Cob: wall cracks

[Christopher Greenslade]

I agree totally with the comments already voiced.You will never stop
cracking totally but by trying to control the drying process you can help to
reduce it.
This can be obtained by the amount of water in the mix, too much clay, not
mixed correctly or drying too quick by the sun / wind.
When lime rendering we use both polythene and wet hessin to reduce shrinkage
/ excessive drying.
It should be remembered even when using the hessin etc.,small cracks can
still appear but generally have no detrimental affect.

Chris Greenslade
----- Original Message -----
From: "Shannon C. Dealy" <dealy at deatech.com>
To: "Roxboro Yurt" <theyurt at yahoo.com>
Cc: <coblist at deatech.com>
Sent: Monday, November 06, 2000 3:33 AM
Subject: Re: Cob: wall cracks


> On Thu, 2 Nov 2000, Roxboro Yurt wrote:
>
> > I have searched the archives and can't seem to find
> > any info on wall cracking.  My cob walls (about 7 ft
> > high at this point) are starting to get little
> > fractures at the bottom in some places where the cob
> > is almost totally dry. Usually about three to four
> > inches long and very very narrow. They don't look too
> > serious, can anyone tell if this is par for the course
> > or something I should be worried about?
>
> Small hairline cracks are quite common in cob and generally are nothing to
> be concerned about.  Usually cracking is caused by shrinkage as the cob
> dries, though it can also be caused by uneven settling of the building or
> excessive point loads on the walls as well.  While a really good high sand
> and fiber cob mix made with a minimal amount of water can greatly reduce
> the amount of cracking, they will not eliminate it entirely.
>
> Shannon C. Dealy      |               DeaTech Research Inc.
> dealy at deatech.com     |          - Custom Software Development -
>                       |    Embedded Systems, Real-time, Device Drivers
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>
>
>