How to Remove a Dark Stain from Hardwood Flooring


Shirley asked:  How do I remove a stain on the hardwood floor from potassium hydroxide that spilled. During the night, some non-acid drain opener spilled on the hardwood floor. I saw the puddle and wiped up what I could with a damp cloth. It left a major dark stain. Can you help with suggestions?

Cleaning a dark stain from hardwood flooring will take a bit of work, but the results will be well worth the effort. The following solution involves several stages. If the stain comes up readily, you may not need all of the supplies listed below. On the other hand, if the stain is stubborn, you’re likely to need every one of them. For best results, follow the steps in order.

You Will Need:


  • Fine grade 000 steel wool
  • Mineral spirits
  • Vinegar
  • Clean rag
  • Household bleach
  • Bowl or small bucket
  • Water
  • Oxalic Acid
  • Stain (to match the undamaged floor) plus supplies needed to re-stain
  • Finish (to match the undamaged floor) plus supplies needed to re-finish

Steps to Remove the Stain:

  1. Before you begin, follow all label directions and make sure there is adequate ventilation in the area. Use fans if necessary to maintain air flow. Always read and heed all safety precautions, including those for skin and eye protection, and spot test a hidden area before you begin.
  2. First, rub the dark stained area with steel wool and mineral spirits.
  3. Next, wet the rag with vinegar and lay it over the stain. Allow it to sit for several moments.
  4. If this lightened the stain, repeat as necessary. If it did not seem to work, wipe off the vinegar and move on to step 5.
  5. Mix a solution of half bleach and half water. Apply it to the stain. Do not get any solution on surrounding wood, only on the stain.
  6. If you don’t notice an improvement, add oxalic acid to the stain. Do not get oxalic acid on the surrounding wood. It will seep in to the wood. Repeat as necessary.
  7. When the spot is gone, neutralize with acid.
  8. Wait for the spot to dry, then sand, stain and refinish to match the rest of the floor.

Additional Tips and Advice

  • Be careful using the steel wool. Only go as deep as the finish or the stain. If you gouge the wood, there is no way to repair it.
  • Do not use water-based cleaners or cleaners that require water for rinsing. Water will ruin the wood floor.
  • Always use caution when working with bleach as it is a hazardous chemical. See Wikipedia for more safety information.



  1. Melody says:

    Thanks for telling us about the vinegar for stubborn stains on wood floors. It really works! The only thing is, with a really stubborn stain, you have to leave the rag on for about a half hour each time. But a really great tip!

  2. David says:

    Vinegar and bleach make poison chlorine gas. This can kill you.

    Your instructions don’t say to mix them, but don’t give any warnings either.

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