Concrete Slab Concerns

wjansenMarch 28, 2010

Hi Guys,

I'm stalling on beginning my basement project because I'm concerned about two aspects of the current concrete floor in my basement:

1 - Uneveness

2 - Control/Expansion Joints

With the control joints, my basement slab is divided into about 8 'sections' of concrete, and after nearly 30 years of settling, they are uneven in random ways - nothing extreme, but more than the 3/16" over 10' requirement.

First, what is the best way to map the 'topology' of an uneven floor? This is more difficult than first imagined. It doesn't appear to be an easy case of spreading some floor leveller in the low spots (would be very expensive if I tried to do the whole floor) as the different floor sections (each maybe 6' x 8') seem to slope slightly differently - any ideas with a basement floor like this?

Also, with the joints (~1" deep grooves between concrete sections to create areas of preferential cracking during settling), should I fill these in (with leveller or concrete) before beginning any flooring or construction?

Thanks for any help you can pass my way as I can't seem to find much on the internet about joints in concrete slabs and how they affect the basement finishing process.


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Depending on how you are finishing the floor you may not have to do anything much at all. If tiling, for instance, any lack of level will be made up by the tilesetter adding more thinset.

The control joints will not telegraph through DriCore, XPS or Delta FL or their equivalents.

To totally level the floor, you can use a laser level the same way concrete contractors do when they pour it.

    Bookmark   March 28, 2010 at 8:03PM
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Dear all,
I am wondering how can make a construction joint in 4th basement slab 700mm thick, -15m form natural ground level, supported by sandy clay soil saturated.
Your help is certainly useful for me
Thanks a lot.

    Bookmark   June 8, 2011 at 11:22PM
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