Small pop-outs are appearing in brick units of a newly completed building. These pop-outs seem to have a white particle at the base, which appears to be the source of the problem.

What is the actual cause?

The problem is caused by the expansion of an inclusion at the base of the pop-out. Because the inclusion in this case is white in color, it may be caused by the presence of free lime (CaO) in the clay body. If inclusions of free lime occur near the surface of the brick unit, pop-outs can be formed as the free lime hydrates and becomes calcium hydroxide [Ca(OH)2]. This reaction results in a volume increase. Exposure to air, and consequently to carbon dioxide in the air, forms calcium carbonate (CaCO3).

If there are a significant number of free lime inclusions throughout the brick unit, future hydration of the free lime to calcium hydroxide could result in further distress and deterioration of the brick unit. The pop-outs also can result in small white streaks if rainwater dissolves the inclusion before it carbonates.

Free lime inclusions can occur in clay brick if the materials used to make the units contain limestone particles. These particles can be changed into free lime as a result of the high temperatures required during the firing of the brick units.

I recommend looking at buildings that are several years old and built with the same brick to see if they are experiencing these problems and if further deterioration has occurred. The pop-outs may be limited to the few that develop shortly after construction, or in some cases may result in delaminations within the brick unit.

The effect of these deposits may be accelerated by heating the brick units for 24 hours or more in an autoclave, such as that used for the crazing resistance test method of ASTM C 126, Ceramic Glazed Structural Clay Facing Tile, Facing Brick, and Solid Masonry Units. This method should cause the free lime deposits within the clay body to hydrate. The likely long-term effect on the clay unit within the wall can be approximated by carefully examining the units before and after autoclaving.

I further recommend submitting samples of brick units that contain these pop-outs to a concrete petrographer or analytical chemist to determine the cause. Depending on the test results, they are able to make some judgments as to the likelihood that these problems will continue.