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GSBN:YakWoman asks about Lime (FWD)
- To: GSBN@...
- Subject: GSBN:YakWoman asks about Lime (FWD)
- From: "Rob Tom" rw_tom@...
- Date: Fri, 07 Dec 2001 18:21:52 -0500
- Reply-to: "GSBN" GSBN@...
- Sender: "GSBN" GSBN@...
The following is a response from Harry Francis, probably the most
knowledgable "Limey" in North America. You may recall that 'Arry contributed
to the "Lime Plaster" issue
of The Last Straw last year, which Athena and Beel Steen guest-edited.
--------- Forwarded message ----------
Date: Fri, 7 Dec 2001 11:39:50 EST
Subject: Re: YakWoman asks about Lime
I think Tom is corrrect...either his mix or your propposed mix will work
fine. I think the contractor is used to using cement for stucco work, and
just a little lime to make it more plastic ( workable). (This is typical of
today's need to get it finished quickly mentality).
The 1:1:6 will work fine, I think, but will be slower setting, than his
The main idea here is to use as little cemnetiscous materials as possible
(lime and/or cement) and as much sand as the cementiscous materiaqls will
hole. The reason is that the heat expansion of sunlight striking the walls
can result in cracks if the materials do not expand uniformally. Literature
says that lime/sand mixes crack less because the expansion of the lime and
the sand are about equal....whereas the cement expands at a different
Cement is often caustic, causing burns of workers hands, etc. Quicklime is
also caustic...not due to the chemistry, but due to the heat generated when
hydrated ( mixed with water). The resulting hydrated lime is not caustic
unless additives have been added making it so...
His concerns about your mix being too hot - caustic - may result from
experience in slaking quicklime. If the hydrated lime is thoroughly soaked
and aged 24/48 hours before using in the mix, any un-hydrated quicklime
will be hydrated and no heat generated.
However, the portland cement will produce sufficient heat on hydration to
cause burns, and many Portlands have sufficient sodium hydroxide contained
make it chemically caustic..and result in chemical burns....to the skin and
The old literature suggests 1:3 ratios cementiscous material to
sand.....with comments to sue as much sand as the stucco will carry....to
prevent thermal expansion cracking.
The contractor may dislike the slow setting of pure lime stuccos, and the
1:1:6 does help the mix harden quicker...and the specific sand used makes
the difference in ratios needed to make a satisfactory project.... the old
NLA handbook suggests no more than 20 % Portland cement be added
"Cement, however, should not be added in excess of 20% of the lime used."
"Then, too, after the lime has hardened it has practically the same heat and
moisture co-efficients of expansion as does the sand it bind in place."
Kelly, I hope these comments help in your negotioations with the
contractor...Admititily, many projects today, are simply Portland cement and
sand, with just a little lime as a plasticizing agent...resulting is short
life, cracks, debonding, etc... and a bad name for stucco....What A
======= End of Forwarded Material =========
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Robert W. Tom
Kanata, Ontario, Canada
please visit: http://www.theHungerSite.com daily
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