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Re: GSBN:test results
- To: "GSBN" GSBN@...
- Subject: Re: GSBN:test results
- From: Paul Lacinski paul@...
- Date: Mon, 30 Sep 2002 18:30:49 +0800
- Reply-to: "GSBN" GSBN@...
- Sender: "GSBN" GSBN@...
Well yes, I find this just as perplexing as everyone else, since it
contradicts my experience just as directly as everyone else's.
Here's what I did for a test: I brought a piece of an old chair
around to the back wall of our house, which is partially covered by a
lime-stabilized clay plaster, about 1" thick, and partially covered
by this same plaster with a 3/8" lime/sand finish coat. (The system
that we always use.) I then attempted to gouge these two plasters
with the corner of the chair, mimicking, as best I could, a portly
and slightly drunk matri or patriarch jumping up from the table to
answer the door or phone or whatever. And what do you know, the
lime-coated wall is much more resistant to this type of abuse than
the clay-only wall.
So, having re-examined the field conditions, I am led to wonder what
might possibly have been different about the lab conditions. The
only idea I have is that 2" is much thicker than I would ever go with
lime, without a pozzolanic additive. (We have poured 2-3" thick lime
concrete with ground bricks or pottery as a pozzolan and come up with
compressive strengths that, while never tested by the psi, are
definately much better than could ever be achieved with earth.
(Children jumping around on windowsills made of this material seem to
have no effect.) I know what when you pick up a chunk of dropped
lime plaster that has been sitting around for a few weeks at the base
of a wall, the surface (3/8" or so) will be well set, while the
material below will be quite weak. I've gouged these limeplops with
a screwdriver before, just to see. The surface is about as hard as a
finshed plaster; the underside is not much better than the gypsum in
So, maybe we have a situation where the lime didn't cure much, except
on the surface, and the cement dried out too quickly to cure
properly. If there are any samples left intact, it would be
interesting to go at them with an awl or screwdriver, to test this
theory. Also- is there any chance it was a bad batch of lime? Was
the bag of lime left around the lab for awhile before it was used?
Was it leftover from a site somewhere? Is there any chance it got
Maybe someone could look at a bit of this material under the special
microscope (whatever it's called) to check on the cement crystal
In any case, thanks again for all of this work. Whether or not I
like the outcomes, I'm very happy that the sb world is moving beyond
testing plasters with the back of a chair.
PO Box 107
463 Main St.
Ashfield, MA 01330 USA