Q: What role does mortar play in a cohesive brick wall?

A: Mortar is a critical factor for a brick wall. It is the ingredient that holds the brick together, keeps brick apart and most importantly, prevents moisture from getting through the wall. In order to keep moisture from penetrating the mortar joints, the joints must be filled as much as possible and the brick and mortar need as much surface area bonding as possible.

There are many variables that affect the surface area bonding. Examples include:

• Brick texture
• Type of mortar
• Air content of the mortar
• Lime content of the mortar
• Water content of the mortar
• Coarseness of the sand
• IRA of the brick
• Fullness of the mortar joints
• Workability of the mortar

Workability is influenced by many factors. Higher air content improves workability and durability, but it reduces bond strength and surface area bond. Hydrated lime improves workability, bond, water retentivity, and elasticity and helps to seal cracks and voids. However it tends to make the mortar more expensive and may require additional material to be handled at the job site. Higher water content may improve workability, but too much water thins the mortar so it cannot hold the brick in position. The strength of the mortar goes down as the water content increases. Sand that contains more large size particles tends to make mortar more workable than sand that contains many small particles. This tends to make the mortar pastier.

Note: There are two generic types of mortar. One is Portland cement with hydrated lime and the other is masonry cement. Normally both types provide similar moisture resistance; however the PCL has higher bond strengths. Each of these mortars is classified into a type N and a type S. Type N must have a compressive strength of 750 PSI, and type S must have a compressive strength of 1800 PSI.