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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
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