Revisions log for Answer #203

Then please also think about weed fleece, padding (to keep the substructure from standing in water on the rocks), and structural protection of the boards from moisture.

For substructure, I would only use a suitable hardwood that does not weatherize as quickly as Douglas fir or even pine (such as Bangkirai or Bongossi).

But why such an elaborate structure with formwork stones? As an alternative, fill KG pipes with concrete. There are plenty of inexpensive and easy options for the non-professional. Last weekend I stacked our substructure on mortar bags (= freeze bags).