I want to use TileClad 2 part hot solvent epoxy on a 2-car garage floor. The floor was painted about 20 years ago, I don't know the product. How important is it to completely remove the old paint before applying TileClad? The old paint is about 50% worn off. I am having lots of trouble with the floor grinder, about 7 hours grinding and still the old paint is not all gone.