I am planning a special variant to solve the ground floor in my old log cabin. Discussion on this can be found in
this thread, for those interested. Overall, there will be a concrete slab on cellular plastic, with a casting of cement-bonded leca closest to the sill timber. This is to achieve decent insulation closest to the sill, and because this casting will be able to follow the unevenness of the sills and all the stones that protrude. The leca will not go under the sill timber, but will be flush with the inside of the wall.
Now, since I won't be able to plaster the outside of the leca casting, I plan to cast with a rather dense mixture, meaning that the pores between the leca balls are filled with cement and aggregate. Worse insulating capacity, but no drafts. What do you think about mixing a concrete of cement and 0-8 gravel and then mixing in an equal volume of leca balls 8-16? Reportedly, the leca has about 50 percent air between the balls, so this should be the right proportions.
Second question, I naturally need to moisture insulate the sill where it meets the leca casting. One idea is to attach an age-resistant 0.2 mm plastic against the inside of the sill, let this go down to the ground and then under the leca casting. This also has the advantage that the plastic acts as a form for the leca casting so that it does not run out under the sill. What do you think about this? This plastic probably needs to be airtight against the sill, maybe through a couple of strands of sealing compound or some kind of adhesive? Another idea is to apply some form of liquid moisture barrier where the sill meets the leca. Ideas?
