Whoah!!! That's what I'm dealing with. It's called black mastic, or black mamie. Mine does appear to be put on with felt paper. Very tough stuff. Looks like you have some pretty hardwood under there trying to peek out. I've spent about $50 on various chemicals (including mineral spirits)and several hours trying to remove it. I'm at the end of my patience with it, the floor is coming out! I am just a single gal, I don't have the time nor the elbow grease so just I bought some hardwood from an old house that is being torn down and starting over. I figured it would be easier for me to tear out the floor and pay someone to just install the replacement.
Good luck to you
