Why isn’t the water retention of masonry mortar the higher the better

While water retention is essential for ensuring proper hydration of cementitious materials and improving workability, excessive water retention in masonry mortar can lead to several undesirable consequences. Here’s why the principle of “the higher the water retention, the better” does not hold true for masonry mortar:

1. Reduced Strength: Excessive water retention can dilute the cementitious paste in the mortar, leading to lower cement content per unit volume. This results in reduced strength and durability of the hardened mortar, compromising the structural integrity of masonry elements.
2. Increased Shrinkage: High water retention can prolong the drying time of mortar, leading to prolonged shrinkage and increased risk of shrinkage cracks upon drying. Excessive shrinkage can result in reduced bond strength, increased permeability, and decreased resistance to weathering and environmental factors.
3. Poor Adhesion: Mortar with excessive water retention may exhibit poor adhesion to masonry units and substrate surfaces. The presence of excess water can hinder the development of strong bonds between the mortar and the masonry units, leading to reduced bond strength and increased risk of debonding or delamination.
4. Delayed Setting Time: High water retention can prolong the setting time of mortar, delaying the initial and final set of the material. This delay can impact construction schedules and increase the risk of mortar washout or displacement during installation.
5. Increased Vulnerability to Freeze-Thaw Damage: Excessive water retention can exacerbate the susceptibility of masonry mortar to freeze-thaw damage. The presence of excess water within the mortar matrix can lead to increased ice formation and expansion during freezing cycles, resulting in microcracking, spalling, and deterioration of the mortar.
6. Difficulty in Handling and Application: Mortar with excessively high water retention may exhibit excessive sagging, slumping, or flow, making it difficult to handle and apply. This can lead to poor workmanship, uneven mortar joints, and compromised aesthetics in masonry construction.

while water retention is necessary for ensuring adequate workability and hydration of cementitious materials in masonry mortar, excessive water retention can have detrimental effects on the performance, durability, and workability of the material. Balancing water retention with other key properties such as strength, adhesion, setting time, and resistance to environmental factors is essential for achieving optimal performance and longevity in masonry construction.