Well over 50 years ago, thin-bed mortarswere born. The thin-bed mortar method revolutionized the way tile was installed and new developments still continue today.
A118.1

When initially developed, A118.1 allowed installers to bond tile directly to the substrate, which was unheard of prior to the introduction of this new product and method.  

 The thin-set method was a stark contrast to the installation methods that were commonplace for years — the conventional mortar bed. This new way lowered the cost of installed tile and spurred the growth of the market for over as many years. This unprecedented expansion has also brought change.

When initially developed, the mixture of Portland cement, sand and water retention agents yielded what became known as Dry-Set Portland Cement Mortar or A118.1. This new product allowed the installer to bond tile directly to the substrate, which was unheard of prior to the introduction of this new product and method. No longer would the slab need to be depressed to receive the thickness of the mortar bed nor a concern with the added weight to the structure. This new and quick installation of tile would change the face of tile installation. However, this is not to say that mortar beds went away, but their volume was diminished significantly.

A118.1 mortars were primarily used to direct bond tile to a concrete surface while eliminating the need to soak the tiles in water prior to installation, hence the name Dry-Set. These products have functioned well, allowing the installer to set more tile per day using fewer raw materials.  No longer was a load of sand, a roll of reinforcing wire and a pallet of Portland cement necessary to complete the task at hand. Now all that was needed was housed in 50-pound bags and simply mixed with water.  But, the introduction of new and larger ceramic tiles and the fact that some of these new items, namely porcelain tile, presented new bonding challenges. More changes were in the future.

These new tile products, including ever-increasing tile size and use application requiring higher bond strength, the ability to deal with a questionable substrates and the need to provide freeze/thaw benefits for exterior installations, brought a new player into the field. The addition of liquid latex and later, dry polymers, gave us a new category — Latex-Portland Cement Mortar or A118.4. These mortars likewise have functioned well, allowing tile to be bonded to surfaces that previously were not considered.

The continued growth of A118.4 mortars created a vast category of materials both in number and application which varied greatly. Some of the products in this group just met the minimum criteria of an A118.4 mortar, while others were well above the minimum threshold. This vast disparity in product capability and purpose made it difficult for all involved, from the architect to the installer. Many installations would function well with a base-grade mortar and were so specified. However, when the product being specified was an extremely dense porcelain or the increasingly popular glass tile, mortars with a much higher bond strength were required. The ANSI committee — realizing the need to differentiate between the lower and upper levels of capability — decided to establish a new category.

The soon to be released new standard is known as “Improved Modified Dry-Set Cement Mortar” and carries the ANSI designation of A118.15. During the development of the standard, the committee considered utilizing the next available ANSI number which was A118.14, but due to the potential confusion between the existing A118.4 and the new A118.14, the selection was moved to A118.15. The separation into two classes of performance now provides the architect with the ability to specify the mortar that meets the requirements of the project.

A118.4

The continued growth of A118.4 mortars created a vast category of materials both in number and application which varied greatly. The ANSI committee — realizing the need to differentiate between the lower and upper levels of capability — decided to establish a new category. The soon to be released new standard is known as “Improved Modified Dry-Set Cement Mortar” and carries the ANSI designation of A118.15.

One additional benefit derived is that the contractors bidding projects will now need to provide the required mortar, Standard or Improved, and will no longer be able to bid the least expensive A118.4 mortar available. In the past, the architect had only one choice in thin-bed mortars, A118.4, regardless of the tile being installed. This scenario was sometimes problematic in that a change order had to be issued to provide the “better” mortar necessary to accommodate the job requirements. This new standard is a win-win situation for all involved. The architect is now able to match the performance of the mortar to the job requirement and the conscientious contractor who wants to provide the best quality possible is no longer forced to bid the base grade product just to remain competitive.

The primary difference between these two standards is in its shear bond strength based on a 28-day period. Glazed wall tile, under A118.4, calls for an average shear strength greater than 300 psi whereas the new A118.15 mortar requires an average shear strength greater than 450 psi — a 50% increase in shear strength. The test for A118.4 mortars bonding porcelain mosaic tiles requires a shear strength greater than 200 psi. The comparable test for the A118.15 is greater than 400 psi, which is double the A118.4 standard. The last comparison group is quarry tile.  Here the test requires exactly the same value, 150 psi.

The increased shear strength is increasingly valuable in many of the new tile products found on the market today. Glass tile is probably the stand out in this group since it can be difficult to bond, and selecting just any A118.4 mortar may not function properly. Another challenge is in the various heat-transferred coatings that are placed on the back of low-temperature-coated glass as detailed in the new ANSI A137.2. The TCNA Handbook issues this caution. “Some low temperature-coated glass tiles are not intended for installation with cementitious materials.  Cement mortar alkalinity may deteriorate those low-temperature applied backings and increase the risk of delamination, particularly in wet areas or humid environments.” ALWAYS follow the manufacturer’s recommendation, which includes both the tile and the setting materials. It is incumbent upon the installer, if he or she is unfamiliar with new products, to contact the manufacturer to determine their specific recommendation for the bonding adhesive and get it in writing.

The 2012 Handbook goes on to say (which predates the new A118.15), “Generally, it is necessary to use high-performing ANSI A118.4 or ISO C2S1 or better mortars to achieve such adhesion.”  We will soon have the A118.15 in place.  Doesn’t it make sense to buy the higher performance product for the “shear” peace of mind, knowing that it will perform beautifully?