[Cob] earthen plaster on drywall

[Graeme North]

Anna

I have successfully used a low shrinkage clay/fine sand plaster with the addition of a goodly dollop of cellulose fibre (macerated office paper) - this helps with any dust/silt suppression, and provides extra reinforcing and bonding. 
It is laid up directly onto the dry wall in a single fairly thin (3-6mm) coat.

All I did was embed a standard dry wall joint fibreglass strip - or else a strip of jute or hessian -  over the dry wall joints to prevent cracking as we went. 
You need to firmly press the earth plaster onto the dry wall with a trowel , and float if off to whatever finish you want as it starts to dry and stiffen.

After 15 years it is still as good as new.

I reckon the overall time involved is much the same as plastering up the joints with dry wall goo, sanding them off, priming and painting would be.

Its easy and looks great.   Even these thin layers help with humidity regulation too I have found, and in one nasty event a colleague experienced, it also helps a lot with fire resistance.

I am sure additional or thicker layers could be added if more bulk was wanted but I have not seen the need.

cheers

Graeme 

 
 
> On 26/02/2017, at 5:49 AM, Shawn King <sbkingster at gmail.com> wrote:
> 
> Hi Anna, I posted a reply a few days ago but I believe I did two things
> wrong - I hit reply to you alone, and I also included a link in the post.
> I am reposting with both conditions corrected. My wife Melissa and I
> applied earthen plasters over unpainted as well as glossy- and
> matte-painted sheetrock successfully. Applications were in the kitchen and
> bathroom, so the approach seems to work quite well in rooms where water
> vapor is produced in concentrated amounts. You need a thin adhesion coat
> first followed by whatever earthen plaster you want. We tried adhesion
> coats based on wheat and rice paste and sand and found they led to staining
> of the final plaster, so we now avoid this method. We now use what we call
> "schmeer" which is just clay rich soil mixed with water and coarse sand to
> make a sticky, gritty paste the consistency of yogurt. We take this and
> smear it onto the sheetrock in a circular motion with pressure to form a
> thin layer, just enough to cover the sheetrock, and let it dry.  Just
> before applying an earthen plaster, we re-wet the schmeer so that it is
> nice and damp, but not so much that it starts to wash back off the
> sheetrock.  The earthen plasters we like are just our somewhat silty
> subsoil (soaked and screened through 1/8th inch screen), water, screened
> horse manure (through 1/4 inch screen), and screened sand, maybe 2:4:1 or
> whatever gets us to a consistency like fluffy tuna salad when mixed wet.
> If we want a plaster color other than the natural result of this mix, we
> wait for the plaster to dry completely and then paint over it with
> lime-buttermilk paint tinted with masons or potters stains. I find earthen
> plasters eat a lot of pigment, wasteful and expensive, so I prefer paint
> for final effects. Hope this helps.  Best, Shawn
> 
> On Wed, Feb 22, 2017 at 12:51 PM, <avjyoung at shaw.ca> wrote:
> 
>> We are having to drywall our cob/strawbale house over the framed areas,
>> rather than time-expensive lathe and plaster as our old house is falling
>> apart and very close to uninhabitable. What, if any, earthen plaster can we
>> put over the drywall to get the different surfaces looking more similar,
>> and avoid using drywall mud and toxic paint?
>> 
>> Thoughts and comments very welcome!
>> 
>> Anna
>> cob-strawbale hybrid in Victoria, BC.
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