Concrete Patio Built On Dirt???

RobJ · May 24, 2006

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I've never seen concrete poured on topsoil and grass but that doesn't mean it doesn't happen. I wouldn't do it at my house and I'm sitting on top of glacial till, basically a gravel pit. I would always remove the topsoil.
)

You are right, down here they bring in bank sand or clay or some other cheap fill, put that on top of the topsoil to build up the foundation and/or to fill so they don't have to pour more concrete than they have to. Only time I've seen them save the top soil is to get to the fill dirt (clay), or in a side of a hill where the foundation was being cut.

But it is different down here because our ground doesn't freeze. The foundation should support itself.

RobJ · May 24, 2006

(
I've never seen concrete poured on topsoil and grass but that doesn't mean it doesn't happen. I wouldn't do it at my house and I'm sitting on top of glacial till, basically a gravel pit. I would always remove the topsoil.
)

You are right, down here they bring in bank sand or clay or some other cheap fill, put that on top of the topsoil to build up the foundation and/or to fill so they don't have to pour more concrete than they have to. Only time I've seen them save the top soil is to get to the fill dirt (clay), or in a side of a hill where the foundation was being cut.

But it is different down here because our ground doesn't freeze. The foundation should support itself.

jdgreg · May 24, 2006

Mike, I'm probably not too far from you, and have the same type of soil. We've talked to a couple of different folks about getting some patio and walk way redone, one of them was a stamped concrete outfit. None of them mentioned it was ok to put it on top of grass. When I had my driveway paved, they came in and scraped out all the old gravel/dirt/weed mix so that they would get a good compaction with the new aggregrate they put down. I cant understand why those yahoos would tell you otherwise, other than make to get the job done quicker and easier, with less work. I aggree, tell the bunch to go packing, the whole outfit sounds shady. /forums/images/graemlins/mad.gif

jdgreg · May 24, 2006

Mike, I'm probably not too far from you, and have the same type of soil. We've talked to a couple of different folks about getting some patio and walk way redone, one of them was a stamped concrete outfit. None of them mentioned it was ok to put it on top of grass. When I had my driveway paved, they came in and scraped out all the old gravel/dirt/weed mix so that they would get a good compaction with the new aggregrate they put down. I cant understand why those yahoos would tell you otherwise, other than make to get the job done quicker and easier, with less work. I aggree, tell the bunch to go packing, the whole outfit sounds shady. /forums/images/graemlins/mad.gif

Tim_in_IA · May 24, 2006

if it is the same price and there is any question, have the excavation and rock done.

Tim_in_IA · May 24, 2006

if it is the same price and there is any question, have the excavation and rock done.

Builder · May 24, 2006

( I am having a stamped concrete patio installed and the workers showed up today. When the salesman was here, he told us how they would excavate down about 4" and put in gravel before pouring the concrete onto the gravel base. The workers showed up today and started building the forms ontop of the grass/dirt without excavating. Their foreman told me that's the way they do it now saying that in the hard clay of Virginia, the water collects in the gravel (above the frost line) and heaves the patio when it freezes. He assured me that since they are using 4" thick 4000 PSI concrete, it would be fine. They have given me a 3 year guarantee in writing. Should I be worried? )

I've been around this stuff for a while and the only guarantee you can make on concrete not built on frost footings is that sometime down the road, it WILL crack.

If you want a guaranteed crack-proof patio, you need to build it on frost footings with rebar on a 24" grid drilled into the footing walls. Then, you've got a great chance that the patio will give you many years of crack-free service.

I'm about 90% sure that concrete poured directly on the ground won't make it more than a year or 2 without cracking.

Builder · May 24, 2006

( I am having a stamped concrete patio installed and the workers showed up today. When the salesman was here, he told us how they would excavate down about 4" and put in gravel before pouring the concrete onto the gravel base. The workers showed up today and started building the forms ontop of the grass/dirt without excavating. Their foreman told me that's the way they do it now saying that in the hard clay of Virginia, the water collects in the gravel (above the frost line) and heaves the patio when it freezes. He assured me that since they are using 4" thick 4000 PSI concrete, it would be fine. They have given me a 3 year guarantee in writing. Should I be worried? )

I've been around this stuff for a while and the only guarantee you can make on concrete not built on frost footings is that sometime down the road, it WILL crack.

If you want a guaranteed crack-proof patio, you need to build it on frost footings with rebar on a 24" grid drilled into the footing walls. Then, you've got a great chance that the patio will give you many years of crack-free service.

I'm about 90% sure that concrete poured directly on the ground won't make it more than a year or 2 without cracking.

Jimbrown · May 24, 2006

They pour it right on top of the ground here in Az all the time. But we really do not have any grass or top soil so they are pouring ring on top of hard packed desert which is almost as hard as concrete and the mositure level is probably close to zero.

Jimbrown · May 24, 2006

They pour it right on top of the ground here in Az all the time. But we really do not have any grass or top soil so they are pouring ring on top of hard packed desert which is almost as hard as concrete and the mositure level is probably close to zero.