[Cob] Alum and Soap over horizontal Lime Plaster surfaces?

[Amanda Peck]

Thanks.  I've seen most of those pages, didn't remember that.

Looks like the plain cob-like mixture worked pretty well, and Bill Steen 
said that he'd never used  the soap/alum method.

Since I'm planning on a good deal of rain-water catchment, lime, alum, or 
soap are not options for me on a roof, and that letter would tend to make me 
think that a really waterproof coating for cob is not the greatest of ideas 
anyway, although keeping driving rain off is a really good idea.

Alum seems to be any of several aluminum salts, usually sulfate?  While 
aluminum is one of the most common minerals in the earth's crust, it doesn't 
seem to be very good for humans to ingest.  There has been at least one 
study that seem to show that aluminum cookware might tend one towards 
Alzheimers, for instance (Vanderbilt university, years ago, I don't know how 
well designed it was, how big the sample was, how they did their 
research--or even how many years ago it was).  The "all natural" crowd would 
prefer deodorants made without any aluminum--although the crystals are 
supposed to be fairly innocuous (and they may indeed be alum).

the lime/clay/sand/(and sometimes) concrete chinking mixture that, ahem, 
fell out of my vertical logs seems to be holding up well in the rain.

The causes for the falling out seem to be (in case you're interested)
a) vertical logs are more likely to let chinking fall out.
b) I was trying to span too great a space.
c) without putting in any kind of rough stuff to hold it--screws sound like 
a pretty good idea, and I've got lots left over.
.............................
Kathy replied to me:
 >
 > Got links?
 >

http://www.potkettleblack.com/natbild/canelo_wall6.html

This is the page where Bill Steen (of the Canelo Project) mentions
about horizontal lime surfaces on roofs in Mexico that use a water
repellent mixture of alum and soap to prevent absorption of water."










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