We just moved into the home my grandfather built in 1932. It sat empty for a few before we moved in. But even after ridding the basement of old furniture and freezers and tons of junk, we can't seem to get rid of the constant “cat box” type odor that seems to be part of the cement floor and cinderblock walls. Even after a good scrubbing, the smell eventually returns. The basement is dry, and doesn't look moldy. Most of the space is exposed building lumber, which is old chestnut. Any suggestions?