Ferrocement/Papercrete/Tile

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.