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GSBN: Digest for 1/6/03



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-> Jeff Ruppert and clay tests
     by Paul Lacinski paul@...
-> Re: GSBN:Jeff Ruppert and clay tests
     by Chris Magwood cmagwood@...
-> Re: GSBN:Jeff Ruppert and clay tests
     by Bruce King ecobruce@...


----------------------------------------------------------------------

Date: 6 Jan 2003 13:57:11 -0600
From: Paul Lacinski paul@...
Subject: Jeff Ruppert and clay tests


Jeff,

Many thanks for this test.  We use clay and lime plasters almost 
exclusively now, but I am still uncomfortable promoting them without 
solid data.  Also, without any real sense of the tensile and 
compressive strengths of these materials, it is difficult to rely on 
them for any portion of the structural component of the buildings, 
even though it is plum obvious that they are capable of carrying at 
least some  of the loads....

Anyway, I hope that you and others on this list will take some 
interest in the work we have been doing with lime stabilized clay 
plasters.  At least in New England, I have found them to be far 
superior to straight clay plasters in three basic areas:  mold 
prevention, weather resistance, and shrinkage.  They also clearly 
have a higher compressive strength.

Here's what I've found:
Mold
We learned about this in a big way in the summer of 1999, which was 
very dry, with no rain from April until the third week in August. 
When were we installing bales and applying clay/straw plaster?  You 
guessed it- the exact weekend the rains began.  I'm convinced that 
every mold spore in the state of Massachusetts woke from dormancy 
that weekend, and the freshly plastered walls erupted in a fur of 
pink, green, and beige mold, which made me feel rather ill and spoke 
badly of straw bale construction to every person who came nearby.  To 
make matters worse, on that weekend the weather changed from hot and 
dry to cool and wet, and the plaster took a very long time to dry 
out.  I tried hydrogen peroxide to kill the mold, and it drank it 
down and grew stronger.  I tried a solution of bleach and water; this 
knocked it back until the bleach went off into the ozone layer.  Then 
I tried a limewash, and the mold receded. 

Mold doesn't grow on the clay, it grows on straw in the plaster mix, 
and on the straw behind the plaster.  We are careful now about 
keeping our milled straw dry; but the key element has been the 
inclusion of lime in the plaster.   We haven't had a signifcant mold 
issue in the three years we've been using lime stabilized plasters.

Weather resistance
In our climate, it's not practical to use clay plaster as a final 
coat; but because of our short construction season the clay base coat 
almost always goes through one winter before receiving a lime finish 
coat and limewash.   So in the spring, I get to inspect the damage. 
There is no question that the lime-stabilized mixes are performing 
better than the clay-only mixes.  On one house, we used both, and 
contrast was amazing.  One whole corner of the clay-only mix had 
eroded away, while on the lime-stabilized mix there was no 
discernible erosion of the horizontal ridges made by the scratching 
tool.  Generally, the only damage we see on the lime-stabilized walls 
is right at the top layer of the winter snow pile, where the snow 
does not melt the usual inch or so away from the face of the wall, 
and the wall is subjected to alot of freeze-thaw.  This is easily 
repaired before the final coat. 
(Incidentally, I love this system of leaving the finish coat for the 
next year.  It allows time for the building to shrink and settle, and 
our finish coats generally show no stress-related cracks.  It also 
leaves plenty of time for the bales to dry off the trendous amount of 
moisture introduced by the base coat.)

Reduced shrinkage
We apply our base coat at about an inch thick, with a sprayer and 
therefore quite wet.  The clay-only plasters would consistently show 
a pattern of short (2-4") vertical cracks, covering the entire 
building.  This was not a long-term problem, as they didn't seem to 
telescope through to succeeding coats; but I like the fact that in 
the lime-stabilized samples these cracks do not appear, except in 
areas that were filled quite deeply.  At the very least, there is 
less chance of water entering the building during the first season, 
before the finish coat is applied.  I also believe the reduction in 
cracking makes for a more solid substate for the finish coat.

Increased compressive strength
Here is where a lab test would be very useful.  There is no question 
that our lime-stabilized plasters are harder and more crush-reistant 
than their clay only forebears; I've pounded on enough walls and 
crushed enough drops with my foot or a hammer to say this with 
certainty.  What I'm not sure of his how much harder....


A further benefit of the lime is that it makes spraying much easier. 
The lime makes the plaster much more slippery, so that there is less 
friction in the spray tube.  With the rather underpowered Quickspray 
Carousel, this is a very significant improvement.  (By the way, if 
anybody has a recommendation for a better sprayer, I'd love to hear 
about it.)

Mixes
The ideal percentage of lime for stabilization varies according to 
the richness of the clay soil used, and also according to the 
specific clay particles in the soil.  The properties of clays vary 
widely.  We usually work with a clay from a brick factory which is 
somewhere in the area of 60-70% clay content.  We have found that a 
1-1 ratio of dry, milled clay to lime, added to 4 parts sand and 2 
parts milled straw, makes an excellent base coat plaster.  This is a 
rairly rich mix, with excellent properties of adhesion and 
workability.  After seeing Jeff's test, we may try increasing the 
sand to six parts, omitting the straw, and using synthetic fibers. 
(We have had very good luck with synthetic fibers in lime plasters.)

I don't know what happens if the mix is too rich on lime; I do know 
that if there is not enough lime, the plaster can actually end up 
feeling spongy and crumbly, much weaker than the original.  I've 
found that this 1:1 mixes usually works well.  It may be overkill for 
some soils, but I've never found a situation where it is too lean on 
the lime.

Caution and Chemistry
My only concern about this mix involves the degree to which vapor 
permeability may be reduced.  In Building with Lime, Michael Wingate 
and Stafford Holmes talk about a low-grade cement being formed by the 
reaction between the lime and some of the minerals in the clay.  This 
is only one of a set of reactions that supposedly combine to form the 
harder plaster.  The others-flocculation (sticking-together) of the 
clay particles, pozzolanic reactions between the lime and minerals in 
the clay, standard carbonation in the lime- don't seem as if they 
would cause significant reductions in vapor permeability.  Though the 
nature of these reactions would certainly vary according to the 
different clays and limes used, it would be useful to have some 
general sense of how this plaster would perfom, compared with the 
clay-only version.
The walls seem to dry well- we always get them down to 14% before 
proceeding with interior or exterior finish plaster- but I don't know 
whether they would dry faster with a clay-only plaster.

So, I hope you find this useful.  If anyone has any ideas or needs 
more specific thoughts or mixes, please let me know.  And maybe 
someone who is more laboratory-oriented than myself wants to crush a 
few samples?  I'd send you a virtual kiss for that, which you are 
absolutely free to refuse!


Peace,

Paul

- -- 
Paul Lacinski
Amy Klippenstein
GreenSpace Collaborative
Sidehill Farm
PO Box 107
463 Main St.
Ashfield, MA 01330 USA
01-413-628-3800


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<html><head><style type="text/css"><!--
blockquote, dl, ul, ol, li { padding-top: 0 ; padding-bottom: 0 }
 --></style><title>Jeff Ruppert and clay tests</title></head><body>
Jeff,
 
Many thanks for this test.  We use clay and lime plasters
almost exclusively now, but I am still uncomfortable promoting them
without solid data.  Also, without any real sense of the tensile
and compressive strengths of these materials, it is difficult to rely
on them for any portion of the structural component of the buildings,
even though it is plum obvious that they are capable of carrying at
least<i> some</i>  of the loads....
 
Anyway, I hope that you and others on this list will take some
interest in the work we have been doing with lime stabilized clay
plasters.  At least in New England, I have found them to be far
superior to straight clay plasters in three basic areas:  mold
prevention, weather resistance, and shrinkage.  They also clearly
have a higher compressive strength.
 
Here's what I've found:
<b>Mold</b>
<font color="#000000">We learned about this in a big way in the
summer of 1999, which was very dry, with no rain from April until the
third week in August.  When were we installing bales and applying
clay/straw plaster?  You guessed it- the exact weekend the rains
began.  I'm convinced that every mold spore in the state of
Massachusetts woke from dormancy that weekend, and the freshly
plastered walls erupted in a fur of pink, green, and beige mold, which
made me feel rather ill and spoke badly of straw bale construction to
every person who came nearby.  To make matters worse, on that
weekend the weather changed from hot and dry to cool and wet, and the
plaster took a very long time to dry out.  I tried hydrogen
peroxide to kill the mold, and it drank it down and grew stronger. 
I tried a solution of bleach and water; this knocked it back until the
bleach went off into the ozone layer.  Then I tried a limewash,
and the mold receded. </font>
<font color="#000000"> </font>
<font color="#000000">Mold doesn't grow on the clay, it grows on
straw in the plaster mix, and on the straw behind the plaster. 
We are careful now about keeping our milled straw dry; but the key
element has been the inclusion of lime in the plaster.   We
haven't had a signifcant mold issue in the three years we've been
using lime stabilized plasters.</font>
<font color="#000000"> </font>
<font color="#000000"><b>Weather resistance</b></font>
<font color="#000000">In our climate, it's not practical to use
clay plaster as a final coat; but because of our short construction
season the clay base coat almost always goes through one winter before
receiving a lime finish coat and limewash.   So in the
spring, I get to inspect the damage.  There is no question that
the lime-stabilized mixes are performing better than the clay-only
mixes.  On one house, we used both, and contrast was amazing. 
One whole corner of the clay-only mix had eroded away, while on the
lime-stabilized mix there was no discernible erosion of the horizontal
ridges made by the scratching tool.  Generally, the only damage
we see on the lime-stabilized walls is right at the top layer of the
winter snow pile, where the snow does not melt the usual inch or so
away from the face of the wall, and the wall is subjected to alot of
freeze-thaw.  This is easily repaired before the final
coat. </font>
<font color="#000000">(Incidentally, I love this system of
leaving the finish coat for the next year.  It allows time for
the building to shrink and settle, and our finish coats generally show
no stress-related cracks.  It also leaves plenty of time for the
bales to dry off the trendous amount of moisture introduced by the
base coat.)</font>
<font color="#000000"> </font>
<font color="#000000"><b>Reduced shrinkage</b></font>
<font color="#000000">We apply our base coat at about an inch
thick, with a sprayer and therefore quite wet.  The clay-only
plasters would consistently show a pattern of short (2-4")
vertical cracks, covering the entire building.  This was not a
long-term problem, as they didn't seem to telescope through to
succeeding coats; but I like the fact that in the lime-stabilized
samples these cracks do not appear, except in areas that were filled
quite deeply.  At the very least, there is less chance of water
entering the building during the first season, before the finish coat
is applied.  I also believe the reduction in cracking makes for a
more solid substate for the finish coat.</font>
<font color="#000000"> </font>
<font color="#000000"><b>Increased compressive
strength</b></font>
<font color="#000000">Here is where a lab test would be very
useful.  There is no question that our lime-stabilized plasters
are harder and more crush-reistant than their clay only forebears;
I've pounded on enough walls and crushed enough drops with my foot or
a hammer to say this with certainty.  What I'm not sure of his
how<i> much</i> harder....</font>
<font color="#000000"> </font>
<font color="#000000"> </font>
A further benefit of the lime is that it makes spraying much
easier.  The lime makes the plaster much more slippery, so that
there is less friction in the spray tube.  With the rather
underpowered Quickspray Carousel, this is a very significant
improvement.  (By the way, if anybody has a recommendation for a
better sprayer, I'd love to hear about it.)
 
<b>Mixes</b>
<font color="#000000">The ideal percentage of lime for
stabilization varies according to the richness of the clay soil used,
and also according to the specific clay particles in the soil. 
The properties of clays vary widely.  We usually work with a clay
from a brick factory which is somewhere in the area of 60-70% clay
content.  We have found that a 1-1 ratio of dry, milled clay to
lime, added to 4 parts sand and 2 parts milled straw, makes an
excellent base coat plaster.  This is a rairly rich mix, with
excellent properties of adhesion and workability.</font>  After
seeing Jeff's test, we may try increasing the sand to six parts,
omitting the straw, and using synthetic fibers.  (We have had
very good luck with synthetic fibers in lime plasters.)
 
I don't know what happens if the mix is too rich on lime; I do
know that if there is not enough lime, the plaster can actually end up
feeling spongy and crumbly, much weaker than the original.  I've
found that this 1:1 mixes usually works well.  It may be overkill
for some soils, but I've never found a situation where it is too lean
on the lime. 
 
<b>Caution and Chemistry</b>
My only concern about this mix involves the degree to which vapor
permeability may be reduced.  In<i> Building with Lime</i>,
Michael Wingate and Stafford Holmes talk about a low-grade cement
being formed by the reaction between the lime and some of the minerals
in the clay.  This is only one of a set of reactions that
supposedly combine to form the harder plaster.  The
others-flocculation (sticking-together) of the clay particles,
pozzolanic reactions between the lime and minerals in the clay,
standard carbonation in the lime- don't seem as if they would cause
significant reductions in vapor permeability.  Though the nature
of these reactions would certainly vary according to the different
clays and limes used, it would be useful to have some general sense of
how this plaster would perfom, compared with the clay-only version.

The walls seem to dry well- we always get them down to 14% before
proceeding with interior or exterior finish plaster- but I don't know
whether they would dry faster with a clay-only plaster.
 
So, I hope you find this useful.  If anyone has any ideas or
needs more specific thoughts or mixes, please let me know.  And
maybe someone who is more laboratory-oriented than myself wants to
crush a few samples?  I'd send you a virtual kiss for that, which
you are absolutely free to refuse!
 
 
Peace,
 
Paul
 
<x-sigsep><pre>-- 
</pre></x-sigsep>
Paul Lacinski 
Amy Klippenstein 
GreenSpace Collaborative 
Sidehill Farm 
PO Box 107 
463 Main St. 
Ashfield, MA 01330 USA 
01-413-628-3800
</body>
</html>
- --============_-1170240260==_ma============--


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Date: 6 Jan 2003 17:22:16 -0600
From: Chris Magwood cmagwood@...
Subject: Re: GSBN:Jeff Ruppert and clay tests

Jeff, Paul, and Bill (and, belatedly, Bruce),

Thanks for your postings recently about clay plasters. I have returned from
Australia with renewed excitement for clay plasters, and also from the
excellent performance of our first load-bearing, earth plastered building
here in Ontario over the past two winters.

I am thinking about theming a near-future issue of TLS "The Case for Clay",
in which case I'd love to use these exchanges you've had on GSBN as a
starting place for a discussion forum on clay plasters which would form the
core of the issue. Would you all be open to your postings being used in
this way (of course, you'd be allowed to edit yourselves!)? And please,
others on this list who have some ideas/input to this discussions, keep
them coming!

Cheers,

Chris


***************************

Chris Magwood / Camel's Back Straw Bale Construction
http://www.strawhomes.ca

Interested in bale building? Have you subscribed to
The Last Straw Journal?
You should!
 http://www.strawhomes.com


----------------------------------------------------------------------

Date: 6 Jan 2003 19:32:09 -0600
From: Bruce King ecobruce@...
Subject: Re: GSBN:Jeff Ruppert and clay tests

on 1/6/03 11:41 AM, Paul Lacinski at paul@...:

> Many thanks for this test.  We use clay and lime plasters almost exclusively
> now, but I am still uncomfortable promoting them without solid data . . .
>  . . . My concern about this mix is the degree to which vapor permeability
> may be reduced.  In Building with Lime, Michael Wingate and Stafford Holmes
> talk about a low-grade cement being formed by the reaction between the lime
> and some of the minerals in the clay.  This is only one of a set of
reactions
> that supposedly combine to form the harder plaster.  The others-flocculation
> (sticking-together) of the clay particles, pozzolanic reactions between the
> lime and minerals in the clay, standard carbonation in the lime- don't seem
as
> if they would cause significant reductions in vapor permeability.  Though
the
> nature of these reactions would certainly vary according to the different
> clays and limes used, it would be useful to have some general sense of how
> this plaster would perfom, compared with the clay-only version.

Paul, Jeff, and all y'all -

Bill Steen (and others) and I have had a slow running conversation on this
subject over the years.  There are so many kinds of clay, occuring in so
many proportions in various natural or bagged soils, and also so many kinds
of lime with varying degress of hydraulicity (ie similarity to portland
cement) that it's maddening to try and extract generalizations about
lime-clay behaviour.

But hey, while we're young and foolish, let's try!

Clay by itself is the binder in earthen plasters, and as we all know, works
really well when done right.  Lime, on the other hand (and portland cement)
will destroy clay's binding force by deflocculating the little water-loving
grains.  That's why highway builders, especially in wet climate/clay soil
places like the UK, like to use lime to both dry and deflocculate soils
before laying down their beloved asphalt paving.  That's also why Bill
reported LOSING strength in earthen bricks when he added lime;  his binder
wasn't binding, which will always put a hitch in ol' Bill's giddyup.  But
that's only the short term (one or two month) picture . . .

 . . . The long term picture has the lime carbonation and low-grade
pozzolanic reaction between clay and lime coming into play, and I'd guess
the strength/durability would keep on growing over the years.  I would also
guess that vapor permeability would decrease, but not very much.
 
> So, I hope you find this useful.  If anyone has any ideas or needs more
> specific thoughts or mixes, please let me know.  And maybe someone who is
more
> laboratory-oriented than myself wants to crush a few samples?  I'd send you
a
> virtual kiss for that, which you are absolutely free to refuse!

Well, gee, Paul, yer mighty cute and all, but I'll pass on the smooch.  We
do, however, have a reasonably accurate rig now set up (part of the EBNet
testing program) that can crush plaster cubes.  We affectionately call this
little hummer  "Jaws", and would be happy to put it to use.  How about,
Paul, you make up a dozen or more 2" cubes each of your clay plaster and
lime-clay plaster, let them set a month or two, and send them out to the
address below;  we'll squish 'em and report the results.  Paul, if you do,
write EVERYTHING down: mix proportions (including water), description of
ingredients, cast dates, method of curing (under a tarp inside in
conditioned space is ideal), etc.

By the way, on Jeff Ruppert's website, he makes reference to the "300 to 400
psi strengths" obtained in the EBNet program.  Due to the bonehead error of
an arithmetic-impaired engineer who shall remain nameless, those numbers are
erroneous in that said engineer forgot to divide by 4 (ie the four square
inch area of the 2" cube).  Anyway, the numbers (87 to 200 psi) are now
correctly reported on the EBNet website, and said engineer has been stripped
of his pocket protector for three months.

Happy New Year to all
at least as much as is possible under the shadow of a Bush,

Bruce King, PE
Director, Ecological Building Network
209 Caledonia St.
Sausalito, CA 94965
(415) 331-7630
fax 332-4072
www.ecobuildnetwork.org
bruce@ ecobuildnetwork.org



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