Jeff Patrick
Joined: 2004-04-15
Location: Bainbridge Island, WA
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The panel that most comes to mind was one of mdf and mild (not stainless) steel, 22 ga.(?). I sealed the back with sprayed lacquer, several coats. I used polyurethane glue because it sticks well to both metal and wood products. The panel was 20"x40" or so. It was a counterweighted vertical sliding door for a fancy desk/storage/shelving thing for an office. I remember it because it was such a nasty bear to remove and replace. The warpage occurred within two weeks of installation and whether this was due to heat, moisture, bad vibes or a combination I don't really know. I made a new one with steel on both sides and it has stayed stable for four years. As you often say, Darryl, its better to play it safe.
After experiencing that I've always veneered both sides so I really never repeated the experiment. Except for a recent project where I only covered one side with some stainless. However in this case the panel was a full one inch thick with maple veneer on the opposite side. And the attachment of this particular composite would preclude it from ever warping (bolted in six places).
Obviously warpage of a metal covered panel isn't due to moisture affecting the outer skin. Temperature and actual glue layer shrinkage must play important roles. Now that I think about it, the nasty panel I had was warped with the metal on the concave side which indicates moisture getting to the sealed but uncovered mdf. It really doesn't take much to warp these thin panels... all life is a balance I guess.
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