Specification

Question: Can tile be directly installed to wood surfaces or foam insulation?
Answer: No. Plywood and OSB are not suitable surfaces for installing tile on walls and foam does not have the tensile
strength to support tile. WonderBoard Lite cement backerboard or lath and a cement scratch coat must be
installed to the wood or foam surface before the installation of tile with an appropriate mortar.
Question: Can tile be installed on painted surfaces?
Answer: On interior dry areas, mortars and adhesives may be used over most latex paints or epoxy paints with
preparation considering that the bond of the tile to the surface will only be as good as the bond of the paint
to that surface. If the paint is well bonded, it can be well cleaned and/or lightly sanded or primed with MBP
Multi-surface Bonding Primer. Tiles can be installed with a suitable polymer-modified, thin-set mortar. In some
cases, the paint should be removed. Do not install over oil-based paints.
Question: What is the requirement for movement joints when tile is installed on walls?
Answer: For exterior applications, the requirements are the same for walls and floors. Install flexible movement joints
every 8-12 feet and at all changes of plane. The minimum movement joint width for 8' OC is not less than
3/8", though larger joints provide better protection to large format tile, with any side longer than 15". Refer to
TCNA / Tile Council of North America Handbook, detail EJ 171 for specific guidelines of movement joints and
factor in the thermal expansion rate of the tile.
For interior applications, the movement joints should be placed every 20-25 feet, unless the tile assembly
exposed to direct sunlight and then they should be spaced every 8-12 feet. Joints are required at all changes
of plane. Always consult with the Project Architect on commercial projects.
Question: What are the guidelines for setting tile on ceilings?
Answer: For porcelain tile there are no specific restrictions for interior ceilings, but some suggest that maximum weight
should not exceed 15 lbs. per square foot. Larger and heavier tiles will require anchoring with mechanical
fasteners. The ceiling framing and sheathing components must be suitable and well fastened. Be sure to consult
your local building code or other authorities having jurisdiction for tile size and weight limits on your specific
project. Use a premium quality, non-sag, improved modified dry set cement mortar meeting American National
Standards Institute / ANSI A118.15 T and proper bedding technique for best coverage to fully collapse trowel ridges.
Tiled steam shower walls and ceilings require additional surface preparation with a “Low-perm waterproofing”
membrane like RedGard
®
Waterproofing and Crack Prevention Membrane and must have a slope of 2 inches
per foot and specially designed movement joints as detailed in TCNA SR613 and TCNA SR 614.
INSTALLATION PRODUCTS TO USE
Question: Is there a flatness guideline to follow when tiling walls?
Answer: To ensure a flat tiled surface, it is important to start with a flat substrate. The wall framing and/or surface should
be installed or corrected so that there are no deviations greater than 1/8" in 10 feet. For shower walls and tub
surrounds, install WonderBoard Lite 7/16" backerboard. If tiling on existing walls, apply and smooth an
engineered cement based patching compound to bring the surface into flatness tolerances prior to installing tile.
Be sure to remove any bond breakers like dust or residues before applying membranes or mortar to any surface .
Question: What is the best way to waterproof a shower wall or tub surround?
Answer: Monolithic application of RedGard Waterproofing and Crack Prevention Membrane will waterproof wet areas
like shower walls and tub surrounds. Apply two coats of RedGard to the wall (continuing to the shower floor and
drain assembly if applicable). A gallon of RedGard will cover 55 square feet in two applications (apply 1/2 gallon
uniformly to 55 sq. ft. and repeat with remaining 1/2 gallon when the first coat dries). Allow the first coat to fully
dry before applying the second and make sure there are no pinholes or voids in the coating. RedGard also acts
as a vapor barrier preventing moisture vapor from the shower entering the wall cavity behind the tile where it
can contribute to mold growth.
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