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GSBN:More on lime

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Hi all, 
I received this excellent explanation from Harry Francis that you all
might want to print out and put in your lime folder (and you should all
have a lime folder if you don't already). Highlight for me was to know
that lime and sand have a very similar coefficient of expansion. STOP
cracks now - use more lime. 
<blockquote type=cite class=cite cite>The 1:1:6 will work fine, I think,
but will be slower setting, than  his  
suggested mix... 
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
can result in cracks if the materials do not expand uniformally.
says that lime/sand mixes crack less because the expansion of the lime
the sand are about equal....whereas the cement expands at a different
rate...causing cracks. 
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
( 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
and aged 24/48 hours before using in the mix, any un-hydrated quicklime
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 to  
make it chemically caustic..and result in chemical burns....to the skin
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
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
Kelly, I hope these comments help in your negotioations with the  
contractor...Admititily, many projects today, are simply Portland cement
sand, with just a little lime as a plasticizing agent...resulting is
life, cracks, debonding, etc... and a bad name for stucco....What A

Kelly Lerner  
One World Design, Design and Consulting 
925 Avis Drive  
El Cerrito, California, 94530, USA  
<<a href="http://www.one-world-design.com/"; eudora="autourl">http://www.one-world-design.com</a>> 
510-525-8582 phone, 510-528-8763 fax