[Cob] Lime Render - FAILURE

[Bill Wright]

Hi Shannon et. Al.,
Thanks once again for the thoughtful response. I have done some sleuthing as you suggested (dig into the wall to see how deep the water goes ;^). Ouch!

I've discovered that where it has cracked the water doesn't appear to be penetrating into the wall much, but the lime-containing top coat is not adhering very well. 

I'm continuing the information gathering process here with all of you (thanks again for being there ;^), and I have circled back to the manufacturer's website (St. Astier), and have discussed my project as well w/ Michel of Trans-Mineral USA, a supplier of St. Astier lime; he has been very helpful as well!

I intend to put together an email soon that offers another way forward based on what I'm learning about lime-renders from the St. Astier information; it is a VERY different approach than the one I employed on my building.

Time will tell.
Bill

Bill Wright, L.Ac., DNBAO
Wright Acupuncture and Massage
251 Auburn Ravine Rd., Ste. #205
Auburn, CA 95603
530-886-8927
"There is no path to healing, healing is the path" 


> On Feb 26, 2017, at 5:56 AM, Shannon Dealy <dealy at deatech.com> wrote:
> 
>> On Wed, 22 Feb 2017, Bill Wright wrote:
>> 
>> https://www.dropbox.com/s/2657yta5fpeyec2/Photo%20Feb%2021%2C%208%2000%2037%20AM.jpg?dl=0
>> DISCUSSION OF PHOTO:
>> You can see in the photo that the lime-containing render is getting saturated with the water from rains blowing onto the building where the prevailing winds are doing their work. IS THIS PROOF that the mechanism at play here is water making its way through the lime-containing render into the earthen brown coat below, and the swelling action of the deeper middle layer cracking the lime-containing outer render? It appears that way to me.
> 
> I'm afraid that all this really tells us is that the wet surface looks significantly different from the dry surface. It doesn't tell us anything about the depth of penetration. There are similar differences between wet and dry areas on the outside of three buildings I have which are just bare cob walls (over 10+ years exposure on all three buildings). Of course since I haven't plastered there is no outer layer for the water to get beneath, however, my bare walls are far more absorbant than the plaster mix you describe is likely to be.
> 
> I'm afraid the only way I can think of to get more information is to pick a spot in a wet area without any nearby cracks, dry the surface of the surrounding area with a towel, cut a hole through the plaster with an
> old chisel and see how deep the moisture goes. You should also be able to tell how well the plaster is bonded to the wall in this area.
> 
>> The question I'm sitting with. . . Will lime-putty in the cracks, and a lime wash on top of that be the best fix?
> 
> This would certainly be my approach, though I would use a lime-sand mix with fine sand rather than straight lime putty to fill in large cracks
> (sand reduces/prevents shrinkage). Ideally you want your patch mix to match your surface as much a possible and refloat the surface to blend the patch in. The lime wash is a good idea, but will not hide any significant differences in the appearance of different areas of the wall (that takes time and multiple coats).
> 
> One thing I just realized, you didn't mention any kind of fiber in your plaster mix. While plasters can be done without fiber, using fiber can greatly reduce the chances of cracking, particularly fine cracks.
> 
> 
> Shannon C. Dealy               |       DeaTech Research Inc.
> dealy at deatech.com              | Biotechnology Development Services
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