Raft Foundation and a New Patio

[planemad]

Hi All

I live in a house that's built on a raft foundation so I have a 3ft concrete border around my house.

I want to do a rear patio at the back but the first 2 patio slabs will be on the raft and the remaining 4m will be on the soil.

As the raft is theoretically always moving separately from the other 4m laid on a lean mix base on top of the soil. What do I need to do to make an allowance for this so that I don't get cracking between the 3ft raft and the slabs laid on the soil?

 

[noseall]

There is not a lot you can do about the differential movement other than going overboard on the remaining part of the patio, i.e. laying concrete under this bit.

Bridging the join with a full slab may help. The other option would be to have a deliberate join at this point though this would likely cause problems in colder wetter weather. A gravelled join would work but I'm not a fan of gravel or any aggregate borders for that matter.

Are you on clay or unstable ground?