Designing For Fire Resistance with Gypsum Panel Systems
Improving building safety through the use of fire-rated assemblies

The following glossary provides commonly used terms and acronyms pertaining to gypsum panel systems, and the construction and building materials industries.

Alligator Cracks
Fine, random fissures or cracks of the finish plaster surface caused by shrinkage.

Anhydrous Calcium Sulfide
A naturally occurring mineral (CaSO4) usually found in gypsum (CaSO4 2H2O) deposits. Dead-burned hydrite (CaSO4) is generally formed by heating gypsum (to remove all water).

ANSI
A nonprofit, national technical association that publishes standards covering definitions, test methods, recommended practices and specifications of materials.

ASTM
Formerly American Society for Testing and Materials, now ASTM, a nonprofit, national technical society that publishes definitions, standards, test methods, recommended installation practices and specifications for materials.

BCMC
Board for the Coordination of Model Codes; part of the Council of American Building Officials Association (CABO).

BOCA
A nonprofit organization that publishes the National Building Code.

CABO
Council made up of representatives from three model codes. Issues National Research Board (NRB) research reports.

Class A
A fire classification for a product with a flame spread rating of no more than 25 and a smoke developed rating not exceeding 50, when tested in accordance with ASTM E84.

Craze Cracks
Fine, random fissures or cracks of the finish plaster surface caused by plaster shrinkage. These are generally associated with lime finish coat improperly gauged or troweled, or with veneer plasters subjected to rapid-drying job conditions.

Double-Up
Successive plaster coat application with no setting or drying time allowed between coats, usually associated with veneer plastering. The double-up coat is applied (from the same mix) to a scratch coat over gypsum base.

Drywall
Generic term for gypsum panels.

Egg Shelling
Fine cracks in a finish coat similar to craze cracks except that bond is partially destroyed, producing concave fragments of the finish.

Fibered Plaster
Usually a basecoat plaster containing organic or inorganic fibers, which promote cohesiveness in the mix.

Finishing Compound
A compound specifically formulated and manufactured for use over taping or all-purpose compounds to provide a smooth and level surface for the application of decoration.

Fire Endurance
Measure of elapsed time during which an assembly continues to exhibit fire resistance under specified conditions of test and performance. As applied to elements of buildings, it shall be measured by the methods and to the criteria defined in ASTM Methods E119, Fire Tests of Building Construction and Materials; ASTM Methods E152, Fire Tests of Door Assemblies; ASTM Methods E814, Fire Test of Through-Penetration Fire Stops; or ASTM Methods E163, Fire Tests of Window Assemblies.

Fire Resistance
Relative term, used with a numerical rating or modifying adjective to indicate the extent to which a material or structure resists the effect of fire.

Fire-Resistive
Refers to properties or designs to resist effects of any fire to which a material or structure may be expected to be subjected.

Firestop System
A system for protecting against the spread of fire through a penetration in a wall or floor where a pipe or other penetrant passes through a fire-rated system.

Firewall
Fire-resistant partition extending to or through the roof of a building to retard spread of fire.

Flame Spread
Index of the capacity of a material to spread fire under test conditions, as defined by ASTM Standard E84. Materials are rated by comparison with the flame-spread index of red oak flooring assigned a value of 100 and inorganic reinforced cement board assigned a value of 0.

Flammable
Capability of a combustible material to ignite easily, burn intensely or have rapid rate of flame spread.

Flash Set
Premature hardening (setting) of a setting material.

Float
A tool or procedure used to straighten and level the finish coat, to correct surface irregularities produced by other tools, and to impart a distinctive surface texture.

Float Finish
Finish-coat texture that is rougher than a smooth trowel finish, and which is derived from aggregate in the mortar.

Floating Floors
Floors in which a base layer and a top layer are acoustically isolated, either by the use of resilient channels, a resilient membrane, or special isolating spring assemblies.

Gauging
A cementitious material, such as gypsum plaster, Keene's cement or portland cement, added to lime putty to provide and control set; also the act of adding gauging material.

Gypsum
The crystal consisting primarily of Hydrated Calcium Sulfate (CaSO4 2H2O) also known as calcium sulfate dihydrate. Also, a naturally occurring mineral that, when calcined, serves as the base to formulate plastering materials and other building products.

Gypsum Lath
A gypsum board used as the base for application of gypsum plaster.
Gypsum Molding Plaster
A calcined gypsum plaster used primarily for plaster casts or molds, sometimes used as a gauging plaster.

Gypsum Neat Plaster
A calcined gypsum plaster without aggregate; common usage is for gypsum plaster used for basecoats.

Gypsum Partition Tile (Block)
A cast gypsum-building unit of various dimensions for use in non-load bearing interior construction for protection of columns, elevator shafts, etc., against fire.

Gypsum Plaster
Ground calcined gypsum (calcium sulfate hemi-hydrate) combined with various additives to achieve specific application, working and set characteristics. Also the generic name for a family of powdered cementitious products consisting primarily of calcined gypsum with additives to modify physical characteristics, and having the ability, when mixed with water, to produce a plastic mortar or slurry which can be formed to the desired shape by various methods and will subsequently set to a hard, rigid mass.

Gypsum Sheathing
A gypsum board used as a backing for exterior surface materials, manufactured with water-repellent paper and may be manufactured with a water-resistant core.

Head of Wall
A type of construction joint where two fire-rated assemblies intersect. Head-of-wall assemblies occur where a wall intersects a floor/ceiling or roof/ceiling. In these construction details, a fire-protective assembly is needed to protect against the spread of fire. An example is where a partition intersects a fluted steel deck. Head-of-wall and other construction joints are evaluated under UL Standard 2079 for their ability to resist flame and temperature transmission as well as hose stream.

High Calcium Lime
A type of lime containing mainly calcium oxide or hydroxide and not more than 5 percent magnesium oxide or hydroxide.

Honeycomb
A material having cells with a hexagonal, thin-walled cell structure similar to that constructed from beeswax by honeybees to hold honey and larvae.

Hydrate
To chemically combine with water as in the hydration of calcined gypsum or slaking of quicklime. Also the product resulting from this combination.

ICBO
International Conference of Building Officials. A nonprofit organization that publishes the Uniform Building Code.

ICC International Code Committee
A nonprofit organization dedicated to developing a single set of comprehensive and coordinated national model construction codes including the International Building Code (IBC).

Inflammable
Capability of a combustible material to ignite easily, burn intensely or have rapid rate of flame spread.

ISO (International Standards Organization)
A non-governmental network of the national standards institutes of 148 countries, on the basis of one member per country, with a Central Secretariat in Geneva, Switzerland, that coordinates the system.

Key
The grip or mechanical bond of one coat of plaster to another coat, or to a plaster base. It may be accomplished physically by the penetration of wet mortar or crystals into paper fibers, perforations, scoring irregularities, or by the embedment of the lath.

Labeling Service
Program allowing a manufacturer to place Underwriters Laboratories Inc. labels on its products that have met UL requirements. A UL representative visits the manufacturing site to obtain samples of the products for testing by UL. In some cases, samples are also purchased on the open market for testing.

Lamination
Placing a layer of gypsum board over another gypsum board or over another substrate using an adhesive product for attachment. Also, the process of manufacturing products with a thin covering adhered using an adhesive.

Land Plaster
Coarse-ground natural gypsum.

Lath
A metal, wood or gypsum material applied separately to a structure that serves as a base for plaster.

Lay-In Panel
Any panel designed to be supported by an accessible suspension system.

Limiting Height
Maximum height for design and construction of a partition or wall without exceeding the structural capacity or allowable deflection under given design loads.

Model Code
Building code, written and published by a building-official association, available to states, counties, and municipalities for adoption (for a fee) in lieu of their own, e.g., Uniform Building Code, Standard Building Code, National Building Code and International Building Code.

Mortar
A mixture of gypsum plaster or portland cement with fine aggregate or hydrate lime, or both, and water to produce a material with trowelable fluidity.

NBS - National Bureau of Standards
National Bureau of Standards, a federal agency. (Now NIST, National Institute of Technology and Standards).

NCSBCS (National Conference of States on Building Codes and Standards)
National Conference of States on Building Codes and Standards, a nonprofit organization formed to increase interstate cooperation and coordinate intergovernmental reforms of building codes.

NFPA (National Fire Protection Association)
National Fire Protection Association. An international technical society that disseminates fire prevention, fire fighting and fire protection information. NFPA technical standards include the National Electrical Code, and the National Building Code.

Noncombustible
Definition excerpted from the International Code Council (ICC): Material of which no part will ignite and burn when subjected to fire. Also defined as a material with a structural base of noncombustible materials as defined, with a surface not over 1/8" thick that has a flame spread rating of 50 or less. The term does not apply to surface finish materials.

Partition
An interior wall that divides one room from another and is not over one story in height. Partitions may be permanent.

Party Wall
A wall or partition separating two occupancies in a building.

Performance Specification
States how a building element must perform as opposed to describing equipment, products or systems by name.

Perlite
A siliceous volcanic glass that, when expanded by heat, is used as a lightweight aggregate.

Plaster
A cementitious material or combination of cementitious materials and aggregate that, when mixed with water, forms a workable mass. When applied to a surface, plaster adheres to it and subsequently sets or hardens, preserving in a rigid state the form or texture imposed during the period of plasticity.

Plaster Base
Gypsum panel with specially treated face paper to serve as a stable backing for plaster applications.

Plaster Bonder
A material applied to a surface to improve the quality of the bond between it and the succeeding application.

Plaster of Paris
Hemihydrate gypsum or calcium sulfate (CaSO4 " 1¼2 H20) without set control additives, used in casting and industrial applications.

Portland Cement
A hydraulic cement produced by pulverizing portland-cement clinker, consisting primarily of fused hydraulic calcium silicates and usually containing calcium sulfate

Potassium Aluminum Sulfate
Alum; a generally recognized accelerator of gypsum.

Prescription Specification
Traditional procedure used on building projects to describe by name products, equipment or systems to be used.

Retempering
A procedure whereby plaster (usually Keene's cement or portland cement) is remixed to a workable consistency using water and/or mechanical action.

Safing
Firestop material in the space between floor slab and curtain wall in multi-story construction.

Safing Off
Installation of fire safety insulation around floor perimeters, between floor slab and spandrel panels.

Through Penetration Firestop
A system for sealing penetrations in fire-resistant floors, walls and ceilings.

Through Penetrations
An opening through a fire-resistive partition or floor/ceiling assembly caused by the need to have a penetrating item pass through it. Through penetrations usually require the use of a firestop system to protect against the spread of fire through the opening.

Type X
A gypsum board with specially formulated core to increase fire retardant properties and improve system fire-resistance rating.

UBC (Uniform Building Code)
Uniform Building Code. Document promulgated by the International conference of Building Officials.

UL
Program allowing a manufacturer to place Underwriters Laboratories Inc. labels on its products that have met UL requirements. A UL representative visits the manufacturing site to obtain samples of the products for testing by UL. In some cases, samples are also purchased on the open market for testing. The public is thereby assured that products bearing the UL label continually meet UL specifications.

Vermiculite
A micaceous mineral expanded by heat and used as an aggregate.

Warnock Hershey International
WHI. An independent fire-testing laboratory.