Floor slab & tile crack diagnosis & repair questions & answers:
FAQs about how to diagnose & repair the different types, sizes, shapes, locations, & patterns of cracks found in concrete floors & slabs. Some floor slab cracks are harmless or even just "cosmetic" while others may spell trouble ahead.
This article series describes the types of cracks that occur in poured concrete slabs or floors and explains the risks associated with each, thus assisting in deciding what types of repair may be needed. This series also 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.
Page top photo of a supported slab on grade design is provided Carson Dunlop Associates, a Toronto home inspection & education firm.
Green links show where you are. © Copyright 2017 InspectApedia.com, All Rights Reserved.
(June 20, 2011) Jack Emery said:
In Australia it is mandatory to reinforce concrete floor slabs with galvanised steel mesh which is laid 1 in. from the top of the slab. This eliminates shrinkage cracking.
I don't know Jack and will research the question further. In Australia as in most countries, the local building code official is the final authority so I'd start there.
But in any case, steel mesh won't completely prevent shrinkage cracks that occur as the result of how the concrete was mixed or because of the absence of control joints where needed in the slab. Steel reinforcment particularly helps a slab resist cracking due to heaving or settlement or loading.
Photo above-left: serious cracking and settlement in a concrete floor slab. See SETTLEMENT vs. SHRINKAGE CRACKS for more about this photo.
(Aug 25, 2011) Anonymous said:
please let me know about kind of cracks in concrete slab
Anon, On this page at Continue reading we provide an INDEX to RELATED ARTICLES that includes a live link to - SLAB CRACK EVALUATION - below it you'll see a list of individual articles describing various types of concrete slab cracks by cause, location, and appearance.
(Aug 29, 2011) worried one said:
Hi, can I upload or email pictures for you to evaluate to condition of the crack(s)?
Sure just use the CONTACT link found at top, left side and bottom of our pages to send me photos. We'll be glad t take a look.
(Nov 4, 2011) mary myers said:
I work on the 3rd floor of a building that was constructed within the past few years so it's fairly new. We use the unfinished 2nd floor for storage. Today a co-worker and I noticed that the unfinished 2nd floor (cement) has cracks in it all of which (mostly) follow the pattern of the beams. They aren't extremely wide but I'm worried that they might be dangerous. We did have an earthquake recently and I'm concerned that's when the damage occurred. The fact that they trace the path of the beams is worrisome. Is this normal? Or does this mean there is actual structural damage?
Mary, it doesn't surprise one that there might be shrinkage cracks in a large concrete slab nor that the cracks might follow the location of structural beams buried in the concrete. No one can assess with certainty the significance of the slab cracking you describe just by a few written notes, but it's possible that what you describe is not a structural concern.
The answer to that question will need to be decided by an onsite expert. But in general, if the floor itself is not structural, that is if it is not supporting the structure, then the risk of a structural collapse is reduced. If the floor actually "bends" over the cracks, that is if it has not remained dead flat as poured, or if the cracks are changing in width or length or if one side of the crack is higher than the other, those sorts of clues indicate ongoing movement and a more urgent need for evaluation by an expert.
Thanks so much for your quick response. We can definitely tell that one side of the crack is higher than others in quite a few places. Other than that, I don't think we know have enough experience to properly evaluate the situation. We did alert the building owner so we are hoping he'll get someone in to look at it. Thanks again, I've learned a lot.
Nov 17, 2011) Amber said:
We had a pipe burst and flood our house, and our basement had ankle deep water which then all soaked into the concrete foundation. it took Servepro a long time to mitigate the damage and dry the house, but even after they finished, the concrete read high on the moisture meters. We went back recently (we are temporarily relocated) and we noticed a crack in the concrete that we are sure was not there before. could this be caused by the moisture and removal?
(Jan 23, 2012) Barbara said:
We have a slab foundation. the home is about 12 years old. It has been through droughts and raining season. We do have some clay soil under our house. I don't see any large cracks. I do some hairling tiny cracks. I do see where the side of one area of the foundation is not a straight vertical line. It gets slightly larger at the bottom (where it meets the ground) It is in one area bout 2 feet. Is this a concern? I don't know how long it has been like that. we have had hte house less than 3 years.
(Feb 5, 2012) Anonymous said:
The house I want to buy is in Key West and is built on concrete. It flooded in Hurricane Gloria. I noticed on the side of the foundation a soft powdery section of the foundation. If the rebar in the concrete has corroded since 2005 would that cause it? Could the problem get worse? Is it a minor repair...less than $10K or something more serious. Should I just walk away?
Anon, I can't tell from just your note, but you may be describing mineral salts left on the concerete surface due to wet conditions - search InspectApedia for "Effloresence" to see photos of this condition as well as its cause, diagnosis, and cure.
(May 23, 2012) Anonymous said:
in the garage of our row house, Windemere, there is a concrete sill (pony wall?) on top of the slab the seam was not sealed and water pours in and freezes in the winter to make a skating rink on our garage floor. we are seniors and this fall potential needs to be fixed. ROHIT refuses so we must do it our self... HOW CAN WE FIX THIS?
Anon I'm sorry but I don't have a clear picture of what's going on so can't give an intelligent "how to fix" answer. Generally we want to keep water away from the building - that's the first choice and approach, rather than relying on a seal at the last possible point of water entry (that's a second band-aid approach). I suggest asking a local mason or building contractor or home inspector for a diagnostic inspection to make the cause of the water clear - that should then lead to a sensible fix.
I am under contract to purchase a newly constructed townhouse in a pod of four. Today I noticed an extensive web of cracks in the basement slab - long, fairly straight cracks in every room! The house is 30-40 feet from an irrigation canal.
My realtor has scheduled a meeting with the contractor to look at the cracks, but I would like a second opinion. How many cracks are too many??
Carey, if the cracks are very straight they may be showing up expansion joints - tough to say without seeing some photos and knowing the construction. Or you may be seeing very fine shrinkage cracks.
You're welcome to send some sharp photos using the CONTACT US link found at page top/bottom. And let us know what the contractor advises.
Concrete crack photo shown here was provided courtesy of CCACB - Connecticut Coalition Against Crumbling Basements. This is a concrete shrinkage pattern but the cracks are much wider than normally seen in cases of concrete shrinkage.
(June 14, 2012) Anonymous said:
I am looking at purchasing a house that has a fairly sizable crack in the floor. It appears that the concrete has seperated. The two sides of the crack are even with little to no heaving. The house does have a problem with little to no roof truss system bracing. This has caused movement, and cracks in the drywall.
andering if this movement in the truss system could have transfered through the walls to the slab to cause a crack up to 1/4" wide in places. It is a floating slab, and there are no visible cracks in the stem wall. Or any other ideas why this may have happened?
(June 19, 2012) Bill Mendenhall said:
Have a house that is 36' wide with crack all the way across. At footing there is a crack, but closed. From inside edge of footing on both walls the crack in the slab is about 1". No wall cracks at slab crack location, but there is sheetrock crack in other locations in the house. Any thoughts? Did the slab shrink? Witnesses to pour said that the temperature was over 100 and the contractor had no water on site.
(June 20, 2012) (mod) said:
Anon: if roof loading on walls caused wall cracks, I'm not sure how wall cracks cause random or cross-floor cracks. Imagine a wall, even securely bonded to a floor slab, leaning outwards. It would require a remarkably strong connection and tremendous force and a bit of a lean before that pressure might affect a concrete floor slab - and if it occurred, the cracking would be most likely close to and parallel to the wall.
I think more likely you are describing a building where the same contractor made multiple mistakes or shortcuts.
at the joint of foundation wall to footing there may appear a joint or seam that looks like a closed, straight "crack" where two different concrete pours (footing and wall bottom) meet.
If there is a regular gap between the floor slab and foundation wall all along the floor / wall length, it may be slab shrinkage, though 1" is 4 x bigger than I ususally see.
Slab shrinkage amount is a function of the concrete mix, site prep, and pour conditions.
If there are no water (nor radon) leaks through this gap it might be OK or you may find later that it is a water entry point; the best fix in that case is to get water away6 from the building and maintain the gutters and leaders.
(July 8, 2012) Shelly said:
Trying to find out what is going on with my home. It was completed in 2005, sat empty until we bought it in Dec of 2007. The stucco is falling off the outside, the right side of my garage door seems to be buckling, the foundation in the garage has spider webbed with small cracks and has one large crack running from the entry door all the way across the garage and outside.
There is a step on top of the concrete foundation, leading to the entry door that seems to be separating from the wall and the foundation, our upstairs A/C (leading to the office above the garage) has stopped being able to cool.
We replaced with a new unit and still so signs of it being able to keep up (almost like I've lost insulation or something?), the laundry room vinyl (just the other side of the garage) is bubbling and pulling away from the wall. This is a pretty new house and I am frustrated. This shouldn't be happening! Suggestions? Thoughts? Insights? Please!
Shelly, your stucco job soundsnlike a problem. But your question is in an article on cconcrete floor crack diagosis. You will find better information reviewing our stucco articles found under "exteriors" (links across page top) or just search InspectAPedia for Stucco Damage to see a list of diagnostic articles.
It sounds to me if there are multiple problems including backfill settlement.
Most likely you or an expert will want to make a few test cuts to see just what is going on.
(July 27, 2012) Garry Everett said:
We have just had a 20 x 15 foundation installed (1 days old) for a patio room and is has numerous cracks already is this normal for a foundation that does not have any stress relief?
Garry, cracks that appear rapidly and early during curing of a foundation or slab may indicate difficult pour conditions such as very hot weather, or a problem with the mix, or even settlement if the site was not properly prepared. You should ask your contractor to take a look at the situation. Keep us posted.
(Aug 13, 2012) Steve Snoreck said:
Looking at purchasing an 35+plus old home. Slab in garage has a crack and has dropped about a(1/2 to 1")on one side all the way across this 2 car garage. Also, where slab crack meets poured foundation walls, there are cracks in the foundation wall and step cracks in brick veneer. Is this a major fix and deal breaker?
Thanks for your help
Steve if the whole slab has settled without cracking and you see a prior concrete line on the garage foundation wall that marks the slab's original height, the explanation may be poor compacting of fill before the slab was poured
(Aug 28, 2012) DMN said:
We recently ( 2wks ago ) had a new concrete patio put in. A sizable crack has now formed. is there any recourse for this? The contractor basically says this happens and we are out of luck. Is he responsible?
(Sept 9, 2012) Mark M said:
We just finished a new house build and have noticed spider cracks in the garage floor running from an interior wall to a centre floor drain. The floor was poured in winter conditions and and 6 months later these cracks are showing up. Is this a building error or part of normal settling? How can this be repaired?
(Sept 20, 2012) Cracked slab causing discolorati said:
Our kitchen floor (either vinyl or linoleum) has started staining over the past six years. The stains look like water stains.
We have a concrete slab underneath and have had some cracking in the garage. But I am wondering whether the kitchen staining could be from a crack underneath the floor. Could water stain the floor without causing any flooding or noticeable issues other than the dark color? The flooring is original, about 20 years old and the discoloring is no where else. Thanks for any response!
It sounds as if you are talking about sheet vinyl flooring. It may stain from a spill from above if the surface has been damaged,or there may be moisture comingnup through the slab.
(Oct 1, 2012) Carol L said:
My home is currently being built. Upon inspecting of the 'slab' there are large cracks that mimic the 2007 Daniel Friedman picture below.
y builder tells me he is going to 'fix' it. How certain can I be that 1. no water will seep through the cracks and 2. that the concrete footers will remain firm and the walls won't have settling issues.
(Oct 1, 2012) Carol L said:
My home is currently being built. Upon inspecting of the 'slab' there are large cracks that mimic the 2007 Daniel Friedman picture below. My builder tells me he is going to 'fix' it. How certain can I be that 1. no water will seep through the cracks and 2. that the concrete footers will remain firm and the walls won't have settling issues.
Nancy, in the article links at the start of this article you will want to read
FROST HEAVE / EXPANSIVE SOIL CRACKS in SLABS - separate article
If your problem is a home built over expansive clay soil there are systems to address the cyclic movement that would damage a slab; without fixing the cause, just fixing the cracks would be futile.
Also you'll want to have an expert examine the building to be sure you're making the right diagnosis and that there is no related foundation damage.
5/4/2014 Mark said:
Is there a way to know if a crack was caused by settlement vs. stress caused by concrete slab that broke vaper barrier for purposes of brining drainage to basement bar.?
What kind of professional is able to evaluate changes caused by this change in slab integrity and give us proper solution in that rain water penetrated this hairline crack recently?
Mark I don't completely understand your description, but in general an experienced foundation contractor, a building inspector with experience in foundation inspections, or if necessary a structural or civil engineer IF that person has expertise and focus on foundations, could all address your question.
Typically we look at the size, pattern, location, history, and context of a crack and usually those data point to a probable cause. If you want to use our CONTACT link to send along some sharp photos of the crack and others from a more distant perspective of the wall or slab and the building and site then I might be able to comment further.
Settlement under a floor slab that causes cracking will usually also show up as out-of-level floors, a difference in floor height on either side of the crack, and possibly we will find correlations with poor site prep (inadequate soil compaction) or mis-handling of roof or surface runoff.
Watch out: check that the cracks don't extend into and continue in the foundation wallls - a potentially more serious problem.
(July 29, 2014) M fetter said:
I had a contractor pour a driveway pad 25' by 32'- 5 in. thick nov. 19 2013. contractor did'nt cover with a blanket temp was aprox 30 deg. outside and didn't cut till four day's later. slab is cracking all over the place. may I have yer input in this matter please ? thnx
I'm doubtful that anyone can diagnose concrete cracking from just your brief e-note; you're welcome to use our CONTACT link (page top or bottom to find email) to send us some photos of the cracking you observe. Cracks might be related to the curing process, shrinkage, settlement, bad mix, etc.
From your note we still don't understand your "cutting" question. But you might want to review the control joints article at CONTROL JOINT CRACKS in CONCRETE where we describe the timing, depth and location of these construction details.
Aug 2, 2014) austin said:
we just experienced a major sewer flood in our basement 2ft that sat for almost 3 days when we were gone. we have a sub floor in the basement and we do know we always had a crack in the basement floor but it now looks like that crack heaved a lot under the sub floor they are removing the sub floor right away but insurance is kinda saying that its impossible for a basemnt floor to heave from a flood is this true?
No, the insurance company is mistaken. It's not impossible for a basement floor slab to heave in response to flooding.
For example, expansive clay below a slab could when soaked, expand and push the slab upwards. Or alternatiely, soaked sewage waters may have caused settlement of poorly-compacted fill below a slab, contributing to uneven settlement of the floor on either side of an existing crack.
Often a careful examination of a crack can find evidence of its age and can identify recent movement by noticing raw or fresh surfaces on either side of a crack in the slab, wall or other masonry material. That detail can help with insurance analysis too.
(Aug 11, 2014) Adam said:
I have an opportunity to buy a property in Northwestern Wa that has a 36x60 slab already installed. I believe it was intended for a modular home that never quite happened. I would like to be able to build a smaller structure on part of the slab, say 24 x 36. Is there a legitimate way to do this?
Probably yes, Adam but you need to do some exploring. Typically the slab would have been poured with a perimeter foundation intended to support the weight of the building on its perimeter or edges. There may have been other points of support inside the slab as well. Without knowing the slab design and ingredients I'd be careful about placing loads just anywhere.
And careful attention to sealing details will be needed at the smaller building's perimeter to prevent water from entering the structure.
You might, for example, need to build a smaller building permiter footing of solid concrete blocks set atop the existing slab. Check with your engineer about the slab thickness, hardness, reinforcement, versus the loads that will be imposed by the new structure. Most likley you'll be fine.
(Aug 11, 2014) Adam said:
Thanks for the response. As a followup question, how would drainage be handled? If the building ends on top of a slab (i.e. a 24x36 structure on a 60x36 slab), how do you stop rainwater from migrating under the smaller-than-the-slab building?
If you are not going to cover the protruding slab with exterior roofs, say as in a porch roof, the use of a sealant at the sills is about all you've got. If I were doing such a job I'd build a new masonry sill at least 1 solid concrete block high and set my wood framed wall sills atop that to permit a water tight seal at the slab and to avoid putting wood onto a sometimes wet surface.
10/10/2014 Eng.Hasan Al-Bahkali said:
very important subject
(July 4, 2015) Philip said:
If structures already in place make it undesirable to expose the foundation wall (for crack repair) along all of its length is it reasonable to install exterior insulation (as in FPSF style) on only a part of the foundation wall? (similar with improved drainage, etc..)
The section with problems is where the foundation is lower (a garage joined to the house but with entrance at lower level)
I'm not sure, Philip. A lot depends on the extent, severity and cause of the cracking, the crack pattern, shape, location, and thus the implication for the stability of the foundation wall. I mean to say if there is a collapse risk clearly we need a professional assessment and foundation repair. If the crack is not structurally significant (engineers may disagree since some call any crack a "failure") and if the only concern is water leakage, sure, steps outside to get water away from the foundation are appropriate.
I'd add that an outdoor repair to get water away from the foundation is a better approach than an interior band-aid anyway, but the cost is usually more as well. Start by making sure roof and surface runoff are directed away from the foundation.
(July 22, 2015) chris west said:
we have several hairline cracks in our concrete basement floor which are leaking. the cracks are hairline, and not wide enough to force any products down in the crack.
any suggestions on how to resolve it?
Hydrostatic pressure is usually more powerful than we'd imagine, so I agree that not only can you probably not successfully force some sealer into a hairline crack but it will probably be ugly.
1. Best: working outside, for example checking surface and roof runoff, remove or redirect the source of water that's passing under the slab
2. Second best: cut a sump pump hole through the floor, install a sump pump, and over time the pump will lower the water table under the floor, relieving the water pressure and stopping leaks up through the floor
3. Hire a repair contractor to cut open the cracks using an inverted Vee shaped cut, making the crack opening large enough to insert an epoxy sealer that can be applied when the contact surfaces are clean and dry.
At InspectApedia.com see WET BASEMENT PREVENTION at inspectapedia.com/Energy/Wet_Basement_Prevention.htm
Use our CONTACT link at page bottom to send me some photos and I can comment further.
(Aug 28, 2015) Dejolly said:
We are building a new home. Just beginning Sheetrock. Have noticed several cracks in concrete slab. All are running east to west pattern. Should we be concerned. Should we calls in a structural engineer?
DeJolly I can't diagnose your slab cracks from just your e-text. They may be shrinkage cracks and not significant or they may be important. Take a look at the article above for examples of both. If the cracks are regular they may be marking pour joints or concrete form locations; if you can't figure out what's going on you can both send us photos of the cracks - our email is at the page bottom CONTACT link, and you can and should ask for help from a local, exprienced masonry contractor or engineer.
Watch out: don't hire a "generic" engineer nor contractor who does not have expertise & experience in concrete construction & crack diagnosis & repair.
(Sept 21, 2015) Anonymous said:
I am purchasing a new construction adult housing. It is a ranch with attached 2car garage. Last week I noticed that the concrete floor of the garage had a criss crossing crack - all the way from front to rear and crossing in the middler from right to the left. Why would new construction already be cracking? I initially looked at this property end of March, but did not think to look at the garage floor.
At that time it was just a shell. windows were in but walls were just studded. I also know that the area is clay. My daughter lives about a mile away, also has clay. Her house is 14 years old and the garage floor has no cracks whatsoever. Why do you suppose this happened?
Omission of control joints
Expansive clay soil - heaving or shrinking and settling
Take a look at the article CONCRETE SLAB CRACK EVALUATION for details
Oct 16, 2015) Jeana said:
My house was built in 1955 on a slab floor. I can feel the floor giving way under my laminate flooring. Its about 10 feet long and the gap is about 4 inches. Can that area be repaired or does the whole front room have to be done? Why would this happen? My pipes are in the walls and go out the opposite way of crack.
With apology that it sounds more glib than intended, any problem can be repaired, the concerns are 1. making the right repair so as not to have to repeat it and 2. cost.
Various methods including insertion of piers or pumping concrete below a sinking slab (mud jacking) are common repairs, but don't start asking for a repair before knowing the cause.
I'm not sure what 4" gap you mean: if you mean a 4" wide crack or floor that has settled 4" that is a major movement and even though your home is built as slab on grade, the building could be unsafe - for example if a sinkhole is developing.
You need an accurate diagnosis of the cause of the problem before a repair can be properly chosen.
(Nov 3, 2015) Joanne said:
Last May I moved into my newly built house. A few weeks ago I turned on the garage floor radiant heat and now I have excessive cracking so much so that my garage floor looks like a jig-saw puzzle. The floor has been in well over a year without any cars parking in the garage. This is a vacation home. We are thinking of spending money and days to fill in the crqacks than epoxy over.
Should I be concerned about the future of the garage floor and not epoxy just yet?
oanne something sounds wrong with the slab construction or the radiant heat floor construction as such cracking is not typical; Before simply filling cracks with an epoxy I'd want to know what's going on. It's possible that insulation was omitted below the slab, that backfill was left soft, or that other snafus are going to mean further trouble. If you have photos of the cracks and also importantly of the floor during construction, use our page bottom CONTACT link to send them to me for comment.
(Nov 7, 2015) Scott said:
We are about to sell our home and have a series of cracks in out garage. This is a concrete slab home. The cracks are raised, at their highest point, 1/4 to 1/8". We know of roots in our yard, but do not have any major trees that close to the house. Are we in big trouble for an inspection?
Scott, not to put too fine a point on it, the range of home inspector competence, ethics, and ability to communicate is stunning, so I can't predict what fuss may be made about cracks in a garage slab. I would want to see the crack pattern, location, building history, signs of ongoing vs old movement and other factors before forming an opinion.
Shrinkage cracks and slab cracks that do not extend into the building supporting structures such as a footing or a concrete wall or stem wall are not normally a structural concern so are less scary.
Not just tree roots but settlement and tipping can cause one side of a floor to be higher than the other across a slab crack.
A crack up 1/4" can be a trip hazard regardless of cause, though depending on its location, repair may not be urgent.
If I thought there was ongoing settlement I might think more extensive investigation was justified and that a costly repair could be required.
At the Article Index link given above you'll find detailed articles on evaluating cracks.
(Jan 10, 2016) Eng.Hasan A AlBahkali said:
concrete craching in hot countries this subject is very important
Indeed proper mix, curing rate, moisture control are critical in good slab installation in both hot and cold climates. You may see contractors covering a slab to protect it from rain, from too-rapid moisture loss, etc. or using special additives to compensate for temperature.
(Jan 13, 2016) Saurabh Heerekar said:
Mine is a newly poured concretre slab just about 2months old,and I have noticed a huge crack on my slab which actullay leaks water drops directly inside the room!
I am seriously concerned about this problem and hoping to get a reply asap!
Note:The water drops aren't leaking from a plumbing pipe defect but from the slab itself!
I agree that this sounds like a serious defect and one that merits an onsite expert; there's not enough in your e text to speculate about cause nor effect on the building.
(Mar 20, 2016) Sue said:
we added an addition on our house which is on a cement slab (no basement).
The addition is in back across the entire back of house which made our kitchen bigger added a bathroom and living room bigger, we put ceramic tile in kitchen and after a few years it had a hair line crack where addition meets the cement the new cement slab we poured is settling, so we fixed the tile and under rug in living room smoothed it together using epoxy in cement and it is cracked again
how can we fix this problem? I am desperate for answers please help! my email is email@example.com
Sadly, Sue, fixing tile cracks traced to slab settlement will never work by being repaired from above. You'd need to understand an fix the cause of settlement of the new slab. It may be that the site was not properly prepared, or a slab is settling on poorly compacted fill, lacks adequate footings, or there could be a problem with handling roof runoff or surface runoff around the home. You need an onsite expert, perhaps an experienced mason, home inspector, or an engineer who is familiar with residential slab failures. Keep us posted.
2016/04/22 Danielle said:
My slab foundation has a crack in an outside corner of the house. It's path is from one wall to the other wall, about 11 inches long.
I discovered this crack when the carpet was removed. I see no water damage, but there is a huge shrub that was planted way too close to the foundation which means the roots may have caused this problem? I have not seen any bugs either. Radon gas is probably not a problem since this house is a sieve (not really great construction). Can I leave this crack alone and carpet over it or should it be inspected?
Danielle I would not carpet over an open crack; I'd seal it first.
Hi I live in Texas and planning to buy the attached home (76210), which is under construction. yesterday when I visit this place, I have observed long cracks all the way from one end of the wall to the other end. (attached two photos IMG_0558.JPG shows only one half of the side).
As I understand this is 3000PSI concrete poured about 2months ago. I have read some where on your site that as long as the lines are not straight it should be okay, however seems these are straight lines and concern me. can you please help with your evaluation?
I didn't find a place to upload in your site, so attached them through email. Thank you for reading my email. - Anon [by private email to editor]
Is the floor dead flat across the cracks?
Was the pour done in sections?
Are there expansive clay problem soils in your area?
Does the floor contain control joints?
Are there pipes or conduit buried in the slab?
Was the soil compacted before the slab was poured?
Looking at the wall-slab abutment, is there sign of slab settlement ?
The floor is not dead flat, but I see a little curve (like U shape) on the floor all across the crack. (the crack is at the bottom of U). Regarding the pour done in sections, I am not sure, I will get that information tomorrow morning from the builder.
The floor was not done in sections, they pour the entire slab in one shot & the seems like floor is not dead flat.
So with the apology that I cannot possibly know what's really going on simply by e-texting, the floor could be settling due to inadequate site compaction prior to the pour, or it could be cracking along lines transmitted from a pipe or conduit or buried form in the slab, or between subsequent pours.
If the slab has settled downwards since pouring (look at the abutment of slab to walls) that would often confirm poor soil compaction in those areas, but that clue is not available in all cases. E.g. if a slab rests on the edge of a footing or is pinned to a wall, it may settle more in the center and not at all at the walls.
The size of your slab cracks are not a huge alarm - the look hairline in width. However depending on what caused them, and considering how early they appear in the life of the slab, more settlement, movement, cracking could be in your slab's future.
Watch out: if you see cracks appearing also in the foundation walls, particularly near the floor slab cracks, I suspect more serious settlement is going on.
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