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

Tuesday, June 26, 2018

A stair-step crack is a diagonal crack but, since mortar is usually not as strong as concrete block or brick, the crack migrates to the mortar joints as it zigzags along a path of least resistance. Sometimes a stair-step crack will mostly follow the mortar joints, then take a short-cut through a defective block or brick, before returning to the stair-step pattern. 

    If you draw a line through the center of a diagonal stair-step crack, then draw a perpendicular arrow to it, you will have the approximate direction of movement—either up or down—of the crack. Many cracks have a “hinge point” at one end and loosely pivot around that point, with the opposite end being wider. Others move more uniformly.


    This crack pattern usually indicates settlement of the corner of a structure (blue arrows). The corner of the house is “laying down,” like the severe example shown below. But it can also indicate heaving of the area to the left of the crack (green arrows), and sometimes requires close examination to determine which side is moving.

    A pyramid shaped crack of joined diagonals, as in the diagram below, is usually indicative of subsidence (dropping) of the area under the pyramid. Because window openings are weak spots when a wall is having settlement or heaving problems, diagonal cracks emanating from the corner of a window are common.


    When the surface of one side of a stair-step crack is forward of the other side, which is what we call “differential,” it indicates a more significant structural problem. One side is rotating, like in the photo below.

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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 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 serious structural problems in a house?

What is engineered wood siding?

Should I buy a house that has had foundation repair? 

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? 

How do I recognize serious structural problems in a house?

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?

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?

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. 


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