New slab cracking concerns

[BadMannerz]

I have been reading for days about slabs cracking. I am concerned about an issue I'm having with a new build and a 3 month old slab.

I haven't found any comparable issued exactly like mine so I figured I would post it. The slab is 2000 sq ft and 5'' thick. It has multiple cracks that have formed and I understand that concrete will crack.

My main concern is a crack that starts at the outside of the apron (where the driveway touches) and runs all the way through the center of the slab and ends directly across. Total this crack is 43' long. The build is 50x40 with a 3' apron. There are no expansion joints or cuts in the slab. During the construction (now that I think about it) I never saw any compaction equipment on site.........

The slab has already been polished to a shine, I mean really polished and I feel like I wasted my money on having my dream shop floor polished at this point. I'm starting to be concerned about even installing my 10k two post?

I will post up pictures this evening.

 

[shadyluke]

My slab (30x40) has no cut expansion joints either. My builder used a "keyway" joint that is set just below the surface. As the concrete cures it cracks on that joint. I'm left with a very straight crack that is much smoother than having an expansion joint.

I also have a 5" slab with fiber and wire.

 

[kd3pc]

no cuts or expansion joint will lead to cracks. Ideally you would want the cuts made earlier on. I would see what others suggest here about making some cuts...or not..especially in light of finished floor.

 

[matt_i]

The idea with the "crack control joints" are they setup a well-defined and eye-pleasing "weakest link" in the concrete to give it a place to relieve internal stresses.

If you don't saw or trowel them in you relinquish control and leave the cracking to go randomly.

Hopefully you put some steel reinforcement so cracks will stay tight over time.

 

[BadMannerz]

There is wire in the slab. But a crack splitting the entire slab from one end to the other? As well as others that are growing as well. Shouldn't expansion joints or relief cuts be common knowledge for a concrete professional? My builder knew from the beginning that the floors were to be polished. The polishing company and my builder actually communicated to make sure they were on the same page. If I had known the slab was going to crack all over the place I wouldn't have paid to have the slab turned into a mirror.

I guess what I'm getting at is this acceptable, or is there negligence involved somewhere that cause this to happen.

My builder will be on site on Monday to see what is going on. So between now and then I want to have all the knowledge available to ask the correct questions to see if somebody screwed up. I hate to think this is something that I have to live with after all this investment.

 

[BadMannerz]

This is why I'm getting concerned over all the cracking (as well as structural concerns and issues in the future). This pic is just an example of the finish.


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[BadMannerz]

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[yaidunno]

I'll start off by stating that I am not an expert in the field. I have helped with some flatwork, so I know enough to be dangerous.

The negligence claim is, IMO, a double edged sward. For a person to hand over $10-20,000 for concrete work without at least knowing the basics, or reviewing the conditions with the contractor prior to the pour, is negligence on the owners part. I'm by no means suggesting that you or anybody else need to be an expert in the field in order to hire it out, but it is a huge investment. And as with any investment, you'll want to cross your "T"s and dot your "I"s. Now, whether the contractor was negligent, or simply not qualified for the job will be very difficult to determine.

I am of the opinion that, depending on soil conditions, the top soil should have been stripped from the build site until a stable soil was found. This usually takes no more then a foot of depth to reach. From there, a suitable base material should be brought in and properly compacted. A vapor barrier can be put down. Rebar would then be laid in a 2'x2' grid. Wire will not do much keep slab sections from shifting, as it will easily be bent and sheared with enough force. Saw cuts would be made in the slab within 6-18 hours to control where the shrink cracks occur.

The entire process above was gone over between myself and the contractor I used to ensure that no surprises were had. Without knowing your location, or details on how the site was prepared, its hard to say if the contractor you used cut corners. If the cracks are simply hairlines and no shifting has occurred, then you don't have much to worry about. If there is separation and shifting occurring, you certainly have reason for concern.

Beautiful floor and workspace you have BTW. I certainly hope that your cracking is only superficial, and you can have some peace of mind regarding your slab.

 

[Cyberbear]

Not knowing where you are located makes it more difficult to suggest why the crack is happening. No contractor I've ever used has claimed they can prevent cracks, too many variables, and often too many fingers in the pie.
I've been very fortunate over the years, as none of my slabs has any cracks, except for a small 6" crack at an inside corner which was expected. My last slab was a 16 yard pour of six bag mix, rebar at 12" o/c, 4 horizontal rebar in the 16" x 24" footings and a monolithic pour of about 4/5" thick.The slab was sealed and properly cured before any construction was done. Your situation suggests a large area under the slab settled after the pour. What happens when you wash down the slab? Are there deep low spots that fill with water? I've read that different parts of the country have differing amounts of naturally occurring chemicals in the water that affect the final out come. Our water here comes from local wells drilled deep into the aquifer.

 

[rburke65]

Did we have any type of contract with the concrete finisher? Relief cuts maybe common knowledge as is mahogany trim, but if it isn't in the contract......if you are not paying for it....you are probably not going to get it. I'm guessing you will have to wait and see what your contractor says

 

[tinmanwpk]

Sorry for your problems. Your floor is beautiful. I understand your concern.

 

[Falcon67]

You'd need a local foundation expert IMHO. Someone familiar with the soil types and that could take a look at how your slab was placed. We're on expansive clay here and it takes footers and grade beams with rebar to keep things fairly steady. My old shop was 4" slab on grade, no footers or beams. It cracked - big time crack - diagonally. The new 24x40 slab hasn't moved a bit - 12x12 footers, 12x12 grade beam longways and three shortways. Your post doesn't indicate your location, but you might review any available foundation requirements for out buildings/garages posted by a local large city planning department. If those call for certain site prep and foundation construction criteria that your slab builder didn't do, you could be in for issues.

 

[Radix2]

First of all, beautiful floor.

Second, you say you are aware that concrete shrinks and cracks as it cures.

So the concern seems to be a crack that goes all the way across. I think this is to be expected for an area that large. I also have a 40x50 area and can see that there are fine cracks in the control cuts that go across the entire slab. It simply makes sense that shrinkage across the large areas will want to go all the way across. So if that us the main issue, I don't think it is particularly unusual.

Unless you have settling and vertical displacements, you have normal shrinkage cracks,

Was the choice to put in control cuts fully discussed during contruction?

I have an additional area where I decided not to put control cuts. Yep has hairline shrinkage cracks, but fits the look I wanted better than sawing it up like patio squares.

 

[machsnell]

Previous poster said shame on you. That's not the case. As a homeowner that is why you hire a contractor to do the right thing or have subs that do the right thing and use standard industry practice at a minimum and make recommendations gained from (hopefully) years of experience performing their trade.

Shame on your concrete sub who did not firmly recommend at a minimum saw cutting joints or using zip strips or some other method of having a joint or two during placement with the remainder happening day after the pour.

You can't have 2000 square feet of concrete without a joint to control the cracking.

Lots of things can be done during and after placement to minimize cracks such as fiber or microfiber in the mix lower slump slower curing with water and blankets or plastic. As well as proper subgrade and stone prep.

At this point to keep the slab I would install saw cut joints close to but not on or crossing the cracks that you currently have they should be somewhat deep in hopes to relieve the stress of the unnaturally occurring crack that you have.

Myself as a contractor I would have mandated that relief cuts we're done after the pour but would have also mandated one or two strips in the concrete during placement to allow for cracking as concrete cured.

Your Builder should have also known this and recommended saw cuts to relieve himself of the liability for cracking if you did not want them.

It is a beautiful floor and I am sure you are crushed to see cracks popping up now that it is finished. PM me if you would like to discuss some details and get some information before your meeting with the builder.

Sent from my SM-G900V using Tapatalk

 

[BadMannerz]

Cyberbear, I am in Central VA.

Rburke65, the entire build was through one contractor, start to finish. The contractor was well aware that the plan was to have the slab polished and how the building was going to be utilized and we even went as far as having the polisher (hired by me after the building completion) and the building contractor talk together about the slab expectations.

Falcon67, the entire build was run legally through the county mandates and all inspections approved.

Radix2. Yes, my main concern is the crack that splits the build down the center. I was never given the option to have control cuts. It was never brought up by the contractor whether I wanted them or not.

Machsnell. I was not even going to reply to Yaidunno. Silly remarks. Nothing was done after the pour. The contractor was gone when I got home. The the next day the apron was formed and poured. The the contractor was gone, The following day he called to make sure I was happy with the entire job (which I was). Two weeks later, I noticed some cracks starting to form. That has led to where I am today. Yes, I am crushed by seeing these cracks popping up! I will take you up on that contact seeing how we are both in VA.

Ebfabman, I do metal fab, build, modify sled pulling trucks, welding, CNC Plasma cutting, vehicle maintenance and repairs, overall gearhead trying to make something more of it.......... Most of the cutting and welding happens in the attached shop that you cant see in this picture.

Here are the pics showing the apron running into the shop, and then inside the shop. Just as a note. The crack is not flush on both sides. A straight edge will catch the lip of the crack. There are other cracks as well, on the apron and inside.

And thank you for the compliments. This much needed additional space has been a dream and I decided to just do it. When a customer wants to bring you a sled pulling truck that's worth 100K or more...... You want to look as professional as possible when you role up those doors for him/here to drop their investment off.




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[yaidunno]

My intent was not to offend you, or anybody else on here. Clearly it has. I am not shaming you, and I apologize if you feel that way. To each their own. Best of luck with your situation, sincerely.

 

[BadMannerz]

Thank you Yaidunno. I did my research the best I could and put trust in a builder. I understand your point. But in the same regard........ I do not expect one of my customers to ask me the type of filler material, the weld processes, the amperage, the amount of post heat, pre heat, or annealing needed after the weld process is finished...... That is why he came to me....... If he already had that information and skill, he would have done it himself. Sincerely.

 

[yaidunno]

Thank you Yaidunno. I did my research the best I could and put trust in a builder. I understand your point. But in the same regard........ I do not expect one of my customers to ask me the type of filler material, the weld processes, the amperage, the amount of post heat, pre heat, or annealing needed after the weld process is finished...... That is why he came to me....... If he already had that information and skill, he would have done it himself. Sincerely.

Completely understood, and looking back, perhaps my wording did come off a bit harsh. As someone who is also in the fabrication trade, i can certainly relate to your analogy.

-Bryan

 

[BadMannerz]

Its all good Bryan.

 

[Rocky98Formula]

Does the crack in your apron line up with the crack through the rest of the slab? And were the apron and slab poured on different days? If so, I find that strange and want to draw attention to that before people chime in.

 

[wake74]

Unfortunately concrete cracking has become the bane of my professional existence as of late, and have been dealing with the PE of record, verses the GC (and their concrete sub), third party concrete experts, the owner, etc.

The one thing I've learned is that all concrete cracks, and the reasons for it are varied, and often difficult to do root cause analysis, even with more structural engineers than you can shake a stick at looking at a specific crack. There are just so many variables when placing concrete on a slab on grade (air temp, wind speed, rebar temp, sub grade compaction, rebar vs no rebar theory, quantity of rebar, does rebar cross the joints, lots of variables in the mix itself).

I'm not a structural PE (just a mechanical), but I would say these look like typical contraction cracks to me. There doesn't appear to be vertical displacement, but hard to tell from the photos. Contraction joints placed at least 1/3 through the slab would have helped this, but I certainly have learned that helped prevent doesn't always equal eliminate. Concrete seems to be a fickle beast with a mind of it's own at times.

Vertical displacement could imply that there was sub-grade compaction issues. I doubt most residential contractors would proof roll the slab, but hopefully, they would at least have had a basic grasp of compaction, and didn't pour the slab right over the top soil.

I would partially disagree with the post above that says you only get what is in the contract. A licensed contractor still has to provide some basic level standard of care. Battling a standard of care case for a residential project would probably not have a positive ROI though.

There are lots of good industrial crack fill products, but despite our best recent efforts (where money isn't really an object), the best filled crack, just looks like a filled crack.

Best of luck, and welcome to the losing sleep over concrete cracks club

 

[BadMannerz]

Rocky98formula, The crack that starts at the apron STOPS directly across the slab from where it starts which is almost dead center of the 50' span of the slab. It is not a straight line however. It wanders off of a direct path about 6' and then comes back to the center line of the slab. Hope that makes sense.

Wake74, Topsoil was removed from the sight, a mixtures of 57's and C&R was used for the back fill. I also might add......... The slab sight has 18" of fall that was back filled using the 57 and C&R mixture.

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These are the major cracks shown in red. Sorry for the poor illustration.

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[willymakeit]

Was there any expansion material placed around the posts? Concrete will usally start out of these reentrant corners. I would also suspect that the crack across the slab is contraction and could be following the pour/place line or cold joint.
There's lots of variables. They don't help now but such things as contraction cuts, transverse bars, the list goes on. A 3rd party inspection only verifies correct materials and methods were used. Strange things still happen.
Do you have any documentation of how the slab was placed, subgrade, reinforcement, slump, mix and testing? This could help your case.

 

[SiGmA_X]

I've never seen that big of a slab without control joints, but even with them, its concrete: it gets hard and cracks.

What does your polisher say about the cracks and the polish? I thought there are fills you can use before polishing that basically eliminate the visibility of the crack. I know that is the case with acid wash and staining - my parents did it with their cabins 1960s slab that had carpet on it before, as well as some cracks.

Good luck, that looks like a great structure and what you do sounds really cool. I'd love to see some of your projects in it once it's up and running.

 

[brownbagg]

it crack because of no control joint. google concrete curl

 

[DougWil]

The rule of thumb is 2.5 (feet) X the thickness (in inches) max, so you should have had a crack control join every 12.5 ft MAX.

A bigger concern is they may have not properly compacted all that 18 inches of fill or compacted at all??

Too late to worry about it now, and you are not alone.

Guys come and post here all the time about the concrete cracking/finishing/curing/dusting issues that could have been reduced or eliminated had they searched or inquired before pouring.

Just enjoy your nice shop and realize you are going to drop stuff and chip, scratch up the floor if you use it.

 

[BadMannerz]

Willymakeit, I do not personally have the documentation on the slab. The contractor an I will be meeting on Monday to discuss what is going on. When I told him my what is happening and what my concerns were he was very surprised to here this. He reassured me he would do what was necessary to correct the situation. He was very easy to deal with during the build process and seams like an honest guy. Hopefully this will work itself out. But in the end, it sounds like I'm going to have to live with a bunch of polished cracks.

 

[wssix99]

Radix2. Yes, my main concern is the crack that splits the build down the center. I was never given the option to have control cuts. It was never brought up by the contractor whether I wanted them or not.

As others have said, your cracks are not structural and look like textbook contraction cracks, cause by tension that builds up when the concrete shrinks as it cures. Initial cracking in the middle would be expected as that is the point of maximum tension/stress. (Once that crack forms, you may see cracks follow in half of the remaining distance as the point of maximum stress changes.)

Food for thought:
- It is possible to have a slab without joints. I have a floor in my house that was designed like this but it takes an ungodly amount of rebar/expense to do this. (My 4.5" slab needed #4 rebar on 8" centers.)
- It is common for some industrial floors to be polished without joints and to let the cracks form as they may.

^ If you look at big box stores, you may find a lot in your area like this. All the tilt-up buildings in my area have the slabs poured, no saw cuts put in, and they just let the cracks form as they may.

So it could be intentional and not negligence, but I would expect a contractor to have enough sense to know that cracks will form and that wouldn't be acceptable for a person's personal garage space - particularly when going to the extra expense to have it finished.


I'm interested to see what the contractor proposes as a fix. There are some things that can be done to make the floor look great - but the aren't cheap.

 

[brownbagg]

yes you can pour concrete without cracks, the problem is, they labor doesnt care if it cracks or not, not their problem

 

[lakeroadster]

The rule of thumb is 2.5 (feet) X the thickness (in inches) max, so you should have had a crack control join every 12.5 ft MAX.

A bigger concern is they may have not properly compacted all that 18 inches of fill or compacted at all??

Too late to worry about it now, and you are not alone.

Guys come and post here all the time about the concrete cracking/finishing/curing/dusting issues that could have been reduced or eliminated had they searched or inquired before pouring.

Just enjoy your nice shop and realize you are going to drop stuff and chip, scratch up the floor if you use it.

And that's an excellent summary! The beast has been born... worry at this point is futile.

Thank you Yaidunno. I did my research the best I could and put trust in a builder. I understand your point. But in the same regard........ I do not expect one of my customers to ask me the type of filler material, the weld processes, the amperage, the amount of post heat, pre heat, or annealing needed after the weld process is finished...... That is why he came to me....... If he already had that information and skill, he would have done it himself. Sincerely.

But for others to learn from this follow this simple rule: "Trust, but Verify."
Compaction can easily be verified by testing once the compaction is completed, and for my slab that testing was less than $200. Have this testing written into your contracts and agreed to up front: http://www.concretenetwork.com/concrete-subgrades-subbases/how-to-compact.html

 

[BadMannerz]

And that's an excellent summary! The beast has been born... worry at this point is futile.

But for others to learn from this follow this simple rule: "Trust, but Verify."
Compaction can easily be verified by testing once the compaction is completed, and for my slab that testing was less than $200. Have this testing written into your contracts and agreed to up front: http://www.concretenetwork.com/concrete-subgrades-subbases/how-to-compact.html

Well put Lakeroadster. I hope others see this thread as information to hold to in the build of a shop. We will see how it goes

 

[Dagny]

Around here you will not find a cement contractor who will guarantee no cracks.

 

[Evilunclegrimace]

I am not a concrete guy and am going to post what I did just for shits and giggles . The wife and I built a 26 by 36 detached garage about 5 years ago. Her dad and brother came down and layed the block for the foundation 2 courses above grade and we left it sit over the winter. We framed the garage and weathered it in and finished every thing except the floor. Doors, roof shingles, wiring, lighting, siding. The next fall we power tamped the floor and put down 12 mils of plastic and poured 5" of 3000 lb. concrete over the plastic with wire mesh set on 2"thick concrete chairs. We power troweled the floor and left it cure for 8-9 days before we set any thing on it The floor was poured in 2 pours about 1/2 of the total area per time with one expansion joint across the 26'width. It has not cracked any were at all. Am I just lucky?

 

[hillbilly slim]

Concrete is a *****! End of story!! If there is not enough heart in the job it can go bad easily!!! The ground needs tending and i mean tending to... Pack it good and pack it hard like she wants it... If the job is done in a hurry, she aint going to be happy. Proper time allowing for air along with moisture and curing is needed. I'm no concrete pro, but have done a lot of concrete and never had any of my pours go sour. Foundations, driveways, and sidewalks all good. Haven't done walls yet, but i feel time and heart is the key... I'm sorry to see these cracks in your garage and the contractor should make it look good when said and done! If not, unfortunately its the American way to sue there ***...

 

[DougWil]

I am not a concrete guy and am going to post what I did just for shits and giggles . The wife and I built a 26 by 36 detached garage about 5 years ago. Her dad and brother came down and layed the block for the foundation 2 courses above grade and we left it sit over the winter. We framed the garage and weathered it in and finished every thing except the floor. Doors, roof shingles, wiring, lighting, siding. The next fall we power tamped the floor and put down 12 mils of plastic and poured 5" of 3000 lb. concrete over the plastic with wire mesh set on 2"thick concrete chairs. We power troweled the floor and left it cure for 8-9 days before we set any thing on it The floor was poured in 2 pours about 1/2 of the total area per time with one expansion joint across the 26'width. It has not cracked any were at all. Am I just lucky?

Well you did plenty right and being cast and cured in the shade helped reduce surface drying, slab curling and the cracking that goes with it.
So did casting on sheet plastic. The slab to plastic friction is lower allowing the shrinking slab to slip instead of being restrained.

But, I bet you do have cracks. They are simply so small that only by wetting the slab and letting the surface dry will the cracks show because they are still damp.

 

[walrus]

The slab has already been polished to a shine, I mean really polished and I feel like I wasted my money on having my dream shop floor polished at this point. I'm starting to be concerned about even installing my 10k two post?

I will post up pictures this evening.

Nice polish on floor, how slippery is that when wet?, be easy to keep swept up.

How close to crack would lift be going?

 

[Evilunclegrimace]

Well you did plenty right and being cast and cured in the shade helped reduce surface drying, slab curling and the cracking that goes with it.
So did casting on sheet plastic. The slab to plastic friction is lower allowing the shrinking slab to slip instead of being restrained.

But, I bet you do have cracks. They are simply so small that only by wetting the slab and letting the surface dry will the cracks show because they are still damp.

I am going to be giving the garage a fall cleaning in a few weeks. When I have it emptied out I will wet the slab down and see what it looks like

 

[walrus]

I am going to be giving the garage a fall cleaning in a few weeks. When I have it emptied out I will wet the slab down and see what it looks like

I've never seen any cracks in my slab either, 30 by 34, 6 inches thick, 4000lb, rebar, vapor barrier, insulation radiant heat and no control cuts.

 

[wssix99]

It has not cracked any were at all. Am I just lucky?

In an ideal world, (with little gravity) if one poured a concrete slab on a perfectly flat and smooth piece of glass and then cured it properly, it would shrink and not crack. (It would just slide along happily and shrink down to it's smaller dimensions.) In the real world, the slab builds up tension as it drags its weight along a rough, interlocking surface as it shrinks down.

The cracking is a game of chance and probability. Your personal fortunes were definitely helped by the expansion joint and probably helped by a smooth compacted surface and your vapor barrier on top. (Although that can work against you in other ways.) Your trade-off for no cracks is that your expansion joint probably opened up a bit and you probably have some nice wide openings where the slab meets the walls.

 

[Catadj78]

It looks to be that they may be settlement cracks. I'll bet the edge towards the older building is higher than the lower area.

18" of fill?