Patio base.... hardcore or compacted chalk?

[pfitz13]

I live in Biggin Hill, Kent which has a solid chalk/flint subsoil (in fact the soil is only about 3 inches thick before you hit the chalk). I have excavated a large area of garden removing about 15 tonnes of chalky hill which is now flat with a solid chalk floor. I am going to lay a patio on this new area. Will compacting this area with a whacker suffice or should I really lay a bed of hardcore under my new slabs.

Thanks for your advice.

[stoneyboy]

pfitz13,
Laying direct on the chalk base will be OK but in long frosty period the chalk will heave lifting the patio.
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