What happens when mortar dries?

When mortar dries, a process known as hydration occurs. Hydration is the chemical reaction between water and the cementitious materials in the mortar mixture. The primary components of mortar, which undergo hydration, include cement, water, and sometimes additional additives or admixtures. The drying process involves the following key stages:

1. Mixing and Application:
   • Initially, mortar is mixed with water to form a workable paste. This paste is then applied to surfaces for various construction applications, such as bricklaying, tile installation, or rendering.
2. Hydration Reaction:
   • Once applied, the mortar undergoes a chemical reaction known as hydration. This reaction involves the cementitious materials in the mortar binding with water to form hydrates. The primary cementitious material in most mortars is Portland cement.
3. Setting:
   • As the hydration reaction progresses, the mortar begins to set. Setting refers to the hardening or stiffening of the mortar paste. The setting time can vary based on factors such as the type of cement, environmental conditions, and the presence of additives.
4. Curing:
   • After setting, the mortar continues to gain strength through a process called curing. Curing involves maintaining adequate moisture within the mortar for an extended period to allow for the completion of the hydration reaction.
5. Strength Development:
   • Over time, the mortar achieves its designed strength as the hydration reaction continues. The final strength is influenced by factors such as the composition of the mortar mix, curing conditions, and the quality of materials used.
6. Drying (Surface Evaporation):
   • While the setting and curing processes are ongoing, the surface of the mortar may appear to dry. This is due to the evaporation of water from the surface. However, it’s important to note that the hydration reaction and strength development continue within the mortar, even if the surface appears dry.
7. Completion of Hydration:
   • The majority of the hydration reaction occurs within the first few days to weeks after application. However, the process may continue at a slower rate for an extended period.
8. Final Hardening:
   • Once the hydration reaction is complete, the mortar achieves its final hardened state. The resulting material provides structural support, adhesion, and durability.

It’s crucial to follow proper curing practices to ensure that the mortar attains its designed strength and durability. Rapid drying, especially during the early stages of hydration, can lead to issues such as reduced strength, cracking, and poor adhesion. Adequate moisture is essential for the full development of the cementitious materials in the mortar.

The specific characteristics of the dried mortar, including strength, durability, and appearance, depend on factors such as the mix design, curing conditions, and the application technique.