Detach 48x28 Garage - Footings

[Pettrix]

Did my pour yesterday. All went well. 35 yards of concrete (4,500 psi winter mix - achieves 1,300 psi within 24 hours). Got kind of crazy with 3 concrete trucks all up on the property at the same time (plant messed up the truck spacing - was supposed to be 4 trucks total with 1 truck every 30 minutes).

Total concrete cost = $6,800 (that also includes house footing - as I am building both at the same time)

Temps in day at 43F and night at 22F. Concrete stayed at 40-42F even at night.

 

[ovrszd]

Great start. Thanks for the pics.

 

[Pettrix]

I am doing a 5" concrete slab for the garage. What do you recommend for rebar spacing?

I got #4 rebar and some say to go 48" oc (on center) and others say to go 24" oc.

 

[ROUSTABOUT]

About to break ground on my 48x28 detached garage and on my engineering footing schedule it doesn't show any footings where the two 18' wide garage doors are. I know they are not "required" as there is nothing being supported wall wise there but someone told me that it's "better" to pour the footing under those doors as to keep the whole garage footing as a rectangle, making it stronger. One would run the horizontal footing bars but no vertical bars would be run since there is no wall being stacked on top of that area.

Is that true? Should I run a continuous footing underneath the garage doors or stop at the door area, and then restart again?

My engineering calls for a footing that is 18" below grade, 24" wide, 12" tall, with three #4 rebars at the bottom of the footing. Garage will be ICF (Insulated Concrete Forms) so I will be stacking ICF (6" concrete core) for the garage walls. I am using 4,500 psi concrete footing pour.

Ifn' ize you, I'd wet set them blocks in the footing. Lay them until just above top finish grade of slab. Then I'd pour the first blocks full of Crete directly out of truck. Pop chalk line around inside and pour away. You can tie wall to slab with rebar. Tie block to footer with rebar. I have been building with ICF since early 1990's.

 

[Pettrix]

So on a garage 5" slab with 4,500 psi concrete. I will put in a car lift. For me rebar schedule, some say to go 48" oc (on center) and others say to go 24" oc.

 

[ovrszd]

I've always been told 24".

2 post or 4 post lift?

 

[ponytug]

My question is why are you using rebar?

To make up for poor soil, or poor base rock?
(I would find a way to get the base compacted out of good material.
Much cheaper than the amount of rebar and concrete needed.)

To hold the pieces together when they crack?
(I would use wire mesh panels)

Or are you wanting to add strength?
For strength, I would go with spacing in the 1-3 times the thickness of the pour, I.e. spacing 5-15", #3-#4 rebar on "chairs" or "dobies" 1.5" high. You want the rebar about a third of the way up from the bottom, I.e. about an inch and a half. I would go for the 5" spacing under where you plan to have the floor lift pads, if you aren't pouring a deeper footing for them. (I would)
Lots more here, if you want it; Concrete Driveway Construction - Thickness, Rebar & More - Concrete Network

Or just go for 10ga wire mesh panels and call it good. Rebar isn't cheap, it is labor intensive, and if you aren't driving big trucks or combines on the floor, you probably don't need it.

Don't use fiber for strength. That is a myth. It does slow early cracking.

Once you do your pour, keep it wet and covered for at least a month to develop strength. You will be glad that you did.

Notice that concrete continuously gains strength the longer it is wet for more than six months. Letting concrete dry early is wasting concrete strength.

All the best,

Peter

 

[dirttoys]

Guys sorry for the dumb question, why do you use block instead of just forming and pouring the concrete to the desired height?

Thanks,

ed

 

[ovrszd]

It's always been a mystery to me how a pour crew can elevate mesh to the middle of the wet slab while they are walking around on it?

 

[ovrszd]

It's always been a mystery to me how a pour crew can elevate mesh to the middle of the wet slab while they are walking around on it?