[Cob] lime render fail or just wet?

[Gena Arthur]

Hello,

I have a small strawbale cottage and when the prevailing winds blow rain into the lime render it does appear wet as well. Not sure if that is helpful or not. 

> On Feb 26, 2017, at 2:01 PM, "coblist-request at deatech.com" <coblist-request at deatech.com> wrote:
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> Today's Topics:
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>   1. Re: Lime Render - FAILURE (Shannon Dealy)
> 
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> ----------------------------------------------------------------------
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> Message: 1
> Date: Sun, 26 Feb 2017 14:56:44 +0100 (CET)
> From: Shannon Dealy <dealy at deatech.com>
> To: coblist at deatech.com
> Subject: Re: [Cob] Lime Render - FAILURE
> Message-ID: <alpine.DEB.2.11.1702261456150.25248 at nashapur.deatech.com>
> Content-Type: TEXT/PLAIN; charset=US-ASCII; format=flowed
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>> 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
> Telephone USA: +1 541-929-4089 |      USA and the Netherlands
> Netherlands:   +31 85 208 5570 |          www.deatech.com
> 
> 
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