Most solid tongue and groove flooring may be repaired. For example, repairs can be performed on floors that have had serious pet stains, that have penetrated in the grain. Old houses that have had carpet down for years or decades are a typical example of this problem. A pet could have been urinating in one place on the carpet where the owner was totally unaware. The urine reacts with the wood over time and causes black stains to develop deep in the wood. Sanding in some cases will not be enough to get the stain out, so replacing wood pieces might be the only possible answer to restore the floors to their original appearance. Occasionally when water has sat too long on a floor and severe cupping or doming distortions (edges either curl up or curl down) have occurred, it may then also be necessary to replace boards.