Tile a Barrier-Free Bathroom: The Mortar Base
Tile setter Tom Meehan shows how to mix, place, and screed a traditional mud bed for a smooth and properly-pitched shower floor
The first step to a mud job, is to put down the tar paper and wire. I first lay down a layer of 15 pound black felt paper and cover the whole floor. I over lap each joint by at least an inch. If the paper is curling, I use a few staples to keep it down while I work.
Next I add a layer of galvanized diamond wire mesh. This is the same product that masons use often for outside stucco work. I use some 1 ¼ inch roofing nails to fasten the wire down. In the main field, I nail at least every 8 inches and on the overlapping seams I nail every 6 inches. Like the tar paper, I over-lap the wire an inch where each sheet meets. The tar paper serves as a moisture barrier and prevents the wood sub-floor from absorbing the moisture out of the cement as it is setting up. The wire is what locks the concrete to the floor. This is how most tile floors were done years ago in many areas of the country and it is still the most solid installation that I know of.
Mixing the cement and setting the screeds – The cement mixture is 4 parts sand to one part Portland cement. Everyone’s shovel fulls are different, but for me, it is 26 good size shovels of sand to a full 94 pound bag of cement. To mix the cement, I pull it through two times dry first in a large mixing tub. On the third pull, I add about 5 gallons of water, depending how wet the sand is. I pour the water at a ¼ pail at a time as I move each one quarter of the cement mixture to one side of the mortar box. Then I pull the cement through two more times. At the end, I hold a handful of cement in my hand and and it will hold firm in place. It is a rather dry mixture compared to other mixes of cement.
The mud is then brought into the room in five gallon buckets and dumped around the perimeter of the room and around the drain. I dump a heavy line around the room 8 to 10 inches high. Then I start to use my steel floating trowel and wooden float to pack down and level off the cement . The wood float is used on the angle to push the cement tight against the bottom of each wall and then later to smooth out the cement. The steel trowel packs down the mud and moves it around before I start to use my levels or straightedges. It is important to keep in mind, that when doing a lot of cement work, it pays to use the best trowels and levels. The quality of the tools makes a big difference in performance of the job.
To Set the drain, I mix up a pail of cement that is a little wetter and richer the rest of the mud. The height here at the drain will be about 1 ¼ inch deep. I used pvc cement for the drain connection to the two inch pipe and push the drain into the fresh mud that I have troweled where it is to set. I then worked the drain into the cement by pushing it left and the right a few times. Clean any excess and the drain is set.
Once I have moved and packed the mud around the border of the room (now about two inches high), I pack the cement around the drain area to set the heights and pitch of the complete room. This will decide the final height and contour of the finished tile floor.
The drain piece that I am using is a Kerdi drain assembly by Schluter Systems. and I set it low enough so I can get a pitch of ¼ in to each lineal or running foot in the showering area. The far reaches of the room where water will never reach, I keep level and flat. This will allow toilets, vanities, or claw foot tub to sit flat and level. In most areas, from the drain to 4 feet out is all I need to pitch and keep the water running to the drain.
Now that the cement is packed down all around the perimeter of the room, I use my long straightedge and levels to set my screed around the border of the room. This means that I level and flatten about a 12 inch path that will border the room. This will now be my guide and it is called a screed. The screed will be about 1 ¼ inches higher than the top of the shower drain. As I mentioned, I will bring the cement in at a level plane towards the drain and then pitch it to the drain when I am in the spray area. I dump more mortar and use my levels to level off the cement in these pathways. There is always a constant use of the steel trowel packing the cement and the wood float smoothing the surface.
Making the big shallow bowl – Now it is time to create the pitch to the drain. I dump a few buckets of cement and pack it heavy in the area between my screeds and the drain.
By making it a little higher than the finished product will be, I can use my trowels and levels to scrape and pitch the floor to the drain. It is important to note that a piece of the tile for the floor should be used to gauge the height of cement at the drain. The top of the tile should be at the same height as the top of the drain when all is said and done. The levels that I use are made by Stabila of Germany and have been made for tile use. These levels are made to be used as straightedges as well as level. I use the levels to taper down the cement from the high point of the screed to the low point of the drain. I am checking the levels constantly and pulling the excess cement towards me. This is actually creating a shallow bowl or cone effect of the showering area. It takes some time to get the feel of this process, but when one can see this bowl effect, all is understood. The cement work becomes a work of art. But we are not done yet. The mud base should now be smoothed out with the wood float to take out any small highs and lows and then hit with the steel trowel to press in a tight shiny finish to the cement. This will allow the cement to have a firm surface and not dust up later on when being worked on.