is a 4″ concrete slab actually only 3.5″ and if so, what is its implication for a garage floor?
I asked my concrete guy for a 4″ slab for my garage and woke up last night in a panic with the feeling that the expansion joint material I saw last night looked a bit short (maybe 3.5″). The joint material is by Nomaco and they do list a 3.5″ tall one in their literature but nothing smaller. I am going to check out the job site before work and measure it but in the event that I find 3.5″ instead of 4″ expansion joint, I need to quickly assess my options.
First question: is concrete thickness typically expressed in nominal dimensions like 2x lumber where 4″ is really only 3.5″?
Second question: if so, does that 1/2″ of concrete matter for a residential garage that will only have cars, SUVs, woodworking equipment and maybe a tractor on it?
My base is #57 gravel which i compacted with a plate compactor several times and as I added gravel, I have wire mesh laid for the whole area and rebar running through the 12″ thick turndown area under the overhead door opening. I don’t recall the PSI rating for the concrete, but the concrete guy uses 3″ slump from a water perspective.
Please help me understand if I am likely to have any issues with setup as listed in the event that it is 3.5″ thick.
Thank you!
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While you deserve the slab you are paying for, I doubt in a residential garage you would see a difference. YOu won't be able to set a 2 post lift on it....
Concrete is not expressed in nominal dimension, they are actual dimensions.
No, a 4" slab should be very close to 4", but will vary depending how level the subslab surface is. Control joints are only cut 1/4 of the depth of the slab, or 1" in your case. An expansion joint is the full depth; which do you have?
The PSI rating isn't terribly important in a slab, as long as it's at least the code minimum of 2500 psi, but if you're leaving the specs up to the contractor, they will almost certainly go with a higher PSI rating.
Thx. I have 3.5” expansion material nailed to the blocks around the perimeter and the concrete contractor has planned 1” deep green saw cuts for control joints after the pour.
Oh got it. The reveal is usually filled with an elastomeric sealant.