One of the most common and preferred setting materials for tile is thinset mortar. Also referred to as thinset, mud, mortar, and other names, thinset is a cement-based adhesive, or bonding mortar, that is used to adhere tile to the substrate. It is a mixture of portland cement, fine sand, and a water retention compound. There are both modified and unmodified thinsets available.
Thinset comes in a dry, powder form that must be mixed with water before using. For the proper results, the water must be mixed with the thinset, allowed to slake, and mixed again before using. Slaking refers to allowing the water to permeate the thinset for a specific amount of time so that the chemicals can interact and become workable. While there are some thinsets sold premixed in buckets, these are not actually thinsets but rather mastic with sand. Always follow the manufacturer’s instructions for mixing thinsets.
When a latex additive or other polymer bonding agent is added to a thinset, it becomes a modified thinset. These additive polymers may be in a powdered or liquid form. The powdered thinset may already have the polymers added and just needs to be mixed with water, or the additives may be added manually, such as mixing the thinset with a liquid latex additive instead of water.
Adding a latex additive or other polymer agent will help the thinset mix retain water for more durability, better flexibility, and increased bonding power. Flexibility is important for allowing the tile or stone the ability to move and fluctuate through the seasons. Specialty polymer agents can also add particular properties to the thinset mix to meet specific installation requirements. Premium modified thinsets will have a higher polymer ratio and be stronger but will also be more expensive.
Modified thinsets can be used in most applications and installations. Unlike unmodified thinsets that cure through only a chemical process, however, modified thinsets cure through a chemical process and a drying process. Because of this, there are certain circumstances where a modified thinset should not be used. For example, with Schluter-DITRA installations, modified thinsets are not recommended. When a modified thinset is between two impervious materials such Schluter-DITRA and ceramic tile, it can take weeks for a modified thinset to fully dry.