I built a simple bar for a café , two units, each 4’x6’x2’. The frame was #1 pine, the front and sides sheathed with ½” A/C pine ply and the top with 5/8” A/C pine ply. The ply was glued and nailed with 15ga. nails and the holes were filled with Famowood. It was then primed and a black polyurethane ‘piano finish’ was applied.
This was in April before our rainy season. Now the nails on the top have lifted very slightly. You can barely feel them but with the brilliant finish, they stand out. The nails on the front and sides are not doing this. There is also a slight bulge of the top around the sides. The butt joints on the corners with the ½” are also okay. I told the client that it was a humidity problem and let’s wait and see what happens after our rain season. Perhaps if it’s seasonal she’ll give me a pass on it.
Unfortunately, here in Mexico, we cannot get birch ply; the A/C five-plies core ply is the standard. ¾” ply is limited to five plies, even if the faces are oak or maple. I’m assuming my problem is because of a ‘green’ sheet of the 5/8” ply, as the ½” is okay. It would almost appear that two things are going on: it's swelling in both directions longitudinally and shrinking in thickness.
What are some possible solutions if I have to repair this? The thought of breaking it down and moving it back to my shop, replacing the top and refinishing is daunting. But I may have to.
(Architectural Woodworking Forum)
From Gene Wengert, forum technical advisor:
The problem does indeed sound like an increase in humidity that then pulled the nails out just a bit. The wood then shrank a little and the nails were left "pulled out" a little bit. If you cannot avoid exposure to high RH, then this is likely going to be tough to fix, as every year it will occur again. At this point you can renail (drive the nails in) and then fill and refinish. The bulge may not be possible to repair. I certainly wonder if these pieces had a moment of exposure to very high RH or even liquid water.
Ringshank is a better choice, but it goes partway to the total solution of a decent wood screw. Look into stainless steel if you never want to revisit the screw again. Galvanized at the very least, but I don't have as much experience with those. You'll probably need to rework the board, rework the attachment devices and refinish the project. You know your materials better, you might rework the warranty a little as well to accommodate all the situations you have no control over. Ideally, the warranty should protect the buyer from shoddy workmanship and protect the manufacturer from shoddy application or maintenance.