A roll-on is normally thicker and stronger than a spray and an epoxy made to be applied by roller and to go over bathroom tiles is made specifically to be layered. A spray is normally mixed with a solvent like thinners so it can come out of a spray gun. The roll-on epoxy is not diluted with any solvents and is applied thicker with a roller and if one knows how and when to apply the epoxy one can apply at least 2 coats to the ceramic wall tiles and 3 coats to the ceramic floor

In Australia waterproofing is supposed to sit under the tiles and can really only be done as per the building code if all the tiles are removed then the waterproofing is done over the whole floor and part walls and then the bathroom is re-tiled. Anyone with a waterproofing licence...like myself shouldn't issue a waterproofing certificate if it's not done this way...and basically this means to have a bathroom waterproofed as per the building code you need to do a full bathroom