Q: I sanded some hardwood floors that were previously painted, but I didn’t (quite) get all the paint off. What will happen if I stain them?
A: If you mean there is still trace paint in the heavy grain, that is to be expected. It is similar with staining a floor. It is impossible to remove all trace of the stain from the grain. When you stain the floor in this case, you will likely still see traces of white paint. You may be able to hide it with a colour match marker.