Laying paving over concrete


Postby Doug62 » Mon Apr 16, 2007 9:36 pm

Hi all,
I am currently renovating the backyard of my house which has an old ugly concrete floor. I have some 600 x 600 paving stones which i was hoping could be layed over the top of this concrete with some sort of substrate (perhaps grit-sand?) between the two. Is this possible? Also, the concrete floor is uneven, sloping down toward the drain. I hoped that a substrate would also even this out but i'm worried about the drainage. Any advise would be greatly appreciated.
Doug
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Postby thedoctor » Tue Apr 17, 2007 5:22 am

The slabs can be laid on sharp sand Doug although we prefer to mix it with cement at a 6 - 1 ratio. It should be laid fairly dry with the rule of thumb being that you canb squeeze a ball in your hand and it should stay in one lump but no water should come out. The slabs should still be laid to a fall, ie sloping, (away from the house, to a suitable drainage point (usually the garden) where the water can run off without hinderance.
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Postby Doug62 » Tue Apr 17, 2007 6:41 pm

Thanks for the reply,
only thing i'm wondering about that is whether water will be able to drain through the sharp sand or sand/cement mix, as i intend to put a gravel border aroud the outside and want any rainwater to filter through whatever substrate I use and to drain into its natural drainage place (which the concrete currently slopes toward). Basically i'm saying i want the water to drain underneath the slabs. Would it be possible to use a gravel mix or is there too much chance of the slabs moving? Or would the sand mix you mention do this anyway?
Regards
Malcolm
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Postby thedoctor » Tue Apr 17, 2007 8:54 pm

The last thing you want is for water to drain through the slabs Doug. Little by little it will erode the sand and cause the slabs to tilt. Patios are pointed to prevent water getting under them as when it does it can soak into the bed of sand/cement and if you look at our project on freeze thaw action you will see how it can wreck the patio.
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Postby susanlee » Fri May 04, 2007 9:38 pm

I've got a similar problem, in that I have a badly- laid concrete area in the back garden which I would like to pave.

Trouble is that it seems the area was laid and then extended in length by a no. of metres. There is a slight gap between the two areas, about 5mm wide.

The concrete base also doesn't slope, so when it is hosed, the water remains in pools until swept away.

Should I lay more concrete on top of the exisitng base to create a slight slope (and also mend the gap): or can I just lay sand/cement on top to create a slope, ignoring the small gap. and laying the pavings on top? OR maybe you can suggest another solution?!

The other thing I wanted to ask : what exactly should I use for the jointing between the pavings?

Hope that someone out there has the answers!
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Postby thedoctor » Fri May 04, 2007 10:30 pm

The gap can be ignored if its only 5mm and laying a bed of sand and cement as described above can enable the slabs to be laid at a suitable fall to allow rain to run off. See our project on pointing patios for details of the mix.
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