We have very old, turn of the century pine floors. Unfortunately they have been stained, and the question is: how to remove the stain without sanding?
You could possibly remove the floor finish (not the stain) with the chemical stripping method I describe in the article available in the search box at the top of this web page. But once the finish is off you will still have to deal with the stain. You see the wood was sanded first, then stained then a few coats of floor finish was applied. You will need to reverse the order to get to that freshly sanded wood. And stripping of the finish is the first step.
If the floor was dye stained (very unlikely) you may be able to remove the stain color with swimming pool bleach (dry calcium hypochlorite). Mix with hot water, until solution is saturated. Apply to the spot and it should work right away, but try twice if needed and wait overnight. Wash off with lots of distilled water and let the wood dry overnight, before refinishing if it did work. You will have raised the wood grain quite a it by now so the floor will need a gentle sanding with a floor buffer and 80 grit screen.
If the floor was pigmented stained (more likely), things will be a bit harder. You see pigment stains are little particles bound in the wood itself, and if the chemical stripping didn’t get any of it out, it very unlikely any other chemical will. But in this case you might try a powerful solvent like lacquer thinner or naphtha to unbind the stain, and scrub the wood with a nylon brush. A messy and fume laden business.
You could also at this point “screen” the floor with a buffer instead. The screen is a abrasive disk, that will remove slowly the surface of the wood until the stain is gone. You will have to hand sand where the machine cannot go.
Be sure to try any of these methods on a small area first, and discover what works best and EASIEST, before you commit to the whole floor.
All in all these chemical methods are not an easy way to go, you might choose instead to have the floor professionally sanded, but consider doing the finish yourself. That’s the fun part any way.