Initial Rate of Absorption (IRA)

Category: science

A measurement tracking the suction speed of water upward into a dry brick unit during one minute of exposure.

Also called suction, IRA dictates how a brick interacts with wet mortar. If a brick has an excessively high IRA (above thirty grams per minute), it will instantly suck the moisture straight out of the wet mortar bed, causing the mortar to stiffen prematurely and ruining the bond strength.

Common Examples

• Because the clay brick displayed a high initial rate of absorption, the masons pre-wetted the units to prevent mortar bond failure.
• Failing to track the brick unit’s IRA leads to rapid water loss in the mortar, creating micro-fissures along the head joint.