Schluter®-KERDI-SHOWER prefabricated shower trays provide a lightweight, quick, and easy
to install solution for the shower base in most applications.
However, the shower base may also be constructed with mortar.
In this installation the drain opening is not in the center of the shower base.
While the prefabricated tray could be modified to fit by cutting and extending with mortar…
…using a mortar base gives greater control in establishing a consistent perimeter elevation.
The Schluter®-KERDI waterproofing membrane has already been applied to the walls. Schluter®-KERDI-BOARD
could also be used. Two built up curbs have been constructed around
where the mortar base will be installed. The Schluter®-KERDI-BOARD-SC shower curbs
are another option. Begin by placing a cleavage membrane, such
as 4-mil polyethylene, over the plywood subfloor. This will prevent the plywood from absorbing
moisture from the mortar before it has a chance to properly hydrate and gain strength.
Then, galvanized metal lath is placed over the cleavage membrane… and fastened to the
subfloor.
Cut the membrane away from the drain opening. Next, prepare the dry pack mortar for installation.
Dry pack mortar is a mixture of clean sand, Portland cement and water.
For the shower base, combine 5 parts sand to 1 part Portland cement.
Begin adding water slowly and blend. Repeat this process until the desired consistency
is achieved. The final consistency of the mortar should
be such that it is damp enough to hold itself together when compressed in the hand but contains
no excess water… (PAUSE)… similar to a sandcastle.
A mortar screed is placed around the perimeter of the shower base.
The screed is tamped and will be leveled to provide a consistent elevation around the
shower base. You will need to set the drain to the appropriate
elevation using shims.
Keep in mind, that over wood substrates, the minimum thickness of mortar required at the
perimeter of the bonding flange is 1 inch. Or ¾ of an inch for concrete substrates.
Measure from the drain to determine the appropriate final height of the perimeter screed to produce
a minimum 1/4 inch per foot slope to the drain along all sides.
We found spare tiles that matched the desired height difference between the perimeter screed
and drain and used them as spacers. Tap the level into the screed until the screed
elevation matches the height of the spacers. This establishes the final height of the perimeter
screed. We use the level along all sides of the shower
base to set the final elevation of the perimeter screed to this height.
The next step is to install the KERDI-DRAIN. This demonstration assumes that there is access
to the plumbing from below so that the drain can be attached to the waste line later.
If there is no access to the waste line from below, please watch the video entitled: “Schluter®-KERDI-DRAIN
Installation with No Access to Plumbing” for a demonstration of how to connect the
drain to the waste line. Place a ring of loose mortar around the inlet
hole in the floor. This mortar contains more water than the dry
pack mixture used in the rest of the shower base.
The drain is firmly pressed into the mortar to ensure full support and prevent damage
to the tile assembly when the shower is in use.
Verify that the drain is at the proper elevation that we determined previously, to produce
the required slope. Check the drain for level and adjust as needed.
Clean the excess mortar from the top of the bonding flange.
Next, the remainder of the shower base is filled with dry pack mortar.
Since the perimeter screed is at the correct height, we can use it and the KERDI-DRAIN
as guides, to tamp and slope the mortar. The installation of the mortar base is now
complete. Typically the mortar is left overnight to
set. As soon as the mortar bed can be walked on,
waterproofing with the Schluter®-KERDI membrane can begin.
Clean any loose sand particles or other debris from the mortar base.
The KERDI membrane is bonded to the shower base using any of our Schluter thin-set mortars…(PAUSE)
or… an unmodified thin-set mortar.
The mortar is mixed to a fairly fluid consistency, but still able to hold a notch.
A 1/4 inch x 3/16 inch V-notched trowel or the Schluter®-KERDI-TROWEL, which features
a 1/8 inch x 1/8 inch square-notched design, is used to apply the mortar.
Apply the thin-set mortar to the mortar base and fleec`e covered bonding flange.
Apply a thin layer of the mortar with the flat side of the trowel to produce solid contact
with the surface and then comb additional mortar using the notched side of the trowel.
The mortar is applied up to the step in the bonding flange.
Apply the KERDI over the mortar base and drain flange.
Embed the membrane in the thin-set mortar using the flat side of the trowel or a drywall
finishing knife to ensure full coverage and remove air pockets.
Be sure the connection between the KERDI and KERDI-DRAIN is secure.
Clean the excess mortar from the step in the bonding flange.
Depending on the size of the shower, it may be necessary to install multiple sheets of
KERDI to cover the entire base. Waterproof integrity is maintained at joints
using 2 inch wide overlaps in conjunction with thin-set mortar.
For example, KERDI sheets may be joined using a 2 inch wide lap seam…(Pause)
…Or KERDI sheets may be butted and covered with Schluter®-KERDI-BAND waterproofing strips
centered over the joint.
Since KERDI-BAND is one-half the thickness of KERDI, build-up at seams is minimized using
this method. In this video, a lap seem is used between
the KERDI sheets applied to the shower base. The entire surface of the curbs must also
be covered with KERDI. The KERDI membrane is installed over the curbs
using the same techniques described previously.
KERDI may be creased prior to installation to help maintain tight corners and make subsequent
tile setting as easy as possible. Place a piece of cardboard over the shower
base to protect the KERDI for the next steps of installation.
Waterproofing connections between the base, walls and curb are made with KERDI-KERECK
inside and outside corners and KERDI-BAND.
Apply thin-set mortar to the area where the KERDI-KERECK inside corners are to be installed.
Embed the KERDI-KERECK into the thin-set mortar using the flat side of the trowel or a dry
wall finishing knife.
Holding one side of the corner in place while embedding the other side in the mortar helps
keep corner installation simple and easy.
Repeat the process at the remaining inside corners.
The next step in waterproofing the shower base is to use KERDI-BAND waterproofing strips
to seal transitions from the base to the walls and curb.
Measure and cut sections of KERDI-BAND such that a 2 inch overlap is achieved at all junctions.
A 2 inch overlap can be achieved at KERDI-KERECK without continuing KERDI-BAND all the way
to the corners of the shower. This will limit build-up of the membrane in these areas and
make setting small tiles easier.
KERDI-BAND may be creased prior to installation to help maintain tight corners and make subsequent
tile setting as easy as possible.
Apply thin-set mortar to the area where the KERDI-BAND is to be installed.
Embed the KERDI-BAND into the thin-set mortar using the flat side of the trowel or a dry
wall finishing knife.
Repeat this process at all remaining joints ensuring that the minimum 2 inch overlap is
achieved at all transitions.
The same technique is used to install KERDI-KERECK outside corners.
Depending on project requirements and installer preferences, the order of KERDI waterproofing
installation may vary, provided that all surfaces are covered and 2 inch overlaps are maintained
at all seams.
The KERDI waterproofing application is now complete.
A water test is recommended before setting tile to verify a successful waterproofing
installation. This evaluation may be required by building code officials on some projects.
Wait 24 hours after the membrane installation is complete to allow for final set of the
mortar and to ensure waterproof performance of the assembly at seams and connections before
water testing.
A demonstration of a water test can be seen in the video entitled: “Schluter®-Shower-Systems:
Water Test”.
The shower area is now waterproof, vapor-tight and ready for tile.
If you still have questions, please contact our Customer Support Specialists. For more
information on Schluter products, visit schluter.com or check out our YouTube channel to view our
videos!