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Posted by Robert Gammon on July 15, 2006, 7:03 am
Judanne wrote:
> Thanks, Bob
>
> Judanne
>
>
>> Judanne wrote:
>>
>>> This is exactly what happened to the slab in my p/s house. The soil had
>>> a
>>> lot of clay in it so there was a lot of movement between winter (wet &
>>> clay
>>> expanded) and summer (dry & clay shrunk). The slab was laid according to
>>> council regulations with extra cement pourings needed (which meant
>>> doubling
>>> the cost) because the clay went deeper than was first thought (of
>>> course!!).
>>>
>> Clay is the best foundation for concrete slabs because the superfine
>> particles compact into a solid mass. In fact clay is hauled in and used
>> as a stabilizer over looser soils. *Any* soil will expand & contract
>> with moisture variations, but clay will do it less. That is why the
>> old saying is: "the only sure things in this life are death, taxes, and
>> cracks in concrete".
>>
>>
>>> There was no long term effect on the p/s performance but tiles laid on
>>> the
>>> cement in the living areas had hairline cracks in them from the seasonal
>>> movement. The tiles were laid within 2 months of the slab being poured
>>> and
>>> I was told (much later) that in order to avoid the hairline cracks I
>>> should
>>> have waited 12 months to put them down.
>>>
>> Concrete takes a while to shed it's water and cure to size & strength.
>> In fact the cureing curve of concrete extends upwards to 30 years. So
>> your waiting for 12 months would have had little effect on hairline
>> cracks. Those are characteristic of concrete and *cannot* be avoided.
>> Larger cracks are avoided by wire and rebar in the concrete - it cracks
>> but doesn't separate into large cracks.
>>
I waited 10 years to install ceramic tiles on a floating slab (several
inches of SAND under it to isolate it from the gumbo [ultra heavy clay]
soil underneath it), and I still have several tiles with hairline cracks
in them.
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