Sandstone patio subbase

[Rossoliver]

Hi,

Ive recently built a low retaining wall for a terrace patio project and I'm at the stage of digging out my subbase for the new sandstone patio (polished 22m sawn slabs, if it makes any odds). Part of the ~50m2 area I plan to patio was already covered with basic concrete slabs. The two main things I'm not 100% confident on are the depth of the subbase - given that my soil is nasty heavy clay (I'm part way through digging for a 100mm subbase) and also I'm wondering if I can use the existing subbase that was under the old concrete slabs for part of the patio - it looks like a fine gravel but not type 1 MOT. Pictures attached and any guidance would be greatly appretiated!

Thanks for your time,

-Ross

http://postimg.org/image/uyt0evlzr

http://postimg.org/image/yel4ofj87/

http://postimg.org/image/56yhy709j/

[Rossoliver]

Another photo showing the whole project area partially dug out - in the centre is where the existing slabs were and there's still a few more to take out (I also figured out how to embed images so I'll include the others of the gravel and nasty soil below):

[r896neo]

you can certainly re use the 6mm grit, but try to mix it in with the type 1.

As for the sub base 100mm will be fine but its probably worth using a geotextile membrane to keep the nasty clay from migrating into the sub base. As you don't need it for strength a light grade one like terram 1000 or equivalent would suit in my opinion.

[Rossoliver]

That's good to know, thanks. I've reused a lot of it around a land drainage pipe running the length of the wall, but I'll mix the rest with the hardcore and see if I can get a hold of a geotextile membrane to cover the clay.

Appreciate the help!