[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
Re: Fwd: Re: GSBN:Re: Lime plaster problems
We should talk at length about this, but here are
a few "shoot from the hip" comments:
My limited experience of mixing lime and earth as
a plaster produced bad results: lots of cracking.
I feel much more comfortable with all earth OR
all lime. But the comments someone made below
about it depending upon the particular soil make a lot of sense.
The original problem described, delamination, in
not at all unexpected under conditions of rapid
drying and/or freezing. ESPECIALLY freezing!
While I really like lime, I really do like the
Frank Meyer approach that we are trying to use on
Sue Murray's SB house: Exterior earthen plaster
with wide overhangs (or other protection) all around.
Let's talk some more. There are certainly others
with more experience than I, but I can throw my
two cents in. Plus I now know a very experienced
lime plaster (trained in England) who lives in Austin.
At 01:23 PM 10/7/2007, you wrote:
Your opinions/comments on this with respect to our local clays?
The original problem was a delamination of the
lime plaster coat, possibly influenced by too
rapid drying (wind picked up while in the
process, and not enough tarps available to cover
and keep it damp) and an unexpected freeze that
night (2 months ahead of the usual frost date).
Possibly also influenced by too smooth a finish on the earthen coat beneath.
Bill's comments about undependability concern me.
I'm halfway thinking I should buy some clay now
- enough to do what we figure will be the
exterior of our place and then some - and set up
some tests. By the time we actually build,
we'll know if the stuff will hold up.
Date: Sun, 7 Oct 2007 09:00:00 -0700
From: Athena & Bill Steen absteen@...
Subject: Re: GSBN:Re: Lime plaster problems
To: "GSBN" GSBN@...
Reply-To: "GSBN" GSBN@...
Sender: "GSBN" GSBN@...
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 time."
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 plaster.
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.
Aul?s, Lleida, Espa?a
(0034)657 33 51 62
www.casasdepaja.com (Red de Construcci?n con Balas de Paja)
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
Asunto: RE: GSBN:Re: Lime plaster problems
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.
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 others
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
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
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.
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>
<<a target="_blank" href="http://sustainablesources.com/contact/">http://sustainablesources.com/contact/</a>>
Don't miss October's Natural Building
Colloquium: <<a target="_blank" href="http://naturalbuildingtexas.org">http://naturalbuildingtexas.org</a>>
Green Building Professionals Directory: <<a target="_blank" href="http://directory.sustainablesources.com">http://directory.sustainablesources.com</a>>
Sustainable Building Calendar: <<a target="_blank" href="http://SustainableSources.com/calendar/">http://SustainableSources.com/calendar/</a>>
Green Real Estate: <<a target="_blank" href="http://SustainableSources.com/realestate/">http://SustainableSources.com/realestate/</a>>
Straw Bale Registry: <<a target="_blank" href="http://sbregistry.sustainablesources.com/">http://sbregistry.sustainablesources.com/</a>>
Books/videos/software: <<a target="_blank" href="http://bookstore.sustainablesources.com/">http://bookstore.sustainablesources.com/</a>>
Gayle Borst, LEED AP