High-quality mortars are the backbone of every ceramic tile and stone installation. The products we use today have several millennia of refinement behind them, providing optimal adhesion under a variety of conditions. However, despite their importance to installations, mortars have a finite realm of applicability. Installers at every experience level develop bad habits that see them using mortars to perform functions well outside this realm. Let’s look at three of the more prevalent mortar misuses and misconceptions about what they can achieve.
I can’t tell you how many failed jobs I’ve come across where the installers used mortar to fix or fill low areas under the tile. This exceeds the performance demands mortars are intended to meet. A thinset mortar is designed to have no more than a ¼” of build under the tile once the tile is beat in. When the ¼” is exceeded, you push the limits of how much the mortar will shrink during the curing process. This can cause unwanted lippage in the finished tile job. Even high-performance large and heavy tile (LHT) mortars that can have up to a ½” of material under the tile after beaten in are not engineered to be used as a flattening agent.