This summer we had a new wood basement built under our house. The floor is concrete and a couple of cracks have showed up all ready. Should I fill these and what should I use? I was told body filler for cars would work.
Please no body filler. You don't mention any water problems (if none, the following will fill the crack). Use polyurethane caulking applied to the crack and scraped with a putty knife. Sprinkle dry sand over polyurethane caulking and brush with a dry paint brush. This will blend with the texture of the concrete. Note: If they are only hairline cracks I would leave them be.