I just undertook a long overdue project. The paint on my garage door is cracking badly and needs to be sanded, primed and painted. When I started to sand the panels however, I discovered that some of them had a whole layer of wood that was buckling and just peeled off with a putty knife. Can anyone help with this? Is this normal? What does this mean for those panels? Would they have to be replaced or can I just sand them down to the layer of wood beneath the one I just peeled off and get them ready for painting? If they have to be replaced, how do I go about to replace them. I would appreciate any advice.