Why does plywood warp after delivery if it was flat at the factory?
Most plywood leaves the factory flat and within EN 635 face-orientation tolerances, then takes a curve in storage or transport. The cause is almost always asymmetric exposure — one face seeing more moisture, more sun, or more pressure than the other. Wrap a stack under a direct-contact tarp, lean a sheet against a wall for two days, or store on uneven dunnage and the panel will move.
How far apart should dunnage be when storing plywood flat?
Every 16 to 24 inches across the length of the panel, with the dunnage running perpendicular to the face grain. Three stickers under a standard 4x8 panel (at each end and the middle) is the working minimum; four is better for sheets stored more than two weeks. The dunnage itself must sit at a uniform thickness across the stack and stay dry.
What moisture content should plywood be at before I install it?
8 to 12 percent for interior service in a heated, conditioned space — cabinets, furniture, paint-grade work. 14 to 18 percent for exterior or unconditioned-space service such as garages, sheds, or formwork. Anything over 20 percent needs acclimatisation before installing into a drier environment; forcing a 22 percent panel into an 8 percent interior is a guaranteed warp.
Does sealing plywood edges really stop warping?
It is the single highest-leverage on-site step. Cut edges absorb moisture five to ten times faster than faces, so unsealed edges are the main pathway for one-sided moisture pull. A single coat of oil-based primer or dedicated edge paint, brushed on within a few hours of cutting, will roughly triple how long a 12 mm panel holds flat in humid storage.
When should I suspect the panel itself rather than my storage history?
Only after the storage history is verified clean — flat dunnage, weighted top, off the slab, sealed edges, no direct-tarp wrap, no leaning against walls. If the panel is still out of plane after that check, flag the batch with the supplier and request a re-inspection against EN 635 tolerances. Frame the conversation as 'the panel may indicate an out-of-tolerance condition,' not 'the panel is defective' — that keeps it factual and lets the mill check production records.
