“There doesn’t appear to be an industry definition for the category of “underlayments,” but this grouping can easily include products such as backer board, liquid and sheet membranes, uncoupling membranes, mortar beds, patching compounds and self-leveling products. No matter which products are being used on a project, the floor or wall surface must be flattened or possibly leveled to meet the industry standards. For the sake of this conversation, we will focus on patching compounds and self-leveling underlayments.
The underlayments used in concert with ceramic and stone tile installations may be, and most likely are, essential to the satisfactory outcome of a project. If the subfloor, be it wood or concrete, is not within the tile industry requirements, something must be done to correct the deficiency prior to starting the installation.
In the past, floor preparation materials were not as readily available as they are today. When an inappropriate subfloor was encountered, it was up to the installer to find a way to make the floor flat enough to install the large-format tile of the day, the infamous 8 x 8, without one tile edge being higher than the adjacent tile. The use of the term “lippage” was not commonplace and may not have been yet created.
Installers in those days needed to be creative in fixing low spots, especially in a wood subfloor…”
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“Underlayments Solve Many Problems”
By: Scott Carothers