The topic of this article was originally addressed in the September 2002 issue of Walls & Ceilings. Since then there have been a few changes that have prompted us to revisit the subject. Most notably, ASTM C1396, Standard Specification for Gypsum Board, which was introduced in 1999 as an umbrella standard that would combine and supersede nine separate gypsum product standards, has been fully adopted. On December 1, 2004 (after a five-year period during which C1396 was being phased in and introduced to the architectural community with the intent of replacing the other nine stand-alone specifications), eight of the nine separate standards were withdrawn by the ASTM C11 Committee on Gypsum and Related Building Materials and Systems. The withdrawn standards were:

• C 36, Specification for Gypsum Wallboard;
• C 37, Specification for Gypsum Lath;
• C 79, Specification for Treated Core and Nontreated Core Gypsum Sheathing Board;
• C 442, Specification for Gypsum Backing Board, Gypsum Coreboard, and Gypsum Shaftliner Board;
• C 630, Specification for Water-Resistant Gypsum Backing Board;
• C 931, Specification for Exterior Gypsum Soffit Board;
• C 960, Specification for Predecorated Gypsum Board; and
• C 1395, Specification for Gypsum Ceiling Board.

And in 2005, ASTM C588, Standard Specification for Gypsum Base for Veneer Plasters, was withdrawn by the same committee. Throughout the body of this article, both the deprecated and current ASTM specification nomenclature will appear parenthetically where applicable; other gypsum products are manufactured in compliance with other ASTM standards that were not superseded by C1396 and will appear as stand-alone titles in parentheses.



A MORE PRECISE NOMENCLATURE

Gypsum board is often called by such terms as drywall, plasterboard, wallboard, or gypboard. All of these terms are acceptable for informal communications. However, a more precise nomenclature exists to clearly specify and identify each of the different gypsum-based board and panel products. Knowledge about the correct term to use for a gypsum material may help you to avoid confusion regarding the correct material intended for installation on a project.

Gypsum board products make up the predominant portion of a family of materials identified as gypsum panel products. Gypsum panel products are defined as sheet materials consisting essentially of gypsum. They can be faced with paper or another material, or may be unfaced. Gypsum boards, glass-faced sheathing materials with a gypsum core, and unfaced gypsum-based products are all considered to be gypsum panel products. Formed gypsum trim pieces and sheet products that have a base that is not predominantly gypsum are not considered to be gypsum panel products.

Gypsum board (defined in ASTM Standard C 1396) is a sheet product that has a noncombustible core made primarily of gypsum with paper on its face, back, and long edges. The paper facing characterizes gypsum board within the gypsum panel products family. While all gypsum panel products are sheet materials with a gypsum core, only gypsum board products have a paper facing.

The gypsum board family can be further divided into wallboard and non-wallboard product types. All individual materials within the gypsum board family are referenced in the global ASTM manufacturing standard for gypsum board, ASTM C 1396. Identified by their technically correct names and by the appropriate ASTM material specification designations, they are as follows:



BOARD AND WALLBOARD

As a specific product, Gypsum Wallboard (C 36/C1396) is a gypsum board produced primarily for use as an interior surfacing for buildings. It is the most often used commodity gypsum board and annually accounts for over 50 percent of all the gypsum board manufactured and sold in North America. Gypsum board with manila color face paper usually installed in residential dwellings and many commercial and institutional buildings is gypsum wallboard. This product is manufactured with regular and fire-resistant cores in a variety of thicknesses.

Gypsum Ceiling Board (C 1395/C1396) is an interior surfacing material with the same physical appearance as wallboard and is often considered to be a type of gypsum wallboard. Gypsum ceiling board is manufactured as a ½-inch thick material; it is designed for application on interior ceilings, primarily those intended to receive a water-based texture finish. It has a sag resistance equal to the 5/8-inch thick gypsum wallboard.

Predecorated Gypsum Board (C 960/C1396) is also considered to be a type of wallboard. Predecorated gypsum board is manufactured to the same criteria as wallboard (i.e., ASTM C 36) and then surfaced with a decorative material in accordance with the C 960 standard.

Other gypsum board products for special applications include the following:

Gypsum Backing Board, Gypsum Coreboard, and Gypsum Shaftliner Board (C 442/C1396) are all designed to be used as base materials in multilayer, solid and semi-solid and shaftwall systems. Gypsum backing board is used as a base layer for other gypsum board materials in systems or as a base for dry claddings such as acoustic tile. Gypsum coreboard and gypsum shaftliner are used to construct systems such as vent shafts, shaftwalls, and area separation walls.

BACKING AND SHEATHING

Water-Resistant Gypsum Backing Board (C 630/C1396) is a gypsum board designed for use on walls primarily as a base for the application of ceramic or plastic tile. It is readily identified by its green-tinted face paper and is commonly referred to as “greenboard.” It has a water-resistant core and a water-repellent face and back paper; it is generally installed in bath, kitchen, and laundry areas. Recent code changes have limited the use of this product in tub and shower surrounds, and one would do well to consult the prevailing code before specifying or installing it in a wet area.

Gypsum Sheathing Board (C 79/C1396) is used as a backing for exterior siding or cladding. It has water-repellent face and back paper and is manufactured with a water-resistant core. Depending on the thickness of the board, gypsum sheathing board may be manufactured with either a square or tongue-and-groove edge. It generally has a brown or light black face paper.

Veneer plaster, a thin gypsum-based plaster material, is applied in one or more coats to Gypsum Base for Veneer Plaster (C 588/C1396), a gypsum board that has a face paper treated to facilitate the adhesion of a plaster finish coat (or two). It is frequently called “blueboard” due to the color created on the face paper during the treatment process. This product should not be confused with Gypsum Lath (C 37/C1396), a gypsum board that is used as a base for the application of full thickness gypsum plaster, not gypsum veneer plaster. Gypsum lath is typically manufactured in sheets that are 16 inches wide and with absorbent face paper. By contrast, gypsum base for veneer plaster is produced in sheets that are the same width as wallboard.

Exterior Gypsum Soffit Board (C 931/C1396) is designed for installation on exterior soffits, canopies, and other horizontal exterior surfaces that are indirectly exposed to the weather. It has water-repellent face and back paper and is more sag-resistant than regular wallboard, and typically has a light brown face paper.

NEW BOARDS AND PANELS

New gypsum product types. There are several more gypsum product types now available on the market. Some are board products (they have a paper facing) and some are panel products (they have a facing other than paper, or have no facing whatsoever), and each is intended to meet a particular need. Standards for some of the newer panel products–such as C 1177 and C 1278 panels–have been created by the ASTM C11 committee and work on other standards is ongoing. The preferred way to obtain information on all of the newer materials is to access the individual manufacturer websites via the Gypsum Association website at www.gypsum.org.

For more assistance with gypsum board and gypsum panel product terminology, consult the current edition of ASTM Standard C 11, Standard Terminology Relating to Gypsum and Related Materials and Systems, or download a copy of the Gypsum Association’s publication, GA-223-04, Gypsum Panel Products Types, Uses, Sizes, and Standards, from our website at http://gypsum.org/pdf/223-04.pdf. And you can always contact a member of the Gypsum Association’s technical staff at 202-289-5440.