the range of tolerance. Section 9.5 of ANSI A137.1 describes the laboratory testing meth- od for variations in mounted mosaic ceramic tiles. That is where we learn how many tiles and grout joints are to be examined and how many varia- tions are acceptable based on the size of the individual tiles on the sheet and overall size of the sheet. I am not certain if the specifications for stone mosaics are similar, but I am able to refer to the following. In the Marble Institute of America’s Q&A Manual (Expert Answers to Technical Questions About Working with Natural Stone) the following is stated with regard for a reasonable tolerance for joint width: “Tolerance is normally correct at a variation from true (specification) of 1/4 of the specified joint width. With a joint width of 3/32”, a tolerance of ± 1/32” is reasonable. A 3/32” joint is correct at 1/16” wide and at 1/8” wide. The joints should “eye up” straight and true. Be careful though, if the joint is specified at between X and Y.” * To paraphrase the first sentence of the MIA’s statement, “a variation tolerance of 1/4 of the specified joint width” may be equivalent to +/- 25% for ceramic mosaics. I have seen many instances where inadequate adhesive has been applied to the mesh allowing individual tiles to become loose or shift. I have seen instances where the adhesive has dried out and allowed the individual tiles to become loose and shift on the sheet. Many of these adhesives are water based; when they become damp they LATICRETE® NXT™ Level is a cement-based underlayment for use in leveling interior substrates including concrete, vinyl tile, cement terrazzo, exterior glue plywood, cement mortar board, cement backer board, ceramic tile and stone. NXT Level produces a flat, smooth and hard surface for the installation of finished flooring. The NXT Level formula is a factory- prepared blend of cement, aggregate and other materials to produce a flow- able, fast-hardening underlayment that can be distributed via pour or pump. Common applications include interior thin bed floors and renovations. NXT Level can be placed from 1/8 - 3” (3 - 76 mm) in a single lift and applied directly over concrete testing at a relative humidity of 95% or less per ASTM F2170. Once cured, NXT Level is durable, fire- and heat-resis- tant, non-combustible, non-sensitive to moisture and maintenance-free. www.laticrete.com. ASK THE EXPERTS –––––––––––––––––––––––––––––––––––––––––––––––––––– 22 TileLetter | April 2017