I am remodeling a second floor bathroom in an Victorian house est 1030's. The bathroom tile was put on with cement blobs about 2 inches thick behind it. It almost looks like cement patties because there are gaps in each corner of the tile corners of the old 4x4 tiles. My guess is that the cement was used to build out the tiles to fit the tub area. now I am retiling the bath and I see behind the tiles this matrix of cement blobs do I close up the holes /gaps with more cement or leave it as it is, I am replacing it with the same size 4x4 squares although today's tiles are thinner. My fear is that the grout may crack since the new tiles are thinner and mold and mildew will be more likely to form over time. Or put a cement board on top of that which will make the wall tile come out farther into the tub area? Is it possible to close up the gap with more cement or mastic to make no holes in the wall behind it?
Laurie ~ Paterson, New Jersey
Hi Laurie. One of the joys of working on an older home is that you never know what challenges await behind the walls when remodeling. In the days when most older Victorian houses were built there weren't many building codes, and contractors and homeowners often felt free to improvise as needed to get a project done. I have never encountered bathroom tiles installed in the fashion you describe, but I can picture an installer many years ago trying to figure out how to make the spacing work and coming up with that solution.
If there are gaps between the cement patties that create space between the tiles and the surface behind them, I'm surprised that cracked grout hasn't been a continual problem and that there isn't mold or mildew behind the tiles.
It may be possible to fill in the gaps with mastic and simply install your new tiles -- that would be the easiest solution. You could also make up the difference in the tile thickness with some additional mastic. However, since you are already doing a lot of work in the area, I think you should do the project so you don't have to worry about repairs for a long time. I recommend that you remove the cement blobs and install wood strips and cement backer board to make up the two inches.
Cement board is waterproof and should provide a solid base for applying your new bathroom tiles. Moisture almost always eventually gets through grout joints and when it does the cement board shouldn't be susceptible to mold or mildew. Your existing cement patties should come off fairly easily if you use a brick chisel and hammer, but make sure you place a piece of plywood or OSB on top of your tub to protect it during the process.
If you are unable to remove the cement down to a smooth surface, you may have to remove whatever material the patties were attached to and install new material. You only need it to be smooth where your wood strips will be attached or you might want to remove the material completely and simply increase the thickness of your wood strips.
Either way you go, this will probably be a very dusty project and you should cover your bathroom fixtures. It can be very difficult to get cement dust out of the nooks and crannies of bathroom cabinets and it may even scratch them. You might want to consider locating a contractor around Paterson, New Jersey who can remove the patties and install the new cement board to get the dirty work out of the way and allow you to concentrate on installing the new bathroom tiles.