What is Thinset Mortar and Where is it Used?

Thinset mortar is an adhesive mix that is made of cement, fine sand, and a water-retaining agent. Thinset mortar is also referred to as thin-set cement, dry-set mortar or dry-bond mortar, or simple mortar.

What is Thinset Mortar and Where is it Used?

Thinset mortar is commonly used to adhere tiles on walls made of cement substrate. These come either as a dry mix that requires mixing or as a pre-mixed bucket that can be applied instantly after opening. The bonding agent and water-retaining agent used for thin mortar preparation vary based on the requirement and hence there are various types of thinset mortar.

Thinset cannot be used for every type of tile application and hence here is a quick guide on different types of thinset mortar and applications.

Types of Thinset Mortar

Thinset has two major classifications:

1. Unmodified Thinset
2. Modified Thinset

Both the mortar mix achieve better quality when they are well-cured so that the hydration products of the mixes are of good quality. Good and complete hydration of mortar requires maintaining a moisture level until the mortar sets.  

Unmodified Thinset Mortar

Unmodified thinset mortar is the simplest mortar with a composition of Portland cement, sand, and water retaining agents. These mortars are also referred to as dry-set mortars. 

These mortars gain strength depending on the moisture that is available for their hydration (curing or hardening). It is used in areas where the chances to retain moisture are less.

Unmodified thin-set mortars are covered by ANSI Standard A118.1: American National Standard Specifications for Dry-Set Cement Mortar.

Modified Thinset Mortar

Modified thinset mortar employs Portland cement, sand, water retaining agents, and required bonding agents like acrylic or liquid latex polymers. In a few conditions, chemical-resistant agents are added to the mix in modified thinset mortar. These mortars gain strength by losing moisture i.e. these mortar get stronger as it dries or cures.

Compared to unmodified thinset mortar, this type has better chances to retain moisture to perform better hydration and hardening. 

Modified mortars are covered by ANSI Standard A118.4 American National Standard Specifications for Modified Dry-Set Cement Mortar.

Difference Between Unmodified Thinset Mortar & Modified Thinset Mortar

Unmodified Thinset Mortar	Modified Thinset Mortar
Unmodified mortar shrinks that result in cracks.	Modified thinset does not shrink as much as unmodified mortar and results in fewer cracks.
Uses natural moisture to create interlocking bonds for security and stability.	Modified thinset has extra additives to sustain the moisture content and interlocking crystals to secure the bond between the tile and substrate. Longer the moisture stronger the bond.
Requires less curing time compared to modified thinset	Modified thinset is rich in moisture that requires air to conduct evaporation and thorough curing time when compared to unmodified mortar.

How to Choose Between Modified and Unmodified Thinset Mortar?

Based on the variations of moisture content and curing time demands for both types, unmodified thinset is used where the chances of ambient airflow are less, and modified thinset is used in applications where there is plenty of curing time available before the next layer.

Applications of Unmodified Thinset Mortar	Applications of Modified Thinset Mortar
Laying tiles on an impervious installation membrane, especially waterproof applications and flooring with waterproof underlayments.	Installation of porcelain tiles and glass tiles
Using as a mortar layer between two impermeable membranes (sandwiched) where drying occurs only through open grout joints. (Prodeso)	Installations over plywood substrates
Installation of ceramic and natural stone	Luxury stones and tile installations, as they are easy to work with.

 

Tiles Installed Over Uncoupling Membranes

Uncoupling membranes, waterproof membranes, and crack-isolation membranes may demand a thinset based on the membrane manufacturer’s instructions. Some of the uncoupling membranes may require a dry thin-set and a modified thin-set mortar.

ALSO READ: What are the Different Types of Adhesives for Tiles?