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Re: GSBN:Re: Lime plaster problems

Tell you what. I've sat and fiddled with pH meters, test strips, checked water, soil, etc. etc. etc. In the end I found no substitute for simply trying different %s of lime with different soils. For my use at home I finally found a soil that works really well and that was by accident when I wasn't even really trying. All the soils we work with in this part of the world are fairly similar when it comes to pH as well as the water. Why this one soil worked better than others is something I don't understand. When I asked Harry Francis recently and asked him to explain the difference, he simply grinned and said "different chemistry." What I do know is that the one soil that works well has a lot of naturally occurring gypsum and that is the only variable I can ID. Does that mean that all soils with gypsum will do the same? I wouldn't dare go so far.

The excessive winds you mention below by themselves are enough to trash and ruin the best of efforts. They alone may be responsible for everything you encountered.

As for old buildings with lime plaster I know one thing that has changed over the years is the lime. Older limes were often fired on site in handmade kilns, etc. Consequently the lime was less pure, more varied in color and usually softer and therefore more flexible. Today's lime is quite a different animal. Consequently comparisons are at best difficult.

On Oct 10, 2007, at 3:05 PM, Andy Horn wrote:

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
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
first bit in so it binds well.

Hope your problem has been solved.

Rikki Nitzkin
Aul?s, Lleida, Espa?a
(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 -
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.



Anvil Straw

-----Original Message-----
From: GSBN [<a  target="_blank" href="mailto:GSBN@...";>mailto:GSBN@...] On Behalf Of John
Sent: Thursday, 27 September 2007 7:53 AM
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
have said.

I would then apply a mix of earth/lime/sand and chaff or chopped

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
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

You can see a house we renedered with earth, then earth/lime/sand/
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

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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The Canelo Project
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The Canelo Project
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Canelo/Elgin, AZ 85611