[Cob] Coblist Digest, Vol 10, Issue 52

[Jill Hogan]

Well done Tony, Cob and cement are not compatible at all. We do a lot of 
restoration and where cement is put anywhere near cob it just breaks the 
cob up
Cob with natural foundation endures for centuaries.
Jill

On 2012/06/22 09:13 PM, Anthony Novelli wrote:
> I don't read every post on this list, but this one caught my eye.
>
> Natural builders need a serious grounding in structural realities, and the services of tensile strength that rebar offers in earthen and concrete structures is justified to ridiculous extreme. Adding stone does nothing to increase tensile strength when creating sculptural details that require such reinforcement. In fact the offer no tensile benefit at all, merely compressive. Straw in the cod provides what native tensile strength there is and with the clay keeps things from powdering into nothing.
>
> There are also a number of factors regarding moisture movement into and out of materials like cob and cement that is a bigger topic. Suffice it to say that the level of saturation necessary to rot rebar out of a cob bench would exceed the capacity of the cob to remain intact.
>
> Tony
>
>
> On Jun 22, 2012, at 12:00 PM, coblist-request at deatech.com wrote:
>>    1. key in the concrete beam (dhowell at pickensprogressonline.com)
>>
>> From: "dhowell at pickensprogressonline.com" <dhowell at pickensprogressonline.com>
>> Subject: [Cob] key in the concrete beam
>> Date: June 22, 2012 6:25:38 AM PDT
>> To: avjyoung at shaw.ca, coblist at deatech.com
>>
>>
>> Anna: "you could set big stones in the concrete as it gets poured"
>>
>> I've thought this same process. It seems like the best way to me. Embed large stones on the top of the concrete while it is still wet and let them sink in a little. This provides that rough surface for keying but doesn't cause a "low spot" so water can be trapped. It is my thoughts that since cob is porous and does transmit water, then even if it does dry out fairly quickly, the rust will eventually set in on the steel and completely deteriorate it. That causes gaps which will probably cave in under pressure and cause severe cracking. Stones embedded in wet concrete will not move, and cob built up around those stones will not move, so you have a product that will not move. Why is there such an infatuation with steel rebar in the building industry? I've seen in the past where a concrete bridge was torn down and they found that the rebar had completely rusted away. So, really this is a good material to use, even in concrete. Think about it; concrete absorbs water, but because it isn't porous it the water doesn't evaporate. If there is steel in there there will be a reaction!
>> Damon
>>
>>
>>
>>
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McGregor Alternative Technology
McGregor Alternative Technology Center "MAT"
Jill Hogan
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McGregor 6708 	023 625 1533
jill.hogan at mat.org.za
www.mat.org.za <http://www.mat.org.za/>

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