Concrete floor slab settlement crack FAQs:

Questions answers on s or Floors. Concrete floor crack pattern analysis, evaluation, diagnosis, repair. Floor crack diagnosis

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.

FAQs on Settlement Cracks in Poured Concrete Slabs

Question: How should I fix a garage floor that has settled six inches or more?

What would be the proper fix to the situation outlined above as "Garage or basement floor sloped or semi-uniform settlement may also produce a tipped floor even if the concrete is not cracked, or the floor may settle uniformly." My floor has sunk and cracked right down the middle about 6" dep in the center. - Ed Barber

[Click to enlarge any image]

Reply: Investigate the cause of garage floor settlement before using slab-jacking or repouring

Ed for a six-inch subsidence in a garage floor it's worth doing some further exploring to diagnose the problem before starting a repair, perhaps by making a small opening and doing some probing.

A garage slab can settle significantly if it was poured on poorly compacted fill. If water is running into that areas, exacerbating fill settlement, the problem can be worse, and of course the total amount of settlement possible depends on the total height of soft fill that was placed inside the garage foundation space.

Minor cracks are just patched for cosmetic reasons or to avoid a trip hazard. But a six-inch settlement: one would either cut out, compact fill, re-pour, or if it looks cost justified, there is a slab-jacking procedure that can lift and support a concrete slab that was not previously adequately supported. Slab jacking is done either by pumping grout under the slab under pressure or by drilling through and driving jacking/supporting pins or piers through the slab to support it.

I would NOT just pour a new slab on top of a settling slab before we thought that the older settling slab had been stabilized.

Question: What is the significance of uniform slab settlement of about 1/4-inch?

I am looking at a supported slab on grade house built in 1948. The slab has cracked along the foundation support wall, and has dropped 1/4 inch uniformly around the south and west walls, the others being covered up by carpeting, but i imagine they are also.

The center of the house is level and un cracked. I noticed that the middle of the slab is very hard and thick, as I had to jack hammer it out to re plumb the bathroom. the concrete on the slab overlap over the foundation wall is brittle, but the central slab is solid. could moisture have wicked in through the foundation wall, or as a result of poor flashing weakened this part of the slab?

I know that this was the condition of the structure dating back to at least the early 2000's but i have no data before that. Perhaps poor surface drainage? - InspectAPedia Fan

Reply: Evaluate the slab settlement for signs of ongoing movement versus stable conditions, check site and roof drainage

Fan,

Uniform slab settlement is often due to compaction of un compacted fill under the slab from original construction. But if the settlement is not uniform that could still be the problem. For example a slab center might be supported atop piers hidden under the slab and poured to support Lally columns used below a center girder. The slab may literally be "hanging" off of the piers at its center and cracking around its perimeter.

Is the slab perimeter floating or is it sitting on the edge of the foundation wall footing? If I see settlement at the slab edges and no cracking nor leaning in the foundation walls around the perimeter I suspect the slab was not resting on footing edges and is thus falling. Or has fallen.

A key question is whether or not movement is over or ongoing. If we think this is old settlement on poorly compacted fill and it's not ongoing, and if there are no accompanying cracks in the supporting foundation walls the repair is not so urgent except to avoid trip hazards (and fix plumbing troubles).

If that surmise is correct, you will also want to be sure to direct roof runoff away from the structure - water under a slab exacerbates foundation settlement or movement.

And finally, a 1948 home, even if it originally had footing drains, doesn't any more unless they were replaced. By now in most cases the old drain system will have clogged. Keep those gutters clear and direct downspouts well away from the home.

Question: Why are there raised lines and indentations with in my lanolieum floor [sheet vinyl flooring lines] installed over a concrete slab floor?

Our house was built only 7 months ago and sits on a monolithic poured concrete slab. My question is why are there raised linens and intentions showing through my linoleum that are continually becoming more noticeable?

My house was built on a monolythic slab and I have brought to the builder attention many time all the moisture found within my yard all over. Our yard is mostly clay and a rock/ dirt mixture they poured on top before sodding.

All our trees and plants keep dying due to all the water. Not to mention my neighbor had a sink hole in her front yard that they state was not the case. What could these raised areas possibly be.

I did find three foundation cracks on the outside which are directly across from each other on both sides of my house and suspiciously the same direction this raised line in my linoleum is running. I know settlement cracks are normal that is why the outside cracks raised no concern but now inside my kitchen you can feel these raised lines while walking that keep expanding and lengthening. Thanks for any information that may help me understand this issues better! - Valerie

Reply: Identify the type and cause of concrete slab crack formation, distinguish from flooring installation errors

Valerie:

If your linoleum floor (sheet vinyl in modern parlance) is showing raised lines and indentations it sounds as if most likely it was installed over an imperfect slab, perhaps one that either had cracks or is now cracking, perhaps due to new home settlement or even concrete shrinkage. I suppose the flooring could have been installed over debris too.

The "fix" should include an inspection and diagnosis of the extent and cause of cracking or settlement, and unfortunately, the fix probably means the flooring would need to come up and new flooring installed over a leveling layer or subfloor material.

Follow-Up:

Thank you Dan
I will contact my home inspector to come out and evaluate the floor. It is becoming more pronounced and noticeable with all the rain we have been getting here on the East Coast. I'll update with an answer.
Thank you again! - Valerie

Well my contractor came to inspect my floors and his explanation was that the expansion joints were separating within our monolythic slab ( by his definition is normal and no rush to be fixed). I was advised by him that it can wait until our ten month inspection to be fixed. He explained that since this line runs the entire length of my home then there will be visible cracks on the outside slab to prove his theory of the joints separating from settlement. Well there are cracks on rack side of the house that are no longer hairline but show visible widening, but he said this is normal.

Needless to say I was not too comfortable with his explanation and called the city inspector who had inspected the process of my home while construction. His explanation summed up in a few words were to contact the state contractors board and submit a formal complaint and get a civil lawsuit started. He believes it is a structural issue while the builder states this is all part of the normal settling process. So I'm feeling a bit in limbo on what to believe at this point. I guess the real answer will be determined when they come and pull up our floors. I will keep you posted. - Valerie

Advice: How to investigate to determine the source of lines telegraphing up through sheet vinyl flooring over a concrete slab

Valerie:

Expansion joints are also called "control joints" and are intended to prevent random cracking in poured concrete slabs by directing the normal shrinkage cracks that occur to form in the expansion joint.

Even if there were no slab movement, an expansion joint could certainly telegraph up its presence through sheet vinyl flooring installed over the slab unless special steps were taken to cover the joint with an appropriate tape and sealant before floor installation, or unless instead, a layer of flooring underlayment was installed.

Settlement cracking and vertical cracks that you are seeing on the house exterior, particularly noting that they are increasing, may be a common problem but they are not "normal" in the sense that they are not good practice and in general are not acceptable. A foundation engineer would call them a "failure".

A common cause of settlement cracks in a concrete slab is improper site work and preparation. For example, pouring concrete over soft, poorly-compacted fill can result in slab cracking and settlement even if reinforcing steel was placed in the slab. And if the contractor used fiber-reinforced concrete and omitted the re-bar (steel reinforcement), pouring over voids or soft fill is still more likely to lead to cracking and settlement.

Fiber-reinforcement helps reduce shrinkage cracking and resists minor movement but in my experience that approach (omitting steel reinforcement) won't protect against settlement cracks over a poorly-prepared site.

If you have photos of the building slab before the finish flooring was installed they might be diagnostic, as might be photos of the floor installation process itself as then we could see what the installer did or did not include.

A question left unanswered by the information we have so far is whether the marks you see in your finish floor are due to the simple presence of the expansion joints and the failure to install an underlayment or whether instead there is ongoing settlement of the floor slab.

We need to obtain a more accurate picture of just what is going on, and to sort out an improper floor installation from an improper slab installation and design.

These investigative steps would help:

1. Inspect the floor for out of level conditions that might indicate slab settlement - a slab defect; inspect the building foundation exterior to see if there are vertical cracks in the edges of the slab that might also indicate slab movement or settlement.

2. lift the flooring in an area where the lines appear and photograph and report to us what you see:

is there in fact an slab expansion joint where the lines appear in the flooring or is it some other crack pattern?

was there an underlayment or any other material provided to cover the expansion joints?

The city inspector's advice to start a lawsuit before we have a confident understanding of what is going on could be a costly mistake.

Once the cause of your floor lines and any slab cracking and movement is understood it will be possible to decide what repair steps would be appropriate.

-- DF

Reader Follow-up: slab cracks are telegraphing up through the finish flooring - is t5his normal?

Regards to my October 2011 question: We had our slab fixed by the builder going on a year now . They sanded down and filled the expansion joints which were large in my opinion. Now the same areas are raising again through the linolieom as it did before.

Is this normal ? Every crack in the house ( around bathtubs, corners of walls, windows) that the builder fixed upon our 1 yr inspection are all re- cracking. The house is now over 2 yrs old. Is this normal as well? - Valerie 2/20/2013

Reply: Recapping some notes on control joints or expansion joints vs. abnormal slab cracks and movement

Valerie,

At a construction conference I chaired a round table of concrete experts (I was not the expert I was the facilitator) on crack issues. One contractor pointed out "Every concrete truck that arrives on the job has four or five cracks in it" - what he meant was that it is "normal" for concrete slabs to crack (usually due to shrinkage) as the slab cured.

The purpose of a control joint is only to control where an otherwise "cosmetic" shrinkage crack appears - that is, we cut a relief gap or "crack" in the concrete that absorbs the stresses of shrinkage - so the 1/16" or so of shrinkage cracking is directed into the pre-formed control joint rather than appearing somewhere else where we don't want to see it.

A control joint, then, controls where in a concrete slab stress cracks appear. Completely separate would be issues of heaving, settlement, or movement in a concrete slab.

Settlement or heaving in a slab could explain why a slab might heave, separate, or move at a control joint. But in all cases that's not "normal" behavior.

The substantive question here is whether or not there is an underlying defect (such as improper soil compaction, improper drainage, other sitework errors) that is serious enough as to merit the cost and trouble of doing something about it. If so, the cost is likely to be significant - which may explain why your contractor wants to pooh-pooh the problem.

I once inspected a home whose gutters dumped water on the head of anyone entering the front door during a rainstorm. When I asked the builder about it he explained that gutters spilling onto people entering the house (at least houses he built) was normal. "They all do that." he explained. He was right. All of his houses did that, because all of his gutters were installed incorrectly. So maybe the cracks, heaving, and ongoing slab problems seem normal to your contractor because all of his homes do that. But normal to him is not necessarily acceptable to you nor anyone else. 

Question:

Is the width and size of a settlement crack within the slab cause for concern? - Vicky 5/1/2012

Reply:

The width and size of a crack in a concrete slab are some but not all of the factors that an expert considers in deciding the level of worry and the need for further diagnosis & repair.

Your onsite expert will look for evidence of cracks and movement in the building foundation as well as in other indoor components (drywall, windows, doors), site conditions and history and other factors as well.

Question: vertical crack in garage foundation wall

Our attached garage exterior wall rests on about a 2' high poured concrete ledge that rests on the footers below grade. We also live on a steep slope (say 70% grade), and recently found a vertical crack that extends from the top of the garage ledge and extending below grade.

The crack is about 1/2" thick and does promulgate through the wall to the exterior. It is obvious we have had some movement of the house, possibly from poor soil conditions. I have gotten several opinions ranging from a contractor offering to install support pylons for ~$20K to applying crack monitrs to see if the crack gets larger....thoughts? - Vertical Cracks in Garage 7/5/12

Reply:

Vertical crack in concrete foundation wall:

If the foundation wall that has cracked is running down that steep slope (as opposed to across it) then I suspect that ground for the footings may not have been properly prepared, excavated or compacted. For example if the down-slope end of the wall footing was poured on poorly compacted fill, later settlement would be no surprise.

There are several pier-type approaches to supporting settling footings - your contractor is not out of line. I see costs from $5K to $10K (possibly even more) per pier for drilled helical piers. Be sure that the repair is planned and executed by a contractor who in fact has experience with installing repair piers.

You didn't give age of the building nor over what period the cracked foundation wall appeared - but I'd be surprised if 1/2" wide vertical foundation cracking due to settlement of one end of the footing was just "initial settlement" - so I'd not be thinking much about further monitoring - especially given the magnitude of the crack.

WATCH OUT: the same mistake could have been made on other, less visible sections of the foundation. I'd check everywhere before ordering repairs - it's more costly to bring in contractors multiple times than to do it right once.

Question: crack in 7-year-old floor slab is getting wider & tiles are chipping

Question: Our home is maybe 7 years old. In the last three years a fine crack in the tile floor has occured that is now visibly wider and causing the tile to chip into both small and large pieces. The crack extends the length of the house and includes the front and back porch slabs.

We are also seeing the wall cracks becoming more visible as well. Foundation inspector 2 years ago stated foundation was within standards. Worried this could become something really costly. - Catherine 1/5/13

Reply:

Catherine,

If there is ongoing slab cracking extending the length of a home I am baffled about why your "foundation inspector" said it was "within standards". What standards? Can you ask him or her that question and let me know?

Certain cracks in concrete slab floors are common and don't pose a structural threat, such as shrinkage cracks (though even these can be a source of leaks) but if you're seeing ongoing cracking that is showing up through tile floors, some further investigation is in order.

Question:

i live in a second story apartment with a balcony. the stairs to my upstairs are on the inside. i pulled the carpet out of my coat closet, which sets right on the opposite side of my outside shed and sets over the inside staircase. when i pulled the carpet up, i noticed a 1/4" crack in the concrete floor/slab. should i be concerned? if not, is there a "repair/sealant" i can use to help it from cracking more as it settles? thank you - T Revell 3/14/2013

Reply:

T Revell,

A 1/4-inch crack in a slab, unless it was a deliberate control joint, is not normal.
If the crack extends into a foundation wall, I'd be concerned about settlement and foundation movement.

If the crack is ONLY in the slab it's much less likely to be a structural concern but still could be a source of water or radon gas entry. There are crack sealant products that can handle the sealing end of the problem.

Use the search box at the top or near the end of any InspectApedia page to search for FOUNDATION REPAIR METHODS or search InspectApedia for FOUNDATION CRACK REPAIR METHODS

Question: Cracks in condo floor tiles in San Diego

(Oct 7, 2016) MarcosC said:
Hi,
Great site!
We recently bought a condo in San Diego, CA. This condo was built in the 70's. When we purchased, we noticed a few cracked tiles and separated tiles that ran across the entire living room area. We've been remodeling and have removed the old tiles and can now clearly see a crack in the concrete floor that runs across the living room (from wall to wall). It is wider and narrower at some points (1/8" to 3/8") at the top.

The crack runs in what I can best describe as a 'lightning bolt' figure - not straight, does not completely loop back but does run in generally the same direction. There clearly is a level difference from one side of the crack to the other. The one side seems to "fall off" and is lower and lower the farther from the crack you go.

What can you tell me about this? Is this something we can buy a DIY kit and repair ourselves? Should we get a professional?
Thank you.

Reply:

I'm way too scared to pretend I can diagnos a structural or other crack from a simple e-texct, Marcos, but I can offer a little advice:

Cracked tiles on a concrete slab most often mean that the slab is settling, heaving, or that it was constructed without needed crack control joints. A new or ongoing 3/8" wide crack in a slab is in my view significant enough to ask for some expert help in diagnosing the cause - thus informing what steps are needed to stop further damage to the floor.

Marcos, please see your question and our reply now found at FOUNDATION REPAIR METHOD FAQs

Question:

(Nov 16, 2016) Kelly Dreilich said:
Our house underwent an inspection and the inspector noticed that the southwest corner of our garage slab has settled 3 in, Red line is apparent. The corner represents foundation to the outside wall to the left and the foundation to the entry to the house from the garage. There are not any cracks, pulling away, separation of any kind on the inside of the garage, outside on the brick wall, foundation etc. No cracks in dry wall both inside the garage and house.

The house is a 13 year old custom home in colorado, just south of Denver. Since that is the most inside part of the garage where there is never any water accumulation ever, and we never get any water in the garage at all. The buyers want someone to come out to inspect the slab and make recommendations. They are fearful that the foundation could be compromised in the the future.

We are the orginal owners and I have noticed that red line since we moved in and the house sat for one year before we purchased it and our inspector did not catch it. But I want to know who is the best and most qualified person to come and inspect this part of the garage, a structural/foundation company or a mudjacking company? I want to at least get two assesements to compare evals. Any advise or recomendations would be appreciated. Kelly my email is kdreilich62@comcast.net and cell phone is 3039139903

Reply:

Thanks for the excellent question, Kelly.

To have room for explanation and references I repeat your question and give a detailed reply in the article SETTLEMENT CRACKS in SLABS. Don't hesitate to ask if questions remain, and do let us know what you're told. What you learn will help other readers.

...

Continue reading at SETTLEMENT CRACKS in SLABS - topic home, or select a topic from the closely-related articles below, or see the complete ARTICLE INDEX.

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SETTLEMENT CRACK FAQs at InspectApedia.com - online encyclopedia of building & environmental inspection, testing, diagnosis, repair, & problem prevention advice.

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