Digging out clay to replace with deck.

[hopetown]

I'm planning to dig out clay backyard to replace with decking.

How deep do you think I need to go? 600mm?

Also, house extension (near planned excavation) is on a concrete slab.

Anything I need to be aware of as to not undermine foundation?

Any advice...

[CraigD]

On recommendation from the timber supplier I used Vermeister decking oil on parts of my brand new vitex deck rather than it greying off. However any weather exposed oiled vitex very quickly blackened off with mould. Unoiled area's went nicely grey. I'm looking at having to clean (oxygen bleach) off...