What do I need to do to install new flooring over old flooring? Our current bathroom floor has dates back to the late '60s and is made up of those little square tiles. While the tiles are in good shape, we'd like to lay a new floor over them to update the decor. So, do I need to fill in the gaps between the tiles with grout before we install the new flooring? If so, what type of adhesive is used to seal the new surface to the floor?