As with any spill, a pet urine stain is easier to remove from a hardwood floor if you catch it early, before it has a chance to penetrate the finish and soak into the wood. This "grace period" is shorter than it is for most liquids, however, because of the presence of uric acid in the urine, which corrodes the floor finish. Once the stain has darkened the wood, removal is difficult and may require sanding, bleaching or even replacement of the affected boards.
If you come home to find a pet accident on your living room floor, the first order of business is to soak up the puddle. Blot with an absorbent rag or a handful of paper towels, taking care to work surrounding area, when the stain may have spread unseen. Rinse the stained area with water and immediately blot up the water. Finish the stain removal procedure by covering the affected area with paper towels, weighing them down with books and leaving them for several hours.
Dealing with Odors
Once the urine is gone, it's important to treat the area for odors -- you may not be able to smell them, but your dog can, and they may lead him back for a repeat performance. Treating the area with an enzymatic pet odor removal product -- following the instructions on the container -- is one option. Another is to cover the stained area with baking soda and let the powder sit for two hours before vacuuming it away.
Old Stains and Discolored Flooring
Once a urine stain has soaked through the finish and discolored the hardwood, the strategy for dealing with it becomes more complicated. You'll have to remove the finish to get the odor and discoloration out of the wood -- if that is even possible -- but before you do this, you should wash the finish with soapy water and dry it thoroughly. If you don't do this first, you might grind uric acid particles from the dried urine into the wood when you sand off the finish. To deal with the discolored wood:
Sand an area several inches wider than the actual stain with a pad sander and 120-grit sandpaper. Once the finish is gone, keep sanding to see if the discoloration comes out of the wood. You probably won't be able to remove all of it, but you may see an improvement -- and who knows? ... You could get lucky.
Treat the wood with hydrogen peroxide from your medicine cabinet for a gentle way to bleach out the color. Rub it into the stain with a sponge, let it dry and repeat as many times as needed. If you don't notice an improvement, move onto stronger bleaches.
Chlorine bleach removes dye stains from wood and may remove urine stains -- use household bleach full strength, or mix a saturated solution of swimming pool bleach and water for a stronger chlorine solution. Rub the bleach into the wood, let it dry and and rinse with water. If that doesn't work, mix a saturated solution of oxalic acid crystals and water, and allow that to soak into the wood. Neutralize this with baking soda and water before rinsing.
If you are successful in removing the stains, the wood will probably appear lighter than the surrounding floor. Even out the color with pigmented wood stain -- you may have to mix one yourself by adding colorants to mineral spirits. Apply one or two coats of wood finish after staining, using a paintbrush to feather the edges of the repair into the floor. The finish will seal any remaining smell into the wood.
When You Can't Remove the Stain
Bleaching doesn't always work, especially if the urine stains are very old, perhaps having soaked through a carpet into the flooring. In this case, the only recourse is to .