[Cob] Lime Render - FAILURE

[Bernhard Masterson]

Hi Bill,


You are correct that wet and expanding clay plaster base coats can crack lime top coats. I could agree that is the primary cause for the cracks low in the wall where repeated direct wetting can occur.


But looking at your photos you also have horizontal cracks at the top of the door arch which seems to me that it would be sufficiently protected by eaves. I do see a discoloration below the cracking on both sides that lead me to ask if there could be other moisture issues in play.


- Are your walls cob?

- Does the cob go all the way to the roof decking? or is there slip-straw above the level of the door? Are the walls uniformly thick?

- If the walls are cob, how long did they dry before plastering? What were the drying conditions?

- What is your interior plaster? and what are the humidity levels inside the building? More vapor permeable interior plaster can allow walls to move moisture to the exterior where once it reaches a plaster with lower permeability can concentrate moisture.


Hope these lines of questions are helpful,

- Bernhard

You can't buy happiness. But you can buy a bicycle, and that is pretty close.

____________________________________http://www.bernhardmasterson.com
Natural building instruction and consultation


________________________________
Message: 1
Date: Fri, 17 Feb 2017 09:43:09 -0800
From: Bill Wright <bill at auburnacupuncture.net>
To: coblist at deatech.com
Subject: [Cob] Lime Render - FAILURE
Message-ID:
        <E2A46CF4-BED9-44FD-AA2F-8DD9066AB891 at auburnacupuncture.net>
Content-Type: text/plain;       charset=us-ascii

Happy New Year of the Fire Rooster All!

I'm attaching photos here for you to view online (below my message ;^).

The images show the cracking of a lime render applied less than (1) year ago over an earthen brown coat. The Brown coat was 3 parts sand to 1 part - 90% indigenous site clay and 10% lime (NHL 3.5). The final lime render was 2.5 parts sand to 1 part - 90% lime (NHL 2.0) and 10% indigenous site clay. A pigment from Trans-Mineral USA was added for color to the recommended acceptable amounts according to the manufacturer of the pigment. (I think TM USA was the source, I know we got our lime from them - St. Austier NHL).

My Natural Home Builder and I believe that the greater than average rains in Northern CA this winter have saturated the lime render to the point of moisture moving thru the lime to the clay brown coat underneath; which is expected, and not usually a problem. . .  Not a problem UNLESS the clay expands and cracks the lime render above; which we believe is the mechanism of how the lime is cracking.

The real problem is two fold:

A. I'll bet my bottom dollar the County will not pass my building w/ cracks in the render - big ouch!

B. The process of water expanding the clay underneath is progressing to the point that the lime is delaminating and falling off in certain areas. While this is not really a huge structural issue, it's a bummer, and it's unsightly to say the least. Over time, it could start to wear down the cob/earthen layer beneath it, which will create more work to fix it.

So, my question is this. . . What would you do next to remedy this situation and create a functioning wall given my current situation?

PICTURES:

https://www.dropbox.com/s/ib58lvdq5crtly4/File%20Feb%2017%2C%207%2059%2025%20AM.jpeg?dl=0


https://www.dropbox.com/s/5y52e8x455ngiuv/File%20Feb%2017%2C%208%2000%2012%20AM.jpeg?dl=0
[https://www.dropbox.com/temp_thumb_from_token/s/5y52e8x455ngiuv?preserve_transparency=False&size=1024x1024&size_mode=2]<https://www.dropbox.com/s/5y52e8x455ngiuv/File%20Feb%2017%2C%208%2000%2012%20AM.jpeg?dl=0>

File Feb 17, 8 00 12 AM.jpeg<https://www.dropbox.com/s/5y52e8x455ngiuv/File%20Feb%2017%2C%208%2000%2012%20AM.jpeg?dl=0>
www.dropbox.com
Shared with Dropbox




https://www.dropbox.com/s/uwfe9b638zsi1z4/File%20Feb%2017%2C%208%2000%2055%20AM.jpeg?dl=0
[https://www.dropbox.com/temp_thumb_from_token/s/uwfe9b638zsi1z4?preserve_transparency=False&size=1024x1024&size_mode=2]<https://www.dropbox.com/s/uwfe9b638zsi1z4/File%20Feb%2017%2C%208%2000%2055%20AM.jpeg?dl=0>

File Feb 17, 8 00 55 AM.jpeg<https://www.dropbox.com/s/uwfe9b638zsi1z4/File%20Feb%2017%2C%208%2000%2055%20AM.jpeg?dl=0>
www.dropbox.com
Shared with Dropbox




https://www.dropbox.com/s/ut8bxeksxbhb2y4/File%20Feb%2017%2C%208%2001%2023%20AM.jpeg?dl=0
[https://www.dropbox.com/temp_thumb_from_token/s/ut8bxeksxbhb2y4?preserve_transparency=False&size=1024x1024&size_mode=2]<https://www.dropbox.com/s/ut8bxeksxbhb2y4/File%20Feb%2017%2C%208%2001%2023%20AM.jpeg?dl=0>

File Feb 17, 8 01 23 AM.jpeg<https://www.dropbox.com/s/ut8bxeksxbhb2y4/File%20Feb%2017%2C%208%2001%2023%20AM.jpeg?dl=0>
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Shared with Dropbox




Many Thanks!

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"