[Cob] Newbie w/ Questions about 1st project

[littlehouseantiques at att.net]

-------------- Original message from Lance Collins : -------------- 

> Hi, 
> 
> I didn't see mention of a dampcourse between your stones and first layer of 
> cob. This is critical to stop rising damp. 
> 
><snip>
> 
> Regards 
> 
> Lance 
--------------------------------------------------------------------

Lance, 

Where ya from?  I had to look up "dampcourse"!  Here in Central PA we'd call that a "moisture barrier" but to be sure that we weren't talking apples and oranges I looked it up and Freesearch defined it as:  

noun {C} (ALSO damp-proof course) UK 

a layer of material which is put in the bottom of a wall in order to stop water rising through the bricks


BUT the cob builders handbook at weblife.org says:  

"Another minus to using a moisture barrier is that it can weaken the connection between the cob and the foundation"

Source for above quote:  http://www.weblife.org/cob/cob_025.html#moisture

I've chosen NOT to use anything to prevent the water from rising through my wall because what ya put in there to stop water rising ALSO prevents water that does get in from drying out.  I live in a superdooper moist environment--1.5 acres of monstrously large hardwood trees whose canopy prevents almost all sun from reaching the ground (extremely acid soil about 99% clay and rock) where only mosses and lichens and acid loving shallow rooted plants will grow.  Even in the middle of a 3 year drought, my place was still WET.  Anyway, I've found for my situation that it works better to let mother nature wet stuff AND dry it than it is to try and thwart her by introducing moisture barriers.  The only thing that would likely help would be a much higher foundation, but man, it would have to be so high (and the base correspondingly wide) that it would be super labor intensive to build.  

I'm sort of doubtful at this stage if COB is going to be a good material for me to use in my particular site (despite reading all the assurances of many sites which claim all ya need to make cob feasible in damp climates are good "hats and boots" approach & lime plasters) so I've been researching mainly with an "eye" on this topic and found the results of the Canelo Project's test wall of particular interest.  You can view photos of this 'test' wall here:  

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

Granted, their test wall was strawbale with half of it finished with lime-over-earth, & the other half finished with earth-over-earth AND it wasn't really a test of moisture resistance rather a test of plaster finishes, but still I think it's pretty informative.  The top cap of the earth-finished part of the wall (which was made of about 4" of very straw-rich COB) was completely dry but the 
straw under the lime-over-earth was moist, partially weakened and discolored.   Their supposition was that the lime doesn't allow for a drying regime in excess of the wetting regime, even in dry hot Arizona (and if it doesn't work in AZ it sure isn't gonna work on my super wet PA site!)  

So based on this I'm going to do a STRAW rich COB for the the last layers of my bench and a straw clay plaster and see how it stands up to a PA winter.  (Snow may be its undoing...but time will surely tell). 

Kathy