Redoing garage concrete floor


How does one redo a concrete floor in an existing garage?
My old floor was shifting and cracking all over the place due to the soil. The floor was divided into 6 segments and at the joints gaps of 1 inch had formed. Not only had gaps formed but some slabs were 1/2" different in height/level - so I removed all the concrete in the garage.
Now I am unsure as to how the concrete should be laid since it is not as simple as laying concrete slab in an open area.
If someone could give me some insight as to how concrete is poured into an existing structure that would be great!
Advice is much appreciated.
Garage Specifications: Length: 8.5 metres Width: 5.5 metres
Desired concrete thickness: 100mm -------------------------------------
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Hi, Is the existing subgrade acceptable? Are you preparing that so that the "same" does not occur?
In any case, pouring concrete in a confined area presents problems..... The same story as painting yourself into a corner. There must be some doors....and or windows? (access)
You can use overhead screed boards on the left and right sides so that there will be no stakes in the concrete pour. Down the center a person can use a metal buried screed form, that represents top of concrete and rod off of that. It remains in the concrete and acts as a "cold" joint, or expansion / contraction line.....
I would make sure to use a "grid" of re-bar in the slab to keep the concrete together. I have had more luck with re-bar and cracking than any concrete wire or 6-6 10-10 mesh used..... Also keeping the rebar at the right height is important so that it does not get imbedded in the sub-grade.
Are you using a vapor barrier? If so, I always make sure it is deep enough to cover with a layer of sand to facilitate concrete pouring.....I never pour on plastic alone.... It can create problems with water and finishing.......
With concrete tools, I always jitter bug the top layer of concrete......always. It helps bring up the fines for the top finish, and set some of the larger rocks below top.
Using a float on a long pole is helpful in a confined area.... I have several mag floats for preliminary surface prep. and then steel trowels on poles for finsih work.
In the past 4 years I have purchased a power float.....that goes on poles also. It is a lifesaver......works wonderful.....can bull float the concrete as well as finish it all from outside the slab.......... It weighs 24# and has a small gas engine......works great.
Knee skids are also beneficial for finishing concrete in confined areas.... I use metal, knee skids, and like "snow" skis.....you can move out over concrete without leaving board marks......of course there is a time when they are most successful as when the concrete is hard enough to use them.
some of my inside pours I have pre-set boards high enough on the walls that a plank can span the area being poured...... You can "walk" a plank out and finsih an area without even getting in the concrete......an aluminum "rental plank works well......or a 2x12.....or scaffold plank.
I do this a lot for colored or stenciled concrete where the surface cannot be walked on......
have fun. I am sure I have missed something...... jloomisconstruction and concrete

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saka had written this in response to http://www.thestuccocompany.com/construction/Re-Redoing-garage-concrete-floor-18079-.htm :
jloomis wrote:

Not yet. We are at this stage now, dig up the soil, lay the vapour sheet, tamper the sand and gravel.

That is the plan, how deep should the sand/gravel be? 1 inch ?

Yes there is a large roller door/side door that can be accessed from the front.

How exactly do these overhead screed boards work? since there is no formwork on the right and left hand sides.

I found a site metalscreed.com so I now have an idea of what these are. Are these expensive? and could they be used on the left and right sides as well instead of using the overhead screeed?

Thanks for your post, it is very much appreciated don't feel so lost now
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On Oct 11, 6:52 pm, sakatumi21_at_gmail_dot snipped-for-privacy@foo.com (saka) wrote:

saka-
You got a lot of good information from jlloomis but I would advise against doing a confined flat work job of 500 sq ft (50 sq m) as your first DIY attempt.
cheers Bob
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A person would need help. I assume saka has some building sense?
(saka) wrote:

saka-
You got a lot of good information from jlloomis but I would advise against doing a confined flat work job of 500 sq ft (50 sq m) as your first DIY attempt.
cheers Bob
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j-
I was getting total "rookie" vibes base on the OP & his reply .......... but flat work scares me, so maybe its just my fear.
I've done a little flat work & I've seen experts do it......I prefer to watch it done. :) The results are much better.
Plus his original post, noting 1" gaps & 1/2" differentials has me a bit concerned. I'd hate for him to do all this work & have the new floor not work out any better than the one he's replacing.
cheers Bob
cheers Bob
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saka had written this in response to http://www.thestuccocompany.com/construction/Re-Redoing-garage-concrete-floor-18086-.htm :
fftt wrote:

Thanks for the replies guys.
Pretty much am a total rookie, but didn't plan on doing this all myself unless it was fairly straight forward, which it doesn't sound like it is. Was hoping to get some info on how it is done (which I did so thank you) so when I get quotes I can access if their method is good. I also have a friend that does concreting but he is fairly new to it.
Yeah, it would not be good if the concrete turned as bad as before. But most likely will be paying someone to do a proper job :)
Thanks again for the info -------------------------------------
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On Mon, 12 Oct 2009 17:14:35 +0000, sakatumi21_at_gmail_dot snipped-for-privacy@foo.com (saka) wrote:

Good. I'm relatively experienced at construction (not a pro, but I can build) and I'd not try that slab myself. (I did a 10m x 20m building/slab a couple of years ago, the only think I contracted out was... The slab!)
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Okay, I gotta ask - is the slab the best or worst thing? ;)
R
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On Tue, 13 Oct 2009 05:55:42 -0700 (PDT), RicodJour

Actually both turned out very well. I'd use the contractor again in a minute, he did a credible job on the slab. The building turned out very well too, better than I'd expected.
I've had to tell several friends that they can't move into my garage... <bg>
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I would bury a pressure treated 2x4 on the left and right side to act as a screed and the form since you do not have any forms.... I cannot see exactly the situation so, I have to guess... The metal buried screeds would work, yet ordering and getting them is another thing.
Subgrade depends on what it is and what its compaction is all about. A person could put sand and or gravel on a lousy subgrade and end up with no changes.... So, if the ground under the "to be poured concrete pad" is good, then a layer of sand and or gravel is fine....I use sand since it retains concrete moisture and facilitates in pouring.... gravel lets the moisture drain down quick.....anyway, either will work. You are in a cover area so the sun factor will not be present. john

http://www.thestuccocompany.com/construction/Re-Redoing-garage-concrete-floor-18079-.htm
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