The horizontal cracks we see most often are near the ground level of concrete block stem-wall type construction. They are caused by rotation of the footing below ground, due to soil movement or a defect in the bearing below it. The wall usually turns outward along a mortar joint, like in the photo above. where the crack near the ground has been caulked but continues to open further. Heaving or sinking of a thickened-edge concrete slab foundation also causes a horizontal crack line, but usually higher on the wall, like in the photo below, in which the diagonal cracks show that the corner is sinking and the horizontal crack indicates the beginning of rotation.

   Long horizontal cracks near the top of a wall are often actually in the concrete tie beam above the block, and caused by corrosion of the reinforcing steel just below the surface. It is called “spalling”.

    Also, horizontal cracks can also appear along mortar joints in a brick wall when the steel reinforcing “ladders” begin to corrode and pop out the mortar.

    To read more about these two problems, see our blog posts There's cracks running along the home's concrete tie beam. What's wrong? and What would cause long horizontal lines of brick mortar to fall out?  Also, 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.

    And we recommend reading 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?  and What causes a vertical crack in drywall? and What causes stair-step cracks in a block or brick wall?

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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? 

• How does concrete spalling cause structural failure if not repaired?

• 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 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?

• 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? 

• What are those powdery white areas on my brick walls?

• 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?

• How can I tell whether my house foundation problems are caused by a sinkhole or expansive clay soil?

        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.