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July/August 2010

ASTM’s Manual 67

A Text about Gypsum

A careful consideration of gypsum begins, as noted in a recently published ASTM manual, with defining the term and its use. Gypsum: Connecting Science with Technology (Manual 67), distinguishes gypsum as a mineralogical term and calcium sulfate dihydrate as a chemical term, rather than using the terms interchangeably. Consequently, author Richard Kuntze writes, “gypsum refers to practical considerations and calcium sulfate dihydrate to chemical or physical processes.”

That’s one way in which the author takes care of what he calls a perceived lack of a gypsum textbook in English. He also notes that natural and synthetic gypsum differ only in physical shape; natural gypsum is deposited from sea water as a crystalline, massive material while synthetic gypsum is produced industrially. The manual details gypsum’s history and geological origins as well as its properties and processing into much-used building materials, but it does not cover gypsum board application to ceilings and walls.

One noteworthy feature of the manual is its technical explanations. For example, “When one heats gypsum one produces hemihydrate and subsequently soluble anhydrite. It was (and is) poorly understood that the formation of soluble anhydrite depends on the water vapor pressure present during heating, or calcination. Alpha-hemihydrate is not formed at atmospheric water vapor pressures as proposed, only at above-atmospheric pressures (steam).” Kuntze explains the production process, and its variations and necessary controls, in detail.

The author provides a perspective gained from decades of gypsum research and expertise while a fellow for the former Ontario Research Foundation and as a consultant with gypsum manufacturers, including CertainTeed, Gypsum Manufacturers of Canada and U.S. Gypsum. Kuntze has been involved with ASTM International since 1960 and participates in several committees, particularly C11 on Gypsum and Related Building Materials and Systems, which he served as chairman from 1972 to 1985.

The book, according to the author, includes these particularly significant sections in its discussion of gypsum and its end products:

  • Chapter 5 on Calcination Processes reviews the proper raw gypsum preparation — from either the natural or synthetic mineral — so that it can undergo heating, or calcination, in various kettle and kiln production methods.
  • In 7.3.2, the text considers foam configuration as produced by foaming agents, which can make the board less brittle without reducing strength.
  • In 7.3.5, the work elaborates on the bond between paper and the core produced by starch, an essential ingredient to create or protect that bond, which also increases the strength of the board.

The manual rounds out a consideration of gypsum with chapters on testing, analysis and installation and health considerations. The sampling and analysis chapter references the use of several ASTM International standards from Committee C11 to evaluate material properties, and the health-related information notes that gypsum itself is considered to be non-toxic although its impurities must be considered separately.