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.
Reinforcement is a component that is generally required within mortar bed floors and walls to impart flexural strength to control shrinkage of the mortar and prevent cracking, and in the case of walls, to support the vertical mortar bed. Proper installation of galvanized wire mesh reinforcement in mud floors is a critical skill that is always within the work scope of tile installers. Installation of metal lath on a wall’s structural backing often falls outside the scope of a tile installer’s work, but it is a related skill that tile installers must at least have knowledge of since it affects the performance of the tile assembly, and in some cases the lath installation does fall in the tile work scope.
In order to function properly, the reinforcement and lath must be continuous (except at inside corners of walls) and properly lapped by 2 inches (50 mm) minimum. In the case of walls, the lath must be installed shingle-fashion. At inside corners of any mud wall, the lath must terminate at the corner, allowing a small gap in reinforcement to allow for independent movement of each wall and directing cracks to the vertical perimeter expansion joint of the tile assembly. The positioning of the reinforcement in mud floors is critical to the performance of the floor. If the reinforcement is too high or too low from the center of the mortar bed, its ability to add flexural strength and adequately reinforce the system may be compromised. Skilled tile setters are expected to maintain the vertical position of the reinforcement in the center 1/3 of the mortar bed. Similarly, the fastening pattern of the metal lath on walls must be installed and spaced as specified.
While installation of the cleavage membrane, reinforcement and lath is important, the primary task faced by installers of mud floors and walls is to properly float the mortar beds flat, level, plumb and to the specified thickness. The ability to float floors and walls accurately is a true skill that takes years to master, and it is the hallmark of a skilled tile installer. A good tile installer is trained to float the mortar to the proper thickness at key benchmarks and to vary the thickness as necessary to correct substrates that are out of flat or out of plumb. At walls, installers must float inside and outside corners that are plumb, as well as maintain plumbness within tolerance in the field of the wall. Dimensions of wall mud must be accurate per the construction documents in order to maintain accurate finish dimensions. Mud floors must be flat and level upon completion, and ready to receive a tile finish. Each of these skills is critical for mortar bed installations.
Installation of tile in a mortar bed may be considered a specialty skill today, but the ability to work with mud is a skill still taught at the preapprentice level by International Masonry Institute. Proficiency in mud work is a hallmark of a BAC union tile contractor. One way design professionals can be assured of mud work that meets industry standards and best practices is to include a requirement in the Quality Assurance paragraph in Section1 of the tiling specification that the tile installers be certified via the Advanced Certifications for Tile Installers (ACT). ACT is an industry-wide certification program developed by TCNA (Tile Council of North America) and their manufacturer members, TCAA (Tile Contractors Association of America), IMI (International Masonry Institute), IUBAC (International Union of Bricklayers and Allied Craftworkers), NTCA (National Tile Contractors Association), and CTEF (Ceramic Tile Education Foundation).
Visit www.tilecertifications.com for more information.