Photograph of - cracked  masonry block foundation wall, probably from earth pressur at original construction - notice the wavy mortar. Drop a plumb line to measure total inwards bulging of this block foundation wall. Types of Cracks in Block Foundation Walls
Crack detection & crack evaluation

  • BLOCK FOUNDATION & WALL DEFECTS - CONTENTS: How to Inspect & Diagnose Concrete Block Foundation Cracks, Leans, Bows, Settlement - Masonry block or "cinder block" foundation defects listed, described & explained; Concrete block or "cinderblock" or concrete masonry unit (CMU) foundation inspection procedures are provided. Cracked block foundation walls; spalled block foundation walls, leaning, or settled block foundation walls are discussed here.
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Damaged masonry block foundations & walls:

How to Inspect & Diagnose Concrete Block Foundation Cracks, Leans, Bows, Settlement. This article explains concrete block or "cinder block" or concrete masonry unit (CMU) foundation inspection procedures and the diagnosis of cracks, bulges, leaning, bowing, and settlement in concrete block foundations and building walls such as damage due to impact, settlement, frost or water damage, and other causes.

Types of foundation cracks, crack patterns, differences in the meaning of cracks in different foundation materials, site conditions, building history, and other evidence of building movement and damage are described to assist in recognizing foundation defects and to help the inspector separate cosmetic or low-risk conditions from those likely to be important and potentially costly to repair.

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How to Identify, Diagnose, & Evaluate Masonry Block (concrete & "cinder block") Foundation & Wall Damage

Photograph of a masonry block foundation collapse

Article Series Contents

[Click to enlarge any image]

Bulged, collapsing concrete block walls

Photograph of a masonry block foundation collapse and repair

The masonry block foundation at the house in these photographs collapsed after a period of heavy rain. The underlying problem was in-slope grade at the rear of the home and trapped roof spillage there, causing lots of heavy wet earth pressure on the wall.

The home inspector had previously observed water damage at the wall and had correctly assessed the outside conditions. The owners had deferred action to prevent further water damage, leading to an unexpected and sudden precipitous collapse of the foundation after a period of unusually wet weather. [Left hand photograph courtesy of Alan Carson, Carson Dunlop, Toronto. These photos are of two different buildings.]

Diagonal Cracks or Step Cracks in Block Walls & Foundations

Photograph of diagonal cracking in concrete block

A diagonal crack can appear in many structural materials and components including block, brick, and concrete foundation walls, chimneys, and and building interior drywall or plaster.

Diagonal cracking usually indicates actual vertical movement in the structure or differential settlement: diagonal cracking in masonry structures usually indicates differential settlement, occasionally frost heaves and more rarely the development of a sink hole under or near the foundation.

Our photo above, discussed at VERTICAL MOVEMENT IN FOUNDATIONS, illustrates severe structural damage to a concrete block foundation wall. Closer inspection shows both stair-step cracking and bulging in this wall, probably due to water and frost pressure from outside.

Diagonal cracks (actually in the form of a stair-step in masonry-unit walls) can appear anywhere in a wall but most often they appear near the building corners. Explanations for the diagonal or stair-step cracks in concrete blocks or bricks near a corner include at least these factors:

  1. Vertical movement is being caused by settlement, frost, or a sink hole or expansive clay soils under and near the foundation wall;
  2. The added resistance to movement afforded by the nearby intersecting wall at the corner causes cracking to appear in a stair-step form following the mortar joints in the concrete block or brick whereas the same settlement or heaving forces might have caused more nearly-vertical cracks if they had occurred closer to the center of the wall.

    In our concrete block wall crack photo shown below you can see both step cracks at the wall corner and a horizontal crack at the bottom of the upper 1/3 of the wall - describing what I think is just this condition.
  3. In areas of freezing weather or expansive soils, spilling of a roof drainage system downspout by the building corner may be concentrating water in that location.

See DIAGONAL CRACKS in BLOCK FOUNDATIONS, WALLS for details about diagonal cracks in both concret block and poured concrete foundation walls and for advice about evaluating the severity of damage.


Frost push damage to foundation wall (C) D Friedman A Carson

Cracks occurring near foundation corners in a masonry block wall are often from water and frost. In freezing climates, "frost lensing" can cause soil to stick to and lift a building foundation when the ground freezes.

These cracks are usually visible in the portion of the concrete block foundtion that remains above grade. The forces at work and this stair-step plus horizontal block wall crack pattern are described in point #2 of the discussion just above.

Horizontal Cracks in Masonry Block Walls

Horizontal cracks in a concrete block wall are more immediately threatening of serious collapse than vertical cracks.

Severely bulged block foundation wall (C) Daniel Friedfman Alan Carson

But for small horizontal cracks (say 1/16" wide) and walls that have minimal bowing (say < 1" inwards) the block wall foundation collapse risk estimate may be reduced.

And where history indicates that the damage is old, perhaps from a single event (damaged during backfill, for example) and not ongoing, the urgency of repair may also be reduced.


An assessment of these factors as well as the effect on the rest of the structure are important.

The photo at above eft illustrates severe bulging in a concrete block foundation wall. The location of the cracks combined with outside observation of backfill level suggests this damage is due to water, frost, and earth pressure.

Photograph of - bowed foundation wall, probably from frost cracking. Drop a plumb line to measure total inwards bulging of this block foundation wall.

In masonry block construction, foundation or wall cracks occur more commonly in mortar joints but can also occur across and through the blocks themselves.

At left we illustrate a wide horizontal crack along the mortar joint of a concrete block foundation wall. The wall also is bulged inwards; measurements showing more than in inch of inwards bow meant that expert evaluation (and probable reconstruction) were in order for this structure.

Vertical Cracking in Concrete Block Walls

Vertical crack at center of block foundation wall (C) Daniel Friedman

Vertical cracks in block foundation walls & expansion and shrinkage cracks in a concrete block wall may occur but are less common than in some other materials.

Our photo above shows step cracks on either side of a large vent opening in the center of a masonry block foundation wall. No header was used across the wall opening top and the two single concrete blocks simply fell-inwards. That movement may explain the step cracks around the top and sides of the opening.

Cracks in masonry walls tend to be more severe in the center of walls from external loading and pressure (from any source).

The damage to the wall occurred during backfill - pressure from both the backfill earth itself and the machine operator who drove heavy equipment too close to the foundation wall. It is possible that that same event caused what appears to be a vertical crack below the window - thought that's unusual: usually backfill produces bulging and horizontal cracks in the mortar joint.

Perhaps the wall was constructed without steel mesh nor other reinforcement.

Vertical crack in a concrete block wall: cause & repair? (C) JSA

Above: a very straight vertical crack in a concrete block foundation wall, extending from the basement floor slab to the top of the foundation wall. The possible causes and need for remedy or repair for this crack damage are discussed at VERTICAL CRACKS in BLOCK WALLS


Spalling Concrete Block Walls & Foundations

Spalling is defined as the flaking off or loss of material in masonry block, brick, concrete or other masonry structures, usually caused by the action of freezing water that has penetrated the masonry surface. Spalling damage ranges from cosmetic to serious, costly and dangerous. Spalling concrete block may tell us about the the history of building construction, movement, events can help diagnose concrete block foundation cracks & damage.

If there is superficial spalling of the block - less than 3/4" deep into the block surface, and if there is no bulging, cracking, settlement, movement, crushing, then most likely we're talking about a water entry and moisture issue and a cosmetic issue. Below the spalling concrete block foundation wall damage is in my opinion superficial and cosmetic, not structural, but it does tell us

  1. that there has been water or roof spillage by the foundation wall
  2. there may be water entry inside the basement or crawl area of the building
  3. that someone knew of this condition as the foundation in one of the photos was painted with a masonry sealer.

Spalling concrete foundation wall - masoanry block damage (C) InspectAPedia Arlene Puentes Spalling concrete foundation wall - masoanry block damage (C) InspectAPedia Arlene Puentes

The photos of spalling concrete block foundation walls shown above were contributed by Kinston NY home inspector Arlene Puentes. See ABOUT for her contact information.

We use the term concrete blocks in these articles where others may refer to this same construction material as concrete masonry unit (CMU), masonry blocks, cement blocks, or cinder blocks. Concrete blocks vary in quality, mostly as a function of the era in which they were made and the raw materials used.

Structural Damage From Spalling Concrete or Masonry Block

Cracking spalling chimney exterior (C) Daniel Friedman Disintegrating cinderblock pilaster (C) Daniel Friedman

At above left the chimnney has been badly damaged by frost: even inspecting from the ground we can see cracks, movement, spalling concrete blocks, and stains indicating that the flue interior is leaking to the chimney exterior. This is an unsafe chimney risking fire or other damage: inspection and repair or replacement are urgently needed.

The photograph at above right illustrates severe spalling damage to a concrete block pilaster. This is enough damage to be considered a structural concern as the pilaster is part of the structure supporting the building above.

Some concrete block, particularly older masonry block containing a high percentage of sand, cinders, or dirt and not enough concrete may be more vulnerable to water damage and spalling damage.

Henry Page Sr. in Poughkeepsie, NY in the early 1900's dug up the family farm, mixed dirt, cinders, and cement using a Sears & Roebuck cinder block kit to make masonry blocks that were used throughout Dutchess County. In time many of these blocks spalled and disintegrated badly where they were exposed to rain splash-up at ground level. But rarely did these flimsy versions of the modern (and harder, stronger, concrete block) lead to a building failure from their innate properties. Rather most building failures involving concrete block are our own fault - causes which we inventory in this article series.

Spalling brick at chimneys and at structural or veneer walls are discussed separately at


Key Defects List for Concrete Block Walls

Severe horizontal cracking in a concrete block foundtaion wall (C) Daniel FriedmanSome common masonry block (or "concrete block" or "cinder block") foundation or structural wall defects to be observed and reported include:


Continue reading at BLOCK FOUNDATION BACKFILL DAMAGE or select a topic from closely-related articles below, or see our complete INDEX to RELATED ARTICLES below.






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Concrete Block Foundation & Wall Damage Articles

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