Mono Slab Cracks- 1.5 weeks old

[Jay H 237]

You can also put plastic or tarps down over the slab to help keep the moisture in so it doesn't dry out so fast.

 

[G-ManBart]

Wait for about three years, my concrete in garage is 4,000 PSI and the cracks started around the three year mark in the control cuts and couple outside of the control cuts. It had rebar every 18" and fiber mesh in the concrete and had absolutely no cracking until about 4-5 months ago which is the three year mark. I am not even bothered by it. The old saying in these parts is there is two forms of concrete "fresh poured concrete and cracked dry concrete"

Roadways last a lot longer than 3 years before they start to crack and break down. Runways last a lot longer than 3 years before they crack and start to break down.

The difference there is the concrete mix, the amount of water added, the time from loading the truck to offload, and even the number of turns the barrel takes before unloading are all carefully controlled for road and runway pours.

 

[ptgarcia]

Roadways and runways are also heavily reinforced and poured very thick compared to building slabs.

 

[PAToyota]

Re: Rebar can cause shrinkage cracking

No they were talking 6'x6' 1/2" rebar

There’s your problem… I wouldn’t go any more than 12” o.c. for such a slab.

Also looks like it cured too quickly and wasn’t kept damp long enough.

 

[wssix99]

Tell that story to my basement floors. They have a differing opinion.

If your basement floors have moved differentially, then the base underneath has also. This indicates that your slab's problems are greater than simple shrinkage cracks.

 

[wssix99]

Also had the company that did the slab out, he is a great guy and will stand behind their work.

Does this mean that the company is going to tear out the slap and re-lay it. Or does it mean that they convinced you that this cracking is acceptable and normal?

 

[Falcon67]

Roadways and runways are also heavily reinforced and poured very thick compared to building slabs.

The access road they are about to pour close to work looks like 1/2 bar 12" OC, maybe 8~12" thick, about 2~3' overlap on the bar ties. Lots of steel. Lots to study while stuck in one lane waiting on traffic.

 

[wssix99]

Roadways and runways are also heavily reinforced and poured very thick compared to building slabs.

Nothing you see here applies to driveways or garages or floor slabs. The rebar in a dynamically loaded roadway is used for different purposes than a simple slab-on-grade. (They also have different spec's that they are designed to.)

As long as the ACI spec is followed, the chances of a slab cracking outside of a control joint are extremely low.

The biggest problem here looks like a shallow control joint. It should be 1/4 the slab depth. If it isn't deep enough, it won't relieve the strain the slab and it might as well not be there at all. (Installers of radiant floors often short this, not realizing the consequences.)

 

[joes169]

I also asked for a second opinion on the rebar spacing and around here in Southern WI 5'x5' spacing is plenty. I even took a trip to look at another guys shop that is a 40x80 mono with 6x6 spacing rebar that was done 10 years ago and it looks great. He even has the small shrinkage cracks like mine, they never raised or got bigger. You can notice them unless you look.

I'm a concrete contractor in SE WI, I can give you a third opinion, I don't see much 6' spacing of rebar here, and I don't know what it would really do anyways. That kind of spacing is what we like to call "feel good steel". If your contractor simply eliminated the cost of the fibers, he cold double the rebar and actually have something.

At a minimum, there should have been at least two 1/2" rebar running continuous around the base of the bottom of the grade beam. Did you witness these?

Does this mean that the company is going to tear out the slap and re-lay it. Or does it mean that they convinced you that this cracking is acceptable and normal?

Your "beloved" ACI has acceptable crack tolerances for slab on grade construction, and these cracks would currently fall well within those tolerances.

 

[redneckcharlie]

I'm a concrete contractor in SE WI, I can give you a third opinion, I don't see much 6' spacing of rebar here, and I don't know what it would really do anyways. That kind of spacing is what we like to call "feel good steel". If your contractor simply eliminated the cost of the fibers, he cold double the rebar and actually have something.

At a minimum, there should have been at least two 1/2" rebar running continuous around the base of the bottom of the grade beam. Did you witness these?



Your "beloved" ACI has acceptable crack tolerances for slab on grade construction, and these cracks would currently fall well within those tolerances.

No need for that type of post. The keyboard experts on this site are all knowing and knowledgeable. After all they had a slab done, knew a guy that had a slab done, watched a youtube video, read this or that, yada yada yada. The correct reaponse is tear it out and "I" wouldnt except anything else. It's fairly comical, especially when it comes to concrete. I like you do this for a living and very few here have any clue how fluid and tempermental concrete work is. I'd bet most here couldn't properly mix and place a 60lb sack.

 

[joes169]

I had a guy that has done cement for many years come out to take a look. He said the cracks are just shrinkage. I should have kept a sprinkler going when the sun is directly on it to not have it happen. He said the control joints are doing their job by stopping the cracks from spreading across the floor. Also had the company that did the slab out, he is a great guy and will stand behind their work.

The cracks do look big in the pictures i posted. I will pit a penny down next to one and post later to have a comparison.

I am running a sprinkler on the slab during the sunny hours until i can get to building the garage in August.

I also asked for a second opinion on the rebar spacing and around here in Southern WI 5'x5' spacing is plenty. I even took a trip to look at another guys shop that is a 40x80 mono with 6x6 spacing rebar that was done 10 years ago and it looks great. He even has the small shrinkage cracks like mine, they never raised or got bigger. You can notice them unless you look.

I hope this can help out others that may have the same issue as me and could nt find much info on the web.

Thanks for all the replies guys.

No need for that type of post. The keyboard experts on this site are all knowing and knowledgeable. After all they had a slab done, knew a guy that had a slab done, watched a youtube video, read this or that, yada yada yada. The correct reaponse is tear it out and "I" wouldnt except anything else. It's fairly comical, especially when it comes to concrete. I like you do this for a living and very few here have any clue how fluid and tempermental concrete work is. I'd bet most here couldn't properly mix and place a 60lb sack.

LOL, I hear you loud & clear!

 

[wssix99]

Your "beloved" ACI has acceptable crack tolerances for slab on grade construction, and these cracks would currently fall well within those tolerances.

I never said that the cracks made the slab structurally unsound. They don't and they can be repaired, filled, etc. The slab can be fully functional - it just looks bad. (BTW - Most of the folks here like their garages to look good.)

In the end, a proper design, proper placement can almost guarantee a crack-free slab.

Situations where finishers take a proper design and back-woods modify it without understanding the consequences, or situations where architects/engineers half-*** a design without referencing the proper guide, or finishers don't follow standard industry practice for placement - cracks will happen. <- All of this is unprofessional. If any of this happened to the OP, I don't see why they should be expected to pay 100% of the fee for an unprofessional job or result.

The assertion that the OP/customer would be responsible for hydrating a curing slab without being given the instruction/warning from the finisher is also asinine. It's like discharging a surgery patient from the hospital, sending them home without instructions, and hoping for the best.

 

[spike0137]

The grade beams did have 2-3 1/2" rebar wired up in them before the pour. If I would have kept water on the slab during the hot days I don't think I would have any cracks. The finishers messed up by not saying this I agree. Reason I think this is because the part of the slab that is completely covered with shade from trees all day long looks great because it is curing slower.

This site can be super helpful but when you have guys like RedneckCharlie and a few others saying they would only accept ripping it out is stupid. I am a carpenter and these are the people I dread to work for because perfect isn't good enough for them. Anyone reading this because they are like me (don't know much about concrete), take everything with a grain of salt. Don't rip off your contractors head cause some keyboard warrior said on this forum the slab needs to be removed because of a few hairline cracks [emoji23][emoji23]

Sent from my SM-G930V using Tapatalk

 

[lakeroadster]

The grade beams did have 2-3 1/2" rebar wired up in them before the pour. If I would have kept water on the slab during the hot days I don't think I would have any cracks. The finishers messed up by not saying this I agree. Reason I think this is because the part of the slab that is completely covered with shade from trees all day long looks great because it is curing slower.

This site can be super helpful but when you have guys like RedneckCharlie and a few others saying they would only accept ripping it out is stupid. I am a carpenter and these are the people I dread to work for because perfect isn't good enough for them. Anyone reading this because they are like me (don't know much about concrete), take everything with a grain of salt. Don't rip off your contractors head cause some keyboard warrior said on this forum the slab needs to be removed because of a few hairline cracks ����[emoji23][emoji23]

Hey spike... Charlie was joking about ripping out the concrete. Re-read his post.

While you're at it, re-read the entire thread. Nobody in this thread said to rip out the concrete. You asked if cracking was "normal" and you got opinions.

I had a mono slab poured about a week and a half ago. I just noticed some cracks in the slab that run across the floor to a edge and all the way down. Is this normal? I

It's only normal to have cracking outside the control joints if the concrete is poured and or finished incorrectly.

That doesn't mean it's a problem... might be, might not be. Depends on the slab location, it's usage and other factors such as reinforcing steel type and location.

You got sold a bill of goods in regards to reinforcing steel spacing... that's the consensus here. And you wouldn't have the hairline cracks outside the control joints if the finisher had kept the concrete hydrated.

I had a guy that has done cement for many years come out to take a look. He said the cracks are just shrinkage. I should have kept a sprinkler going when the sun is directly on it to not have it happen.

All this is on your contractor... not you.

 

[lakeroadster]

For future ref..

Going To Pour Concrete Slab, How Will I Know I Got The Strength I Wanted?

Slab On Grade.. More Opinions Than Carter's Got Liver Pills

Proctor Compaction Testing of Sub-Grade Material

 

[joes169]

The grade beams did have 2-3 1/2" rebar wired up in them before the pour. If I would have kept water on the slab during the hot days I don't think I would have any cracks. The finishers messed up by not saying this I agree. Reason I think this is because the part of the slab that is completely covered with shade from trees all day long looks great because it is curing slower.

This site can be super helpful but when you have guys like RedneckCharlie and a few others saying they would only accept ripping it out is stupid. I am a carpenter and these are the people I dread to work for because perfect isn't good enough for them. Anyone reading this because they are like me (don't know much about concrete), take everything with a grain of salt. Don't rip off your contractors head cause some keyboard warrior said on this forum the slab needs to be removed because of a few hairline cracks [emoji23][emoji23]



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"Redneckcharlie" was simply joking and poking fun at all of the people here that must live in a bubble of perfection.

I'm still curious how deep the control joints are, especially as they approach the edge/grade beam. I simply think they weren't sawn deep enough.

Also, I've found that outside concrete on foam insulation, subjected full sun tends to set & cure much quicker than if it were on gravel. I usually douse these slabs in water-based curing sealant to attempt to slow them down.

Best of luck, and get to framing!!!

 

[wssix99]

And you wouldn't have the hairline cracks outside the control joints if the finisher had kept the concrete hydrated.

I don't think this is the case.

There are lots of variables here and hydrading the curing concrete can help balance the equation, but I don't think that's the biggest factor:

There is a crack in the vicinity of a control joint. This demonstrates that there is stress in the slab - right where one would expect it to be. However; it didn't happen in the control joint. This is likely because the control joint isn't deep enough. If that cut isn't 1.25" deep, (it doesn't look like it's close...) then the likelihood of it doing its job is greatly diminished:

http://www.cement.org/learn/concret...ntraction-control-joints-in-concrete-flatwork

 

[cherrybomb]

I live in Wi. and 30 years ago,built a garage with 4 foot walls in the ground for our frost depth,built the garage before winter.Used the garage all winter and the following summer did the slab.24/30 and had the mesh and fiber.Being inside and watering it for a solid week and not driving on it for another 10 days was probably overkill,but I was looking at the big picture.Had expansion around outside of slab and that plastic t-style groove joint,no cracks,very happy.The soil was all clay,and medium grade slope,thats why I did the frost walls.I also had another pour that cracked after 10 years and while we had a drought summer,at one corner,thinking soil contracted.So I guess watering made a believer out of me.

 

[wssix99]

So I guess watering made a believer out of me.

I'd be willing to bet that the OP's contractor in 1940 didn't water the slab.

This type of thing isn't a major factor in thin slabs cracking and most of what we talk about isn't thick enough to benefit from the practice. (Thicker industrial slabs, that have a greater propensity to curl, are different.)

I think that many folks who actively hydrate their slabs have also paid attention to all the more impactful details that will prevent cracking.

 

[stikman56]

Looks like the concrete dried to fast imo. I've poured a good amount of concrete and have only gotten cracks like that I'm very hot days when the concrete dried super quick or didn't get sprayed down enough. I would t worry about it but I would keep an eye on it. I've never heard of rebar being spaced so far apart, that seems wrong.

Yep, my thoughts too. Keep it wet. I sprayed our foundation for this house as much as I could until the framers got here, which was about 4 weeks later. It looks great. I have been told this by a guy who does bridges, keep it wet and start as soon as you can after the pour. Slow cure is the best cure.