[Cob] Welsh slate for moisture barrier

[slanlusan at slanlusan.co.uk]

Hello, I am new to this list. My name is Stephanie and I live in the very
north of Scotland. I recently finished excavating a 200 year old ruined
stone/clay mortar walled, turf roofed cottage on my croft. We plan to
rebuild it on its current foundations with the stone from the excavation
and lime mortar for the plinth then build the rest in cob with a lime
render. The cottage site seems to have pretty good drainage regardless of
being in my wettest field and is built on a slight mound. I plan to dig a
curtain drain around the building plus another beyond to catch runoff but
worry about rising damp. Obviously, I do not have the option of putting
the drainage underneath the foundation and wonder if I should put a layer
of welsh slates embedded in lime on top of the stone foundation for a
moisture barrier for the cob above? Anybody ever tried this? I read in
Becky Bees book that it could be an option putting in a natural moisture
barrier to protect from rising damp. I have access to alot of free welsh
slate so would be a good option for us if its a good idea. Any advice
would be appreciated.

Stephanie