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Posted by Judanne on July 10, 2006, 2:40 am
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!!).
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.
The bedroom floors were not tiled but were painted with (outdoor) cement
paint and the cracks were much less apparent there. Cement paint on the
slab or epoxy sealers will be the way for me next time. No cracked tiles
and much less expense to finish off the floor.
Judanne
> We're having a house built in a rural mountain area where the
> predominant composition of the soil is decomposed granite and a little
> clay. Our house is a passive solar design and uses a rock floor (about
> 3 feet high, 2" rocks or gravel) over a water barrier. The floor of the
> house is 4" thick reinforced concrete on top of the rock floor. Because
> of concerns about ground water, a French drain was installed around the
> perimeter of the house. In one room of the house, the concrete floor
> shows signs of cracking (about 1/16" cracks with about 1/8" uplifting).
> The design of the rock and floor and been approved by engineers and
> been used many times by this builder with no structural problems. At
> certain times of the year, a hole at one side of the house that is
> deeper than the rock floor seems to have water in it which makes me
> think that the ground water can rise and fall.
>
> The contractor speculates that areas with a little more clay may have
> swollen a bit and caused the uplifting. Does this seem likely? Is there
> a way to control this type of uplifting? I realize it is hard to make
> an assessment without seeing the site. What sort of professional should
> we look for for advice?
>
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