Kelly Hart is your host at greenhomebuilding.com, and has built his own home using a hybrid earthbag/papercrete technique, which can be seen on the Earthbag page. He has adapted the concepts popularized by Nader Khalili and his "superadobe" building, by filling the bags primarily with crushed volcanic rock. This creates insulated walls that are similar to strawbale, except that they are completely impervious to damage from moisture, insects or rodents. The earthbags are plastered both inside and outside with papercrete. Kelly has produced a video, titled Building with Bags: How We Made Our Experimental Earthbag/Papercrete House, which chronicles the adventure of building this house, and shows other earthbag houses as well. Another video program that he produced is A Sampler of Alternative Homes: Approaching Sustainable Architecture, which explores a whole range of building concepts that are earth friendly. One of the homes shown in this video is a hybrid strawbale/wood framed home. Kelly spent many years as a professional remodeler, and is available to answer questions about what he has done, or consult about other hybrid projects.
Q: My husband & I are looking into building a ferrocement dome (modular units). What do you feel is the feasibility of sandwiching a layer of papercrete blocks between 2 layers of ferrocement? Since we are potters, ultimately ceramic tile and grout will be used for the finish. The wall would probably end up over 12' thick. I am aware that papercrete wicks moisture. Will this effect the ferrocement? I envision the dry papercrete wicking moisture too quickly from the outer layer of cement as the cement is applied. Then again. if the papercrete is moist as the last layer of cement is applied, will the papercrete ever have a chance to dry out being stuck between two layers of ferrocement?
A: It is an interesting concept that you propose. There would certainly be advantages to the arrangement, if it could technically be accomplished. With the ferrocement on the inside you should get plenty of thermal mass, and the papercrete would provide the insulation. The trick would be to get the papercrete to dry out after you poured the final coat of cement, and this might be quite difficult; some formulas of ferrocement are virtually water proof. My suggestion might be to forgo that final coating of ferrocement, and allow the papercrete to be the outer layer. This papercrete could be done in a couple of pours, so that the first one is highly insulating, with mostly paper and little mineral material. The next pour could be more much more sand with the paper and cement, to give a more durable, fireproof layer. This is basically what I did with my house, and it has worked out well. If the initial ferrocement shell is mixed to be waterproof, then you could simply allow the papercrete layer to breath and evaporate moisture as needed. Sealing it to moisture would be another option, but any water that does manage to get through might be trapped there for some time. This might take some experimenting, perhaps trying it unsealed at first, and the sealing it later if this seems necessary.