SB: Re: earth plaster for commercial use

[Rob Tom <ArchiLogic@yahoo.ca>]

9/23/2002 2:26:58 AM, Athena & Bill Steen 
<absteen@dakotacom.net> wrote:

>I think I have to echo John Salmens  sentiments.  I don't think it 
>would hold up to peoples expectations.  
[sneep]
>On Sunday, September 22, 2002, at 10:55 AM, John Swearingen 
wrote:
>
>> We'd like to do an earthen plaster on a medical office 
>> we're designing, but we have two reservations:
>> 1.  Will it take hard use?  banging, scratching, kids kicking, mops?
>> 2.  What would be the best surfacing for medium sanitary 
>> requirements (smooth, washable)?
>>
>> These issues point to using pise (earth plus cement) with a lime 
>> plaster coat...but we'd rather just use dirt....

>> Comments ?

Dear John;

Rather than echo the thoughts that BCJohn and Beel have already 
offered and with which I must agree,  I 'd like to raise the point 
that the "conventional" wall surfacing materials which are typically 
used in medical offices and clinics (namely gypsum board sheathing) 
don't stand up all that well to "banging, scratching, kids and 
"mops" either.

In order to make the gypsum board serviceable, ding/scratch -
resistant "goalie pads" in the form of vinyl baseboards, chair rails, and 
the steel angles on corners are de rigeur .  I don't see why the same 
strategy couldn't be applied to walls finished with earthen plasters.

If we are to believe the results of the plaster testing done by 
Bruce, King of Sausalito's mob 
( see http://www.ecobuildnetwork.org  ) where the data indicates that 
earthen plasters outperformed Portland cement/lime plasters in the 
compression tests (results of whose validity I'm not entirely convinced 
just yet ) one might draw the conclusion that earthen plasters would 
stand up *better* to wear and tear than would conventional gypsum 
board sheathing which usually only has a thin film of paint protecting it.

In fact,  one might argue that earthen plasters would be *more* 
suitable in a medical office setting because gypsum board will support 
unhealthy mould growth whereas earthen plaster can be ingested (as 
Kalin, son o' Athena & Beel will be happy to demonstrate) without 
any deleterious effect and some might suggest, to theraputic effect.

One might even argue that the "dust" can be breathed without any ill 
effect (as farmers have been doing for millennia while tilling the land) 
so long as one doesn't contaminate it with gunk in attempts to 
"stabilise" it. (On this point, I may be standing on shakey ground since 
I can't cite any data to support the statement.)

It's interesting to note that with gypsum board wall finishes, where 
broad expanses of washable wall surfaces are required, they are clad 
with earthen mixes (ie fired clay tiles) so one might argue that it's a 
matter of adjusting the properties ( ie hardness, texture, type of clay 
and degree of vitrification) of the earthen mix to suit the task.  

Or it may simply be a matter of furniture placement (no, not in the 
Feng Shui sense) to keep abrasive humans and their destructive 
gadgets away from the walls, which is the usual practise anyway.
(ie Furniture usually inhabits the periphery of a space, thereby 
providing a physical barrier between the walls and humanoids)

That being said, I do wonder what logic behind using PISE 
would be (in any scenario, not  just the Skillful Meany's proposed 
clinical setting) ?

Granted, PISE requires only about 15% of the cement that a Portland 
cement plaster mix requires on a per unit volume basis but the PISE 
typically has to be applied a lot thicker than would a PC plaster so 
there may not be any real reduction in the amount of  cement used, if 
one is vying for Greenie points.  

Moreover, "dirt" is classified as a contaminant in Portland cement 
mixes and its inclusion is viewed as being detrimental to the 
performance of the finished product (from a concrete or PC stucco 
point of view). 

To get the best results from Portland cement in terms of performance  
qualities, the aggregate should consist of  a good gradation of  particle 
sizes with a minimum of fines so as to present a minimum surface area 
that needs to be coated by the cement paste, hence minimising the 
amount of cement required and the amount of mixing water used 
(which contributes to shrinkage cracking in any plaster mix, 
cementitious or otherwise).

Given the above, it would seem that mixing Portland cement with the 
extremely fine particles of which clay usually consists, in a PISE 
application is not an optimal use of the high embodied energy material 
and hence, not all that Green, or "natural" for that matter. 

The "proper" aggregate to use with Portland cement (from a 
performance perspective) is clean sand, and it's just as natural as 
clayey earth, so why is a PC plaster viewed as being less natural than 
PISE ? If anything, one might argue that PISE is less natural, the 
process requiring fancy gizmos in order to produce it whereas with 
PC plaster, a little sweat and a wheelbarrow for mixing it in is all that 
is required.

I can't help but wonder if something like psyllium or that prickly pear 
cactus juice might not be a more appropriate stabiliser to use with 
earthen mixes ?

And if finishing the earthen plaster with a coat of lime plaster anyway, 
why would the substrate need any Portland cement in it  at all ?

I gather that the clients want to make a statement of their philosophy 
by using natural materials like SB & earth ? 

It would seem that rather than try to make the natural materials 
perform to the expectations that Western society has come to expect 
of modern manufactured materials (thereby reducing those natural 
materials to mere pastiche and in some cases, less healthful than their 
conventional man-made counterparts as a result) , perhaps the design 
should try to accommodate the qualities (and weaknesses) of the 
unadulterated earthen material  (easy for me to spout, but not so easy  
to implement  but do-able  nonetheless... I suspect) by configuring it 
and the building elements in such a way that mops/jamfaces/violent 
adults cannot wreak havoc upon the material.

And even if the material does eventually become worse for wear due 
to unforseen circumstances in spite of the thoughtful design (ie $#!+ 
happens)  "So what ?"  It's easy to fix. Right ?

One might also argue that a medical clinic (ie a place which promotes 
healthful lifestyle *choices*) in California (a place which is noted for 
looking at "alternatives") would be the ideal place to use an 
unadulterated earthen plaster .

 ~~~*~~~
 Rob Tom
 Kanata, Ontario, Canada
<ArchiLogic@CHAFFyahoo.ca>
(winnow the "CHAFF" spamguard from my edress in your reply)

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