“Mud-Set” or “Mud-Bed” are terms used for a 3/4" Portland cement and mason sand sub-surface for ceramic, porcelain & natural stone residential tile flooring. “Mud-Setting” the floor to accept tile is the ideal substrate: to provide a sound, flat and level floor, to provide a water-resistant base, and to add structural stability to new and old floors.
"Thinset" is an adhesive mortar made of cement, fine sand and a water retaining agent such as an alkyl derivative of cellulose. It is usually used to attach tile or stone residential tile flooring to surfaces such as cement or concrete. The application of the mortar adhesive is usually 3/8" thick or less, thus defining the procedure as a "Thinset."
The basic materials used in the tiling industry in the last century have traditionally been Portland cement and sand. They are used to make the mortar to form the mud beds for tile flooring and walls. Portland cement was also the adhesive used to hold the tiles in place. Everything was done over a “mud bed.” The process had been perfected and was well understood by the professions of the forties, fifties and early sixties. There were no “thin set” products or thin set method in place for setting tiles.
With the development of “Greenboard,” or moisture-resistant Sheetrock, in the sixties and cement backer board in the seventies, “thin set” products and setting methods were developed for setting tiles. For residential walls, mud work as we once knew it is too labor-intensive and too heavy for today's residential trends. Ceramic tile floors installed directly over cement or cement backer board can last for the life of the house, and there are isolation membranes that can afford the same long-lasting results. For some special applications, mud set tile installation are still more appropriate.
Floor tile installation using a mud set is labor intensive and adds about $3.00 per/square foot installation cost. The assumption has always been that this process produces the most uniform, durable finished floor for high impact, high traffic areas. There is some validity in that assumption.
A thinset installation is as good as the substrate it covers. If the substrate meets required tolerances, a quality installation can be had. A variety of high performance thinsets gives you strength, flexibility and chemical resistance to meet the requirements of most any environment.
The surface you cover is the key to success in thinset. A mud set mortar installation gives you room for error in the substrate. If the sub-surface has issues that a thinset installation can't accommodate, then a mud set solution becomes the solution by default. Problem involving slab cracks, for instance, can often be solved with a mud set installation where a thin set installation can't.
Keep in mind that even with a mortar bed installation, the installer is still going to use a thinset adhesive.