Chalk In A Sub Base

[Onoff]

For my patio sub base I'm using a lot of the local flint that I'll whack down. Up until now I've been picking out the chalk but do I need to? Seems hard enough a material, should whack down well and remain in place and sticky when damp. Thinking a whacked flint / chalk sub base then sand/cement dry mix pre the slabs.

 

[Porkypine]

Tunnels cut in chalk just stay up with no support, I wouldn't worry about it, chalk's pretty solid stuff.

 

[Agrismith]

There are several different types of chalk. Some will be fine for this purpose others not. It also depends on the consistency of the flint aggregate used. Aggregate requires a good percentage of fines within it to bind properly.
Saying this if its only going to have foot traffic and is away from trees and vegetation it doesn't take an awful lot to support a patio. A good quality geo membrane under the sub base is the most important factor