Achieving 80% mortar coverage, or 95% in exterior and wet areas, is the minimum tile mortar coverage standard in ANSI A108.5. It is also the purpose of the Trowel & Error video produced by the NTCA and members of its Technical Committee. Yet larger tile sizes, evolving thixotropic properties of mortars, development of specialized trowels, and the complexities of labor keep mortar coverage a consistent topic of conversation in NTCA Technical Committee meetings and in our industry overall.
With the release of the new Trowel & Error video in both English and Spanish, it’s important to recognize that achieving proper mortar coverage has always been a challenge for installers. When tile grew to 24”x24” – considered very large in the mid-1990s – NTCA Executive Director Emeritus Joe Tarver knew improper mortar coverage was a challenge that would injure the industry if he didn’t do something about it.
Sleuthing out proper mortar coverage
Tarver devised a system to demonstrate troweling techniques in the back room of his NTCA office. Using specially-cut large-format plexiglass and tempered glass that would reveal mortar coverage, he kept experimenting with troweling techniques.
At the time, it was standard procedure to apply bonding material with a notched trowel in a figure 8 motion. But despite trying different mortars, different mortar consistencies, conventional and latex modified mortars – and a variety of trowel sizes and notch sizes and configurations – Tarver could only achieve 40% to 60% coverage at best. But late one night, with enough mortar to make one more try on a large glass tile, Tarver troweled it on in a parallel manner, put the glass tile in place, and slightly moved the glass forward and backward, collapsing the ridges and reaching 95% coverage. Success!
Troweling in one direction, short side to short side, then moving the tile to compress the ridges and let air escape, were the key to achieving proper coverage. It would soon become the predominant lesson to be shared with NTCA members in the Trowel & Error video. The concept was true when first documented on film by Tarver and his friend Bob Roberson of David Allen Company, and it remains true today. By the way, Roberson also came up with the catchy title for the video, which he copyrighted on behalf of the NTCA in 1996.
Continuing challenges to proper coverage
Yet, the challenge of collapsing mortar ridges under tile continues to cause problems due to tile installers failing to apply the tile mortar properly with parallel ridges. Many also fail to embed the tile properly by moving it perpendicular to the mortar ridges.
The use of the 1/2”x1/2”x1/2” square-notched trowel further hinders proper mortar coverage. This 1/2” trowel became popular with large-format tiles due to its ability to spread more mortar over the substrate. However, the distance between the notches makes it virtually impossible to collapse all the ridges properly, especially with rectangular tiles in an offset pattern. These trowels are no longer recommended, and the new Trowel & Error video illustrates why. The NTCA Technical Committee also put a precautionary statement on the use of 1/2”x1/2”x1/2” notched trowels in the NTCA Reference Manual this year, and most tile mortar manufacturers do not recommend their use.
The updated Trowel & Error video, now in its fourth version thanks to the production support of Custom Building Products, continues Tarver’s tradition of using glass tile panels to illustrate the collapsing trowel ridges behind the tile. It also shows larger tiles than the previous version of the video. Though the original Trowel & Error video was initially distributed to members on VHS tape as a training tool, today any installer, contractor, manufacturer or consultant can access it on their phone. Now this valuable information can be put to work right in the field where it is needed most.
Association involvement
The new Trowel & Error videos are one more way the NTCA Technical Committee helps provide tools to installers for their success. Thanks to Woody Sanders of D.W. Sanders Tile and Stone Contracting, who is installing (and destroying) tile in the videos, Mike Micalizzi of Custom Building Products, who oversaw production of the videos, Lupe Ortiz of IMTEF who proofed the Spanish language version, and to Chairman James Woelfel, Vice Chairman Nyle Wadford, and CTEF’s Scott Carothers for their technical expertise. Technical Committee members Jan Hohn and Chris Walker have also contributed to the project previously.
It is this kind of involvement from the NTCA Technical Committee that ensures Trowel & Error continues to serve as the vital resource it was first created to be, illustrating how to properly meet ANSI A108.5 standards for the installation of tile with tile mortar.
The new Trowel & Error videos can be found on the NTCA YouTube Channel:
Trowel & Error (English): https://youtu.be/zfMmbJWFbSY?si=AU7GV7sWKBHecUat
Errores Al Alisar La Superficie (Spanish): https://youtu.be/OR4T8x2ubuQ?si=0ci2tJ6r6JjwAf15 (this actually says Errors When Smoothing the Surface)
Chris Woelfel
Chris Woelfel, M. Ed., is Partner and Business Manager at J.G. Woelfel & Associates, Tile and Stone Consultants. A member of the NTCA Technical Committee, she has long been an advocate for qualified labor and adherence to industry standards. She spent over 15 years in the tile contracting business at Artcraft Granite, Marble and Tile Company, with prior work experience as an award-winning journalist, video producer, external and internal communication strategist, and public relations director.
