How to Seal Pet Stains on Subflooring

Things You'll Need

  • Black light

  • Enzymatic pet cleaner

  • KILZ Complete or Zinsser B-I-N primer and sealant

  • Chalk or masking tape

  • Fine-grit sandpaper


Apply the KILZ or Zinsser primer and sealant in a well-ventilated area; keep pets and children away from the area until you apply new flooring.


KILZ and Zinsser B-I-N primers cover stains and odors; if using other primers, apply a coat of polyurethane over them. Use the oil-based KILZ primer, not the water-based one; it will not cover pet stains. Use enzymatic cleaners specific for pet stains, not other types of stains (such as blood).

Cats and dogs urinate on carpeting and floors for a variety of reasons.

When pets urinate on carpeting or other flooring, it sometimes leaks down through the carpeting and padding into the wooden subfloor. If this happens, unpleasant odors from the subflooring will permeate throughout your home. To remove these odors, replace the flooring and clean all stained areas of the subfloor to kill odor-causing bacteria and seal the spots to contain the odors. This not only improves the scent of your home, it also prevents your pets from remarking the soiled areas in the future.

Step 1

Remove carpeting, padding and other flooring around the areas you suspect urine has leaked into the subfloor. Find the soiled areas on the flooring you cannot see with the black light. When using the black light, turn all lights off. The black light illuminates all biological fluids including old, dried-in urine or feces, which appear to glow. When removing an entire room of carpet or flooring, use the black light on the subfloor itself to locate pet urine stains, and outline them with chalk or masking tape.

Step 2

Apply an enzymatic pet cleaner (like Nature's Miracle) to the soiled areas and allow them to dry thoroughly for 24 to 48 hours. These cleaners contain special enzymes that convert organic waste materials such as urine and feces to carbon dioxide and water. They continue to eliminate the odors and waste materials even when dry. When you apply the enzymatic cleaners, do not oversaturate the wood to prevent it from warping. Repeat this step if odors remain after initial application.

Step 3

Sand the stained subfloor area very lightly by hand to prepare it for the sealant. Sweep up or wipe away the dust. Do not sand the area enough to change its height, which would make the floor uneven.

Step 4

Paint the stained subfloor areas with KILZ Complete or Zinsser B-I-N, mildew-resistant, oil-based primers and sealants that block odors and stains. Allow the paint to completely dry. Repeat the application after one hour. If any stains bleed through after the second application, re-apply and let dry until you completely cover the stains (allowing one hour of drying time between applications).

Step 5

Replace the flooring with new carpet, wood or tile. Since you have sealed the stains, no odor will come through the new flooring.