Dryset Mortar

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What is thinset mortar, dryset mortar, or drybond mortar?

Thinset mortar is a blend of cement, very finely graded sand, and a water retention compound that allows the cement to properly hydrate. Tile set by the thinset method is adhered to the substrate with a thin layer of “thinset” cement. The terms thinset cement, thinset mortar, dryset mortar, and drybond mortar are synonymous. This type of cement is designed to adhere well in a thin layer – typically not greater than 3/16th thick. For example, a 3/8″ notch trowel will produce a 3/16th inch thick coating after the tiles are pressed in to the cement. While very minor adjustments in height can be made, this method is not appropriate for adjusting the level or flatness of a surface – rather the tile will follow the plane of the substrate.

The American National Standards Institute (ANSI) defines the properties of thinset mortar in the A118.1 specification.

What is latex-modified thinset?

Thinset cement, to which polymers have been added, is commonly called latex-Portland cement mortar. In fact, this term is a bit of a misnomer. The original polymers used to modify thinset were based on latex and the term originates from their use. Today, there are over 10,000 polymers considered by cement chemists when formulating their products. Polymers such as EVA, PVA, SBR, and others are all commonly used in the industry. Many of these polymers are acrylics and not latex chemicals.

The use of these polymers allows specific properties to be imparted to the cement; commonly, freeze/thaw resistance, improved flexibility, and improved adhesion. There are also polymers used to make the cement waterproof or sufficiently elastic so that it acts like an anti-fracture membrane.

The American National Standards Institute (ANSI) set minimum performance levels for latex-Portland cement mortars in the A118.4, A118.15, and the A118.11 specifications.

What are the advantages of thinset installations?

Thinset applications are less expensive and typically faster to install than mortar bed applications. However, as the tile is bonded directly to the substrate, any variation or movement in the substrate can affect the tile. Also, there are many types of polymer-modified thinsets on the market allowing the specifier the opportunity to match the thinset properties with the project requirements. In many mortar bed installations, the mortar bed will be allowed to cure and then polymer-modified thinset will be used to bond the tile.

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