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[SB-r-us] Fwd: GSBN:Jeff Ruppert and clay tests

OK, Paul says OK, OK to post this message over here.  In fact, he says 
he's willing to join up and maybe tell us about his travels to the far 
east, work with Kelly, and the like and I'm trying to twist his arm 
into posting some photos.

But anyhow, part of this message already was here, but it is the bottom 
part that did not and I think contains some valuable information.

Have fun,

Begin forwarded message:

> From: Paul Lacinski paul@...
> Date: Mon Jan 6, 2003  12:41:31 PM America/Phoenix
> To: "GSBN" GSBN@...
> Cc: howe@...
> Subject: GSBN:Jeff Ruppert and clay tests
> Reply-To: "GSBN" GSBN@...
> Jeff,
> Many thanks for this test.Ê We use clay and lime plasters almost 
> exclusively now, but I am still uncomfortable promoting them without 
> solid data.Ê 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 someÊ 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.Ê At least in New England, I have found them to be far 
> superior to straight clay plasters in three basic areas:Ê mold 
> prevention, weather resistance, and shrinkage.Ê 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.Ê 
> When were we installing bales and applying clay/straw plaster?Ê You 
> guessed it- the exact weekend the rains began.Ê 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.Ê 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.Ê I 
> tried hydrogen peroxide to kill the mold, and it drank it down and 
> grew stronger.Ê I tried a solution of bleach and water; this knocked 
> it back until the bleach went off into the ozone layer.Ê Then I tried 
> a limewash, and the mold receded.Ê
> Mold doesn't grow on the clay, it grows on straw in the plaster mix, 
> and on the straw behind the plaster.Ê We are careful now about keeping 
> our milled straw dry; but the key element has been the inclusion of 
> lime in the plaster.ÊÊ 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.ÊÊ So in the spring, I get to inspect the damage.Ê 
> There is no question that the lime-stabilized mixes are performing 
> better than the clay-only mixes.Ê On one house, we used both, and 
> contrast was amazing.Ê 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.Ê 
> 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.Ê This is easily repaired 
> before the final coat.Ê
> (Incidentally, I love this system of leaving the finish coat for the 
> next year.Ê It allows time for the building to shrink and settle, and 
> our finish coats generally show no stress-related cracks.Ê 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.Ê The clay-only plasters would consistently show a 
> pattern of short (2-4") vertical cracks, covering the entire 
> building.Ê 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.Ê At the very least, there is less 
> chance of water entering the building during the first season, before 
> the finish coat is applied.Ê 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.Ê 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.Ê What I'm not sure of his how much harder....
> A further benefit of the lime is that it makes spraying much easier.Ê 
> The lime makes the plaster much more slippery, so that there is less 
> friction in the spray tube.Ê With the rather underpowered Quickspray 
> Carousel, this is a very significant improvement.Ê (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.Ê The properties of clays vary widely.Ê We 
> usually work with a clay from a brick factory which is somewhere in 
> the area of 60-70% clay content.Ê 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.Ê This is a rairly rich 
> mix, with excellent properties of adhesion and workability.Ê After 
> seeing Jeff's test, we may try increasing the sand to six parts, 
> omitting the straw, and using synthetic fibers.Ê (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.Ê I've found 
> that this 1:1 mixes usually works well.Ê 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.Ê 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.Ê This 
> is only one of a set of reactions that supposedly combine to form the 
> harder plaster.Ê 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.Ê 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.Ê If anyone has any ideas or needs 
> more specific thoughts or mixes, please let me know.Ê And maybe 
> someone who is more laboratory-oriented than myself wants to crush a 
> few samples?Ê 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
Athena & Bill Steen
The Canelo Project
HC1 Box 324
Canelo/Elgin, AZ 85611

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