The Brew Cabin

Nothing more annoying than wobbly tables and chairs on a patio.
Contractors are proposing compacted black garden soil with a thin layer of compacted builders (soft) sand, as the base for a patio made of 600x600x50 pressed concrete slabs. Until a few days ago there was a cultivated flower bed where the patio is to be.
Frost heave damaged an inadequately founded all weather tennis court a few metres away. It might be several years before we have a long period of hard frost, but when it happens will the soil not heave. The patio would never be quite the same.
For all the difference in cost, would it not be better to put 35-50 mm of sharp sand on a base of crushed stone?

Indeed it would - in fact, it would be better to lay them on a bed of GRIT sand/cement at around 10:1 over a stone sub-base, as is recommended on the Laying Flags page.

Black soil suggests a high organic content, so it would be better to get that out. Soft sand is a key indicator of the rogue John Wayne gene in your so-called contractor. No decent contractor would ever lay flags on soft or Builders' sand. So, not only would I recommend reviewing your bedding materials; I'd recommend reviewing your choice of contractor!

Thank you very much. It turned out to be 'concrete sand', but this batch had an awful lot of fines or clay. I did a good dig out myself and took the black earth away and spread it thin on beds! I bought Type 1 and made them use it as a base around 85 mm deep. Job looks OK but then most newly completed jobs do I suppose.

I hope it turns out good for you - Concreting sand is the same (near as dammit) as a grit sand, so it should be ok.

All we need now is a bit of decent weather so you can get the patio furniture out again and check for stability! :)