[Aztlan] Plasters, cements, etc

[rod44 at comcast.net]

OK, being among other things a structural engineer, I know a little about this.
 First, for some terminology definitions:

1.Cement is any product that is "gluey" and therefore serves as a binder for any other material. Man has experimented with many different substances for cements including  clay, tar, gypsum, lime, puzzolanas (from volcanic ash) and more modern Portland cement.  Many of these we still use, ei  asphaltic concrete for roads, gypsum plaster for interiors (in the form of prefabricated "dry wall" panels), puzzolana as an additive to Portland cement concrete.

2. Plaster is any fine grained mixture of a cementitious material (see above) with a filler (such as fine sand or silt) that can be troweled on a surface to smooth out a finish.  Mesoamerricans used primarily lime plasters.  True "stucco" (much misused term) is a plaster made from Portland cement or other hydraulic cement.

3. Lime  is made by calcinating any calcium carbonate source (limestone, shells, bones) by heating it to over 900 C (popularly called "burning")  which drives of the CO2 leaving cacium oxide (quick lime) then wetting it to create Calcium hydroxide (slaked lime).  This slaked lime when mixed with fine aggregates creates a spreadable lime plaster.  Mixed with coarser sands you make lime mortar and with rocks in it it is lime concrete.  These products harden by re carbonation of the calcium hydroxide by taking CO2 from the air and turning back into CaCO3 (from where we started).

 4. Hydraulic cements such as Roman Puzzolanic cements and Portland cements have an extremely fine component of aluminum silicate and Calcium silicate, etc, which when wet react with each other to form extremely complex calcium aluminum silicates (such as tobermorite).  This reaction is not dependent on exposure to air and can take place underwater (hence the term "hydraulic cement).  These cements can be used, as any other, to make plaster (real stucco), mortars, grout or concrete depending on the quantities and size of aggregates used.   Most of our modern stucco, mortar and concrete is Hydraulic Portland cement, although often lime and sometimes puzzolanas are used as additives.

Most modern gypsum plaster  nowadays is used in prefabricated panels known as "dry wall" or "sheet  rock" and as such extensively used. for interior walls and ceilings.


As somebody pointed out: the use of sloppy masonry covered in plaster is NOT  decadent but instead, a technical innovation  (same as small stones mortared together in lieu of huge megalithic dry masonry held down by its weight)   (you should come see what some of our modern CMU walls look like before we stucco them!)


We are starting a research project at the IMS to determin the quantitis of lime actually used inh Maya lime plaster, lime mortars and lime concretes.  (we think it is not as much as has been suspected)

Joaquin J. Rodriguez III  PE. SECB
Vice President and Director of Research
Institute of Maya Studies
Affiliate of  Miami Museum of Science