Basic Thin-Set Mortar
Basic thin-set mortars cost less than specialized mortars but do not contain special bonding agents. Basic thin-set mortars are specifically engineered to bond only to basic clay-bodied ceramic tile and porous natural stone tiles like slate and travertine.
Modified Thin-Set Mortar
Thin-set mortar manufacturers add special bonding agents to certain thin-set mortars including acrylic glue agents, creating "modified" thin-set mortars. Modified thin-set mortars provide an extra bond to nonporous materials such as porcelain tile, granite tile and composite tiles. Modified thin-set mortars offer an excellent insurance plan for your hard work by protecting against loose or hollow shower tiles. They are available in a liquid form (which must be added to plain thin-set mortar) or ready-mixed in a bag.
Flexible Thin-Set Mortar
Flexible thin-set mortars are polymer-modified and also containing additional anti-crack components. Flexible thin-set mortars are costlier than traditional and modified thin-set mortars, but offer protection against substrate cracking (up to a certain width). They are ideal for existing shower remodels that require setting new tile over rough, cracked, or older substrate surfaces.
Medium and Thick-Bed Mortar
Medium and thick-bed mortars are also polymer-modified, and contain chemicals and components that protect against sagging and settling issues commonly associated with heavy, large-format tiles and natural stone. Choose this mortar if you plan to install thick natural stone tiles that vary in thickness and weight.