undertile
Undertile is a term used in tiling to refer to a tile that is installed beneath a primary or visible layer of tiles. This secondary layer is often used to provide a more stable and uniform substrate for the main tiling. In some applications, undertiling is employed to improve the thermal insulation of the floor or wall. It can also be used to create a moisture barrier, protecting the underlying structure from water damage, especially in wet areas like bathrooms and kitchens.
The materials used for undertiling vary depending on the specific requirements of the project. Common undertile