Choosing & Installing Ceramic Tile Flooring
A wire reinforced mortar bed performs as an excellent assembly for ceramic tile floors installations. Using a slip sheet with the wire reinforced mortar bed is a proven technique that isolates movement from the concrete or wood framing assembly beneath the ceramic tile installation. Depending upon the substrate, using 2 inch by 2 inch 16/16 gauge reinforcing wire fabric in the middle of the mortar bed for horizontal installations and 3.4 pounds per square yard expanded metal lath, applied over weather resistive barrier paper and mechanically fastened directly to studs, or 2.5 pounds per square yard expanded metal lath applied over weather resistive barrier paper and mechanically fastened over solid backing for vertical applications, produces reliable results.
Thin-set mortars were developed in the tile industry for direct bond to concrete slab on grade construction. Ceramic tile installed with dry-set or latex portland cement mortars over concrete slab on grade construction with correct expansion joints perform as long as the concrete slab on grade assembly performs. Concrete slabs designed commercially normally includes 3000 to 3500 pounds per square inch concrete without accelerators, cured for at least 28 days, without contaminants on the concrete surface, makes a concrete slab that is excellent for tile to be thin-set to the concrete slab on grade. The 3500 psi concrete slab is typically less permeable than concrete slabs made to lower psi strengths. The concrete slab designed residentially is normally designed for 2000 to 2500 psi strengths. The concrete slabs may be made square or different configurations to meet the house designs. Concrete by its own nature typically shrinks during the curing process with potential cracking of the concrete at stress load locations, from inside corners of the concrete slab, and will normally crack in squares as long as correct placement of wire in the concrete slab has occurred. The cracking pattern of concrete without correct wire reinforcement in the concrete will be more random. The lower strengths of concrete are more permeable to moisture migration.
In the 1960's and 1970's, homes were being designed and built with larger square footage and ceramic tile was introduced into showers, countertops, fireplaces and as flooring. Installations in the wire reinforced mortar bed installed in this time frame are typically still performing today. As builders chose to have more floor tile installed, minor problems and call backs occurred. Tile thin-set directly over the concrete slab on grade construction would crack, when minor shrinkage cracks would occur in the concrete slab. With the growth in the tile industry, floor covering design centers worked with builders and created a standard of care to use a slip sheet. The slip sheet is strictly for purposes to reduce minor shrinkage cracks of the concrete slab, and cracking of the concrete slab from inside corners of concrete, and to prevent these cracks from transferring up through the tile assembly. The homeowners typically did not want to pay the additional costs for installing the entry and floor covering areas in a wire reinforced mortar bed. The floor covering design center typically coordinated carpeting, wood flooring fireplaces, and other interior options for the home buyer. The Ceramic Tile Institute performed independent investigations and found many slip sheet assemblies subject to failure. Adhesion of the slip sheet to the concrete slab; and moisture migration through the concrete slab are among other reasons the Ceramic Tile Institute cautioned the designers and professional tile contractors from using these type of slip sheet products. The slip sheets being used were 15 pound asphalt saturated paper, upside down vinyl, paper, and today include scribing felt and perforated low emulsion asphalt paper. The floor covering design center learned to warrant the slip sheet except for moisture migration through the concrete slab. Total responsibility of warranty was put on the floor covering design center except for where moisture migration through the concrete slab could be shown as being the source of the problem. The professional tile contractor cautioned against the usage of a slip sheet. A feud, so to speak, was created between the floor covering contractors and the tile contractors.
In the 1970's, waterproof membranes were developed for thin-set application. In the 1980's, the thin load bearing bondable anti-fracture waterproof membranes came into recognition, with industry standards for performance and testing developed. The Ceramic Tile Institute tested, through independent laboratory testing, products that performed. NobleSeal TS, Dal-Seal TS, Mer-Kote BFP, Composeal Gold were among products approved by the Ceramic Tile Institute to be used in a slip sheet application, to reduce minor shrinkage cracks in the concrete slab, and reduce moisture migration through the concrete slab. The Ceramic Tile Institute and manufacturers of these and similar membranes promoted these products to be installed using method assembly F-122 in the Tile Council of America Handbook For Ceramic Tile Installation.