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acerunner 09-17-2010 04:28 PM

Leveling concrete slab
 
I am considering leveling my concrete slab to install flooring. The largest difference in elevation is about 3~4", so not a job for self-leveling compound. The total area is about 400 sqft. What kind of cement mix should I use? Is this a feasible project for someone who's never done concrete work before?

I wanted to leave this to the pros, but at the price they charge, I can live with skipping this part of the project. The leveling will only be a base for flooring, so the finish doesn't need to be pretty, just level.

stuart45 09-17-2010 05:29 PM

1 Attachment(s)
You could use a flooring screed, which is a semi dry mix of flooring sand and cement 3/1 or 4/1. You can get a really good, level finish with this method. It is the normal way to finish concrete floors here.
Attachment 24904

acerunner 09-17-2010 08:45 PM

is that something i can buy and mix on my own, or do I need a concrete truck?

steveel 09-17-2010 09:24 PM

Is that a large rise and fall over 400 sq ft? I don't really know. In my ignorance I was wondering if your slab might be moving. Something to ponder if you haven't done so.

acerunner 09-17-2010 09:26 PM

no, its done that way for drainage. instead of sloping out towards the garage door like modern homes. It is sloped inward into a floor drain.

stuart45 09-18-2010 06:45 AM

Quote:

Originally Posted by acerunner (Post 503072)
is that something i can buy and mix on my own, or do I need a concrete truck?

You can mix it yourself and lay it in bays of about 6ft wide.
You can also use a self leveling wet screed nowadays as shown here.
http://www.youtube.com/watch?v=5WOAPU2PiQc

acerunner 09-18-2010 12:07 PM

how much does the stuff cost?

stuart45 09-18-2010 01:19 PM

About $100 a cubic yard(UK prices)

acerunner 10-03-2010 02:02 PM

i happen to see an episode of holmes on homes where he had to level a guy's garage. They mentioned you need a minimum of 4 inches over the existing slab. Is that accurate? What if you're existing isn't off-level by that much? Can you blend in the new concrete with the high points of the existing, like what is done with self-leveling compound?

Daniel Holzman 10-03-2010 05:25 PM

You can bond new concrete to old, but you need to be a bit careful. First the old concrete has to be clean and scratched, which is usually done with a grinder. The overlay, if it is thin (less than 4 inches), should be done using a special mix designed for the purpose. See the Thoro Corporation, which makes all kinds of mixes for special purposes. Concrete work is not all that difficult, but it is very hard work physically, and must be done fairly rapidly, else the mixture begins to harden and is impossible to screed, level or finish. You need an adequate number of people, hopefully someone who has done it before.

There is the mixing part, transporting the mix to the work site, placement, screeding, finishing, and measuring for level. You need to plan it all out, else it can go horribly wrong, which is odd for such a seemingly simple operation.

steveel 10-03-2010 06:52 PM

(just guessing)

I wonder if the job in that TV show needed a 4" top slab due to a problem with the old one, or if they did it that way because they had the headroom and didn't need to use the specal stuff Daniel mentioned for <4" top slabs? (I assume that stuff is more $ than the stuff for >=4" slabs)

acerunner 10-06-2010 04:22 AM

Quote:

Originally Posted by Daniel Holzman (Post 510893)
You can bond new concrete to old, but you need to be a bit careful. First the old concrete has to be clean and scratched, which is usually done with a grinder. The overlay, if it is thin (less than 4 inches), should be done using a special mix designed for the purpose. See the Thoro Corporation, which makes all kinds of mixes for special purposes. Concrete work is not all that difficult, but it is very hard work physically, and must be done fairly rapidly, else the mixture begins to harden and is impossible to screed, level or finish. You need an adequate number of people, hopefully someone who has done it before.

There is the mixing part, transporting the mix to the work site, placement, screeding, finishing, and measuring for level. You need to plan it all out, else it can go horribly wrong, which is odd for such a seemingly simple operation.

Do you have a link or a name of the product? I can't seem to find it.
I have a pretty good idea what NEEDS to be done, but without experience, that doesn't means much. And yeah I agree, definitely labor intensive. I've seen it done, and the guys are sweating bullets.

Would it make sense for a beginner to so smaller sections at a time? If I decide to tackle this job, I'd probably have to rent a portable mixer. I was thinking doing something like 6'x6' sections with 2x4 forms that I can use as screed guides. Otherwise, I don't even know how to begin screeding a 23'x20' area and still stay level.

acerunner 10-06-2010 04:26 AM

Quote:

Originally Posted by steveel (Post 510931)
(just guessing)

I wonder if the job in that TV show needed a 4" top slab due to a problem with the old one, or if they did it that way because they had the headroom and didn't need to use the specal stuff Daniel mentioned for <4" top slabs? (I assume that stuff is more $ than the stuff for >=4" slabs)

I think its the latter. The floor was not level, so they proceeded to gut the floor (in typical Holmes fashion) only to discover that it was too difficult. The floor was structurally solid. So they went to plan B of pouring new concrete right over it. They did as Daniel said, grinding the floor and apply bonding agent.

Daniel Holzman 10-06-2010 07:25 AM

See http://www.thoroproducts.com/pdf_app..._thorobond.pdf
for a description of Thorobond, a product for bonding concrete to concrete (also works on plaster), specifically designed to maximize bond of thin lifts.


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