Can you plaster over earthbags, with cob, both inside and outside? Either the original version, or hyperadobe (linked below)? Assume the earth used has no portland cement in it or anything like that. If earthbag was used, would I need to use burlap instead of those white bags I see in most photos, to give the cob something to stick to?
I am thinking this route because the soil doesn't have enough clay for cob in my yard or locally where it would be feasible to dig enough clay for a structure, but there is always ads for free fill dirt.
Please take a course in both earth bag and cob before really thinking about doing this. It is extremely hard word. I see many of these workshops and they are wonderful but yet people fail to see just how hard this work is. If you can get 15 to 20 people to hang out with you for 8 hours a day for a month, you could build a pretty nice little natural house in several different modalities from cob, earth bag, timber frame, straw bale, etc. At just 15 people that is 120 "man hours"/day at 30 days equals 3600 man hours for the month. That should get you a shell up and perhaps a dried in roof if all materials and tools are onsite available and working. Prep, planning and finish work will take a minimum of 30 to 60 more days. If you take the 3600 and divide by 10 hour day for an individual, you are looking at 360 day to build a simple house. These number can fluctuate in both direction depending on the method you choose, skill sets, and experience to apply them.
As for, can you plaster, in a word yes, but it's not the time to go into details, as it is more complicate than just one entry without know a fair amount more information.