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.
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
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:
Vertical movement is being caused by settlement, frost, or a sink hole or expansive clay soils under and near the foundation wall;
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.
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.
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
cracks in a concrete block wall are more immediately threatening of serious collapse than vertical cracks.
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.
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 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
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.
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 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
that there has been water or roof spillage by the foundation wall
there may be water entry inside the basement or crawl area of the building
that someone knew of this condition as the foundation in one of the photos was painted with a masonry sealer.
The photos of spalling concrete block foundation walls shown above were contributed by Kinston NY home inspector Arlene Puentes. See ABOUT InspectApedia.com 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
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
Some common masonry block (or "concrete block" or "cinder block") foundation or structural wall defects to be observed and reported include:
Leaning or tipping masonry block walls: a concrete block or concrete masonry unit (CMU) wall may tip
inwards at its top (a leaning or tipping wall failure) due to pressure from water and wet soils, from frost, from the
weight of nearby vehicles driving along the wall (oil truck coming to deliver heating oil), or by defects and tipping wall footings.
Buckled concrete block walls: often due to pressure or loading from water, frost, earth, or nearby passage of vehicles -
potentially urgent depending on circumstances and amount. Bulging or buckling masonry block wall failures (shown at above-left) are also called "bending" failures.
Horizontal displacement or "shear failures" occur in concrete block walls, particularly ones which were built without
vertical steel reinforcement, and may be caused by pressure from water and wet soils or other forces. If we observe portions of a wall
sliding horizontally past other wall segments we've found a shear failure.
A common shear failure can be seen when the bottom course
of masonry blocks in a foundation wall is held in place by a floor slab and when the upper portion of the wall has been pushed inwards
so that the upper blocks are projecting past the lower ones.
Such walls are also often tipping or leaning or may be buckled and
broken open along horizontal mortar joints in the wall.
Cracks in concrete block walls: along the mortar joints, or less often right through
the masonry blocks themselves, can be the result of pressure from water and wet soils, frost, nearby vehicles, or
differential settlement in a footing.
If a foundation wall crack is vertical and fairly uniform in width, but the wall on
one side of the crack is higher than on the other, we're looking at differential settlement which will probably be
traced to the footings.
If a foundation wall crack is vertical and wider at its top than its bottom, we may be looking
at footing settlement in which the footings have "bent" and settled unevenly, such as when a footing has been placed
over unevenly compacted fill or where there was bedrock or a large boulder under a portion of the footing permitting
settlement such that the footing has settled down on one or both sides of this "high point".
At least one author also
posed that a concrete masonry unit wall which has a vertical crack near its center and whose crack is wider at its top
than bottom has cracked due to wall shrinkage along its length.
His explanation was that the top of the wall was free
to shrink but its bottom was held in place by the footing, making a crack wider at top than bottom. However
other experts (D.Wickersheim) assert that concrete block walls do not shrink significantly during curing, though wet masonry
blocks might change a bit in dimension during drying.
Crack patterns in concrete or other masonry foundation walls can occur as vertical, diagonal, stair-stepped, or
horizontal patterns which we discuss and among which we distinguish in more detail at FOUNDATION CRACK DICTIONARY
Missing components such as headers where the wall has been modified, steel reinforcement wire or re-bar (if required by local codes).
Missing footings, piers or other reinforcement
Impact damage which has broken masonry blocks or dislocated them
Point loading cracks or fractures
Other cracks through or across concrete blocks as opposed to cracking in the mortar joints.
Unlike poured concrete, concrete blocks do not shrink with age or curing. When investigating cracks through concrete blocks, check the other possibilities.
Poured concrete sister walls, additions of pilasters, additions of steel reinforcement, or repeated re-coating
of a wall with parging cement are all indications of past damage and/or water entry problems that merit further evaluation
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.
Questions & answers or comments about damaged concrete block foundations: causes, crack & movement patterns, diagnosis, repair, inspection procedures..
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Diagnosing & Repairing House Structure Problems, Edgar O. Seaquist, McGraw Hill, 1980 ISBN 0-07-056013-7 (obsolete, incomplete, missing most diagnosis steps, but very good reading; out of print but used copies are available at Amazon.com, and reprints are available from some inspection tool suppliers). Ed Seaquist was among the first speakers invited to a series of educational conferences organized by D Friedman for ASHI, the American Society of Home Inspectors, where the topic of inspecting the in-service condition of building structures was first addressed.
Defects and Deterioration in Buildings: A Practical Guide to the Science and Technology of Material Failure, Barry Richardson, Spon Press; 2d Ed (2001), ISBN-10: 041925210X, ISBN-13: 978-0419252108. Quoting: A professional reference designed to assist surveyors, engineers, architects and contractors in diagnosing existing problems and avoiding them in new buildings. Fully revised and updated, this edition, in new clearer format, covers developments in building defects, and problems such as sick building syndrome. Well liked for its mixture of theory and practice the new edition will complement Hinks and Cook's student textbook on defects at the practitioner level.
Masonry structures: The Masonry House, Home Inspection of a Masonry Building & Systems, Stephen Showalter (director, actor), DVD, Quoting: Movie Guide Experienced home inspectors and new home inspectors alike are sure to learn invaluable tips in this release designed to take viewers step-by-step through the home inspection process. In addition to being the former president of the National Association of Home Inspectors (NAHI), a longstanding member of the NAHI, the American Society of Home Inspectors (ASHI), and the Environmental Standard Organization (IESO), host Stephen Showalter has performed over 8000 building inspections - including environmental assessments. Now, the founder of a national home inspection school and inspection training curriculum shares his extensive experience in the inspection industry with everyday viewers looking to learn more about the process of evaluating homes. Topics covered in this release include: evaluation of masonry walls; detection of spalling from rebar failure; inspection of air conditioning systems; grounds and landscaping; electric systems and panel; plumbing supply and distribution; plumbing fixtures; electric furnaces; appliances; evaluation of electric water heaters; and safety techniques. Jason Buchanan --Jason Buchanan, All Movie Review
Arlene Puentes, ASHI, October Home Inspections - (845) 216-7833 - Kingston NY
Greg Robi, Magnum Piering - 800-822-7437 - National*
Dave Rathbun, P.E. - Geotech Engineering - 904-622-2424 FL*
Ed Seaquist, P.E., SIE Assoc. - 301-269-1450 - National
Dave Wickersheimer, P.E. R.A. - IL, professor, school of structures division, UIUC - University of Illinois at Urbana-Champaign School of Architecture. Professor Wickersheimer specializes in structural failure investigation and repair for wood and masonry construction. * Mr. Wickersheimer's engineering consulting service can be contacted at HDC Wickersheimer Engineering Services. (3/2010)
*These reviewers have not returned comment 6/95
Books & Articles on Building & Environmental Inspection, Testing, Diagnosis, & Repair
Sinkholes and Sudden Land Subsidence References, Products, Consultants
"A Hole in the Ground Erupts, to Estonia's Delight", New York Times, 9 December 2008 p. 10.
History of water usage in Estonia: (5.7 MB PDF) jaagupi.parnu.ee/freshwater/doc/the_history_of_water_usage_systems_in_estonia.pdf
"Quebec Family Dies as Home Vanishes Into Crater, in Reminder of Hidden Menace", Ian Austen, New York Times, 13 May 2010 p. A8. See http://www.nytimes.com/
"Quick Clay", Wikipedia search 5/13/2010 - http://en.wikipedia.org/wiki/Quick_clay
Florida DEP - Department of Environmental Protection, & Florida Geological survey (http://www.dep.state.fl.us/geology/default.htm) on Florida sinkholes: Effects of Sinkholes on Water Conditions Hernando County, Florida, Brett Buff, GIS in Water Resources, 2008, Dr. David R. Maidment, Photos - Tom Scott, Florida Geographic Survey - Web Search 06/09/2010 - http://www.dep.state.fl.us/geology/geologictopics/jacksonsink.htm
and - http://www.dep.state.fl.us/geology/geologictopics/sinkhole.htm
Lane, Ed, 1986, Karst in Florida: Florida Geological Survey Special Publication 29, 100 p.
Foundation Engineering Problems and Hazards in Karst Terranes, James P. Reger, Maryland Geological Survey, web search 06/05/2010, original source: http://www.mgs.md.gov/esic/fs/fs11.html Maryland Geological Survey, 2300 St. Paul Street, Baltimore, MD 21218
"Frost Heaving Forces in Leda Clay", Penner, E., Division of Building Research, National Research Council of Canada, Canadian Geotechnical Journal, NRC Research Press, 1970-2, Vol 7, No 1, PP 8-16, National Research Council of Canada, Accession number 1970-023601, Quoting from original source
The frost heaving forces developed under a 1 ft. (30.5 cm) diameter steel plate were measured in the field throughout one winter. The steel plate was fixed at the ground surface with a rock-anchored reaction frame. heave gauges and thermocouples were installed at various depths to determine the position and temperature of the active heaving zone. The general trend was for the surface force to increase as the winter progressed. when the frost line approached the maximum depth the force was in excess of 30,000 lb (13,608 KG). Estimates of the heaving pressure at the frost line ranged from 7 to 12 psi (0.49 to 0.84 KG/cm) square during this period. The variation of surface heaving force was closely associated with weather conditions. Warming trends resulting in a temperature increase of the frozen layer caused the forces to decline.
Leda clay slopes in the Ottawa valley are vulnerable to catastrophic landslides. More than 250 landslides, historical and ancient, large and small, have been identified within 60 km of Ottawa. Some of these landslides caused deaths, injuries, and property damage, and their impact extended far beyond the site of the original failure. In spectacular flowslides, the sediment underlying large areas of flat land adjacent to unstable slopes liquefies. The debris may flow up to several kilometres, damming rivers and causing flooding, siltation, and water-quality problems or damaging infrastructure. Geologists and geotechnical engineers can identify potential landslide areas, and appropriate land-use zoning and protective engineering works can reduce the risk to property and people.
Deposits of Leda clay, a potentially unstable material, underlie extensive areas of the Ottawa-Gatineau region. Leda clay is composed of clay- and silt-sized particles of bedrock that were finely ground by glaciers and washed into the Champlain Sea. As the particles settled through the salty water, they were attracted to one another and formed loose clusters that fell to the seafloor. The resulting sediment had a loose but strong framework that was capable of retaining a large amount of water. Following the retreat of the sea, the salts that originally contributed to the bonding of the particles were slowly removed (leached) by fresh water filtering through the ground. If sufficiently disturbed, the leached Leda clay, a weak but water-rich sediment, may liquefy and become a 'quick clay'. Trigger disturbances include river erosion, increases in pore-water pressure (especially during periods of high rainfall or rapid snowmelt), earthquakes, and human activities such as excavation
After an initial failure removes the stiffer, weathered crust, the sensitive clay liquefies and collapses, flowing away from the scar. Failures continue in a domino-like fashion, rapidly eating back into the flat land lying behind the failed slope. The flowing mud may raft intact pieces of the stiffer surface material for great distances.
Kochanov, W. E., 1999, Sinkholes in Pennsylvania: Pennsylvania
Geological Survey, 4th ser., Educational Series 11,
33 p., 3rd printing April 2005, Pennsylvania Department of Conservation and Natural Resources / Bureau of Topographic and Geologic Survey, DCNR Educational Series 11, Pennsylvania Geological Survey, Fourth Series, Harrisburg,
1999 - web search 06/05/2010, original source: http://www.dcnr.state.pa.us/topogeo/hazards/es11.pdf - Quoting from the document introduction: The first 18 pages of this booklet contain an explanation of how sinkholes
develop. In order to tell the sinkhole story, it is important to discuss
a number of related geologic disciplines. The words used to describe sinkholes
and these disciplines may be a bit unfamiliar. However, general explanations
are given throughout the booklet to help clarify their meanings.
Key words are printed in bold type for emphasis. The more important
ones are defined in a Glossary that begins on page 29.
The remaining sections, starting with “Sinkholes in the Urban Environment”
(page 18), deal with sinkholes and their impact on our environment.
This includes recognition of subsidence features and sinkhole repair.
 Sarah Cervone, [web page] data from the APIRS database, Graphics by Ann Murray, Sara Reinhart and Vic Ramey, Vic Ramey is
the editor. DEP review by Jeff Schardt and Judy Ludlow. The web page is a
collaboration of the Center for Aquatic and Invasive Plants, University of Florida, and the Bureau of Invasive
Plant Management, Florida Department of Environmental Protection contact: firstname.lastname@example.org [A primary resource for this article
 Center for Cave and Karst Studies or the Kentucky Climate Center, both at Western Kentucky University
Vanity Fair - web search 06/04/2010 http://www.vanityfair.com/online/daily/2010/06/what-caused-the-guatemala-sinkhole-and-why-is-it-so-round.html
Sinkholes, Virginia Division of Mineral Resources,
Virginia Department of Mines, Minerals and Energy, www.dmme.virginia.gov Virginia Department of Mines, Minerals and Energy Division of Mineral Resources
900 Natural Resources Drive, Suite 500 Charlottesville, VA 22903 Sales Office: (434) 951-6341 FAX : (434) 951-6365 Geologic Information: (434) 951-6342
http://www.dmme.virginia.gov/ divisionmineralresources.shtml - Web search 06/09/2010
Sink Hole & Related Engineering References
Newton, J. G., 1987, Development of sinkholes resulting from man's activities in the eastern United States: US Geological Survey Circular 968, 54 p.
Sinclair, W. C., 1982, Sinkhole development resulting from ground-water withdrawal in the Tampa Area, Florida: U.S. Geological Survey Water-Resources Investigations 81-50, 19 p.
White, W. B., 1988, Geomorphology and Hydrology of Karst Terrains: Oxford University Press, New York, 464 p.
Williams, J. H. and Vineyard, J. D., 1976, Geologic indicators of subsidence and collapse in karst terrain in Missouri: Presentation at the 55th Annual Meeting, Transportation Research Board, Washington, D.C.
Barry F. Beck, A. J. (1999). Hydrogeology and Engineering Geology of Sinkholes and Karst. Rotterdam, Netherlands: A. A. Balkema.
Beck, B. F. (2003). Sinkholes and the Engineering and Environmental Impacts of Karst. Huntsville, Alabama: The American Society of Civil Engineers.
Beck, B. F. (2005). Sinkholes and the Engineering and Envrionmental Impacts of Karst. San Antonio, Texas: The American Society of Civil Engineers.
Tony Waltham, F. B. (2005). Sinkholes and Subsidence, Karst and Cavernous Rocks in Engineering and Construction. Chichester, United Kingdom: Praxis Publishing.
Whitman D., G. T. (1999). Spatial Interrelationships Between Lake Elevations, Water Tables, and Sinkhole Occurence in Central Florida: A GIS Approach. Photogrammetric Engineering and Remote Sensing , 1169-1178.
Sinkholes in Guatemala, Guatemala City, Wikipedia - web search 06/04/2010 - http://en.wikipedia.org/wiki/Guatemala_City
Carson, Dunlop & Associates Ltd., 120 Carlton Street Suite 407, Toronto ON M5A 4K2. Tel: (416) 964-9415 1-800-268-7070 Email: email@example.com. The firm provides professional home inspection services & home inspection education & publications. Alan Carson is a past president of ASHI, the American Society of Home Inspectors. Thanks to Alan Carson and Bob Dunlop, for permission for InspectAPedia to use text excerpts from The Home Reference Book & illustrations from The Illustrated Home. Carson Dunlop Associates' provides extensive home inspection education and report writing material.
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The Home Reference Book - the Encyclopedia of Homes, Carson Dunlop & Associates, Toronto, Ontario, 25th Ed., 2012, is a bound volume of more than 450 illustrated pages that assist home inspectors and home owners in the inspection and detection of problems on buildings. The text is intended as a reference guide to help building owners operate and maintain their home effectively. Field inspection worksheets are included at the back of the volume.
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