If you are remodeling an older home one that was built prior to 1965 then there is a high probability that the tiles in your bathroom are placed on a 1 – 1/2 inch thick mortar bed.
Mortar beds are really the best way to install tile in a wood frame home because they provide a thick stable surface that will not cause your tile to crack.
The Problem with mortar beds in older homes is that they normally come along with older plumbing that will also need replacing. You can probably bet that half the homes built prior to 1965 also have lead pipes for the waste lines and copper for the water feed lines.
If you start working on your floor and need to remove the mortar bed you should remember that there is a high probability that you will damage a water feed or waste line so turn the water off and be prepared to cut the ceiling below the room to get any water out that you can’t reach.
With that said it is always recommended that when you pull tile from any surface that you replace the surface it was attached to. If you are working in a new home and they use ceramic backer board as your substrate then you will most likely damage it when pulling up your old tile.
If you are replacing tile on a Mortar Bed you will need to chisel the tiles off with a small sledge hammer and heavy carbide chisel so even if the bed looks somewhat undamaged it probably has a number of cracks in it that will fail either immediately or very soon after you install new tile.
So, the answer is Yes you pretty much always need to remove any substrate down to the plywood or wood boards that make up the floor in older homes when you replace the tile.
Because this is a pretty difficult job for even a professional you should follow some of these steps to make your life easier.
Removing a Mortar Bed Floor
The first thing you want to do is turn off the water to that room from outside the room. this may mean going into your basement if there are shutoff valves or it may mean turning off the main valve to your home if you are on a second floor. Turing the water off under the sink or at the toilet won’t stop the water if you damage a pipe in the mortar bed when removing it.
Now that the water is off you want to remove anything in the way like toilets, sinks, vanities and bath tubs you will replace.. if you are not replacing the tub leave it…
Start by digging a test hole. First remove one or a few tiles in the center of the room and dig down to see what is under the mortar. Plywood is best but most likely you have an older home with floor boards.. don’t confuse that with hardwood floors .. these are 1 inch thick boards that go over your floor joists because plywood was not used back then.
If you have wood boards you don’t want to be violent when taring up the floor because you will damage them. You may also find damage or rot from water leaks that will require either new boards or plywood to restore the area.
Now instead of hammering out all this tile by hand what you want to do is go to your local rental store and rent a 1 inch rotary hammer with a chisel bit. Tell them that you have regular house current and need to chisel up a mortar bed and they will fix you up.
If not you can also buy one.. I suggest if you are doing this find a discount retailer and don’t pay over $100 for the hammer and chisel set.
Now you need to get your first large chunk of mortar bed out.. try to get a 1 foot chunk out by chiseling around it.
After you get the first chunk out you can work between the floor board and the bed with the rotary hammer at the same time you are chiseling out paths above .. this will let you pull up large chunks of mortar bed.
After you get out as much as you can you will need to inspect the boards or plywood and make repairs before you install either a new mortar bed or cement backer board.
You will also need to make repairs and test the water lines prior to installing anything.
If you have lead pipes they will need to be removed back to the vent pipe and replaced with pvc pipe. This is not that difficult but does require a special rubber union between the cast iron and pvc.