While sanding removes the top layer of wood, the success of stain removal depends on how deep the stain has traveled. Organic stains like pet urine often soak deep into the cell structure of the wood. In many cases, these stains are permanent even after sanding. If the discoloration remains after a deep sanding, your options are limited to patching the damaged boards or opting for a darker stain color that may help mask the affected areas through color integration.
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Does refinishing remove permanent deep stains?
Refinishing can remove stains that are superficial or reside within the finish layer. However, if a stain has penetrated deep into the wood fibers, such as dark pet urine or oil-based substances, even sanding may not completely eliminate the discoloration.