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. 


    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:

 What is the average lifespan of a house foundation?

 What causes vertical cracks in fiber cement siding planks?

 • What causes raised white lines of residue on a block wall that are crusty and crumbling? 

 What is the difference between soil subsidence, heave, creep, and settlement? 

 How much ventilation is required for the under-floor crawl space of a home? 

 What causes stair-step cracks in a block or brick wall?

 What causes a horizontal crack in a block or brick wall? 

 How can I tell if a diagonal crack in drywall at the corner of a window or door indicates a structural problem?

 What causes the surface of old bricks to erode away into sandy powder? 

 What are the pros and cons of concrete block versus wood frame construction?

 Should I buy a house with a crawl space? 

 Why is my stucco cracking? 

 There's cracks running along the home's concrete tie beam. What's wrong? 

 What would cause long horizontal lines of brick mortar to fall out?

 How do I recognize structural problems in a retaining wall? 

 What is engineered wood siding?

 What is a "continuous load path”?

 Should I buy a house with asbestos siding?   

 How can I tell if cracks in the garage floor are a problem or not? 

 What do you look for when inspecting vinyl siding?

 Why is housewrap installed on exterior walls under the siding? 

 Why did so many concrete block homes collapse in Mexico Beach during Hurricane Michael? 

 How can I tell if the concrete block walls of my house have vertical steel and concrete reinforcement?

 Should I buy a house with structural problems? Should I buy a house that has had foundation repair? 

  What are those powdery white areas on my brick walls?

 What causes cracks in the walls and floors of a house?

 How can I tell if the exterior walls of a house are concrete block (CBS) or wood or brick?

 What are the common problems of different types of house foundations? 

• What are the warning signs of a dangerous deck?

    Visit our EXTERIOR WALLS AND STRUCTURE page for other related blog posts on this subject, or go to the INDEX for a complete listing of all our articles.

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