[Cob] lime/earth plaster

[Howard Switzer]

Yes, Ziggy, and in my experience the seam between earthen and lime plasters
was not a problem, perhaps if the wall had settled, or something like that,
it might have shown up but... what of significance we did learn was that
the lime based plasters were WAY more structural, surface bonding the bales
together in such a way as to require a sledge hammer along the head and
bead joints, inside and out, to break a bale loose while the earthen
plasters broke up and off the bale faces easily without a heavy pounding.
This building was begun in a workshop at the Ecovillage Training Center at
The Farm in Summertown, TN, which had been pole framed in a workshop led by
Joe Kennedy but had not gotten a roof ...but which had straw walls
installed in a workshop anyway.  It was subsequently used to test a number
of material combinations and fiber reinforcements of earthen and lime
plasters on the bale walls. The next year it was painted up in colors, the
next year or so signs of the bales deterioration inside the plaster was
evident as water had run down the pole rafters and into the bales rotting,
we discovered, a 6-8 inch column of straw straight to the ground.  Thus the
occasion for tearing it down and seeing just how strong the plasters were.
The experience led me to believe the lime based clay plasters, were much
superior in strength and durability.  Another benefit has been that we've
had no need for control joints, even across dissimilar materials, like
coming down the straw wall, across a wood floor band(papered and meshed)
and down a CMU, Faswall or earth bag wall with no cracking since 1997 when
we went with it "off the Farm. "  Repair has been as easy as it is with
earthen plasters.  We've recommended people use lime/clay to bond the bales
before they go to straight earthen plasters.  Despite that experience I
could not convince a farm resident when he was about to plaster his bale
house that he would be happier with the lime/clay plaster.  He chose
instead to shot-crete the house with cement stucco, one coat.  When of
course a number of cracks appeared he then ground out the cracks with a
grinder and filled them with building sealant.  Also, to the touch the
walls feel hard and sharp unlike the gentle tactile feel that earthen and
lime plasters have.

On Mon, Jul 2, 2012 at 8:49 AM, Dean Sherwin <greenbau at att.net> wrote:

> suggest a galvanized construction/expansion joint strip between the two,
> as used in commercial stucco applications to prevent cracking where there
> is a large extent of plaster.  Makes a firm edge and keeps the different
> types separate.
> you can caulk the thin gap with flexible matching caulk if the line is a
> problem, but it may also be a good feature
> dean
>
>
> On 6/30/2012 3:00 PM, coblist-request at deatech.com wrote:
>
>>
>>
>> Today's Topics:
>>
>>     1. Dealing with seams between lime and earthen plasters?
>>        (Brian Ziggy)
>>
>>
>> ------------------------------**------------------------------**
>> ----------
>>
>> Message: 1
>> Date: Fri, 29 Jun 2012 17:23:18 -0500
>> From: Brian Ziggy <evacindustry at gmail.com>
>> To: coblist at deatech.com
>> Subject: [Cob] Dealing with seams between lime and earthen plasters?
>> Message-ID:
>>         <**CABUX4XjHQGXEmZ1MB2k6cXBS99VWc**aoOBOHXRtuy9cS=7mj9rA at mail.**
>> gmail.com <7mj9rA at mail.gmail.com>>
>> Content-Type: text/plain; charset=ISO-8859-1
>>
>> Hiya all:
>>
>> I am in the process of designing our plaster selection for our new timber
>> frame & straw bale home. I have not done extensive lime plaster work
>> before. We'd like to do a mix of lime and earth on the exterior, or
>> different plasters depending on the individual susceptibility of each wall
>> to rain damage.
>>
>> I'm doubtful of how well a seam between earth and lime plasters would do.
>> Has anyone ever plastered with earth and lime on the same wall with a
>> seam?
>>
>> - ziggy
>>
>>
>
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-- 
Howard Switzer - Architect
668 Hurricane Creek Road
Linden, TN 37096
931 589 6513
www.earthandstraw.com

"You never change things by fighting the existing reality.
To change something, build a new model that makes the existing model
obsolete."
-- Richard Buckminster
Fuller<http://www.goodreads.com/author/show/165737.Richard_Buckminster_Fuller>