- POST a QUESTION or READ FAQs about how to repair cracked or settled concrete slabs, floors, or foundations
- Fixing Hairline Cracks In New Concrete
- Fill Hairline Cracks In Concrete Floor
- Hairline Cracks In New Concrete
- Fixing Hairline Cracks In Concrete Driveway
- Fixing Hairline Cracks In Concrete Walls
- Fixing Hairline Cracks In Concrete
- Hairline Crack In Concrete Definition
Hairline cracks that are too narrow for sand are filled and repaired with two passes of the CrackWeld resin. To repair wide cracks or cracks with a void underneath, first fill the crack partially with sand to prevent the CrackWeld resin from running out. Basic steps for repairing a basement floor crack. Hairline concrete cracks can be done without the sand. Wide concrete cracks can first be filled partially with the sand then start with step 2. This crack weld material sets up very quickly, only do 10 - 15 feet at one time. How to Build and setup a Concrete Foundation for Garages, Houses, Room additions, Etc Part 1 - Duration: 30:30. Odell Complete Concrete 3,463,406 views.
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Concrete slab crack repair methods:
This article describes methods for repair of cracks that occur in poured concrete slabs or floors and explains the need for accurate crack cause diagnosis and impact on structure before repairs are attempted.
Cracks in concrete floors or slabs occur in poured concrete slabs may be found both in basement and in slab on grade or 'patio home' construction and have a variety of causes and cures that we discuss here. This article series describes how to recognize and diagnose various types of foundation failure or damage, such as foundation cracks, masonry foundation crack patterns, and moving, leaning, bulging, or bowing building foundation walls.
We also provide a MASTER INDEX to this topic, or you can try the page top or bottom SEARCH BOX as a quick way to find information you need.
Repair Methods for Cracks in Concrete Slabs & Floors
[Click to enlarge any image]
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.
Our photo (left) shows cracks developing in a slab on grade in a homein Alaska. Built over thawing permafrost, the cause of these cracks needs to be understood before a proper repair can be designed.
Article Series Contents
Accurate Diagnosis of Slab Crack Cause, Impact on Structure, Repair Needs
Before attempting to choose a repair method for concrete floor slab cracks,
Diagnose the cause of the slab movement and cracking. Only by an accurate diagnosis of the cause of cracking or movement in a floor slab can we be assured that the crack repair will be durable and appropriate. In fact some types of floor cracks, such as hairline concrete shrinkage cracks may not need repair at all.
In contrast, a concrete slab may have settled over poorly-compacted or washed-out fill (such as in some garages) without cracking (tipping instead), but repair may still be necessary to correct slope, provide drainage, or to prevent further settlement or even collapse.
Types of Cracks in Slabs
Each type of basement slab, floor slab, or slab on grade crack is discussed and described in articles at this website. Understanding the differences among these concrete crack types is an important first step in diagnosing their cause and their significance to the structure.
- Shrinkage cracks in a slab are unlikely to be of any structural concern but can be a source of water entry or radon entry in buildings and may forma tripping hazard. The photo at left shows a typical concrete slab shrinkage crack.
Details are atSHRINKAGE CRACKS in SLABS
Also see SHRINKAGE vs EXPANSION vs SETTLEMENT. - Settlement cracks in a slab indicate inadequate site preparation, such as failure to compact fill on which a slab was poured.
See SETTLEMENT CRACKS in SLABS for details. - Frost heaves or expansive soil damage can cause substantial damage to basement, crawl space, or garage floor slabs in some conditions.
See FROST HEAVE / EXPANSIVE SOIL CRACKS in SLABS for details.
List of Slab Crack Repair Methods Articles
Please see the individual slab crack repair articles listed below
- Control Joint Cracks in Concrete - adding control joints may be necessary to reduce further slab cracking if the joints were omitted in the original construction
- SEAL CRACKS by POLYURETHANE FOAM INJECTION - non-structural cracks (often the case with poured floor slabs) may simply need to be sealed in floors (or walls) to stop leaks
- SEAL CRACKS IN CONCRETE, HOW TO - more poured concrete crack sealing methods
- Standards for Repair of Cracks in Floors - so how bad does a crack have to be in order to decide that repair is necessary?
Cracks come to the job along with the concrete, riding in the same truck! At a Journal of Light Construction conference (Boston 1985) a lecturer informed us that 'Every concrete truck that comes to your job to pour a slab has at least four cracks in it. It's upto you to either provide control joints, or not. If you leave out control joints the cracks will occur in a messier pattern atnatural stress points in the slab.'
The bad news about typical floating slab construction (where the soil is not compacted) is that anything that causes the soil to settle risks slab cracking and settlement. Flooding, leaks, or simply poor handling of roof and surface runoff can send water under a building where it causes loose soil to settle.
The good news about cracks in floating slab construction is that the damage is to the floor, not to the structure that is supporting the building. Only if you see a floor slab crack that continues up in the foundation wall where the crack meets the wall would the structure be obviously involved.
More good news: if there is significant soil settlement under a floating slab, the slab is likely to break and follow the settling soil downwards; a sudden precipitous collapse of a floating slab is less likely than the next case we describe.
Standards for Repair of Cracks in Concrete Floors
Settlement cracks may form a tripping hazard even if they are not traced to a structural concern.
While there are few construction acceptance standards for floor slab cracking, one, 'Quality Standards for the ProfessionalRemodeling Industry' NAHB, recommends that cracks in basement floors which exceed 3/16' in width or 1/8' in vertical displacement should be repaired.
The same standard provides that cracks in slab-on-grade floors shall not exceed 1/16' in width or in vertical displacement.
The same standardprovides that cracks occurring in control joints in concrete slabs are normal and acceptable. [We suggest that this lastcriteria should apply to crack width but not to vertical displacement.
Fixing Hairline Cracks In New Concrete
Reader Q&A - also see the FAQs series linked-to below
On 2019-08-28 by (mod) -
No. YOu posted this question and we replied in detail at inspectapedia.com/structure/Concrete_Crack_Repairs_Sealants.php
SEAL CRACKS in CONCRETE, HOW TO
On 2019-08-28 by robert paganoni
when tide comes in and cracks in floor leak will a pressure relief valve stop leaks
On 2018-09-24 by (mod) -
In order to decide what to do about a crack in a concrete slab we need to have some diagnosis of its cause, and its history, that is over what period of time the cracking has occurred, and other site factors that may affect it such as control of water or surface runoff, original site preparation, compaction of backfill, reinforcement of the slab, Etc.
Forgive me but without any of that information I don't think that a guess about what to do to prevent further cracking would be very reliable.
On 2018-09-24 by Cynthia
We have a crack outside on the concrete slab, below our decking. The crack runs the entire width of the slab. What would you suggest we do to keep this from getting worse/wider?
Thank you!
On 2018-05-04 by (mod) -
Andy
I suspect that the concrete mix was incorrect, perhaps too much water and sand and gravel and not enough concrete. YOu'll need to remove and replace the footer.
On 2018-04-28 by Andy
I poured a 10 inch thick footer and it is 16 inches wide I let the footer set for 1 day and then the next day I layed 120 block on it,the next day I layed 300 block ,
then a day later I layed 300 more block,then I let it set for the winter,my wall cracked in two spots ,when spring came I dug down to the bottom of the footer and I noticed that only 7 inches of the footer set up and the other 3 inches of the footer was soft,I was wondering how did that happen and how do I fix it
On 2017-11-15 by (mod) -
Around the column you see a crack in the slab - what, radiating out from the column or just a circle around the column?
The first question is: is the column settling down through the slab: is it separated from the beam overhead, or is the beam sagging? If so your contractor will need to support the beam, open the floor, build a proper pier and install a new column.
On 2017-11-15 by Md. Rashed
How to repair slab crack ...
the crack see in around the column
On 2017-04-20 by (mod) -
Jorge, I can't diagnose the cracks and loose concrete from just your one line text - as there are plenty of possible causes: building movement, water, frost, impact, improper construction, foundation settlement, omission of a control joint, or simply poor mix of the concrete.
http://inspectapedia.com/structure/Concrete_Floor_Cracks.php might help you understand the crack s' cause and impact on your structure.
On 2017-04-20 by jorge
We noticed cracks on the concrete slab on second floor and some loos pieces of concrete. What can cause this?
On 2017-03-15 by (mod) -
Anon since slabs are flat - and walls are vertical, I think you're saying that there's a crack at the slab-to-wall intersection; that may be due to slab shrinkage if construction is new, or slab settlement.
On 2017-03-15 0 by Anonymous
My contrete slab developed a crack on the wall
...
Continue reading at CONTROL JOINT CRACKS in CONCRETE or select a topic from closely-related articles below, or see our complete INDEX to RELATED ARTICLES below.
Or see CONCRETE SLAB CRACK REPAIR FAQs - questions & answers posted originally at this page
Or see these
Concrete Crack Diagnosis & Repair Articles
Suggested citation for this web page
CONCRETE SLAB CRACK REPAIR at InspectApedia.com - online encyclopedia of building & environmental inspection, testing, diagnosis, repair, & problem prevention advice.
INDEX to RELATED ARTICLES: ARTICLE INDEX to BUILDING STRUCTURES
Or use the SEARCH BOX found below to Ask a Question or Search InspectApedia
Share this article
...
Ask a Question or Search InspectApedia
Try the search box just below, or if you prefer, post a question or comment in the Comments box below and we will respond promptly.
Search the InspectApedia website
Technical Reviewers & References
- ...
Books & Articles on Building & Environmental Inspection, Testing, Diagnosis, & Repair
- Mark Cramer Inspection Services Mark Cramer, Tampa Florida, Mr. Cramer is a past president of ASHI, the American Society of Home Inspectors and is a Florida home inspector and home inspection educator. Mr. Cramer serves on the ASHI Home Inspection Standards. Contact Mark Cramer at: 727-595-4211 mark@BestTampaInspector.com
- John Cranor is an ASHI member and a home inspector (The House Whisperer) is located in Glen Allen, VA 23060. He is also a contributor to InspectApedia.com in several technical areas such as plumbing and appliances (dryer vents). Contact Mr. Cranor at 804-747-7747 or by Email: johncranor@verizon.net
- Quality Standards for the Professional Remodeling Industry, National Association of Home Builders Remodelers Council, NAHB Research Foundation, 1987.
- Quality Standards for the Professional Remodeler, N.U. Ahmed, # Home Builder Pr (February 1991), ISBN-10: 0867183594, ISBN-13: 978-0867183597
- 'Concrete Slab Finishes and the Use of the F-number System', Matthew Stuart, P.E., S.E., F.ASCE, online course at www.pdhonline.org/courses/s130/s130.htm
- Sal Alfano - Editor, Journal of Light Construction*
- Thanks to Alan Carson, Carson Dunlop, Associates, Toronto, for technical critique and some of the foundation inspection photographs cited in these articles
- Thanks to reader Michael Witten for technical editing, October 2010
- Terry Carson - ASHI
- Mark Cramer - ASHI
- JD Grewell, ASHI
- Duncan Hannay - ASHI, P.E. *
- Bob Klewitz, M.S.C.E., P.E. - ASHI
- Ken Kruger, P.E., AIA - ASHI
- Aaron Kuertz aaronk@appliedtechnologies.com, with Applied Technologies regarding polyurethane foam sealant as other foundation crack repair product - 05/30/2007
- Bob Peterson, Magnum Piering - 800-771-7437 - FL*
- 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
How to Identify & Evaluate Shrinkage Cracks in Poured Concrete Slabs
Please see the main text version of this article at Shrinkage Cracks in Slabs
We discuss the recognition and significance of concrete shrinkage cracks in detail at Shrinkage Cracks in Slabs. Just below you can read a summary of this topic.
Shrinkage cracks in poured concrete are easily recognizable and can be distinguished from other types of cracks that occurlater in the life of a foundation wall or floor slab. The photograph of cracks above were taken of shrinkage cracks in a concrete slab floor in a home built in 2006.The cracks in this case ranged in width (measured across the crack) from 'hairline' (less than 1/16') to about3/32' in the basement floor slab of this particular home. They may appear larger. What is unique about shrinkage cracks in concrete is that they usually appear to be discontinuous, as shown inthis photo. The crack will meander along in the concrete, taper to a stop, and then continue beginning in a parallelline to the first crack, meandering again through the concrete. This is characteristic of concrete (or mud) shrinkingwhile giving up its moisture. You can see the shrinkage of even a perfect concrete floor slab with no visible cracks in the field of its surface if the floor was poured inside of an existingfoundation. Look for the gap between the edges of the slab and the foundation wall? Look also for the stains or concrete debris on thewall at the slab level? These confirm that at the time the slab was poured it was touching the wall. |
Shrinkage Cracks in a Basement or other Slab May Be Severe and May Combine with Settlement
Fill Hairline Cracks In Concrete Floor
Depending on the mix and pour conditions as well as the site work preparation significant concrete shrinkage cracks can appear in a basement slab. On occasion we may also see vertical dislocation in a floor slab crack, that is, one side has settled or tipped away from the other side of the cracked concrete.
Our photographs above show shrinkage cracking and ensuing minor settlement cracks occurring in the same poured concrete basement floor. We suspected that site drainage defects or possibly nearby site blasting for additional construction contributed to the 1/16' to 1/8' vertical dislocation across some of the cracks in this floor where the cracks were about 3/16' wide.
Slab Cracks may Permit Basement Water Entry or Radon Gas Entry
Happily the building owner at the site where we made the photos above did not report water entry through these openings, though it certainly might be expected as the home ages and its footing drains stop working, particularly if surface runoff and roof runoff are not kept away from the building.
Photos of Concrete Floor Slab Shrinkage Points of Origin
The photo at left shows some concrete shrinkage cracks that are larger than usual. Note that these cracks begin at building foundation wall inside projection corners - a condition that probably creates stress points as the slab cures. If you click on and enlarge the photo you can see clear evidence that the cracks are discontinuous, multiple, and very roughly parallel in this area - good evidence that they were caused during the concrete curing process and not by a later event which 'broke' the slab. When we see combined slab shrinkage and slab settlement condition we suspect that the concrete pour not only allowed for excessive shrinkage, or perhaps shrinkage without control joints, but also the pour was made on top of poorly prepared soils. For example if a slab is poured on poorly-compacted soil, after shrinkage cracking occurs, we may see uneven settlement among sections of the cracked slab. Settlement cracking following shrinkage cracking may also occur. In both of these cases we anticipate that significant horizontal dislocation in a poured concrete slab should be small unless steel reinforcement was omitted or was improperly installed. Since some contractors use a fiber-reinforced cement and may omit steel reinforcement in floor slabs, this condition may occur. |
when tide comes in and cracks in floor leak will a pressure relief valve stop leaks
On 2018-09-24 by (mod) -
In order to decide what to do about a crack in a concrete slab we need to have some diagnosis of its cause, and its history, that is over what period of time the cracking has occurred, and other site factors that may affect it such as control of water or surface runoff, original site preparation, compaction of backfill, reinforcement of the slab, Etc.
Forgive me but without any of that information I don't think that a guess about what to do to prevent further cracking would be very reliable.
On 2018-09-24 by Cynthia
We have a crack outside on the concrete slab, below our decking. The crack runs the entire width of the slab. What would you suggest we do to keep this from getting worse/wider?
Thank you!
On 2018-05-04 by (mod) -
Andy
I suspect that the concrete mix was incorrect, perhaps too much water and sand and gravel and not enough concrete. YOu'll need to remove and replace the footer.
On 2018-04-28 by Andy
I poured a 10 inch thick footer and it is 16 inches wide I let the footer set for 1 day and then the next day I layed 120 block on it,the next day I layed 300 block ,
then a day later I layed 300 more block,then I let it set for the winter,my wall cracked in two spots ,when spring came I dug down to the bottom of the footer and I noticed that only 7 inches of the footer set up and the other 3 inches of the footer was soft,I was wondering how did that happen and how do I fix it
On 2017-11-15 by (mod) -
Around the column you see a crack in the slab - what, radiating out from the column or just a circle around the column?
The first question is: is the column settling down through the slab: is it separated from the beam overhead, or is the beam sagging? If so your contractor will need to support the beam, open the floor, build a proper pier and install a new column.
On 2017-11-15 by Md. Rashed
How to repair slab crack ...
the crack see in around the column
On 2017-04-20 by (mod) -
Jorge, I can't diagnose the cracks and loose concrete from just your one line text - as there are plenty of possible causes: building movement, water, frost, impact, improper construction, foundation settlement, omission of a control joint, or simply poor mix of the concrete.
http://inspectapedia.com/structure/Concrete_Floor_Cracks.php might help you understand the crack s' cause and impact on your structure.
On 2017-04-20 by jorge
We noticed cracks on the concrete slab on second floor and some loos pieces of concrete. What can cause this?
On 2017-03-15 by (mod) -
Anon since slabs are flat - and walls are vertical, I think you're saying that there's a crack at the slab-to-wall intersection; that may be due to slab shrinkage if construction is new, or slab settlement.
On 2017-03-15 0 by Anonymous
My contrete slab developed a crack on the wall
...
Continue reading at CONTROL JOINT CRACKS in CONCRETE or select a topic from closely-related articles below, or see our complete INDEX to RELATED ARTICLES below.
Or see CONCRETE SLAB CRACK REPAIR FAQs - questions & answers posted originally at this page
Or see these
Concrete Crack Diagnosis & Repair Articles
Suggested citation for this web page
CONCRETE SLAB CRACK REPAIR at InspectApedia.com - online encyclopedia of building & environmental inspection, testing, diagnosis, repair, & problem prevention advice.
INDEX to RELATED ARTICLES: ARTICLE INDEX to BUILDING STRUCTURES
Or use the SEARCH BOX found below to Ask a Question or Search InspectApedia
Share this article
...
Ask a Question or Search InspectApedia
Try the search box just below, or if you prefer, post a question or comment in the Comments box below and we will respond promptly.
Search the InspectApedia website
Technical Reviewers & References
- ...
Books & Articles on Building & Environmental Inspection, Testing, Diagnosis, & Repair
- Mark Cramer Inspection Services Mark Cramer, Tampa Florida, Mr. Cramer is a past president of ASHI, the American Society of Home Inspectors and is a Florida home inspector and home inspection educator. Mr. Cramer serves on the ASHI Home Inspection Standards. Contact Mark Cramer at: 727-595-4211 mark@BestTampaInspector.com
- John Cranor is an ASHI member and a home inspector (The House Whisperer) is located in Glen Allen, VA 23060. He is also a contributor to InspectApedia.com in several technical areas such as plumbing and appliances (dryer vents). Contact Mr. Cranor at 804-747-7747 or by Email: johncranor@verizon.net
- Quality Standards for the Professional Remodeling Industry, National Association of Home Builders Remodelers Council, NAHB Research Foundation, 1987.
- Quality Standards for the Professional Remodeler, N.U. Ahmed, # Home Builder Pr (February 1991), ISBN-10: 0867183594, ISBN-13: 978-0867183597
- 'Concrete Slab Finishes and the Use of the F-number System', Matthew Stuart, P.E., S.E., F.ASCE, online course at www.pdhonline.org/courses/s130/s130.htm
- Sal Alfano - Editor, Journal of Light Construction*
- Thanks to Alan Carson, Carson Dunlop, Associates, Toronto, for technical critique and some of the foundation inspection photographs cited in these articles
- Thanks to reader Michael Witten for technical editing, October 2010
- Terry Carson - ASHI
- Mark Cramer - ASHI
- JD Grewell, ASHI
- Duncan Hannay - ASHI, P.E. *
- Bob Klewitz, M.S.C.E., P.E. - ASHI
- Ken Kruger, P.E., AIA - ASHI
- Aaron Kuertz aaronk@appliedtechnologies.com, with Applied Technologies regarding polyurethane foam sealant as other foundation crack repair product - 05/30/2007
- Bob Peterson, Magnum Piering - 800-771-7437 - FL*
- 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
How to Identify & Evaluate Shrinkage Cracks in Poured Concrete Slabs
Please see the main text version of this article at Shrinkage Cracks in Slabs
We discuss the recognition and significance of concrete shrinkage cracks in detail at Shrinkage Cracks in Slabs. Just below you can read a summary of this topic.
Shrinkage cracks in poured concrete are easily recognizable and can be distinguished from other types of cracks that occurlater in the life of a foundation wall or floor slab. The photograph of cracks above were taken of shrinkage cracks in a concrete slab floor in a home built in 2006.The cracks in this case ranged in width (measured across the crack) from 'hairline' (less than 1/16') to about3/32' in the basement floor slab of this particular home. They may appear larger. What is unique about shrinkage cracks in concrete is that they usually appear to be discontinuous, as shown inthis photo. The crack will meander along in the concrete, taper to a stop, and then continue beginning in a parallelline to the first crack, meandering again through the concrete. This is characteristic of concrete (or mud) shrinkingwhile giving up its moisture. You can see the shrinkage of even a perfect concrete floor slab with no visible cracks in the field of its surface if the floor was poured inside of an existingfoundation. Look for the gap between the edges of the slab and the foundation wall? Look also for the stains or concrete debris on thewall at the slab level? These confirm that at the time the slab was poured it was touching the wall. |
Shrinkage Cracks in a Basement or other Slab May Be Severe and May Combine with Settlement
Fill Hairline Cracks In Concrete Floor
Depending on the mix and pour conditions as well as the site work preparation significant concrete shrinkage cracks can appear in a basement slab. On occasion we may also see vertical dislocation in a floor slab crack, that is, one side has settled or tipped away from the other side of the cracked concrete.
Our photographs above show shrinkage cracking and ensuing minor settlement cracks occurring in the same poured concrete basement floor. We suspected that site drainage defects or possibly nearby site blasting for additional construction contributed to the 1/16' to 1/8' vertical dislocation across some of the cracks in this floor where the cracks were about 3/16' wide.
Slab Cracks may Permit Basement Water Entry or Radon Gas Entry
Happily the building owner at the site where we made the photos above did not report water entry through these openings, though it certainly might be expected as the home ages and its footing drains stop working, particularly if surface runoff and roof runoff are not kept away from the building.
Photos of Concrete Floor Slab Shrinkage Points of Origin
The photo at left shows some concrete shrinkage cracks that are larger than usual. Note that these cracks begin at building foundation wall inside projection corners - a condition that probably creates stress points as the slab cures. If you click on and enlarge the photo you can see clear evidence that the cracks are discontinuous, multiple, and very roughly parallel in this area - good evidence that they were caused during the concrete curing process and not by a later event which 'broke' the slab. When we see combined slab shrinkage and slab settlement condition we suspect that the concrete pour not only allowed for excessive shrinkage, or perhaps shrinkage without control joints, but also the pour was made on top of poorly prepared soils. For example if a slab is poured on poorly-compacted soil, after shrinkage cracking occurs, we may see uneven settlement among sections of the cracked slab. Settlement cracking following shrinkage cracking may also occur. In both of these cases we anticipate that significant horizontal dislocation in a poured concrete slab should be small unless steel reinforcement was omitted or was improperly installed. Since some contractors use a fiber-reinforced cement and may omit steel reinforcement in floor slabs, this condition may occur. |
Hairline Cracks In New Concrete
How to Inspect & Evaluate Cracks at Control Joints in Concrete
We discuss the recognition and significance of control joints in poured concrete slabs in detail at CONTROL JOINT CRACKS in CONCRETE. Just below you can read a summary of this topic.
The first photograph shows an expansion joint in a basement floor slab. Notice that we donot see other cracks in this slab.Shrinkage cracks that occur at control joints such as shown in the second, close up photo here, are occurring where they are supposed-to,although the width of this particular crack was surprisingly large. These cracks are not normally a defect in the slab but may bea source of water or radon entry into the building and may need to be sealed. Use a flexible sealant.
Settlement Cracks in poured Concrete Slabs
We discuss the recognition and significance of settlement cracks in poured concrete slabs in detail at Settlement Cracks in Slabs. Just below you can read a summary of this topic.
Settlement cracks in a conventional concrete floor slab which has been poured inside a separate foundation wall (and oftenresting at its edges on the building's foundation wall footings) are usually not connected to the foundation wall and are not supportingany structure [except possibly Lally columns, discussed next]. These cracks may not be a structural concern, but there are caseswhere a serious hazard can be present, such as garage floor cracking when the floor was poured over soft, loose, inadequately-compactedfill and where the floor slab was not pinned to the garage foundation walls. Soil settlement under a garage floor, perhaps aggravatedby groundwater which can increase soil settlement, can lead to first hollowing-out of space below the floor and second, suddencollapse of the floor structure. We have used a heavy chain, dragging it across the garage floor and listening to changes inthe sound it produces, to find areas of significant soil voids below the floor. The pitch of the chain noise drops significantlywhen passing over a void below the concrete.] |
Settlement cracks in a concrete floor around a supporting Lally column might be indicativeof a serious problem such as building settlement if the columns are settling. Independent footings may have been provided supportingLally columns in the building interior and those may be settling independently of the floor slab which may have been pouredaround and even over them (See photo above). But beware, where slab thickness and local building codes allow, supporting columns may beardirectly on a poured floor slab without their own (deeper) pier or footing. In that case floor slab cracking and settling can causecolumn movement and may be a structural concern.
Settlement cracks in a monolithic slab or floating slab floor may be more serious, depending on their extent since in thiscase the edges and other portions of the slab are, unlike the cases above) expected to support the upper portions of the building structure.
A monolithic concrete slab is one which includes the building footing as part of the slab, created in a single continuous pour of concrete.
A floating concrete slab is one which is poured at a (generally) uniform thickness on the ground without a separate footing.[Beware, in areas of wet soils, expansive clays, freezing climates, or unstable soils, floating slabs may be exposed to extra stressesand may tip or crack. Proper site work and drainage are important as is proper engineering design of such structures.
Frost Heaves or Expansive Soil Cracks in Poured Concrete Slabs
We discuss the recognition and significance of frost heaving damage and cracks in poured concrete slabs in detail at Frost Heave/Expansive Soil Cracks in Slabs. Just below you can read a summary of this topic.
Frost heaves or expansive soils damage to building floor slabs can range from minor to extensivein buildings depending on soil and weather conditions, site preparation, and slab construction details, as weelaborate here. The photograph above shows a rather straight crack across a garage slab near the garage entry door.What is happening here and why is this particular crack straight if it's a frost or soil heave crack? In freezing climates building foundations include a footing which extends below the frost line. Thisis true for both the occupied space as well as garages. When a concrete slab is poured either abuttingthe top of such a foundation, or poured extending over the edges of such a foundation, there isrisk of cracking across the concrete at the interior edge of the buried footing. |
The combination of water under a garage floor (watch out for driveways and sites that slopetowards the garage or home) and freezing can cause the portion of the slab which rests directlyon the soil to move up and down during freeze/thaw cycles. Since a garage is often coldernear the garage entry door than in other areas, there is extra risk of these cracks occurringthere, but they can occur anywhere. When there is freezing and heaving of a slab, particularlyone which omitted reinforcing steel, or did not extend the steel over the footing, thesegarage floor slab cracks may appear during freeze/thaw cycles.
Similar floor slab damage might occur in areas of expansive clay soils if the propermoisture level is not maintained.
Basement floor heave patterns - frozen floor drains:Basement floors can be frost heaved in other patterns in buildings which areunheated or which lose heat. We have found basement floor slabs broken and heavedabove buried drain lines which ran below the basement floor of a home whichremained unheated during freezing weather.
A clogged drain sitting full of liquidcombined with prolonged freezing weather was the culprit in most of these cases.The heaved concrete was raised following exactly the path of the frozen (and burst)buried, clogged drain line. This problem can be epidemic in older homes whichwere constructed using a downspout drain line extending below the basement slab.
Basement and garage floor random heave and crack patterns: Cracked and heaved concrete or settled concrete can occur in more random patterns in any concrete floor where there has been frost heaving, soil contraction/expansion, or simple soil settlement, as shown in this photograph. |
Garage or basement floor sloped or semi-uniform settlement may also producea tipped floor even if the concrete is not cracked, or the floor maysettle uniformly. This condition occurs if the concrete was reinforcedby steel or fiber cement, but was poured inside of a separate concreteor masonry block foundation. We see this condition more often in garagesin which the slab was reinforced but poured on poorly-compacted soil.The problem may be worst if in addition to poor compaction, water runsunder the slab, causing additional or more rapid soil settlement.
My first construction job (for pay) was to rake level the backfillsoil that the contractor had dumped inside of the newly-completedgarage foundation in a series of homes. No compaction of any kindwas performed. When a lot of fill, several feet or more in depth,was required to bring the slab to the desired height, there wasa good chance that the slab would settle or tip in the future.
Garage slabs which were poured inside of the foundation walls butwhich were pinned to the foundation sides (typically usingre-bar set into holes punched into the masonry block foundation),the slab was resistant to settlement or movement even if therewas modest soil settlement below.
In a garage where the slab has settled you can often spot the originallevel of the slab and thus can measure the amount of settlement. Look fora concrete line above thelevel of the top of the slab and found along the masonry block or poured concrete foundationwall. we have seen this line ranging from a fraction of an inch to six to eight inchesabove the current level of the slab!
Fixing Hairline Cracks In Concrete Driveway
Standards for the Acceptance or Repair of Cracks in Concrete Floors in New Construction
Fixing Hairline Cracks In Concrete Walls
Settlement cracks may form a tripping hazard even if they are not traced to a structuralconcern. While there are few construction acceptance standards for floor slab cracking, one, 'Quality Standards for the ProfessionalRemodeling Industry' NAHB, , recommends that cracks in basement floors which exceed 3/16' in width or 1/8' in vertical displacement should be repaired.The same standard provides that cracks in slab-on-grade floors shall not exceed 1/16' in width or in vertical displacement. The same standardprovides that cracks occurring in control joints in concrete slabs are normal and acceptable. [We suggest that this lastcriteria should apply to crack width but not to vertical displacement.]
Books & Articles on Building & Environmental Inspection, Testing, Diagnosis, & Repair
- Our recommended books about building & mechanical systems design, inspection, problem diagnosis, and repair, and about indoor environment and IAQ testing, diagnosis, and cleanup are at the InspectAPedia Bookstore. Also see our Book Reviews - InspectAPedia.
- Best Practices Guide to Residential Construction, by Steven Bliss. John Wiley & Sons, 2006. ISBN-10: 0471648361, ISBN-13: 978-0471648369, Hardcover: 320 pages, available from Amazon.com and also Wiley.com. See our book review of this publication.
- Decks and Porches, the JLC Guide to, Best Practices for Outdoor Spaces, Steve Bliss (Editor), The Journal of Light Construction, Williston VT, 2010 ISBN 10: 1-928580-42-4, ISBN 13: 978-1-928580-42-3, available from Amazon.com
- The Journal of Light Construction has generously given reprint permission to InspectAPedia.com for certain articles found at this website. All rights and contents to those materials are ©Journal of Light Construction and may not be reproduced in any form.
- Appliances and Home Electronics, - energy savings, U.S. Department of Energy
- Avongard foundation crack progress chart for structural crack monitoring
- Basement Moisture Control, U.S. Department of Energy
- Building Pathology, Deterioration, Diagnostics, and Intervention, Samuel Y. Harris, P.E., AIA, Esq., ISBN 0-471-33172-4, John Wiley & Sons, 2001 [General building science-DF] ISBN-10: 0471331724ISBN-13: 978-0471331728
- Building Pathology: Principles and Practice, David Watt, Wiley-Blackwell; 2 edition (March 7, 2008) ISBN-10: 1405161035 ISBN-13: 978-1405161039
- The Circular Staircase, Mary Roberts Rinehart
- Construction Drawings and Details, Rosemary Kilmer
- Crawl Space Moisture Control, U.S. Department of Energy
- 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.
- Design of Wood Structures - ASD, Donald E. Breyer, Kenneth Fridley, Kelly Cobeen, David Pollock, McGraw Hill, 2003, ISBN-10: 0071379320, ISBN-13: 978-0071379328
This book is an update of a long-established text dating from at least 1988 (DJF); Quoting:
This book is gives a good grasp of seismic design for wood structures. Many of the examples especially near the end are good practice for the California PE Special Seismic Exam design questions. It gives a good grasp of how seismic forces move through a building and how to calculate those forces at various locations.THE CLASSIC TEXT ON WOOD DESIGN UPDATED TO INCLUDE THE LATEST CODES AND DATA. Reflects the most recent provisions of the 2003 International Building Code and 2001 National Design Specification for Wood Construction. Continuing the sterling standard set by earlier editions, this indispensable reference clearly explains the best wood design techniques for the safe handling of gravity and lateral loads. Carefully revised and updated to include the new 2003 International Building Code, ASCE 7-02 Minimum Design Loads for Buildings and Other Structures, the 2001 National Design Specification for Wood Construction, and the most recent Allowable Stress Design. - Building Failures, Diagnosis & Avoidance, 2d Ed., W.H. Ransom, E.& F. Spon, New York, 1987 ISBN 0-419-14270-3
- Domestic Building Surveys, Andrew R. Williams, Kindle book, Amazon.com
- 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. - Guide to Domestic Building Surveys, Jack Bower, Butterworth Architecture, London, 1988, ISBN 0-408-50000 X
- 'Avoiding Foundation Failures,' Robert Marshall, Journal of Light Construction, July, 1996 (Highly recommend this article-DF)
- 'A Foundation for Unstable Soils,' Harris Hyman, P.E., Journal of Light Construction, May 1995
- 'Backfilling Basics,' Buck Bartley, Journal of Light Construction, October 1994
- 'Inspecting Block Foundations,' Donald V. Cohen, P.E., ASHI Reporter, December 1998. This article in turn cites the Fine Homebuilding article noted below.
- 'When Block Foundations go Bad,' Fine Homebuilding, June/July 1998
- Slab on Grade Foundation Moisture and Air Leakage, U.S. Department of Energy
- ...
Fixing Hairline Cracks In Concrete
- Carson, Dunlop & Associates Ltd., 120 Carlton Street Suite 407, Toronto ON M5A 4K2. Tel: (416) 964-9415 1-800-268-7070 Email: info@carsondunlop.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.
- The Illustrated Home illustrates construction details and building components, a reference for owners & inspectors.
Special Offer: For a 5% discount on any number of copies of the Illustrated Home purchased as a single order Enter INSPECTAILL in the order payment page 'Promo/Redemption' space. - TECHNICAL REFERENCE GUIDE to manufacturer's model and serial number information for heating and cooling equipment, useful for determining the age of heating boilers, furnaces, water heaters is provided by Carson Dunlop, Associates, Toronto - Carson Dunlop Weldon & Associates
Special Offer: Carson Dunlop Associates offers InspectAPedia readers in the U.S.A. a 5% discount on any number of copies of the Technical Reference Guide purchased as a single order. Just enter INSPECTATRG in the order payment page 'Promo/Redemption' space.
- The Illustrated Home illustrates construction details and building components, a reference for owners & inspectors.
- 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.
Special Offer: For a 10% discount on any number of copies of the Home Reference Book purchased as a single order. Enter INSPECTAHRB in the order payment page 'Promo/Redemption' space. InspectAPedia.com editor Daniel Friedman is a contributing author.
Or choose the The Home Reference eBook for PCs, Macs, Kindle, iPad, iPhone, or Android Smart Phones.
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Building inspection education & report writing systems from Carson, Dunlop & Associates Ltd - Commercial Building Inspection Courses - protocol ASTM Standard E 2018-08 for Property Condition Assessments
- Home Inspection Education Courses including home study & live classes at eleven colleges & universities.
- Home Inspection Education Home Study Courses - ASHI@Home Training 10-course program.
Special Offer: Carson Dunlop Associates offers InspectAPedia readers in the U.S.A. a 5% discount on these courses: Enter INSPECTAHITP in the order payment page 'Promo/Redemption' space. InspectAPedia.com editor Daniel Friedman is a contributing author. - The Horizon Software System manages business operations,scheduling, & inspection report writing using Carson Dunlop's knowledge base & color images. The Horizon system runs on always-available cloud-based software for office computers, laptops, tablets, iPad, Android, & other smartphones
Hairline Crack In Concrete Definition
Publisher InspectApedia.com - Daniel Friedman