What causes a vertical crack in an exterior concrete block or brick wall?
Wednesday, March 27, 2019
Vertical cracks are rare in a concrete block or brick wall, because the mortar is usually weaker structurally and the crack will zig-zag along the mortar joints, only occasionally fracturing directly through the brick or block as it continues along. The near-vertical cracking could be caused by settlement, heaving, or soil subsidence due to tree roots, but most often a vertical crack is due to thermal expansion and contraction of a long wall.
One place where a true vertical crack can also occur is at the intersection of two perpendicular masonry walls that are poorly bonded, like in the photo below.
A perfectly vertical crack in the middle of a stucco wall can also occur in a structure behind is wood frame, not block, as in the photo at the top of the page. Cracks can occur in this type of wall for all the same reasons, but tend to happen at the vertical seams where the cement boards under the stucco are abutted. It can also be a hairline vertical crack, like in the photo below, due to thermal expansion/contraction of the underlayment. These cracks should be sealed to maintain a watertight wall, but are not structurally signicant.
Here is an example of an vertical crack in a block wall that runs through both mortar joints and the middle of the block. When a long block or brick wall expands and then contracts, often the contraction is not quite as much as the expansion, and repeated cycles lead to a crack like this.
Although it is a classic example of thermal cracking, it is also somewhat wider at the top than the bottom, as shown below. So settlement has occurred to the ends due to concentrated roof loads there, which was facilitated by the thermal crack.
Although crack patterns can often lead you directly to the underlying problem, sometimes a more in-depth analysis is necessary. See our blog post How do you analyze a crack from cause to effect? for more on this.
Also, see our other posts How do I recognize serious structural problems in a house? and What are the places to look for structural cracks in a house?
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To learn more about exterior walls and structures, see these other blog posts:
How To Look At A House
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