Warranty Considerations - Choosing & Installing Ceramic Tile Flooring
Many builders have conscientiously worked to improve the quality of the concrete for residential construction. Increased concrete strength and reduced permeability of the concrete greatly reduce the problems with floor coverings installed over the concrete. Post-tensioned and pre-tensioned concrete slabs are installed by many builders to improve the quality of the finished concrete surface.
Since the finish materials are not known when the home is under construction, many builders will supply a smooth concrete slab. The tile industry would prefer a fine or medium broom finish for bonding ceramic tile or a membrane directly to the concrete slab. If vinyl, resilient flooring is to be used, the concrete is preferred to be a smooth concrete slab prior to installation.
California was in drought for a number of years. When the rains began in the 1990's, we began investigating moisture/dry problems. Moisture/dry is used to explain the moisture wicking, percolating, migrating up through concrete slab and affecting the inside of the building structure. Moisture may cause loss of bond or de lamination of the slip sheets installed with mastic over the concrete slab. Sources of moisture may be attributed to water drainage from the roof, exterior concrete and ground draining toward the building instead of away from the building, inadequate drainage on the perimeter of the concrete slab, dense soils that hold water and allow water tables to get up to the level of the concrete slab, concrete slabs with accelerators (as an example if 2% calcium chloride is used to speed the setting of the concrete slab, then after curing, the moisture will migrate, wick and percolate up through the concrete slab due to temperature differentials on the two sides of the slab), and closed homes with heating and/or air conditioning that when operating , can pull moisture up through the concrete slab. Dampness, cold growth, efflorescence, are typical signs of moisture/dry problems with concrete slab. Type C & D marbles installed on floors with moisture migration are subject to uncompleted metamorphism. When asphalt paper is used as a slip sheet, and moisture migration occurs, the moisture can create a liquid tea reacting with mastic and/or asphalt in the paper and cause discoloration of the surface of the marble tile.
In 1993, American National Standard For Load Bearing, Bonded, Waterproof Membranes For Thin-Set Ceramic Tile and Dimension Stone Installations was adopted as ANSI A118.10-1993. This industry standard for a material that performs both as a slip sheet and a waterproof membrane
Many mortar and adhesive manufacturers made mortars specifically for bonding to concrete slab subject to bending and flexing. The mortars were called flex mortars. The intention of the flex mortar was for the tile and mortar to flex up and down with the deflection or bowing of the concrete slab. The flex mortar manufacturers, when challenged, agreed that the flex mortar was not designed for reducing concrete crack in the slab from transferring through the finished tile assembly. There maybe new generations of mortars and adhesives now and in the future. It is the responsibility of the mortar and adhesive manufacturer to state what capability the mortar and adhesive does or does not have. If crack isolation is important, ask the manufacturer. If moisture is already present in the concrete slab, and a membrane assembly is being installed, consider using a rapid setting mortar to bond the load bearing, bonded waterproof membrane to the concrete slab.
Analysis of slip sheets
- A slip sheet used with a wire reinforced mortar bed works and performs very well. The only caution is against using polyethylene sheeting in a location where temperature differential may cause water sheeting to occur through condensation.
- A load bearing, bonded, waterproof membrane works well for a thin-set application over concrete slab to reduce minor shrinkage cracks from transferring up through the tile assembly and prevents moisture/dry problems of moisture wicking up through the concrete slab. Follow manufacturers directions.
- Use a slip sheet to isolate only minor shrinkage cracks in the concrete slab from transferring up through the concrete slab. The assembly is subject to failure with moisture/dry problem in concrete slab.
- Bond ceramic tile directly to properly prepared concrete slab . Minor shrinkage cracks in the concrete slab may transfer through the finished tile assembly.
The owner may be given a choice of the above A through D items. The cost of the above A,B,C are approximately the same whereas the D option allows a lower square foot cost.
When an owner chooses the method based on financial consideration, and the lower cost assembly does not perform, assuming everything is installed correctly, then the cost of the failure is assumed by the party making the choice of the assembly. This is based on a legal doctrine.
