Stucco Consistency

Searching a crime scene is a complex process (25), involving poHce, crime scene technicians, and forensic scientists. The procedure requires careful documentation, collection, and preservation of the evidence. Trace evidence (26) in criminal investigations typically consists of hairs (27,28) both natural and synthetic fibers (qv) (29,30), fabrics glass (qv) (31,32) plastics (33) sod plant material budding material such as cement (qv), paint (qv), stucco, wood (qv), etc (34), flammable fluid residues (35,36), eg, in arson investigations explosive residues, eg, from bombings (37,38) (see Explosives and propellents), and so on. 

Rammed earth or "pise" walls consist of clay-containing earth built up in layers between removable shuttering. "Wattle and daub," a hazel lattice covered in mud and straw, is another variation on the theme. If you have space, straw bales make cheap building units, but need a good coat of stucco. 

ABSTRACT In gypsum board xoduction. the amount of water required for a stucco slurry with a suitable fluidity is considerably greater than the amount necessary for hydration of the stucco. Since excess water must be removed by drying, it is advantageous, from an energy point of view, to reduce the consistency or water demand of stucco. Constant board density is maintained thereby through increased addition of foam. 

KEY WORDS gypsum, stucco, disintegration, water demand, consistency... 

A relatively pure form of natural gypsum (Terra Alba) consisting of 98.6% CaSO ZHjO was used for this study. The gypsum was ground to pass a 150-p.m (No. 100) sieve and calcined in a laboratory kettle designed for both continuous and batch operation. In this manner, three 15-kg lots of stucco were prepared by continuous calcination, and three 5-kg lots of stucco were calcined by the batch process. To two lots of the latter, either calcium chloride or surfactants were added. 

The stuccos prepared in the laboratory were aged at ZTC and 65% relative humidity for various periods of time. Two stucco properties, that is, consistency and disintegration, were determined immediately after calcining and after various periods of aging. These tests were continued until equilibrium values had been reached the times required to reach these values are given in Table 1. The consistency test methods and the techniques to obtain particle size data, as well as the treatment of these data, are described briefly below. 

All consistency measurements were conducted by adding 0.2-g sodium citrate to 100 mL of gaging water to prevent premature stiffening caused by hydration of the stucco. 

This type of measurement is widely used in Europe [West German Industrial Standard (DIN) Test Methods for Gypsum Plaster (DIN 1168)] to determine the so-called water stucco factor, that is, the amount of stucco in grams that can be wetted by 100 mL water. The method consists of sprinkling stucco into the water at a specific rate without mechanical mixing. Therefore, it differs from other consistency measurements in that only spontaneous disintegration occurs. Pouring Consistency... 

This consistency measurement is also commonly used in North America. Stucco water slurries are mixed for 7 s in a high-shear Waring Blendor to simulate... 

The mixing procedure used in this test, that is, 60 s in a high-shear Waring Blendor, is intended to produce maximum disintegration of the stucco particles [6j. The viscosity of a slurry mixed by this method if measured by a Ford cup viscometer, and the water solid ratio with which a specified flow time is obtained is taken as the consistency. 

Figures 3 through 6 illustrate the effect of aging time on consistency and disintegration, as well as the relationship between consistency and disintegration for continuously calcined Terra Alba. These data show that both consistency and disintegration decrease with time and suggest a linear relationship exists between these properties. Regression analysis of the data yields slopes, intercepts, and correlation coefficients of these curves a.s given in Table 2. Similar data for batch calcined stucco are summarized in Table 3.

The addition of calcium chloride ch surfactants during the calcination appears to modify the relationship between consistency and disintegration. Preliminary data suggest that the consistency of stucco containing these admixtures is no longer a direct function of disintegration, but that surface properties play a significant role. 

Masonry cements These are used for preparing bricklaying mortars and stuccos, and must not be used in concrete. They are usually complex proprietary formulations containing Portland clinker and a number of other ingredients that may include limestone, hydrated lime, air entrainers, retarders, water-proofers and colouring agents. They are formulated to yield workable mortars that allow rapid and consistent masonry work. Subtle variations of masonry cement in the US are plastic cements and stucco cements. These are designed to produce controlled bond with masonry blocks. 

The process begins with raking of the masonry mortar joints to a depth of in.. Dust and debris were then washed away and the walls were predampened. Contaminated surfaces were to be scored with an axe. Stucco was then prepared in a fluid, workable consistency, and was applied in two hfts. The first lift was intended to fill the raked masonry joints and to provide a thin base-coat over the masonry surface. The second coat was installed over the soft base coat to a depth of j in. and was immediately finished. The stucco was then cured for several days. The stucco recipe in Table 6 is cited ... 

In all cases, the optimum water-cement ratio produces mixes that are nearly incoherent. Although they compact well under impact or trowel pressure, they are relatively dry as compared with typical portland cement mixes, and more fluid consistency would be a desired convenience, particularly for work involving forming and pouring of concrete or application of stucco. 

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