laying down patio

29 Jun 2017
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United Kingdom
Hi, I have a very small concrete area at the back of the house that extends onto lawn. I want to lay a patio and raise it a bit. Have just removed a concrete path that went alongside the garden and would like to use that material. As I understand I need a layer of hardcore and sand on top before placing the slabs on top? Is this correct?
I am planning on leaving a 4cm gap between the fist slab and the house wall which will be filled with pebbles.
I will also be securing a border around the patio area to stop slabs moving as I dot want them concreted on to the ground.

If I use the broken cement, do I have to break it into smaller pieces and compact it before adding the sand? or can just I just fill the are with the hardcore as best I can and then fill the gaps with sand and then add more sand on top to flatten the area before placing slabs down?

I am doing this right?

Many thanks,
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Where is your dpc on the house? Your finished paving should finish 150mm below dpc. Is your existing concrete low enough to allow you to lay on top of it?

Re using hardcore is ok if mixed with and used in combination with new sub base like mot type 1 but simply lumps of broken concrete on their own is not a stable sub base.

Block paving is laid on compacted grit sand and flags should generally be laid on a sand and cement bedding mix.

You can not lay unbound bedding such as just sand over a concrete base because the concrete is impervious to water and therefore the sand stays saturated with water and over time will make the paving sink and dip.

If you do want to go over your concrete you can use your broken up concrete from the path and go over the top of it with small gravel such as 10mm. This will fill any voids and make it easier to get a nice level surface to lay paving on. You must then if going this route lay your paving on a bed of sand and cement which will set rigid. 6:1 grit sand to cement for example.

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