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Slab on slab

slugboy6000 | Posted in General Questions on

I’m considering the construction of a 6-8″concrete slab on an existing 4″ concrete slab.  Because the existing slab would be somewhat larger than the new (3′ at most), could water infiltrate in between the two slabs and cause issues when it freezes?

I’m in Ontario, Canada.
The old slab is in good condition, 4″ thick, has a poly VB under it and is too big for the small crappy outbuilding on it.


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  1. mikeolder | | #1

    I'd either enlarge my new house, or demo the old slab smaller than the new slab.

  2. slugboy6000 | | #2

    The later is an interesting idea, thanks Mike.

  3. mikeolder | | #3

    I'm in the same situation, but never considered building over the old foundation, but mine has shallow stem walls to. I'm hoping to find a farmer who wants to control erosion.

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