I have a small rotting spot at the bottom of my back door and it's almost to the point where I could put my finger through it. I don't have the cash to replace the door right now, but what would you suggest I patch it with before painting it? I have seen interior/exterior wood filler by Elmer's and others. Someone suggested Bondo like the kind used in auto body shops. Any prep steps you suggest as well?
Dig out any rotted wood that you can get to. Soak the wood with wood hardener around the patch area to stabilize the rotted/deteriorated wood that you couldn't get to. Fill with bondo or wood filler in 1/4" layers until slightly bulging from the patch area. Chisel/file/sand down when the final layer is almost completely dry with a sanding block. Prime and paint. The patch should outlast the rest of your door!