How can we remove the black stains on wood floors caused by moisture or pet urine which soaked through carpet years ago?
Kevin Hancock: Mix one tablespoon of oxalic acid with one cup of warm water and apply it liberally on the entire surface. Allow overnight drying and remove residue with a wet rag or sponge. Most of the black stains should be removed. A second application might be necessary on difficult stains.
Greg Williams: Remove the coating on the wood by stripping or sanding. Apply a saturated solution of oxalic acid to the entire area, not just the stains themselves. Allow it to dry, and wash with a wet rag or sponge. Repeat if necessary. Wash off any white residue with clean water with a bit of baking soda added. Sand lightly after the wood dries, but don’t breathe the dust. Read the directions, and wear gloves, eye protection, and a dust mask.