Q: We have a house with 60+ year old oak floors. There were 30+ year old area rugs, that had a reddish/brown pad under them. The pads left black dots across the floor. Can these be cleaned/removed or do the floors need to be sanded?
A: You may have a bit of an issue with this. These black dots are probably water stains from the carpet being steam cleaned or shampooed over the years. The moisture telegraphed to the center of the bumps on the underpad, it sounds to me. So, yes the floors will have to be sanded. Hopefully the stains can be removed. If not you would then have to stain the floors to hide the marks. This all hinges, of course, on whether these old floors are thick enough to handle a full sanding. It depends how many times they have been done in the past and how thick they were originally.
Follow-up Q: Thanks for that info Craig. I should have said that the rugs were never cleaned or wet. A rug guy thought that perhaps the rug mat/pad might have had some clay in it? The dots are uniform across the entire rug area, 1 inch apart horizontally and vertically. Some areas the dots are darker, but again it is uniform.
A: Even a tiny bit of moisture over time could do it. Perhaps dampness from beneath, transferring slowly through the floor over the years. The pad was just another layer to slow that moisture down and trap it against the wood. I did a floor years ago which had that pattern on the wood. It wasn’t even dark spots. It was just the outline of the pattern, as if it had been x-rayed into the wood. It was the strangest thing. It didn’t even sand out.by