[Cob] plaster as thermal mass

[Barbara Roemer and Glenn Miller]

Of plaster thickness, Ianto Evans suggested at the Natural Building
Colloquium at Black Range about four years ago that perhaps the best
building envelope would have a cob exterior, a bale insulation wall section,
completed by an interior plaster of 1 1/2 - 2", in effect a cob atop bales
which would provide insulated mass.

At The Canelo Project at Bill and Athena Steen's place, the plaster rest on
bale buildings is commonly 1 1/2", and at the corners it's perhaps 2" thick.
Additional mass is built in through furnishings of cob and lime and clay
plastered bales, and in clay and lime/clay floors.  There was no air
conditioning in any of the buildings I spent time in, all very comfortable
in arid S.E. AZ in July.  Nice combinations of bale/cob/straw clay provided
insulation and mass.

Even thin layers (less than 1/4") of earth plaster over drywall seem to
provide distributed mass, tempering the heat of the day by 4 to 5 degrees
relative to what the temps were prior to plastering.  I'm not certain why
this would be true, since it's thin, but perhaps the sheer volume of mud
laid on so many surfaces, including the walls and ceilings, is just enough
to make a difference.  Or perhaps the plaster surfacing causes the drywall
itself to act differently.

Lots to experiment with.