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Concrete Slab Question

Posted By: Tbar

Concrete Slab Question - 07/01/22 02:27 PM

I just had a 50’ x 70’ concrete slab poured and it has a couple of low spots.

Over a 50’’ span what is acceptable tolerance of deviation?
Posted By: TX Hntr

Re: Concrete Slab Question - 07/01/22 03:37 PM

Pretty common standard for most is 1/4” in 10’.
Posted By: Tbar

Re: Concrete Slab Question - 07/01/22 07:36 PM

Originally Posted by TX Hntr
Pretty common standard for most is 1/4” in 10’.


Thanks.

Any idea where I could find that in writing?
Posted By: Thundervee

Re: Concrete Slab Question - 07/01/22 07:54 PM

https://www.stoversliquidation.com/blog/concrete-floor-slab-flatness-and-levelness/
Posted By: fredeboy

Re: Concrete Slab Question - 07/01/22 07:57 PM

If you just hired Jose concrete crew you will not find that in writing cheers
Posted By: BigPig

Re: Concrete Slab Question - 07/02/22 02:43 AM

Originally Posted by TX Hntr
Pretty common standard for most is 1/4” in 10’.


Local foundation repair companies look for 3/4+ inch over a 20 foot span
Posted By: fredeboy

Re: Concrete Slab Question - 07/02/22 02:02 PM

Originally Posted by BigPig
Originally Posted by TX Hntr
Pretty common standard for most is 1/4” in 10’.


Local foundation repair companies look for 3/4+ inch over a 20 foot span


Boy talk about setting the bar low!!
Posted By: Texas buckeye

Re: Concrete Slab Question - 07/02/22 02:34 PM

If i had a concrete slab poured that was 50x70 and it had some low spots of a quarter inch or more, i would be pissed and asking for it to be done again.

I am no concrete guy, but i am pretty certain foundation repair folks are looking for settling of more than a 3/4 inch difference (if thats the number, i have no reason to suspect it isnt). This is very different than having pockets within the new slab that are just poorly smoothed with low spots.

when you see poor concrete work and good concrete work, it is obvious. I fully expect a slab to have some minor spots of standing water when hosed down, but a quarter inch of depression is a lot, and that is a lot of water (couple of stacked quarters) vs just a minor pooling that isn’t as deep as a single quarter.

For reference, a quarter is 0.06inches thick, so 4 quarters stacked is 1/4 inch thick.
Posted By: BigPig

Re: Concrete Slab Question - 07/02/22 03:30 PM

Originally Posted by fredeboy
Originally Posted by BigPig
Originally Posted by TX Hntr
Pretty common standard for most is 1/4” in 10’.


Local foundation repair companies look for 3/4+ inch over a 20 foot span


Boy talk about setting the bar low!!


I’ve seen new construction homes be a 1/2 inch out in that 20 foot span. It’s just a bad form job. I assume this discrepancy is why the foundation repair companies look for 3/4+ before recommending repair.
Posted By: BigPig

Re: Concrete Slab Question - 07/02/22 03:32 PM

Originally Posted by Tbar
I just had a 50’ x 70’ concrete slab poured and it has a couple of low spots.

Over a 50’’ span what is acceptable tolerance of deviation?



Unless you’re building precision race chassis, I wouldn’t be concerned about 1/4 inch over 50 feet. It won’t hold water and probably won’t be noticeable once walls are up and it’s filled with stuff.
Posted By: Tbar

Re: Concrete Slab Question - 07/03/22 03:55 PM

Just didn't like the elongated area at the top and the circular area top right. Neither are 1/4" low but are just 1/16th shy of it.

The other spots are negligible.

[Linked Image]
Posted By: Jman

Re: Concrete Slab Question - 07/03/22 04:18 PM

I wouldn't worry about that - once it is framed and finished out you won't notice that. If your outside walls are good and level you're good.

Plus that concrete lives and breathes for at least a month before it is considered fully cured.
Posted By: glens

Re: Concrete Slab Question - 07/03/22 08:11 PM

What kind of soil slab poured on? They drill pillars around perimeter and load bearing walls?
Posted By: blanked

Re: Concrete Slab Question - 07/04/22 12:05 AM

Flooring company for vinyl plank says 3/8 inch for 10 foot radius. They use a leveling compound to bring to spec.
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