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Reply To: | The listserv that doubts. |
Date: | Mon, 12 Nov 2007 18:35:41 -0500 |
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Okay, I've been silently stalking this forum for several months now and I guess
it's about time I pipe in and introduce myself. John Walsh here and some of
you may have met me in San Juan or sat in for my presentation Monday
morning with Dorothy Krotzer.
I have to agree with you Mike. Natural cement (the American variety) was
exceptionally common down south in the latter half of the 19th century. I find
it regularly in Florida, Geogia, and the Carolinas. Much of Rosendale cement
was shipped widely and of course Louisville cements representing the second
largest cement producing region in the country (available in the 1830's) and
Georgia cements (available by 1850) were used regularly. Add to this the St.
James cements and extensive Potomac valley manufactories and there should
be no doubt that the cements were available. And yes, stuccoes were
another popular application of the cement that I find pretty often. In fact,
Dorothy and I presented last week on natural cement stuccoes that we
identified at the College of Charleston ca. 1851.
But as a materials scientist, I have to take exception with your classification
of natural cement as a pozzolan. Pozzolans are any type of reactive silicate
(usually glassy or poorly crystalline) that require lime to be activated. The
reaction is caclium hydroxide (from the lime) with the base-soluble silica (from
the pozzolan) producing caclium-silicate-hydrates, essentially the same
primary binder material created through the hydration of most cements
(natural or otherwise).
Natural cements are true hydaulic cements meaning they react readily with
water to produce the binder (of course, I know you know this so forgive
me...this bit is more for any casual reader). As such, they require no lime
addition to do what they do. In fact, I very rarely find any lime at all added
to natural cement mortars in the U.S.. Unlike portland cement (which never
was really formulated for useful masonry properties and hence is a
compromise), natural cements tend not to require the "sweetening" properties
of lime. As you've said, elasticity is different in addition to other properties.
Shrinkage is different as well which is why I usually find natural cement
mortars surviving quite happily with narrowly graded and rounded sands with a
sand to binder ratio of 1.5 to 1. Try that with a straight portland.
Anyway, I have to get back to writing reports so that I can enjoy some
stuffing (with Italian sausage as the aggregate of course) next week.
John Walsh
--
To terminate puerile preservation prattling among pals and the
uncoffee-ed, or to change your settings, go to:
<http://listserv.icors.org/archives/bullamanka-pinheads.html>
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