Shower Walls Next
After the pan assembly is completed and tested, I install
the wall tile substrate down to the pan membrane, covering the
upturned membrane that is fastened to the walls. Then I set the
wall tile, positioning the bottom edge of the first course of
tile 1/8 to 1/4 inch above the finished floor tile height to
allow room for a control joint (backer rod and sealant).
It’s important to use control joints wherever walls or
walls and floors intersect (see "Preventing Tile Failures,"
2/97, for more on tile control joints).
The main reason I set the wall tiles first is that it would
be hard not to damage the floor tiles while setting the wall
Floating the Mortar Floor
Before installing the mortar bed, I thread the adjustable drain
screen into the body of the clamping ring drain, setting it at
the finished height of the tile floor. Then I place a
free-draining material like pea gravel or even plastic tile
spacers around the base of the drain to prevent the deck mud
from plugging the weep holes.
Adjust the finish drain stem to the proper height
(left). To prevent mortar from plugging the drain’s weep
holes, circle the drain with plastic tile spacers
I float out approximately half of the deck mud, lay in a
piece of reinforcing wire, then cover the wire with the
remaining deck mud. For reinforcement wire I use 16/16-gauge
2x2-inch mesh, 13/13-gauge 3x3-inch mesh, or 16/13-gauge
After half of the mortar bed is placed and troweled
level, reinforcing wire is laid on the mortar bed (left) and
covered by the final layer of mortar. Then 1x3/8-inch screed
strips are set and leveled at the perimeter of the shower
I compact the deck mud by beating it in with the wooden
float, then float the bed to its final slope. The finished
height of the mortar bed should position the floor tile 1/16 to
1/8 inch above the top of the drain, and 1/8 to 1/4 inch below
the bottom edge of the wall tile. I’ve notched the top
front edge of my wood float so that it rides along the bottom
edge of the wall tile and leaves the proper space.
The screed strips and the top of
the drain are used as guides to accurately level the
mortar bed (top). The screed strips are then removed
and the voids filled with mortar (middle). To ensure
that the tile finishes flush at the drain, carve a
small secondary slope around the drain perimeter, using
a sample tile as a gauge (bottom).
Using a damp sponge, I’m careful to remove any deck
mud that finds its way onto the wall tile.
I use thinset mortar to bond the tile to the mortar bed. The
floor tiles can be installed while the deck mud is fresh or the
next day, when the setting bed has hardened. Since Portland
cement shrinks slightly as it cures, setting tiles over a fresh
mortar bed is tricky. For this reason, I prefer to let the
mortar harden before setting the floor tiles. The thinset
mortar should be allowed to cure for at least 24 hours before
grouting (check with the manufacturer for details).
Michael Byrne was a tile contractor for more than 25
years, and is now executive director of the Ceramic Tile
Education Foundation in Clemson, S.C.
To the untrained eye, properly mixed deck mud looks like
it’s far too dry to be of any use. Most tradespeople
assume that deck mud should be plastic and pliable —
similar to brick mortar.
But good deck mud should have just enough moisture to hold
the mixed ingredients together when squeezed into a ball. This
stiff consistency allows the mortar to be tightly compacted,
which is critical for tile floors.
The working characteristics of deck mud also differ
significantly from other types of mortar. I "carve" (rather
than trowel) deck mud to final height, using the lead edge of
my wooden float.
Students at our classroom facility in Clemson, S.C., are
taught to test their finished floor setting beds by standing on
the bed immediately after it has been floated and finished
smooth. If the setting bed is mixed and compacted properly, the
fresh bed should not show any heel marks after it’s been
Setting bed mortar contains two ingredients: Portland cement
and sand. An acceptable mix consists of four to six parts
clean, sharp sand to one part Portland cement. Sharp sand
particles compact better than rounded ones.
I mix my deck mud in a large mortar box. I place all the
sand in the box, sprinkle some water on top, and use a
mason’s hoe to pull the sand back and forth to lightly
coat the particles with water. I add the Portland cement and
pull the mixture back and forth until it’s thoroughly
mixed. Finally, I add just enough water to achieve the required
consistency, then mix it thoroughly again.