FAQ

STANDARDS
Question: Is there a standard for installing large format tile?
Answer: Yes, porcelain and natural stone tile manufacturers recommend the use of a polymer modified mortar for
installation of large format tile to concrete, plywood and synthetic membrane surfaces. TCNA recommends
the use of mortars meeting ANSI A118.4, A118.15 (improved performance cement mortar) and A118.11 (for
plywood surfaces) for these installations. The latest developments by Custom Building Products in mortar
technology utilize specialized, spray dried polymers in their polymer-modified medium-bed mortars. These
mortars require only the addition of water at the jobsite.
Question: What size tile determines large format?
Answer: Any tile or stone with at least one edge greater than 15".
Question: Do large format tile installations require a special thin-set or adhesive?
Answer: It is recommended to use a medium-bed mortar when installing large format tile to compensate for
irregularities in the tile and substrate. Common thin-set mortars shrink as they cure — the displacement of
water causes the mortar to retract and pull the tile as it hardens. When this occurs with a thick layer of a
common thin-set mortar it can leave an uneven surface from tile to tile known as “lippage,” an unwanted
finish result, or crack the tile. Mortars with medium-bed features are formulated to control the amount of
shrinking that occurs during the curing process, allowing the tile to stay true to adjacent tiles.
Custom Building Products has developed a line of medium-bed mortars that are easy to spread, offer
non-slump/non-slip support, and are available in rapid setting formulations that quickly lock tile into place
— so that within a matter of hours the installed tile is ready for grouting. Whereas standard mortars are
capable of a setting bed 3/32” to 3/16” thick, a thin-set mortar with medium-bed features can span from
3/32" up to 3/4" thickness after beat-in, providing maximum support and coverage.
INSTALLATION
Question: What procedures should I follow to set large tile?
Answer: TCNA, with the support of the tile installers, has developed specific recommendations for the installation of
large format ceramic and natural stone tile.
 •Medium-bedmortarsshouldbeusedtoinstalltileswithoneedgegreaterthan15",whenthenal 
embedded thickness of the mortar will exceed 3/16".
 •Crackisolationoruncouplingmembranescanimprovetheperformanceofthetileinstallationin
above-ground installations.
 •Theactualgroutjointwidthshallbethreetimesthevariationinthefacialdimensionofthetileandnever
less than 1/16".
 •Runningbondpatternswillhaveamaximumoffsetof33%fortileswithoneedgegreaterthan18".
It is advisable to review the current TCNA guidelines in the handbook before beginning an installation
project involving large format tile; there are changes to the guidelines regularly as new tiles are introduced
or better methods are observed and passed along.
Question: How do I prepare the surface before setting large tile or stone?
Answer: The most important consideration when setting large format tile is that substrate flatness is paramount to
the success of the installation. The ANSI (American National Standards Institute) specification for the
Installing Large Format Tile
Frequently Asked Questions
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