I've never built anything with cob, but I love the aesthetics of it and that I can build using materials easily at my disposal. I'm reading as many books and watching as many videos as I can about the subject.
The problem is that I live in humid East Texas. In the summer, the days AND the nights are moist and hot. So the thermal mass provided by cob won't really help with my situation. I can't depend on passive heating/cooling here. I'm wondering if I could sandwich a section of aircrete (aka foamcrete) between the walls of cob to provide more insulation. Would this impede cobs ability to let moisture pass through?
Never tried it, so won't pretend to know, but will toss a few thoughts out for consideration. Concrete is fairly permeable. I believe more so than cob. Water passing through should not be a problem. concrete may also wick water out of the cob next to it, so potential over drying of the two surfaces. Concrete has a different expansion rate than cob. bonding the two might create problems.
You have got me thinking of some ideas, however. I never considered a dry stack concrete block (CMU)wall with think cob plaster on either side. Might be worth some consideration. A lot of buildings in Texas made of CMU (formerly known as cinder blocks) and they stay cool in the summer, and are easy to heat in the mild winters. Easy to build, since no masonry is required. Cost effective. thanks for the idea to ponder.