Cob: healthy home data

On Mon, 31 Jul 2000 19:47:42  
Shannon C. Dealy wrote:
>While the referred to posting suggests that the clay is the source of the
>mold, a close examination (which I have done on several occasions) will
>show that the mold/fungus/whatever-it-is is always growing on a piece of
>the straw (or whatever fiberous material you are using in your mix) that
>is at the surface of the wall.

(This is Mark Piepkorn using Sarah's email address.)

While Shannon's certainly giving an accurate assessment of his experience, it might not be universal. In an article at http://www.strawbalecentral.com/earthplaster/earthplaster.html , earth-plasterer Keely Meagan writes about mold and earth plaster:

"At a recent job we switched clays for the finish coat, put out a lot of work in one day to get it on the walls, and the next day we were surprised to see the wall covered with little white fuzzy spots. We hoped they would disappear as the wall dried, but instead they stained the wall, leaving the rich color with lots of lighter blotches. Wiping it with a borax solution or hydrogen peroxide changed the color and the texture... so we redid the wall, adding dissolved borax to the plaster. Had it been summer, when we could have had better ventilation and faster drying, this would not have been such a big problem - but that mold was fierce and I think borax would have been necessary anyway.

"Mold spores can come in with the dirt or straw. Use clean chopped straw and try changing your dirt if you discover mold. Ventilate well. Adding borax or lime to the mix will kill molds. If you develop mold when plaster is on a wall, spray it with hydrogen peroxide to kill it before adding new plasters."

Ianto discussed his theory about cob being astringent with me a while back, but didn't have anything definitive to back it up. (Not that I doubt him on the matter.) OTOH, limewash and lime plaster are known to be "clean", killing mold spores and many bacteria. Since lots of the old cob houses are finished with limeplaster or limewash, maybe there's more reason for it than abrasion and erosion resistance.

[snip]
>After the wall has dried more and loses it's "damp earth" look, the growth
>seems to disappear.
>
>For what it's worth, I have seen similar looking growths (mold/whatever)
>on the ground around here (Western Oregon)

(Sarah here)

Shannon- 

Was it long white fuzz? which grew in a matter of hours? (I encountered mold of the same type in both the northern and southern hemispheres, in humid climates. It vanished very quickly, when exposed to sunlight. I've never seen it growing on anything other than cob.)

Sarah
formerly at sarahm at erols.com


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