The classic method of laying tile floors and walls in setting beds built up of sand, cement and sometimes wire or lath reinforcement over the floor or wall structure is a work technique that has declined in recent years as thinset mortars and thinset installation methods have been improved and become more prevalent. However, mortar bed techniques for installing tile will never disappear completely as they remain appropriate for certain types of applications such as heavy duty areas of use, cases where the variable thickness of the mortar (mud) bed is appropriately used to correct an irregular substrate and other instances where the design professional or building owner has a preference for this classic method of installation. Design professionals and specification writers should have a basic understanding of mud floors and walls and should require the installing contractor to meet minimum qualification requirements for this specialized type of work. This article will examine the components of mud work, including installer qualification criteria.
A cleavage membrane is component often specified in mud work to provide a bond break in floor and wall assemblies if differential movement is expected between the tile assembly and the substrate. Cleavage membrane materials vary, but they are often paper-based, delicate and easily damaged. A qualified tile installer will take care not to tear, puncture or otherwise damage the cleavage membrane during the installation process, and if damage does occur, the installer will replace and reinstall the material. Floors and walls both require minimum overlaps in the cleavage membrane, generally 4 innches (100 mm) for floors and 2 inches (50 mm) for walls; and the laps at walls must be applied shingle-fashion. Failure to install the cleavage membrane to these criteria may result in ineffective bond break or moisture intrusion into the wall or floor structure.