Floor slab & tile crack diagnosis & repair FAQs set 3.

 

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.

Page top schematic showing a supported slab on grade design is provided Carson Dunlop Associates, a Toronto home inspection & education firm.

Diagnose & Fix Cracks in Concrete Slabs & Floors

These questions & answers about the cause, diagnosis, cure or prevention of types of cracks in concrete slabs and floors were posted originally at CONCRETE SLAB CRACK EVALUATION - home - be sure to see that article.

Some of these Q&A were also posted first as comments on this page that you are viewing.

[Click to enlarge any image]

Question: long hairline cracks from one wall to the other in a Texas home

2016/04/26

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 2 months 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]

Reply:

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 ?

Reader Follow-up:

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.

Moderator:

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.

Reader question:

(Aug 25, 2011) Anonymous said:

please let me know about kind of cracks in concrete slab

Reply:

Anon, See -

• CONCRETE SLAB CRACK EVALUATION
• CONCRETE SLAB CRACK REPAIR

those pages provide descriptions various types of concrete slab cracks by cause, location, and appearance.

Reader question: how do I send you slab crack photos for comment?

(Aug 29, 2011) worried one said:

Hi, can I upload or email pictures for you to evaluate to condition of the crack(s)?

Reply:

Worried

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.

Reader question: upper cement floor has cracks that trace the pattern of beams below

(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?

Reply:

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.

Reader follow-up

marym said:

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.

Reader question:

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 the 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?

Reply:

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.

Reader question:

(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?

Reply:

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.

Reader question: web of cracks in basement slab in every room

(June 14, 2012) Carey said:

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??

Reply:

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 above was provided courtesy of CCACB - Connecticut Coalition Against Crumbling Basements.

This is NOT a trivial concrete shrinkage pattern - the cracks are much wider than normally seen in cases of concrete shrinkage.

For that type of cracking be sure to also

review FOUNDATION DAMAGE by MATERIAL or INCLUSIONS where we discuss Iron sulfide mineral (pyrrhotite) cracking

Reader question: big crack in the floor has caused movement

(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.

Reply:

(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.

Bill,

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.

Reader question: 2005 home sat empty, stucco falling off, foundation & steps separating

(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!

Reply:

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.

...

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Continue reading at CONCRETE SLAB CRACK EVALUATION - topic home, or select a topic from the closely-related articles below, or see the complete ARTICLE INDEX.

Or see CONCRETE SLAB CRACK FAQs-4 - more-recent Q&A about diagnosing & fixing cracks in slabs

Or see these

Recommended Articles

• CONCRETE COLD POUR JOINTS
• CONCRETE FOUNDATION, WALL, SLAB DEFECTS
• CONCRETE REINFORCEMENT, FIBER
• CONCRETE SHRINKAGE CRACKS
• CONCRETE SHRINKAGE CRACK REPAIR
• CONCRETE STAINS: ID & REMOVAL
• CONCRETE SLAB CRACK EVALUATION
• CONCRETE SLAB CRACK REPAIR

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CONCRETE SLAB CRACK FAQs-3 at InspectApedia.com - online encyclopedia of building & environmental inspection, testing, diagnosis, repair, & problem prevention advice.

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INDEX to RELATED ARTICLES: ARTICLE INDEX to BUILDING STRUCTURES

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