Waterproofing ceilings is optional for showers and bathtub surrounds, but considered best
practice when tile will be installed on these surfaces. Waterproofing ceilings is required
in steam shower and steam room applications. This video demonstrates application of Schluter
-KERDI-BOARD over solid backing using thin-set mortar to prepare a ceiling
for tile installation. Here s how to do it.
Installing a rigid panel overhead can be easier and cleaner than a flexible membrane.
Solid backing has been installed on the ceiling. In this case gypsum board is used. The walls have
already been made waterproof with KERDI-BOARD. Any thickness KERDI-BOARD may be used when
fully embedded in thin-set mortar. KERDI-BOARD is bonded to the ceiling
using unmodified thin-set mortar. The mortar is mixed to a fairly fluid
consistency, but still able to hold a notch. Choose a notched trowel to apply the mortar
such that full coverage to the surface of the KERDI-BOARD can be achieved. Based on
surface conditions and the thickness of KERDI-BOARD used in this application,
we chose a 1/4 inch x 1/4 inch square-notched trowel. In some cases, a larger sized notch may
be required to achieve full coverage. Clean any dust or other debris from the
surface of the solid backing. Dampen particularly dry and porous
substrates in order to help prevent premature drying or skinning of the thin-set mortar.
Apply unmodified thin-set mortar to the KERDI-BOARD. 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.
Apply a thin layer of the mortar to the ceiling where the KERDI-BOARD is to be
placed with the flat side of the trowel to produce solid contact with the surface.
Embed the KERDI-BOARD in the thin-set mortar using a float or similar to ensure full coverage.
Depending on the size of the ceiling, it may be necessary to install multiple sheets of
KERDI-BOARD to cover the entire surface. Seams are constructed by butting adjacent
panels and installing Schluter -KERDI-BAND waterproofing strips, centered over the joint.
Apply unmodified thin-set mortar to the area where the banding is to be installed.
Embed the KERDI-BAND 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.
Install Schluter -KERDI-KERECK preformed inside corners using unmodified thin-set mortar.
Apply the mortar to the area where the KERDI-KERECK is to be installed.
Embed the KERDI-KERECK into the thin-set mortar. 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 final step in waterproofing the ceiling is to use KERDI-BAND
to seal wall-to-ceiling transitions. Measure and cut sections of the banding 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.and I d The KERDI-BAND may be creased prior
to installation to help maintain tight corners and make subsequent tile setting as easy as possible.
Apply unmodified thin-set mortar to the area where the banding is to be installed.
Embed the KERDI-BAND into the thin-set mortar Repeat this process at all remaining
joints ensuring that the minimum 2 inch overlap is achieved at all transitions.
Fastener penetrations are also sealed with KERDI-BAND using unmodified thin-set mortar.
Once the entire ceiling is covered with the KERDI-BOARD and seams and corners are sealed
with KERDI waterproofing accessories, the assembly is waterproof, vapor-tight, and ready for tile.