Sharing information and promoting earthbag building
|Curing the Fill Material
Questions answered by Kelly Hart
Q: Is it possible to build an earthbag wall even if it has been soaked by rain? Will this have an effect?
A: It really depends on what the bags are filled with, how much effect this will have on the integrity of the wall. You certainly do want the wall to dry out eventually, so the best thing is to allow this to happen naturally, by providing a roof over it to keep off more rain, and by not putting anything over the bags that will keep them from drying out...but of course, you also want to keep the direct sunlight off the bags. Once the earthbags are thoroughly dry, then you can preserve them with a protective plaster.
Q: I think I would prefer walls that 'solidify' during the tamping process. I saw this kind at the Cal-Earth institute and liked them. They make me feel safer about the redundancy of the bag as only a temporary form. My question is, if I build during the winter, (Gallup/Zuni New Mexico with freezing nights and milder days) will I have a problem with the earth setting up during tamping? Does the slightly moist mixture need some 'curing time' which would be interfered with by the freezing temps at night?
A: Cal-Earth does what they call "Super adobe", which is basically common adobe soil (30% clay, 70% sand) that has been dampened. As this dries out it hardens into a very solid material. If the damp soil freezes, it can expand and fracture, so it becomes less solid. So if you used this method, you might want to throw some blankets or something over the wall at night to keep this from happening.
Q: We have started building our earthbag house.. and it is going surprisingly fast. We're nearly half way up the walls and love it already. We are building on reclaimed TIFF mines and using the "leftover's" from the mining operation to fill the bags which is a mixture of small sharp rock, sand, and red clay. It compacts very well and the walls aren't budging. The clay retains water for a long time and there has been a lot of press about mold lately, I am wondering if we should give some time to let the walls dry out before covering with stucco?
A: Soil rarely harbors mold; usually you need a more porous and organic medium to support mold. On the other hand, you don't want to trap moisture within the wall for very long either. My suggestion is to either allow the soil in the bags to dry out thoroughly, or plaster them with something that will breath enough for the walls to dry our over time. I advocate breathable walls anyway, as this is generally more healthy for both the building and the inhabitants.
Q: How long should I wait until I plaster the bench? Is there a way to test for dryness? For this project I can cover it with a tarp. We have every other day rain for a couple hours. Otherwise hot (90°) and dry. I will be leaving the country soon, so best if I can just tell my guys that in 1 or 2 weeks they can go ahead and plaster with cement.
A: If you loosely cover the bench with a tarp so that it is still airing out, I would expect it to dry sufficiently in a couple of weeks.
Q: My son is soon to be working on a hyperadobe project in southern Arizona. He's concerned about construction during freezing weather. Where he's at the low temp average in December and January is 30.4, and the number of days in December and January that drop below freezing averages 18.5. Do you think if the walls were blanketed, much like concrete construction, would that be adequate? How long do you think the walls need to be kept above freezing? Some of the walls will be stabilized with portland cement, at the bottom of the wall and at openings, and we are assuming that should be treated as if it were concrete construction.
A: I would think that in that location those minimal freezing times would not interfere with progress on an earthbag project. I would expect that the freezing temperatures occur mainly at night, and if the wall were blanketed then any light frost would not be a problem. Concrete actually produces some heat during its curing time, but it is much more vulnerable to frosts than adobe soil.
Q: Do Earthbag walls need to "breathe" in order to fully cure, and stay free of mold or musty odor?
A: Earthbag walls do need to breathe in order to cure, especially if the fill is at all moist initially. A somewhat permeable plaster, at least on the inside, is important long term.
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