We have all heard the phrase, “I have been doing it this way for 30 years and never had a problem,” but do we know that he or she never had a problem over that length of time, especially when it comes to something really simple such as how to handle a tile trowel?
Before troweling the thinset mortar, the substrate must be flat to the appropriate industry requirement and clean. To achieve the minimum mortar coverage, the American National Standard Institute (ANSI) A108.5-2.2.3 states: “Contact area shall not be less than 80%. Contact area on all exterior installations or interior wet installations shall not be less than 95%. The 80% (in dry areas) or 95% (in wet and exterior areas) shall be sufficiently distributed to give full support of the tile with particular attention to all corners and edges of the tile. To achieve the 80% or 95% coverage, select a notched trowel sized to facilitate the proper coverage. Embed the tile or tile assembly in the mortar by pushing in a direction perpendicular to the combed ridges to fully collapse them and achieve specified coverage.”
However, there is another key component in obtaining the required coverage. The trowel manufacturers design tile trowels to be held at a 45° angle to the substrate as seen in the above image, which includes the trowel, thinset, and a speed square. A speed square has one 90° angle, and two 45° angles that demonstrate the correct angle which can help the seasoned installer change a possible bad habit. This technique will require getting accustomed to a new “feel” while also building a strengthened muscle memory.
A further illustration of this requirement is included in the installation standard for gauged porcelain tile and gauged porcelain tile panels/slabs (GPTP) A108.19 (interior) and A108.20 (exterior). Section 13.7 in part states: “Use the appropriate trowels and troweling technique (hold at least a constant 45° angle) and take care to keep the ridges straight and of consistent height. This is crucial to achieving required coverage.”
The consistent height statement in the last paragraph is essential. When spreading mortar, an installer who extends his/her reach beyond what is comfortable, especially on horizontal surfaces, can lower the trowel angle which places less mortar on the substrate. Conversely, if the installer curls his or her wrist as the trowel comes toward them, the angle of the trowel is increased which places more mortar on this side of the tile than what was applied on the other side at the extended reach.
This combination of errors gives the installer a thinner amount of thinset on one side of the tile and a much thicker amount on the other side which makes it difficult to minimize lippage on each edge.
This technique really works and can save the installer time and effort. Remember, it is all in the wrist.
