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 framing to prepare a ceiling for tile installation.
Here’s how to do it. The minimum KERDI-BOARD
thickness required is 1/2 inch for framing spaced at 16 inches on center and 3/4 inch
for framing spaced at 24 inches on center. KERDI-BOARD is attached to framing using wood
or metal screws and corresponding Schluter®-KERDI-BOARD-ZT washers.
The screws must be of sufficient length to reach a depth of at least 3/4 inch in wood studs and at
least 3/8 inch in metal studs. The walls have already been
covered with KERDI-BOARD. Fasteners are placed every 6
inches on center in ceiling applications. Depending on the size of the ceiling,
it may be necessary to install multiple sheets of KERDI-BOARD to cover the entire surface.
Abut the panels over the center of the framing or other solid backing.
Screws may be placed between adjacent panels such that the washers fasten both panel edges.
Seams are made waterproof by installing Schluter®-KERDI-BAND waterproofing strips.
Measure and cut sections of the banding such that a 2 inch overlap is achieved at all junctions.
KERDI-BAND is bonded to KERDI-BOARD using 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 unmodified thin-set mortar to the joint where the KERDI-BAND will be installed.
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. 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. Fastener penetrations are also sealed with
KERDI-BAND using unmodified thin-set mortar. The banding may be cut in sections
or applied across the ceiling. It is only necessary to continue the band
2 inches past the last fastener; this can help avoid buildup at ceiling-to-wall transitions.
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. 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.
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. Once the entire ceiling is covered with
the KERDI-BOARD and seams, corners, and fastener penetrations are sealed with
KERDI waterproofing accessories, the assembly is waterproof, vapor-tight, and ready for tile.