Plaster for e-bag house in Upper Peninsula

Hello,
My husband and I have begun building an earth-bag roundhouse with a square gable self supporting roof in the Upper Peninsula. Our fill for the bags is road base with roughly 5% clay using 1 1/2 gallons of water per bag. We've made some test bags and they've cured well and hard. Our question is about the earthen plaster on the outside. We get about 31 inches of rain per year, and about 106 inches of snow, clay is very hard to find around here. We've read about using lime and/or cement on the outside of the bags, but our knowledge on this is limited. Any advice would be greatly greatly appreciated as we have a very short building time span.
Also if we do not find some plaster that will work time permitting would it be possible to cover the bags till spring in tarps?

Hello Tim,

Our question is about the earthen plaster on the outside.

I think I addressed some of this on another post you shared on with some videos, about the very negative aspects of OPC cement renders/plaster and OPC in general. As for earth plasters on the outside of EB architecture, I personally do not recommend them at all, even with large roof overhangs for DIY builders. Lime plasters with the correct lathing has some merit, but I am not overly confident in the entire poly bag application in general and all my EB work long time ago was with hemp and sisal bags, which if/when I would do any other EB work, is what I would insist on. If using a poly bag then I would recommend a "poly netting" (no metal) to act as the lathing for the plaster. One could also build a very functional "rainscreen wall" without much effort and cover the structure in "board and batten" or "shake/shingle." All the "poly bags" require is protection from UV degradation and abrasion from impact as there "structural integrity" hinges on them staying intact.

Also if we do not find some plaster that will work time permitting would it be possible to cover the bags till spring in tarps?

I see absolutely no reason why not, and would recommend a "scrim plastic" like "Dura Scrim" for such an application.

Regards,

j

Hi Tim,

First a shameless plug for the plaster manufacturer that I work with; http://limestrongfinish.com This is the best plaster I have ever used and the pumice makes it somewhat insulative. It is a pozzolan plaster that behaves like NHL2.

You can also make a good plaster with big box store items like type s hydrated lime and sharp sand. The three coats will have different additives like hair, pigment and possibly a pozzolan like wood ash or metastar, but this is not a difficult process.

As Jay has already stated, a plastic mesh lath is probably necessary to get a good bond to the bags. Ensure that you will have a month or so of non-freezing, decent weather before plastering so the lime can fully carbonate before foul weather hits. If it doesn't, don't worry the plaster will just need a lime wash(this is how we pep up lime plaster that is looking faded) a little sooner than usual.

If you need tips or ideas on pozzolans or colors, just post here and we'll get you going!

All Blessings,
Bill