This can potentially be the case with plywood, where, even before you've put too much weight on your shelves, their edges are curved or cupped. Bob Beacham, House Digest's expert carpenter and ...

For curved curbs: Cut off the liner against the plywood 1/2-in. below the top of the form. For straight curbs: Start at the top of the curb and carefully cut the liner to width. Wrap the liner ...