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Old 05-22-2008, 01:37 PM   #1
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Poor quality concrete slab

We pulled up a carpet in preparation to install new tile flooring and found the concrete surface underneath to be sandy and cracked. The room seems to be a former porch which was enclosed and about 3-4 inches of substandard concrete poured over the original slab. We chipped out a hole and can see a good hard original slab under the new layer. There is a hollow sound when the floor is tapped so it obviously hasn't bonded to the original floor. It is quite clear that tile won't stick to this sandy surface. I thought perhaps Hardie backer board might be the solution but see on their website that it has to be laid with thinset too, which wouldn't adhere to a sandy surface. I am wondering if there are any sealing products which anyone could recommend or any other possible solution other than breaking up the concrete and repouring.


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Old 05-22-2008, 03:25 PM   #2
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If by sandy you mean that it isn't "sticking" to itself and is easily eroding away then I can't see how anything will bond to it since it will just separate from itself.


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Old 05-22-2008, 04:54 PM   #3
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Capping a concrete slab with amother concrete cast and seperating the two with a layer of sand is a common practice.

If the surface is casting off sand no matter what there is no fix for that short of removal.
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