Hi, just spent a couple of days bashing up ceramic floor tiles from my bathroom floor. In all the advice i have read it says to lay a layer of plywood over the floor boards when laying a tiled floor ( will do this when retiling) however under the tiles i am removing there is the layer of tile adhesive and then what appears to be some sort of rubber layer (dark grey stuff which is a pain to get up) and no plywood!. What is this stuff and is it easier/better than laying a layer of plywood?