Substrate Tolerances for Thin-Bed Methods:
For thin-bed ceramic tile installations when a cementations bonding material will be used, including mortar for large and heavy tile (formerly medium bed mortar): maximum allowable variation in the tile substrate - for tiles with all edges shorter than 15", maximum allowable variation is 1/4" in 10' from the required plane, with no more than 1/16" variation in 12" when measured from the high points in the surface. For tiles with at least on edge 15" in length or longer, maximum allowable variation is 1/8" in 10' from the required plane, with no more than 1/16" variation in 24" when measured from the high points in the surface. For modular substrate units, such as plywood panels or adjacent concrete masonry units, adjacent edges cannot exceed 1/32" difference in height.
For thin-bed ceramic tile installations when as organic adhesive or epoxy adhesive will be used: maximum allowable variation in the tile substrate is 1/16" in 3' from the required plane with no abrupt irregularities greater than 1/32".
Thin-bed stone tile installations: maximum allowable variation in the tile substrate 1/8" in 10' from the required plane.
Project specifications shall include a specific and separate requirement to bring the substrate into compliance if a thin-bed method is specified but substrate does not meet the flatness requirements.
Substrate Tolerances and Large Tile:
As tile size increases, the negative effect of substrate irregularities is compounded. If specifying a thin-bed method, project specifications should include a separate specification and requirement (such as a pourable underlayment) to bring the substrate into compliance if the substrate does not meet the required flatness tolerance. Alternatively, when specifying tile with any edge longer than 15" consider specifying a recessed installation substrate and a mortar bed (thick-set) method to produce a tile substrate that meets the more stringent flatness requirement for large format tiles. There is no "medium bed installation method" that can be used to flatten the substrate while installing the tile, as mortar (including LHT mortar) is not intended for truing or leveling substrates or the work of others.
Flatness and Lippage:
With regard to flatness, the amount of substrate variation generally is reflected in the finished tile installation. For any application, a tiled floor should comply with the flatness requirements in ANSI A108.02: no variations exceeding 1/4" in 10' from the required plane. Conformance to this standard requires that substrates conform to the following: For tiles with all edges shorter than 15" maximum allowable variation is 1/4" in 10' from the required plane, with no more than 1/16" variation in 12" when measured from the high points in the surface. For tiles with at least one edge 15" in length, maximum allowable variation is 1/8" in 10' from the required plane, with no more than 1/16" variation in 24" when measured from the high points in the surface. For modular substrate units, such as plywood panels, adjacent edges cannot exceed 1/32" difference in height. Additionally, the effect from irregularities in the substrate increases as the tile size increases. A substrate tolerance of 1/8" in 10' may be required.
Because the flatness of wood and concrete substrates can change over time, it is recommended that the designer make provisions for evaluating substrate flatness just before installation of the tile. Project specifications should make clear which trade is responsible for the required alterations of the subfloor is found not to be in compliance with the flatness requirements. Alternately, the designer may choose to specify a mortar bed method or a pourable underlayment installed my the tile contractor to ensure substrate flatness sufficient to facilitate a flat tile installation.
Lippage is most significantly influenced by substrate flatness and tile warpage. Allowable lippage is calculated by adding the actual warpage of the tile supplied, plus either 1/32" or 1/16" based on tile type and size and grout joint width. Specifying wider grout joints allows for more gradual changes. To minimize lippage due to warpage, specify tile that meets the dimensional requirements for rectified tile according to ANSI A137.1, and use a larger grout joint. Some patterns, such as a 50% offset (brick joint) pattern, accentuate the effects of warpage and result in more lippage than other patterns would. Cushioned or beveled edge tiles can minimize the effects of lippage.
In addition to taking measures to ensure a flat substrate, designers should consult with the tile manufacturer to discuss grout joint size and tile pattern selections that will minimize issues relating to flatness and lippage.
Maximum Allowable Deflection for Substrates:
For ceramic tile installations maximum allowable floor member live load, concentrated load, impact load and dead load shall not exceed L/360, where "L" is the clear span length of the supporting member per applicable building code. For natural stone tile installations, maximum allowable floor member live load, concentrated load, impact load and dead load deflection for wood framed floor systems shall not exceed L/720, where "L" is the clear span length of the supporting member, per applicable building code.
Proper Spacing for Wood Subflooring and Wood Underlayments:
Plywood subflooring, OSB subflooring and plywood underlayment shall be installed with proper spacing between the sheets (typically 1/8", except if specified otherwise by the wood manufacturer). If the subfloor or underlayment is installed without proper spacing, this condition cannot be corrected by the tile installer. It is the responsibility of the homeowner or owner's subflooring or underlayment installer to ensure proper spacing is used as failure to do so may not be obvious and the tile installer cannot be expected to discover such. If expansion takes place in wood subflooring or underlayment installed without proper spacing, the tile installation could fail.
Color - Natural Stone Tiles:
Natural stone tiles are a product of nature and variations from piece to piece should be expected. Veins, colors, fissures, texture and factory filled holes should not be viewed as defects, but as inherent qualities of a product made by nature. Installers should not be expected to control these variations, responsibility rests upon the homeowner, builder, designer, owner or general contractor.
Light colored stone tiles may appear darker in wet areas due to water absorption. This condition may become permanent when exposed to water for an extended period of time.
Some stones are acid sensitive and will etch when exposed to acidic foods and harsh cleaning products.