New Garage Concrete Floor

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  #1  
Old 04-13-09, 11:00 AM
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New Garage Concrete Floor

Hello,

I have a 250 square foot concrete garage floor that has sunken badly with severe cracks. I'm in the process of getting bids to tear out the old concrete and pour a new one. One contractor has recommended digging down 1 foot, add in a 5 inch course gravel bed with wire mesh, build forms, possibly rebar, and pour at least 6 inches of concrete on top. A few questions if you don't mind;

- Is this the way to go?
- What is the best type of gravel to use?
- Do I need rebar or wire mesh or both?
- Should I have the contractor intall expansion joints?
- In terms of PSI what would be appropriate for a garage?
- If I go with fiber mesh can I eliminate the rebar or use in addition to it


Thank you very much. Appreciate it.

Sean in NY
 
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Old 04-13-09, 08:11 PM
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Most garage floors were installed without footings or any other support which is why yours sunk & cracked in the first place. So I would say that it's a good idea to do something other than just pour a new slab. Compacted gravel, probably #8 is what will be used with the mesh. I don't think rebar is needed.
 
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Old 04-14-09, 04:58 AM
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Thanks Pulpo for responding. One quick follow-up; what guage sholud I be going with on the wire mesh?

Sean
 
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Old 04-15-09, 05:37 AM
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It sounds like your contractor knows his stuff but I think you need to find out the cause of this failure before you jump in and began to treat the effect. What can you tell us about soil bearing capabilities? Was the garage built on top of fresh fill, swamp muck, or an old sawdust pile? If the contractor removes one foot of this substandard earthen materiel how much of the bad stuff is left? Does ground water play a part and what will we do if it's presence is part of the problem?

I believe since you seem to be retrofitting a floor in what is proving to be a problem area I would wire up a grid of 3/8 "rebar to your 6" X 6" wire mesh. As Far as fibers are concerned, save youor money. It's obviously easier on the crew which is not a bad thing in and of itself but not nearly as substantial as steel. In my opinion forget the fibers and use the money saved on extra steel.

bs5
 

Last edited by bullshooter5; 04-15-09 at 06:07 AM.
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Old 04-15-09, 11:48 AM
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Thumbs up Garage Floor..

Thanks for the response Bull. I was told by an old timer in the neighborhood that there is lots of sand in the area my house was built on. All I have to do is go down a few inches with a shovel and I hit sand? Could the sand be an issue? If so, how do I get around it? The land grade is completely flat. In terms of drainage there is only one downspout on the corner of the garage in the front that I have an extension on to pull water away from the foundation. I'm not really sure if ground water is part of the problem. How would I find out if it is? Thanks again for your help.
 
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Old 04-15-09, 04:19 PM
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Compacted sand makes a very good base for a concrete floor. The key word here is "compacted'. freshly dumped sand uncompacted may not have been the best base especially if several feet was dumped in loosley one day and the floor was poured the next. Damp sand compacts better than dry sand it really does not sound as if ground water is causing your floor to heave so my question remains why would this floor have failed in the first place. In addition to some of the issues we already dealt with I suppose a really bad batch of overripe and over hydrated redi mix could be to blame. If so I'm reasonably confident it has to be better this time around.

bs5
 
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Old 04-27-09, 04:48 AM
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Thanks much Bull - appreciate the response. One more quick follow-up if you don't mind. In terms of expansion joints do you think I need one in a 250 square foot garage? One contractor said to put one right in the middle of the floor, one said don't even bother putting one in as its not necessary, and one said put them strategically around the edges which I didn't understand at all.
 
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Old 04-27-09, 02:12 PM
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I don't think I would place an expansion joint anywhere in this garage floor. place the new concrete right next to the block or poured foundation to buttress the wall. On the other hand I would definitely cut a thin control joint with a dry diamond abrrasive concrete blade as soon as you can get on the newly poured floor. This action should send a signal to the concrete gods where the floor should crack. Use a cross patteren to quarter the floor through any floor drain if you have one.

So somebody told you he would put an expansion joint in the middle of a garage floor? Not in any garage floor I pour.
 
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Old 04-27-09, 07:24 PM
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Bullshooter,
a good concrete man knows the difference between an expansion joint and a crack control joint, but almost no one else does. Everyone else calls any joint in concrete an "expansion joint". That's one reason for so much confusion concerning joints in concrete... the general public is mistaken in their terminology. Heck, I even know concrete guys who call them wrong!
 
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Old 04-27-09, 07:32 PM
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Sean, the guy who said place them strategically around the edges is partially correct. Expansion joints are strips of compressible material placed between a rigid structure like a wall and the new concrete, or sometimes in the middle of a large slab. Expansion joint material is usually tar-impregnated compressed fiber, poly foam, rubber, or sometimes wood. My point is that there is an actual separation between the two areas, not just a cut groove (which is called a crack control joint).
 
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Old 04-27-09, 08:32 PM
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Thanks Pecos and Bull. I am becoming more informed and your feedback here will help me make the correct decision when I hire for this project in the next two weeks. I do have one last inquiry. I promise this is it . Along with pouring the new slab my contractor will be installing fiber glass mesh with thinset on the block foundation around the perimiter of the garage and finish it off with california stucco. My question is should I have him pour the slab first then finish the block or finish the block first and then do the pour. My contractor said he would pour the slab first then come back to take care of the block. He said it would be a cleaner way to do it. What approach would you guys take? Thanks much.

Sean
 
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Old 04-28-09, 08:42 PM
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Since it seems outside framed walls and roof are in place so that means you will be splashing mud on the inside of the block. I don't see how that can affect messing with the reinforced stucco which I presume is outside. Bottom line.......doesn't matter when you apply stucco.

bs5
 
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Old 04-29-09, 06:06 PM
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Coming in late here. Don't get this. If theres a block foundation wall there it should be high enough above finish grades on the sides to pour Crete up against it. Where that meets felt expansion should be applied in all inside perimeters with 3/8 bar through felt for a knuckle joint to flex but not rise or fall.

Many times depending on job conditions I use "screed rail" for a control joint for cracks if the floor is under roof. It more of a commercial application but it also helps in placing the concrete instead of wet benching it.

Screed rail..CT 512KK
Masons Supply: Catalogs: Concrete Forming & Accessories: Screeds
 
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Old 04-29-09, 11:55 PM
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Thank you both for the feedback. Appreciate it.
 
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