[Cob] Another inquiry on sealants...

[Henry Raduazo]

If you have a good roof over a cob structure there is no reason other  
than esthetic to do anything else to it. If you wall is going to set  
out in the rain you need to do something and nothing that I have  
found is perfect. You must also consider the environment that the cob  
is in. The worst situation is a warm heated house and a cold exterior  
exposed to water. Here the only thing that I know of is lime finish  
because it sheds water and permits evaporation of moisture from  
inside the wall.
	If both sides of the wall are equal temperature and the same  
humidity then you can coat the wall with almost any water proofing  
that you want. My wood shed has an earth plaster roof that is painted  
with boiled linseed oil to make it waterproof. Linseed oil tends to  
darken and even turn black over time. There are other penetrating  
sealers that do not discolor, but they are a bit more expensive.  
There is still a small leek in one section of my 7 foot by 30 foot  
roof, but I think I can fix that with another coat of linseed oil. I  
am also experimenting with driveway sealer. If you did this in a real  
house you would need a well ventilated attic space that would  
separate the roof from the living area.

Ed

On Nov 3, 2010, at 5:06 PM, Benjamin Brownell wrote:

> I've done some searching and reading and testing on this question,  
> but thought I would still check in here for new insights or advice.  
> I feel like there must be alternatives to the two standard answers  
> on weather-protecting earthen structures--
> a) just cover it already with proper roofing, or b) give it a  
> natural finish (oil, lime, etc) but watch closely and plan for upkeep
>
> I'm curious if people have had success with other treatments, even  
> 'industrial' versions, that could allow for durable application in  
> public settings without utterly sacrificing the aesthetic qualities  
> of the substrate. I believe rammed earth buildings are often sealed  
> with versions of silane/siloxane that is a semi-breathable  
> treatment often used on concrete, but have not tried it (nor know  
> of a tested version for natural plasters). I have seen cob  
> partially painted with latex to some good effect. There are a  
> multitude of other more and less frightening compounds available.  
> Perhaps this is heresy to purists, but I'd like some alternatives  
> to get mainly sculptural demonstration works into the public eye  
> and not watch them fall apart with the slightest neglect/overuse.  
> Not so concerned about breathability in this case, although I think  
> different treatments for different exposure levels could be  
> combined for maximum benefit/minimum impact.
> Any info, speculation, anecdote is welcome!
>
>
>
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