The title of theHandbookhas been changed to reflect the newly-added methods and recommendations for installing glass tile and natural stone tile. Previously, theHandbookdid contain some general information and cautions for installing glass tile, such as acceptable and unacceptable substrates and the need for high quality bonding mortars. However, the Handbookdid not call out specific installation methods as acceptable, with the recommendation instead being to consult the glass tile manufacturer for an appropriate method. Likewise, while many methods in theHandbookwere used for the installation of stone tile and were referenced by the Marble Institute of America (MIA), those methods were not specific to stone and did not provide stone-specific criteria.
But, over the past year, the TCNA glass tile manufacturers’ subcommittee, with input from contractor representatives of the National Tile Contractors Association (NTCA), identified which methods are suitable for installing glass successfully, and what additional design and installation considerations need to be factored in when glass tile is selected. TCNA also worked with the MIA and NTCA to determine the same relative to installing stone tile. The resulting recommendations were then considered, tweaked, and ultimately approved by theHandbookCommittee of industry experts. The result? Vast improvements to the 2011Handbookwith regard to guidelines for installing glass and stone tile.
What are the new Handbook guidelines for installing glass tile?Glass tile will now be listed as an option in 70Handbookinstallation methods. Within those methods, some added precautions are also listed:
- Emphasis on the need for movement accommodation
- Recommendation to use white mortar for translucent glass
- Consideration of the floor service rating and how glass tile may affect it
- Requirement to consult glass tile manufacturer for allowable membranes and membrane placement.
The glass guide also provides installation requirements, some of them heretofore lesser-known, even among seasoned installers:
- “With translucent glass tiles, setting material color and full coverage are essential; white is commonly recommended. Avoid using setting materials from different production batches and check for bag-to-bag color consistency.”
- “For hollow-shaped pieces (v-cap, quarter round, crown caps, etc.), back-butter the tile but do not fill the cavity. Excess setting material can shrink and may cause cracking or ghosting.”
What are the new Handbook guidelines for installing stone tile?Instead of incorporating stone information into existing methods, as was done for glass, separate stand-alone methods were created for installing natural stone tile, also called dimension stone. This approach was taken to provide theHandbookuser clear insight into the difference between selecting engineered products like glass and ceramic tile, which can be manufactured to meet specified performance criteria, and harvested products, like stone, which cannot.
Consider the example above regarding service ratings for floor installations. Natural stone tiles range widely in performance. Some stones, for example many limestones, are softer than typical ceramic tiles and would be expected to break and show abrasion more easily. But other stones would perform as well as ceramic on a floor. The one generalization that can be made is that it is wise to research a stone’s performance in consideration of the intended use.
Because of the variability of natural stone, the 2011Handbookrequires stone tile to be installed using an unbonded (floating) mortar bed for installations larger than 100 square feet where the substrate is post-tensioned concrete. The stone guide explains: “because dynamic movements of post-tensioned slabs have proven problematic for directly-adhered natural stone, Method F111 is the only method of installation over post-tensioned slabs, on-ground or above-ground.” By contrast, ceramic tile can be bonded directly to post-tensioned concrete provided that a more deformable mortar is used to accommodate the inherently increased amount of movement in such slabs as compared to traditional-style reinforced concrete.
Where the substrate is wood framing and subflooring, again a mortar bed method of installation is preferred for stone. Backer board is only provided as an option over wood subflooring if two layers of structural plywood subflooring are installed and joists are spaced no more than 16” on center. This is because of “the discontinuity of the system at seams between the subfloor panels,” which can result in cracked stone. The second layer of plywood reduces cracking by reducing differential deflection of adjacent framing members. The unbonded mortar bed method simply accommodates the differential deflection by providing a separation of the installation from the subfloor.