in the field to scarify the fiberglass mesh and resin, and install with a portland cement-based mortar with the hopes that the roughened surface aids in the bond. At the time of this writing, the authors were unable to verify that any manufacturers of port- land cement-based thin-set mortars endorse this practice. Increased risk is therefore encountered by the installing contractor, as there is no warranty from the setting-material manufacturer. While a portland cement-based product that has adequate bond capacity with fiberglass/resin- backed stones could likely be for- mulated, none exist on the market today. Interviews with some manu- facturers indicate that the primary concern is the variety of resinous adhesives that may be used on the stone backing, and the inability of the thinset manufacturer to test their product with all adhesives that could potentially be used. These products vary from country to country, and potentially from lot to lot or within lot by the same pro- ducer. Performing bond tests with the proposed products is one way to verify performance, but there is still a risk that the stone producer changed types of adhesives during the production of the lot, rendering the initial test results inapplicable. Lack of bond; lack of standards Improper application of the mesh to the back of tile or stone also represents a challenge. Insufficient quantity of epoxy/resin, or a stone that has not been properly cleaned prior to resin/mesh application, can lead to a bond failure. A thin layer of fine dust, which is quite common in a stone-manufactur- ing environment, can render the mesh easy to pull off in the field, presenting a weak layer within your installation that can lead to failure. Quality control variables may also exist in the mixing ratios, mixing process, and curing of the adhesive. While insufficient bond between the mesh and the stone seems an obvious fault of the stone STONE ––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––– This mesh-backed stone has not yet been removed for inspection. A combination of bonded membranes, stone mosaics and incorrect troweling membrane all contrib- ute to shower failures for stone tile. Improper application of the mesh to the back of tile or stone also represents a challenge. “ ” 82 TileLetter | December 2017