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RE: GSBN:Re: Lime plaster problems

Dear Bill and others
Much appreciate your well considered most informative response.
Please do forward me the paper you were talking about thanks.

I have done some investigation into the mineral content of the soil talking
to a knowledgeable engineer / farmer who said that the red  soils we used,
which are common to the area are generally quite acidic  .... He also
explained that there used to be pine plantations in that specific area and
guessed the PH would be about 4,5 to 5. He also suggested that we could
check the PH of the water we used...if you think that will also influence
the results. He said with farming that meant they usually have to add quite
a lot of extra agricultural lime to the soil to help balance the PH. If what
you are saying is that with acidic soils/water we should use a stronger lime
mix ...then I guess our mix did not have enough lime in it. We used 25% lime
mix and probably should have used a 33% lime mix???? The mix was 2 parts
soil, 7 parts sand and 3 parts lime. (The receipt I used was to substitute 1
part of the 3 parts of sand with the adobe mix)

Our adobe mix was 2 parts soil and 1 parts sand and made excellent bricks
which were very well cured and the whole wall had had months of curing
before any plastering. 

Apparently the soils (from Dolerite bedrock) apparently have a very high
aluminum content...not sure if that would have played a part in it???

Not sure about the sodium carbonate levels but the potassium and phosphate
levels are very low (2-3 parts per million).

The soils also have a fairly low P.I. and we did not experience much
shrinkage. However we did wet the walls down very well before applying the
plaster and may have even over done the wetting of the walls afterwards as I
wanted to ensure the lime cured well......however this was negated in the
most part by the unusually occurring and excessive winds, which occurred
during the middle of the days over the period I was there. With the pressure
to get the job all done while I was up there, we pressed on, instead of
postponing the whole thing as in retrospect is what I should have done.

Furthermore in retrospect the keying was certainly not sufficient.

Historically in the Cape, which I am more familiar with, most of our old
earth buildings (of which there are many 100 - 300 years old) were always
protected with a good coat of lime plaster. Sometimes however lime plaster
was not used and rather a cow dung earth plaster was used followed by
regular coats of lime wash...though at the coast where we experience strong
wind driven rains a lime coating was the norm. No doubt our forefathers knew
a thing or two about lime that helped them get it right.....so I have always
had the greatest of confidence in lime plaster....up until now!

Kind thanks

Architects & Consultants
A. R. HORN B.A.S. (UCT), B.Arch (UCT), Pr.Arch (SACAP),       MIA, CIA
Telephone: 021 462 1614, Fax: 021 461 3198
Cel: 082 67 62110
4th Flr, The Armoury
160 Sir Lowry Rd
web site:  HYPERLINK www.ecodesignarchitects.co.za
email: andy@...

-----Original Message-----
From: GSBN [<a  target="_blank" href="mailto:GSBN@...";>mailto:GSBN@...] On Behalf Of Athena &amp; Bill
Sent: 07 October 2007 04:00 PM
Subject: Re: GSBN:Re: Lime plaster problems

I'll plead busy as well and before I made any comments I wanted to  
make sure they would be somewhat thorough.  There are a few things  
that have become evident to me over the years when it comes to lime  
over clay plaster.  In mho I would have to say that results are  
unpredictable and undependable.  I'm not saying it can't or doesn't  
work, but rather that outcomes vary widely. David Bainbridge  
mentioned in his earlier post the Getty people in Los Angeles as a  
resource.  I've made it a point to talk with them every few years  
about lime plaster and in particular their work with prickly pear  
cactus gel.  Anyhow in one of the last conversations we had they told  
me that there was a growing sentiment amidst the conservation  
community that the use of lime plaster over earth surfaces was not  
such a good idea.  They mentioned that although lime had better  
permeability than cement and allowed the earth to dry better when  
wet, it was still too different from an earthen substrate for it to  
work dependably.

My experience basically says the same thing.  For me the whole issue  
comes down to what type of earth plaster is underneath.  Apparently  
some are much better than others and just what all the variables are  
I can't say.  I think it will take some time to get a better grasp on  
it.  Clearly I would suggest that if the substrate has a lot of clay  
there is a likely possibility that if water is absorbed through the  
lime plaster and passed on to the earth substrate then obviously the  
clay will expand and have a tendency to push the lime plaster away  
therefore causing the two to separate.  If the earth plaster is weak  
then the connection will break down over time.  So in short I guess  
what I'm saying is that the earth plaster has to be of a really good  
quality for any chance of success.  It needs to be strong and not  
have an overly high content of expansive clay.  Another very  
important piece is that the earthen plaster substrate must be  
thoroughly dry as earth plasters shrink when drying. If that process  
is not complete the earth will pull away from the lime plaster and  
leave it hanging in the air. And as others have pointed out the  
surface needs to be extremely well keyed for the lime to adhere.  I  
don't think you can under-do that aspect.  Additional measures like  
that of placing sharp jagged stones in the plaster would also help  
such as the practice of "rahuela" used in Mexico where stones are  
placed in the mortar joint between adobes.

I think it was David that also mentioned the Japanesete We have  
worked closely with a pair of Japanese plasterers over recent years  
and it is important to note that the Japanese approach relies heavily  
on use of a glue when mixing what they call "Shikkui." Traditionally  
rice flour was used but was replaced with seaweed gel during a time  
of food shortages.  In general I would say that their plastering  
practices are far more meticulous than anything I've seen in this  
part of the world and in the words of the best plasterer from there  
that I can think of, "there is great difficulty in the connection  
between the two coats and at best it does not last for a very long  

Having said all this I will say that my comments apply primarily to  
exterior finishes and I've not yet experienced any problems with  
interior or protected locations.  But I should add that we also  
typically include a percentage of some glue material in the lime  

John Glassford suggested the use of lime/clay as an alternative and I  
think that it can be a very good one.  Much here depends upon the  
reaction between the clay soil and the lime. Over the years I've  
watched varying reactions, some soils produce exceptional results,  
others marginal.  I recently cornered Harry Francis who once worked  
for the American Lime Association while we happened to be together  
recently in Washington DC.  I told him that the using pH as an  
indicator of the right type of mix was not proving true all of the  
time.  Like he always does Harry went home and searched his extensive  
resources and just emailed me a paper that addresses some of those  
variables particularly soils with high levels of potassium and sodium  
carbonates.  I haven't had time to really absorb the content, but if  
any of you want a copy I would be happy to forward it.

I've already said more than I had intended, but to sum it up I would  
not suggest that we recommend the use of lime plaster over earthen  
substrates as a general practice.  I would suggest that it be adopted  
only after some testing and experimentation has been done and with a  
warning that the results are always guaranteed.

On Oct 7, 2007, at 7:10 AM, Rikki Nitzkin wrote:

> Sorry to chime in so late...been busy. Its just that I haven't seen  
> anywhere
> that in the responses to remind Andy that it is very important to  
> wet down
> as well as scratch the base layer of plaster before applying a new  
> coat, and
> if the material is different (lime on clay in this case) really rub  
> the
> first bit in so it binds well.
> Hope your problem has been solved.
> Rikki Nitzkin
> Aul?s, Lleida, Espa?a
> rikkinitzkin@...
> (0034)657 33 51 62
> www.casasdepaja.com (Red de Construcci?n con Balas de Paja)
>> -----Mensaje original-----
>> De: GSBN [<a  target="_blank" href="mailto:GSBN@...";>mailto:GSBN@...] En nombre de Brian  
>> Hodge -
>> Anvill
>> Enviado el: jueves, 27 de septiembre de 2007 22:20
>> Para: 'GSBN'
>> Asunto: RE: GSBN:Re: Lime plaster problems
>> Hi Andy,
>> I agree with John. We have been doing a very similar thing for  
>> about 5
>> years and have not found it necessary to add the lime putty top  
>> coat. We
>> have even done it without chaff with a great deal of success.
>> Regards
>> Brian
>> Anvil Straw
>> -----Original Message-----
>> From: GSBN [<a  target="_blank" href="mailto:GSBN@...";>mailto:GSBN@...] On Behalf Of John
>> Glassford
>> Sent: Thursday, 27 September 2007 7:53 AM
>> To: GSBN
>> Cc: Andy Horn
>> Subject: Re: GSBN:Re: Lime plaster problems
>> G ' day Andy
>> My two rands worth mate.
>> You will need to remove the lime coat and scratch up the earth as  
>> others
>> have said.
>> I would then apply a mix of earth/lime/sand and chaff or chopped  
>> straw.
>> All depends on the clay content of your earth but I would look at
>> something like this 3 parts soil 2 parts lime 3 parts sand 1 part  
>> chaff.
>> I use buckets for this mix.  It works well and binds well with the
>> earthen render.  Then if you want you can apply a finish coat of lime
>> render however I have not found that necessary in most cases  
>> except for
>> look.
>> You can see a house we renedered with earth, then earth/lime/sand/ 
>> chaff,
>> then lime/sand, here:
>> <a  target="_blank" href="http://glassford.com.au/Jumbo.htm";>http://glassford.com.au/Jumbo.htm</a>
>> No delamination no cracks and it is nearly 6 years since we finished
>> there.
>> Was in Cape Town a few weeks ago but did not have time to see much it
>> was a Rotary trip with Hout Bay.  We will be back next year for an
>> extended visit, see you then.
>> Kind regards
>> The Straw Wolf
>> Huff 'n' Puff Constructions
>> <a  target="_blank" href="http://www.glassford.com.au/";>http://www.glassford.com.au/</a>
>> 61 2 6927 6027
>> Mount Kilimanjaro Climb 28/8/07 <a  target="_blank" href="http://www.coolamonrotary.com/kili/";>http://www.coolamonrotary.com/kili/</a>
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Athena &amp; Bill Steen
The Canelo Project
HC1 Box 324
Canelo/Elgin, AZ 85611

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