Bulging in a Clay Brick Wall
What causes a clay brick wall to bulge outward as we see in Photo CBW-1?
A bulging clay brick wall is an unexpected sight to most observers. When one becomes aware of a bulging brick wall one is usually startled at first. One then wonders, “Will this wall fall over?” To that question I can give a definite, “Eventually. Sometimes sooner, sometimes later.”
The first thought is to blame the bulging on the recent wind storm or lightning or other weather event. And, these causes do need to be considered. But, usually there is a more common damage producing mechanism that cause this bulging. The latter is the subject of this article.
The material of clay brick is generally comprised of fired clay. When the brick are removed from the oven they are very dry. As they cool they begin to absorb moisture and swell. This results in the brick units very slowly and permanently becoming larger in size.
Brick also expands and contracts with a change in temperature. When heated by sunshine the brick expand. When they cool at night they shrink. Unfortunately, when some brick expand and then shrink, they don’t return to their original dimensions. This results in the brick very slowly and permanently becoming larger in size.
This swelling and expansion are commonly accommodated with expansion joints. Expansion joints are the vertical and/or horizontal separations that divide the masonry wall into smaller panels or a space at the top of the wall that will accommodate an increase in height of the wall. In larger buildings, especially commercial type buildings, expansion joints often appear as horizontal lines in the brick work at the floor lines or vertical lines spaced at the columns or edges of large windows or spaced horizontally at 25 to 50 feet. (Note here that 25 to 50 feet is probably TOO far apart.)
These joints are usually filled with a soft, squishy sealant material. If these joints are not adequately spaced, that is, spaced too far apart, or the joint is not wide enough, or the brick units expand more than estimated, the wall grows in length and height and squeezes the sealant out of the joints. And if the wall is restrained from growing in length and height, it may buckle outward to accommodate the growth, like a roadway sometimes does in the heat of the summer. This buckling is similar to a yard stick being pushed down against the floor until it bulges outward.
Another mechanism can also cause expansion in a wall: corrosion of the steel lintels over the window or door openings. The corrosion and expansion of the steel makes the joint wider which lifts the brick above the joint (Photo CBW-3). The lifting increases the height of the wall and if it is restrained at the top and bottom, it will buckle and bulge outward.
Thus, there can be one of many or a combination of mechanisms that cause a clay brick wall to bulge outward as seen in the photos.