I have removed vinyl tiles from a concrete floor (very hard work)but am left with big patches of black tile adhesive. Can I lay floor leveling compond on top of the old adhesive or must I remove it? I have spent a full day trying to remove the adhesive but still have a lot left to do. I have used a heavy duty scraper and a mallet so far. A bit of boiling water on the floor seems to help but it is very hard work. Please can anybody help?