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Mesh-Backed Stone and Tile

Recently, the tile and stone market has witnessed a prolifera tion in the offering of larger and thinner surfacing materials and an increased preference for unique varieties of stone, including those displaying heavy veining. As demand for these products has grown, stone manufacturers have reacted by applying fiber glass mesh and/or resin backing to stone tiles and slabs more frequently. Mesh backing and/or resin has been used for decades to provide reinforcement to both natural stone tiles and slabs. Typically, this backing is fiberglass mesh, and is adhered to the stone with epoxy, polyester or other varieties of resinous adhesives. This backing serves to stabilize the natural stone during pro duction, transportation, and installation. Based on the varied nature of stone, one lot of the same stone may have a fiberglass mesh, while the next lot does not. The decision to apply or not apply a mesh or resin backer is made by the stone producer, and therefore the likelihood of having mesh or resin applied to a giv en stone type may be greater from one producer than another. There may even be inconsistencies within the same producer’s material, with one lot having mesh or resin and a different lot of the same material having no mesh or resin. There are many common examples of natural stone that often see fiberglass mesh backing applied, including Crema Marfil, Onyx of all varieties as well as other brecciated or heavily veined stones. It is possible, however, to find fiberglass mesh or resin backing on nearly all varieties of stone. Typically, fiberglass mesh backed stones must be installed with a suitable epoxy setting material. Standard Portland ce ment based setting materials may not bond with the resinous backing/adhesive, leading to the potential for either immedi ate or long-term bond failure. Additionally, the high alkalinity of the cement based mortar may have a negative effect on certain backing types, possibly causing bond failure, especially in wet or submerged areas. Stones with fiberglass and/or resin backing may not be suitable for wet or submerged applications; therefore, it is advised that you work closely with your supplier to determine suitability of a specific material for a particular application. The TCNA Handbook Natural Stone Tile Selection Guide regard ing Fiberglass Mesh Reinforced Stone, notes that “Such rein forced stone tiles require epoxy bonding mortar.” This includes all reinforced backed stone. The limitations and/or cautions sections of technical data sheets for Portland cement-based thin set mortars often in clude written prohibitions against using the product with mois ture-sensitive stone or resin-backed tiles or stones. These cau

tions will frequently direct you to use an epoxy-based adhesive by the same manufacturer.

It has been a common practice in the field to scarify the fiber glass 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 ver ify that any manufacturers of dry set cement 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 like ly be formulated, none exist on the market today. Interviews with some manufacturers indicate that the primary concern is the variety of resinous adhesives that may be used on the stone backing, and the inability of the dry set cement mortar manu facturer to test their product with all adhesives that could po tentially be used. These products vary from country to country, and potentially from lot to lot or within lot by the same producer. Performing bond tests with the proposed products is one way to verify performance, but there is still a risk that the stone pro ducer changed types of adhesives during the production of the lot, rendering the initial test results inapplicable. 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-manufacturing environment, can render the mesh easy to pull off in the field, presenting a weak layer within your installation that can lead to failure. Qual ity control variables may also exist in the mixing ratios, mixing process, and curing of the adhesive. While insufficient bond be tween the mesh and the stone seems an obvious fault of the stone supplier, the installing contractor still has an obligation to verify the existence of suitable bond. There are no industry standards for the application of mesh. Many different alternatives have been introduced to the market over the past several years, including a full fiberglass coating, which based on anecdotal reports, appears to have had a great er risk of bond failure than mesh. Additionally, the use of epoxy/ resin with a sand aggregate has been introduced to the market. This sand backing may help to increase the mechanical bond to the setting material but does not necessarily act to reinforce the stone, which is the ultimate goal of applying the backing. Travertines with epoxy backing, but no mesh, have also been found on the market. As is the case with all stones with epoxy backing, you must determine the suitable setting material be fore proceeding.

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NTCA Reference Manual | 2024 / 2025

Chapter 6 | Natural Stone Installations