Questions About Floating Concrete Slab For Garage

 
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Old 10-07-2010, 07:31 PM   #1
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Questions About Floating Concrete Slab For Garage


24x24x8h garage

What is an ideal base material and base material depth for a 4" concrete floating slab under a 24x24x8h garage?

How much should the perimeter base material and concrete be thickened?

How many rows of rebar do you put around the perimiter?

What size?

Do you recommend fiberglass or welded wire mesh to reinforce the concrete?

What mix is recommended for a floating slab under a garage?
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Old 10-07-2010, 11:08 PM   #2
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Re: Questions About Floating Concrete Slab For Garage


Compacted soil,
3-4" sand,
10 mil. moister barrier,
#3 rebar spaced 24" O.C. both ways or 10 gauge wire mesh.
No fiberglass,
2500 P.S.I. conc.


Andy.

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Old 10-07-2010, 11:15 PM   #3
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Re: Questions About Floating Concrete Slab For Garage


we always use 4000 for slabs. Overkill?
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Old 10-08-2010, 01:48 AM   #4
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Re: Questions About Floating Concrete Slab For Garage


30 mpa concrete, form details as per image, on top of minimum 8" of road crush compacted.
notice the double row of rebars around the perimeter. 24" centres for the field. 1/2" bar size.
no need for the poly under it around here. the base is all gravel. You can't make a puddle on my property if you peed on a sheet of plastic... and it is not an occupied space, so the poly is not required by code, afaik.
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Old 10-08-2010, 01:54 AM   #5
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Re: Questions About Floating Concrete Slab For Garage


Quote:
Originally Posted by buckeyeso2 View Post
we always use 4000 for slabs. Overkill?
not to me.
4000 psi equals 30 mpa

http://www.mc2-ice.com/support/estre..._strengths.htm
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Old 10-08-2010, 05:55 PM   #6
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Re: Questions About Floating Concrete Slab For Garage


The typical grade beam slab is close to what jlhilsap posted, except for a 12" height, 10-12" width. 2- #4's continuous min, with the floor re-inforcement up to the contractor. For us, usually #3's on 3' centers or so. Always 4000 psi, the few bucks more saves us labor in finishing and holds up better to freeze/thaw.
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Old 10-08-2010, 06:05 PM   #7
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Re: Questions About Floating Concrete Slab For Garage


We always use 1/2" or 3/4" washed stone under slabs around here, lets any incidental condensate or moisture drain away. And if any part of the slab is going to be exposed to freeze/ thaw cycle, use 4% entrained air- cheapest thing you can add to concrete, and hold up better in the weather. 4000 psi.
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Old 10-08-2010, 09:57 PM   #8
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Re: Questions About Floating Concrete Slab For Garage


jomama, how does the 4000 psi save labor on finishing? thanks for your reply
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Old 10-09-2010, 08:04 PM   #9
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Re: Questions About Floating Concrete Slab For Garage


Quote:
Originally Posted by needestimate View Post
24x24x8h garage

What is an ideal base material and base material depth for a 4" concrete floating slab under a 24x24x8h garage?

How much should the perimeter base material and concrete be thickened?

How many rows of rebar do you put around the perimiter?

What size?

Do you recommend fiberglass or welded wire mesh to reinforce the concrete?

What mix is recommended for a floating slab under a garage?
Chech with your local city hall for the spec. Here in cleveland ohio and some surrounding suburbs the code for a 24x24 attached or detached garage foundation poured monolithic is 6" wide x 36" depth footer, 4" slab on grade. The code is 8" above grade with a 6" wide curb, 1/4in per foot pitch in floor. Now I do understand it is hard to dig a 6" or 8" wide footer, unless you can use a track trencher. Most use a mini and dig 12"-14" width. Soil compaction can vary, depends on your location, 4" undercut is good with a #57 lime stone base compacted. Rebar in the footing is a good idea every 12-24in bent 90deg into the floor #4 rebar. Fiber mesh not fiberglass is a good secoundary reinforcement. I would use #10 wwm as your primary. Pour a 6 1/2 sac blend with 6% air, that is a standard mix type here in cleveland with slabs exposed to freeze thaw. A moisture barrier is a good idea if you are heating the structure, a 6 mill is good. If you are not heating the structure then you can leave it out, the choice is yours. Since you are in new york,your weather is simillar to ours in cleveland, use a 4000-4500 p.s.i concrete, stone base, not sand, and also a footer at a min 36" depth. for the freeze thaw. Hope this helps

Last edited by CONCRETE MIKE; 10-09-2010 at 08:19 PM.
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Old 10-10-2010, 08:30 AM   #10
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Re: Questions About Floating Concrete Slab For Garage


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Originally Posted by needestimate View Post
jomama, how does the 4000 psi save labor on finishing? thanks for your reply

I actually typically use the straight bag equivalent to 4000, but faster set times, "richer" surface, and an overall nicer finish all contribute to the tools being loaded up and on the way home much sooner.

I'm not sure how it is in other regions, but I've never heard of a 2500 psi mix used for flatwork here. We pour 3000 just for footings.
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Old 10-10-2010, 08:48 AM   #11
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Re: Questions About Floating Concrete Slab For Garage


Needestimate....... That username......


Please don't shoot....I'm gonna play the role of curmudgeon..

There are too many variables to give one answer...


Unless someone on here is actually in your township, they really can't answer those questions...


It's all about the local code... go to city hall and talk to the inspector
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Old 10-10-2010, 05:32 PM   #12
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Re: Questions About Floating Concrete Slab For Garage


Quote:
Originally Posted by jomama View Post
I actually typically use the straight bag equivalent to 4000, but faster set times, "richer" surface, and an overall nicer finish all contribute to the tools being loaded up and on the way home much sooner.

I'm not sure how it is in other regions, but I've never heard of a 2500 psi mix used for flatwork here. We pour 3000 just for footings.
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Old 10-10-2010, 09:37 PM   #13
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Re: Questions About Floating Concrete Slab For Garage


2500 is what we call "lean" concrete- we use it to fill in space, such as when specs call for footings to bear on solid rock, we will usually try to overshoot 6" to 1', and bring it back up to footing bearing with lean concrete, then place the footing section on top of that. Cheaper to overshoot and fill in rather than hoe ram high rock down to bearing. Footing concrete is usually 3000, like Jomama said.
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Old 12-23-2010, 07:29 PM   #14
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Re: Questions About Floating Concrete Slab For Garage


Quote:
Originally Posted by jomama View Post
I'm not sure how it is in other regions, but I've never heard of a 2500 psi mix used for flatwork here. We pour 3000 just for footings.

Must be a regional thing because here in MN we also pour our footings 3000-3500 and everything else is 4000. We have actually poured 4500 psi for floors before just to cut down on the finish time. I actually cant imagine trying to trowel a floor poured with 2500psi mud.
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Old 12-23-2010, 08:40 PM   #15
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Re: Questions About Floating Concrete Slab For Garage


We operate on your area too, and arround here we use as a base material #1 and #2 washed stone or #1 and #2 crushed run, no vapor barrier on garages, no thickened perimeter, and just a very few builders do grade beams, we always use on our jobs # 5 rebar on a 3'x3' grid and doweled to foundation, no floating slabs on garages, fibers are up to the builder and 4000 psi concrete with 5%-7% air entrainment is mandatory, steel trowel everything but the first 3' in from door; we've done a few all broom finished garages(like they should be) but is taking a while to educate the builders and homeowners arround here, we hope that we can do it more often though.
Good Luck and Happy Holidays to all in this forum!
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Old 12-23-2010, 09:14 PM   #16
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Re: Questions About Floating Concrete Slab For Garage


Why would you want a broom finished garage?
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Old 12-24-2010, 09:54 AM   #17
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Re: Questions About Floating Concrete Slab For Garage


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Why would you want a broom finished garage?
I could understand brooming a garage floor because I have seen alot of floors that have been burned almost black and as soon as a little water gets on them its like walking on ice. But most people do want to be able to sweep their garages and that doesnt work very good with a broom finish. We usually just skip the last time around with the machine on garage floors so they are just a little bit gritty.
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Old 12-24-2010, 11:17 AM   #18
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Re: Questions About Floating Concrete Slab For Garage


In the areas were freeze/thaw cycles occur, garages should be considered outside applications, for which is mandatory the use of air entrained concrete; air entrained concrete should not be steel troweled, just mag trowels should be used, the more sleek your floor is, the weaker and more prone to spalling and delamination it is, a just mag finish floor is not acceptable in most cases, but a broom finish one is more appealing and better with traction too, like mw31 mentioned, in warm climate areas, this is not a big concern, but here is the biggest cause of premature slab failures; the worst problem is, that must people arround here think the way you think, but the few we've convinced to do it the right way, at the end , realize that is not that bad like they thought it would be and feel very good about not having to worry about the same problem happening to them again, a slab done this way, with proper prep work , reinforcement, control joints, maintenance and care will last a lifetime, there's no better warranty than that one, and that's the only reason why people would want a broom finish garage. Merry Christmas to all !
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Old 12-24-2010, 03:24 PM   #19
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Re: Questions About Floating Concrete Slab For Garage


We have one of the worste freeze/thaw cycles in the country here in Cleveland Ohio. Although all our garage floors around here have a trowel finish most guys still use no air or half air. The garage is still under cover and protected and is not subject to the weather of exterior concrete. Many of the garages are attached and generally stay much warmer than a detached garage. Still never seen any problems with the concrete except for the section that sits under the garage door and is technically outside. I use half air in our garages and never had any problems with any of them. I don't think anyone wants a broom finish garage floor. I even know a few guys who use full air in there garage slabs, they just don't get as good as a finish on them as they have to get off of the slab sooner.
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Old 12-24-2010, 05:05 PM   #20
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Re: Questions About Floating Concrete Slab For Garage


I'm not sure you do. Freeze thaw is constant cycle. You can have 3-5 hard freezes. Where in the southwest they can have anywhere from 25-35 cycles. In the Midwest ect, once you guys freeze, you freeze till summer. What I'm saying is once it gets cold, it stays cold where in the southwest they freeze, thaw, freeze thaw and so on. It's a constant process.
I know because I've been to seminars on it.

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