[Cob] Lime Render - FAILURE

[Bill Wright]

Hi,
Thanks for the thoughtful responses!

A LOT of good insight here. I think it most fruitful to follow Shannon's lead on drawing attention to Pic #2 that I sent. (I'm including it below again for your reference). I think it's important to focus on this picture because the other pics are likely settling cracks as has been posited by a few of you. Though the cracks at the corners of the South wall are suspiciously close to the cracks in Pic #2 that are adjacent to the Doors on the South wall.

The other reason it's important to focus on Pic #2, is that it represents the LEFT (looking from the exterior) side of the French Doors on the South Side of my building, and the RIGHT side is just as bad, if not worse!

This area of the building gets the most moisture, and after our substantial, extended rains this year, this elevation all along the South wall appears wet. In other words, it's darker from water that has soaked in a bit. How far has it soaked in? Dunno! But it's the areas to the left and right of the door that are cracking AND delaminating. So what's, "behind" those areas?

I've listed the brown and finish coats here previously, and the wall in question is a 100% cob wall. What IS there as well, helping form the curve in the wall, and helping the cob/brown coat/finish lime coat connect to the framing for the doors is. . . Expanded Metal Lathe. So the layers in sum are: Cob wall, expanded metal lathe bridging the wooden door frame to about 12" onto the cob wall, and screwed into the cob wall w/ 3.5" deck screws, brown coat, finish lime render. 

This is an art studio, and no one lives in the building, nor is anyone in it very much as of late. I make that point to rule out moisture coming from within the building leading to moisture issues. The other question of the wall being too wet BEFORE the lime render went on. . . No way. The building sat in our baking summers, and drought laden winters for a couple seasons; our concern was that they were TOO dry to apply the lime render.

So, I'm back to thinking the lime render (or whatever I should call it?!) is letting too much water penetrate, and the expanding clay beneath is opening up cracks in the outer layer. Am I cracked?! (Sorry. . . Pun intended ;^)

If that's the case, what to do? I could patch the cracks, but I'm not secure that is a good long term solution. Any suggestions on a clear, water resistant coating I might apply OVER the exterior?

PIC #2 INCLUDED HERE:

https://www.dropbox.com/s/5y52e8x455ngiuv/File%20Feb%2017%2C%208%2000%2012%20AM.jpeg?dl=0

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" 


> On Feb 17, 2017, at 3:03 PM, Shannon Dealy <dealy at deatech.com> wrote:
> 
> 
> [snip]
>> 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).
> 
> Hi Bill,
> 
> Based on what I am able to see, it appears to me that pictures 1, 3 and 4 are settling cracks. Number one could be due to foundation issues in that area, or issues with how the wall was constructed near that area. It doesn't look particularly bad given the amount of time that has passed, so it may be that everything has stabilized. Pictures 3 and 4 appear to be due to shifting/settling/shrinking around embedded wood (door/window lintels and embedded log - I'm assuming something is embedded in the cob above the door) note that the cracks originate and end at these points.
> This is quite common if the wall and wood haven't had a long time to cure around these areas, since wood and cob shrink very differently as they dry.
> 
> I do not believe that any of these cracks are due to rainfall issues as the moisture from rainfall heavily favors the base of the wall and these cracks are not preferentially occuring at the base of the wall. Why is water more of an issue at the base?
> 
>  - The upper wall is better protected by roof overhangs
>  - The upper wall receives greater airflow so it dries much faster
>  - rain splash from water hitting the ground and rebounding onto the
>    building is limited to the first couple of feet
>  - rain splash from plants next to the building can be higher up,
>    but the plants themselves are generally mostly at the base
>  - the humidity is higher closer to the ground (where the water from
>    recent rainfall is), slowing the drying at the base
> 
> Additionally, the finish render mix you describe should be highly resistant to water. If you have water issues behind this mix, I think it would be more likely to come from moisture within the house working its way through the walls (breathing, cooking, showering, ... give off a lot of water, I've discussed this issue previously), though I think it is unlikely given where you live.
> 
> I've seen and worked with similar exterior plasters on a number of buildings in Oregon with 40+ inches of rain each year. Some had problems, but it was not due to the rainfall in any case I am aware of.
> 
> The only picture that causes me any concern is number two and my question would be what (if anything) is embedded in the wall in that area as well as what is on the other side of the wall? Embedded wood, plumbing, shower on the other side, etc. Even this area is not a major concern to me unless the render starts flaking off (at which point you may be better able to assess what is going on behind it).
> 
> 
>> A. I'll bet my bottom dollar the County will not pass my building w/ cracks in the render - big ouch!
> 
> For this issue, I would simply make a small batch of plaster mix, matching as exactly as possible the original mix you used. Wet the area around the cracks, then fill them in with an excess of the new mix and refloat the surface of the wall around the crack to blend it in. I would start with the crack in the least visible area and get your technique down before doing the others. It is important to note here, that the color will not match for quite some time, even if your mix is exactly correct as the area needs to reach the same level of moisture as the surrounding wall, and the lime needs to react with CO2 in the air for a time to catch up with the state of the rest of the wall. I don't recall how long it took for my last patch job (jar window broke) to match the rest of the wall, but I think it was measured in months.
> 
> 
>> 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?
> 
> None of your pictures show an area where the lime is actually falling off, so it is hard to say for that case. One of the problems that cracks can cause once they are present (due to settling or other issues) is they can allow water a pathway into the wall, and in some cases, even channel the water in. At this point, the greatest danger is usually from freezing as this causes the trapped moisture to expand and forcefully separate the plaster from the wall. If you have freezing temperatures in your area, I think this is more likely than water expanding the clay in the walls.
> 
> FWIW.
> 
> Shannon C. Dealy               |       DeaTech Research Inc.
> dealy at deatech.com              | Biotechnology Development Services
> Telephone USA: +1 541-929-4089 |      USA and the Netherlands
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