Garage Concrete Slab - Rebar Schedule

[Pettrix]

4" concrete slab - I called out for #4 bar at 12" oc for the house and garage. Of course the contractor says that's "overkill" and he recommended #3 bar @ 24" oc. I am a little leery with #3 bar since it's so thin and the spacing is bigger than I like.

Rebar is actually inexpensive. #4 rebar in 20' lengths is $5 per stick. So I don't see much savings in a 24x28 deep garage

 

[comancheflight]

Your garage, your money, nuf said

 

[Streetcar]

The 12" spacing will work better at controlling cracks

 

[Wagtail]

Your garage, your money, nuf said

Ditto.

Mind you, not knowing your contractor, he/she could simply be offering you a cost saving alternative. A concrete slab is one of the most expensive parts of building. It was darn near half the cost of my 5-bay shed!

 

[coralhead]

If your subgrade is not fully compacted the rebar will not stop cracks but will keep them from opening up.

 

[robstaples]

Depth location in slab is most important. Many pours have rebar on bottom that adds no value. For my floor , I use 6by 6 inch wire mesh and chairs to set depth. Cracks haven't opened.

 

[ray66v]

I spec out everything I want on my bid sheet, and hand it to the estimator.

If they look at it, and start saying. "You don't want this, and you don't need that", I thank them for their time, and say goodbye.

When I put my current barn up, I hired out the framing. The first two contractors tried, (unsuccessfully), to convince me, I didn't need concrete poured in the holes for the poles to sit on. That, a precast "plug" would be just fine. I was also told, I didn't need, laminated poles, or a steel plate, in the header for the O/H door.

The third guy who came out, looked at my spec sheet, and said, "Okay, no problem".

That was the guy who got the job. :thumbsup:

I don't believe any of my specs, were overkill. The laminated poles are straight, they don't shrink, or twist. The poured concrete doesn't settle. And, that header didn't sag in the middle.

A few of my customers, whom I do repair work for, are engineers. They often spec, what I do consider to be ridiculous levels of overkill.

I just made two laundry room shelves for one, that were 1.5" thick, solid wood. But, that's what he wanted, so I made them. :confused3:

If you want the rebar 12" o.c., find a guy who will do it, without questioning you.

 

[fidowanttobe]

Rebar is cheap, concrete isn't. And no do-overs. Also, don't skimp on the base.

 

[EddieWalker]

24 inch centers with 3/8's rebar is common practice here in East Texas, but I've spoken to people who have built in other areas with Hurricanes or Earthquakes, and code requires a lot more rebar and for it to be a lot thicker. More is better, and if you can afford it, then go for it.

The main reason concrete cracks is from too much water in the mix. Water increases volume, and when it dries up, the concrete is still covering the same amount of area, but with less volume to it, so it cracks. Rebar holds it together. The more rebar, the smaller the cracks.

When pouring concrete, the crews want it as wet as possible because that makes it easier for them. For commercial projects, and things like skyscrapers, they do a slump test to make sure there isn't too much water in the mix. The test is very simple, you put the concrete in a small one quart pail, turn it over and see if it holds the shape of the pail. Just like building sand castles at the beach. Since nobody is going to do your job with concrete that dry, the challenge is going to be to keep the water to a minimum.

 

[Gem99ultra]

4" concrete slab - I called out for #4 bar at 12" oc for the house and garage. Of course the contractor says that's "overkill" and he recommended #3 bar @ 24" oc. I am a little leery with #3 bar since it's so thin and the spacing is bigger than I like.

Rebar is actually inexpensive. #4 rebar in 20' lengths is $5 per stick. So I don't see much savings in a 24x28 deep garage

The contractor has no idea as to how much weight you might put on that slab sometime in the future. Don't skimp on the rebar. In fact, if you can afford it, going to 6 inches on the garage with #4 rebar would not be overkill in my opinion. Who knows - someday you may want to park a big ole heavy tractor in there. Or maybe some sort of machine.

Build it like you want it, not to the convenience of the contractor! But, if you mention that you'll be checking the slump as EddieWalker suggested, they'll probably run from you like a scared rabbit. ...especially if you're asking for a firm bid turn-key contract. Finding a knowledgeable contractor is utopia, especially if he'll build your project like you specify.

If you want to know something about 'slump' - do a Google for "Concrete slump test from Wikipedia". There's a good explanation of what it is and how to do it. That's the right way to determine the water content of concrete.