undue stress that could warp the door. When this occurs, a change in weather conditions will almost always straighten out the problem.

The application of a paper or vinyl laminate to the back of panel with a decorative veneer face is a widespread practice in the kitchen cabinet industry. However, it is important to understand that this creates a condition that retards moisture movement from one side of the panel, while allowing unrestricted moisture movement from the other. The practice, by the nature of its design, can, and often does, result in rapid loss of moisture from the
unlaminated side of the panel only. This will almost always result in uneven stresses in the panel, and warpage is likely to result.

When warpage is evident prior to fabrication by the user, the stresses creating the warp may be counteracted by re-stacking the panels so that every other panel is reversed from the way it is originally stacked. This facing of the affected panels, coupled with a minimum of one runner for every 16” of paneling, and weighting down with a unit of any heavy material, may offset the stresses sufficiently to reduce or cure the problem. It is important to use runners of uniform thickness, evenly distributed under the faced load. The panels must remain in the faced condition for a minimum of 48 hours, and the longer they remain faced, the more effective the remedy. The same measures many be used on panels that do not exhibit warp until they are cut to some other dimension. This may occur because cutting a panel exposes previously unexposed surfaces that are now able to allow more rapid movement of moisture in a different direction. Components exhibiting this tendency may be treated in the same fashion as full sheet stock as mentioned above.