In several recent projects, the owner selected a brick with an IRA less than 3. Can sufficient bond be achieved with this dense of a brick?
IRA (initial rate of absorption) is a measure of how much water a brick absorbs on the surface in 1 minute. As a general rule, the highest bond occurs with brick having IRA values between 5 and 30 grams per minute per 30 square inches of brick surface. Most brick with IRA values less than 5 can achieve sufficient bond. When combined with some mortars, however, some low IRA brick have developed lower than normal bond because the brick tend to float on the mortar. Before using a brick with a low IRA, consider performing bond strength tests on prisms made with the brick and mortar proposed for the project. Other factors, such as the roughness of the brick surface and the mortar type, also influence brick-mortar bond.