# Slab



## Engineer22 (Mar 16, 2018)

I did do some research on this and am simply confirming!


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## PowerStroke79_PE (Mar 17, 2018)

Engineer22 said:


> I did do some research on this and am simply confirming!
> 
> *What is the required thickness of concrete cover, for underside of slab on grade (to protect rebars I believe)*
> 
> [SIZE=14.6667px]*Is the answer 3"?*[/SIZE]


Thats straight out of ACI.


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## youngmotivatedengineer (Mar 17, 2018)

Correct,  this straight from ACI. You should tab this section or create a copy to have it readily accessible since this is an easy look up question.


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## Engineer22 (Mar 17, 2018)

Awesome, thank you! @youngmotivatedengineer


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## EBAT75 (Sep 11, 2020)

Joined recently. Saw this. I beg to differ.

Key is cast against and permanently exposed to earth vs exposed to earth or weather.

The former needs 3 “. Applies to walls, vertical cuts etc. The latter needs 2” or 1 1/2” depending on bar size and applies to slabs on ground (placed on, not against) unless the slab is subject to alternate wetting and drying in which case it would be 3”.

As an example, a 4” slab with #5 bar even would not work with 3”. (4 - 3 - 5/8) would leave only 3/8” for top cover. Clearly not enough.

ACI Commentary clarifies all of this. In any code Commentary provides the underlying thinking. My old, real copper penny worth.


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