Remove mold on hardwood floor

Spray the oak floor with a 50% solution of white vinegar solution mixed with water and let stand for an hour, then clean with hot soapy water. Alternatively clean the floor with a steam mop, as either method will kill the mould on your floor.

First off is it mold or a purple/black stain? Red Oak stains purple black if in contact with water for any length of time. I have never seen the stain removed without sanding through the stain.

Even if you refinished the patch with the same exact finish, you would see the repair. The final coat should go over the entire floor. The floor would need to be clean and lightly sanded (screened) to let the latex bond to the oil urethane. Ensure the latex you are using IS compatable with going over oil.

I also felt bad when I found mold on my favourite hardwood floor. It is very expensive flooring, I soul taken care of this more. Well once this happened, I need to clean it anyhow. I have use vinegar, soap and water to remove it. I have also used some hardwood floor cleaning solution. After that almost all mold cleaned up easily, but some mold had gotten into the grain of the hardwood. The grain tends to suck up anything liquid, including the polyurethane used to finish our wood floors, which left those areas imperfectly sealed and able to absorb moisture. In these areas, the mold was able to grow a few millimeters into the wood, making it impossible to wipe away.

I decided to do the hardwood floor refinishing. I chose water-based low-odor polyurethane to refinish the sanded areas. The floor was originally finished with an oil-based polyurethane, so I didn't expect the refinished areas to match exactly. If the appearance really matters, you should probably refinish the entire floor.