ASTM C 11 :- Standard Terminology Relating to Gypsum and Related Building Materials and Systems1

  This standard covers terminology relating to gypsum
and related building materials and systems. The terms are
generically defined.

3. Terminology

  • Accelerator—a material that reduces setting time.
  • Accessories—products fabricated for the purpose of forming
    corners, edges, control joints, or decorative effects. 
  • Adhesive—a substance capable of holding materials together
    by surface attachment. 
  • Admixture—a material other than water, aggregates, hydraulic cementitious material, and fiber reinforcement that is
    used as an ingredient to modify properties and is added to the
    batch before or during its mixture. 
  • Aggregate—an inert granular material which may be added
    to gypsum plasters. (C35) 
  • All purpose compound—a compound formulated and
    manufactured to serve as both a taping and a finishing
    compound.
  • Anhydrite—the mineral consisting primarily of anhydrous
    calcium sulfate, CaSO4. 
  • arris (of an arch), n—the outside corner or angle formed by
    the meeting of a wall surface with the curved surface of an
    arch
  • Anhydrite, n—the mineral consisting primarily of anhydrous
    calcium sulfate, CaSO4.
  • Arris (of an arch), n—the outside corner or angle formed by
    the meeting of a wall surface with the curved surface of an
    arch (see Fig. 1).

  • Base coat, n—any or all layers of plaster in place prior to
    application of finish coats.
    DISCUSSION—The first application is normally called a scratch coat
    and the second application is referred to as a brown coat.
  • Bedding coat, n—that coat of plaster to receive aggregate or
    other decorative material of any size, impinged or embedded
    into its surface, before it sets. 
  • Bond plaster, n—a calcined gypsum plaster specially formulated for application over rough monolithic concrete as a
    bonding coat for a subsequent gypsum plaster layer.
  • Bridging, n—in framing, sections of wood or metal pieces used
    between framing members to stiffen, give lateral support,
    and minimize rotation. 
  • Brown coat, n—the second layer in three-coat plaster application.
    building construction joint, n—a designed division of a
    building that allows movement of all component parts of the
    building, in any plane, which may be caused by thermal,
    seismic, wind loading, or any other force. The construction
    of the separation is accomplished by one of the following
    methods: (1) manufactured devices suitable for this
    application, or (2) by field fabrication of suitable materials.
  • Calcined gypsum, n—a dry powder; primarily calcium sulfate
    hemihydrate, resulting from calcination of gypsum; cementitious base for production of most gypsum plasters: also
    called plaster of paris, sometimes called stucco.
  • Calcium sulfate, n—the chemical compound CaSO4. 
  • Cementitious material, n—a material that, when mixed with
    water, with or without aggregate, provides the plasticity and
    the cohesive and adhesive properties necessary for
    placement, and the formation of a rigid mass.
  • Check cracking (in joint systems), n—short, narrow cracks
    randomly oriented in the surface of the dried joint compound. 
  • Coat, n—a layer of plaster applied in a single operation.
  • Combined water, n—the water chemically held, as water of
    crystallization, by the calcium sulfate dihydrate or hemihydrate crystal. 
  • Compressive strength, n—the maximum load sustained by a
    standard specimen of a material when subjected to a crushing force.
  • Consistency, n—a property of a material determined by the
    complete flow force relation.
  • consistency (normal), n—the number of millilitres of water
    per 100 g of gypsum plaster or gypsum concrete required to
    produce a mortar or a slurry of specified fluidity. (C472) 
  • control (expansion-contraction) joint, n—a designed separation in the system materials that allows for movement caused
    by expansion or contraction of the system. The construction
    of the separation is accomplished by one of the following
    methods: (1) manufactured devices suitable for this
    application, or (2) by field fabrication of suitable materials.
    core (of gypsum board), n—the hardened material filling the
    space between the face and back papers consisting substantially of rehydrated gypsum with additives.
  • Cored tile or block, n—see gypsum tile or block. (C52) 
  • Cornerbead, n—an accessory for outside corners.
    corner reinforcement, 
  • Exterior, n—a preformed section of
    wire or expanded sheet steel, for the reinforcement of
    exterior stucco external corners (arises).
    cure (portland cement plaster or stucco), v—(1) to provide
    conditions conducive to the hydration process of portland
    cement plaster or stucco, or (2) to maintain proper temperature and a sufficient quantity of water within the plaster to
    ensure cement hydration. 
  • Density, n—the weight per unit volume of a material. (C472)
  • Dried sample, n—a sample devoid of free water. 
  • Edge (of glass mat gypsum panels), n—the bound edge as
    manufactured. 
  • Edge (of gypsum board), n—the paper-bound edge as manufactured.
    edge trim, n—an accessory to cover exposed ends or edges of
    gypsum board.
    embedding compound—see taping compound. 
  • end (of glass mat gypsum panels), n—the end perpendicular
    to the bound edge. The gypsum core is always exposed. 
  • end (of gypsum board), n—the end perpendicular to the
    FIG. 1 Arris (of an Arch) paper-bound edge. The gypsum core is always exposed.
  • Expansion joint, n—see control (expansion-contraction)
    joint. 
  • face, n—the surface designed to be left exposed to view or to
    receive decoration or additional finishes. 
  • facer, n—a woven or nonwoven fabric or membrane on the
    surface of a gypsum board or gypsum panel product that is
    an integral part of the product. 
  • featured edge, n—an edge configuration of the paper bound
    edge of gypsum board that provides special design or
    performance.
  • fineness modulus, n—an empirical factor obtained by adding
    total percentages of a sample of aggregate retained on each
    of a specified series of sieves and dividing by 100. The sieve
    sizes used are: No. 100 (150 µm), No. 50 (300 µm), No. 30
    (600 µm), No. 16 (1.18 mm), No. 8 (2.36 mm), No. 4 (4.75
    mm), 3⁄8 in. (9.5 mm), 3⁄4 in. (19.0 mm), 11⁄2 in. (38.1 mm)
    and larger, increasing in the ratio of 2 to 1. 
  • finish coat, n—the final layer of plaster applied over a basecoat
    or other substrate. 
  • finishing compound, n—(sometimes called topping 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-resistance classification, n—a standard rating of fireresistance and protective characteristics of a building construction or assembly. 
  •  flame spread classification, n—a standard rating of relative
    surface burning characteristics of a building material as
    compared to a standard material.
  •  flexural strength, n—the maximum load sustained by a
    standard specimen of a sheet material when subjected to a
    bending force.
    floating, v—the act of spreading, compacting, or consolidating
    to achieve a specified uniform appearance.
  • framing member, n—stud, plate, track, joist, furring, and other
    support to which a gypsum panel product, or metal plaster
    base is attached. 
  • free water, n—all water contained by gypsum board or plaster
    in excess of that chemically held as water of crystallization. 
  • Gauging plaster, n—a calcined gypsum plaster designed to be
    mixed with lime putty. (
  •  glass mat, n—a woven or non-woven fabric of glass fibers with
    or without a binder. 
  • Glass mat gypsum panel, n—a gypsum panel product with
    glass mat facers.
    grout, n—gypsum or portland cement plaster used to fill
    crevices or to fill hollow metal frames.
  • Gypsum, n—the mineral consisting primarily of fully hydrated
    calcium sulfate, CaSO4·2H2O or calcium sulfate dihydrate.
  • gypsum backing board, n—a 1⁄4 in. to 5⁄8 in. gypsum board for
    use as a backing for gypsum wallboard, acoustical tile, or
    other dry cladding.
    water resistant gypsum backing board—a gypsum board
    designed for use on walls primarily as a base for the application
    of ceramic, or plastic tile. 
  • Gypsum base for veneer plasters, n—a gypsum board used as
    the base for application of a gypsum veneer plaster. 
  • (gypsum board, n—the generic name for a family of sheet
    products consisting of a noncombustible core primarily of
    gypsum with paper surfacing.
  • Gypsum casting plaster, n—a calcined gypsum plaster used
    primarily to form objects, such as lamp bases, art ware, and
    novelties, and so forth. 
  • Gypsum concrete, n—a calcined gypsum mixed with wood
    chips or aggregate, or both. 
  • Gypsum core board, n—a 3⁄4 in. (19.0 mm) to 1 in. (25.4 mm)
    gypsum board consisting of a single board or factory
    laminated multiple boards, used as a gypsum stud or core in
    semisolid or solid gypsum board partitions.
  • Gypsum formboard, n—a gypsum panel product used as the
    permanent form for poured gypsum roof decks. (C318/
    C318M)
    gypsum lath, n—a gypsum board used as the base for
    application of gypsum plaster. 
  • perforated gypsum lath—a gypsum lath having perforations
    to provide mechanical keying of the basecoat plaster.
    foil-backed gypsum lath—the same as plain gypsum lath
    except that in addition, the back surface shall be covered with
    a continuous sheet of pure bright finished aluminum foil.
    type X lath—a gypsum lath specially manufactured to
    provide specific fire-resistant characteristics. 
  • Gypsum molding plaster, n—a calcined gypsum plaster used
    primarily for plaster casts or molds, sometimes used as a
    gauging plaster. 
  • gypsum neat plaster, n—a calcined gypsum mixed at the mill
    with ingredients to control working quality and setting time. (C28/C28M)
    DISCUSSION—Neat plaster is either fibered or unfibered. The addition
    of aggregate is required on the job. 
  • Gypsum panel products, n—the general name for a family of
    sheet products consisting essentially of gypsum.
  • Gypsum plaster, n—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, n—a gypsum board used as a backing for
    exterior surface materials, manufactured with waterrepellant paper and may be manufactured with a waterresistant core. 
  • gypsum tile or block, n—a cast gypsum building unit. (C52)
    gypsum veneer plaster systems, n—veneer plaster applied in
    accordance with Specification C843 to gypsum base for
    veneer plasters. 
  • Gypsum wallboard, n—a gypsum board used primarily as an
    interior surfacing for building structures. 
  • foil-backed gypsum wallboard—a gypsum wallboard with
    the back surface covered with a continuous sheet of pure bright
    finished aluminum foil. 
  •  type X gypsum wallboard—a gypsum wallboard specially
    manufactured to provide specific fire-resistant characteristics
    (C36/C36M). 
  • Gypsum wood-fibered plaster, n—a calcined gypsum plaster
    containing shredded or ground wood fiber added during
    manufacture. 
  • Hemihydrate, n—the dry powder, calcium sulfate
    hemihydrate, resulting from calcination of CaSO4·2H2O,
    calcium sulfate dihydrate. 
  • See calcined gypsum.
    joining, n
    —the juncture of two separate plaster applications of
    the same coat, usually within a single surface plane.
  • joint compound, n—generic term referring to all compounds
    used for taping or finishing gypsum board, or both. See all
    purpose compound, finishing compound, taping compound. 
  • joint tape, n—a strip of tape made from paper, metal, fabric,
    glass mesh, or other material, that is commonly used in a
    joint system to reinforce the joints between adjacent gypsum
    panel products. 
  • glass-mesh joint tape, n—joint tape made from multidirectional glass yarn. 
  • Paper joint tape, n—joint tape made from paper and designed to be embedded in the joint compound. 
  • Self-adhering joint tape, n—a glass-mesh joint tape designed
    to adhere without requiring mechanical attachment. 
  • Keene’s cement, n—an anhydrous gypsum plaster characterized by a low mixing water requirement and special setting
    properties, primarily used with lime to produce hard, dense
    finish coats. 
  • key, n—the grip or mechanical bond of one coat of plaster to
    another coat, or to a substrate.
    DISCUSSION—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.
    lath—see gypsum lath.
  • load-bearing partition, n—a partition designed to support a
    portion of the building structure. 
  • Machine direction, n—the direction parallel to the paperbound edge of the gypsum board. 
  • Manufactured sand, n—the fine material resulting from the
    crushing and classification by screening, or otherwise, of
    rock, gravel, or blast furnace slag.
  • masonry cement, n—a hydraulic cement for use in mortars for
    masonry construction, containing one or more of the following materials: portland cement, portland blast furnace slag
    cement, portland-pozzolan cement, natural cement, slag
    cement, or hydraulic lime; and in addition usually containing
    one or more materials such as hydrated lime, limestone,
    chalk, calcareous shell, talc, slag, or clay as prepared for this
    purpose. 
  • Mechanical bonds, n—the attachment created when plaster
    penetrates, into or through, the substrate, or envelops irregularities in the surface of the substrate. 
  • Members (in application of gypsum panel products),
    n
    —framing to which gypsum panel products are attached. 
  • Mill-mixed plaster (ready-mixed plaster), n—material formulated and dry-blended by the manufacturer, requiring only
    the addition of and mixing with water. 
  • Mortar, n—a mixture of gypsum plaster with aggregate or
    hydrate lime, or both, and water to produce a trowelable
    fluidity. 
  • Natural sand, n—the fine granular material resulting from the
    natural disintegration of rock or from the crushing of friable
    sandstone. (C35)
    neat gypsum plaster—see gypsum neat plaster. 
  • Nominal thickness (of gypsum panel products), n—the
    manufacturer-stated thickness of the gypsum panel product.
    perlite aggregate, n—a siliceous volcanic glass expanded by
    heat.
  • perm, n—a unit of measurement of water vapor permeance; a
    metric perm, or 1 g/24 h·m2
    ·mm Hg. U.S. unit, 1 grain/
    h·ft2
    ·in. Hg. 
  • (E96/E96M) permeability, n—the property of a porous material that permits
    a fluid (or gas) to pass through it; in construction, commonly
    refers to water vapor permeability of a sheet material or
    assembly and is defined as water vapor permeance per unit
    thickness. Metric unit of measurement, metric perms per
    centimetre of thickness. See water vapor transmission,
    perm, permeance.
  • permeance (water vapor), n—the ratio of the rate of water
    vapor transmission (WVT) through a material or assembly
    between its two parallel surfaces to the vapor pressure
    differential between the surfaces. Metric unit of measurement is the metric perm, 1 g/24 h·m2
    ·mm Hg; U.S. unit, 1
    grain/h·ft2
    ·in. Hg. See water vapor transmission,
    permeability, perm.
  • Plaster bond, n—the adhesion between plaster coats or between plaster and substrate. 
  • Plastic cement, n—a hydraulic cement to which one or more
    plasticizing agents (but not more than 12 % by volume) have
    been added during intergrinding or blending to increase the
    workability and molding qualities of the resultant cement
    paste, mortar, or plaster. 
  • Plasticity, n—the property of freshly mixed cement paste,
    mortar, or plaster which determines its workability and
    molding qualities. 
  • Portland cement, n—a hydraulic cement produced by pulverizing clinker consisting essentially of hydraulic calcium
    silicates, and usually containing one or more forms of
    calcium sulfate as an interground addition. 
  • portland cement plaster, n—a plaster mix in which portland
    cement or combinations of portland and masonry cements or
    portland cement and lime are the principal cementitious
    materials mixed with aggregate. 
  • Purity, n—the percentage of CaSO4·
    1⁄2 H2O in the calcined
    gypsum portion of a gypsum plaster or gypsum concrete, as
    defined by Specification C28/C28M, for Gypsum Plasters.
    The percentage of CaSO4·2H2O in the gypsum or the
    gypsum portion of fully hydrated, dry, set gypsum plaster. 
  • Ready-mixed plaster, n—a calcined gypsum plaster with
    aggregate added during manufacture. (C28/C28M)
    recessed edge, n—see tapered edge 
  • Relative humidity, n—the ratio of actual water vapor pressure
    to the saturation water vapor pressure at the same
    temperature, expressed as a percentage. 
  • Retarder, n—a material that extends setting time.
    round edge, n—a rounded, paper-bound edge formation on
    gypsum board, commonly used for gypsum lath.
  • Saddle-tie, for furring, n—a single or double strand of wire
    used to attach furring members to framing members of wall
    or ceiling assemblies. See Fig. 2.
    saddle-tie, for furring, v—to attach furring members to framing members of wall or ceiling assemblies using a single or
    double strand of wire. See Fig. 2.
    saddle-tie, for wire hangers, v—to attach wire hangers to main
    runners. See Fig. 3.
    sample as received, n—a representative portion of product or
    material in the state received by the testing laboratory. 
  • Scratch coat, n—the first layer of plaster applied over lath or
    other substrate.
    set, n—the chemical and physical change in plaster as it goes
    from a plastic, workable state to a rigid state. See setting
    time. 
  • Setting time, n—the elapsed time required for a gypsum plaster
    to attain a specified hardness and strength after mixing with
    water. 
  • Shipment (of gypsum panel products), n—the quantity of
    gypsum panel products shipped by a manufacturer and
    included on a single invoice. 
  • Smooth-trowel finish, n—a uniform finish free of grainy or
    coarse areas, trowel marks, or other avoidable imperfections. 
  • Spinout,, n—the continued rotation of a screw without further
    penetration into the substrate. 
  • Steel drill screw, n—self-drilling screw with the ability to drill
    its own hole and form or cut mating threads without
    deforming its threads or breaking.
  • Stucco, n—a portland cement-aggregate plaster mix designed
    for use on exterior surfaces. See portland cement plaster. 
  • Synthetic gypsum, n—a chemical product, consisting primarily of calcium sulfate dihydrate (CaSO4·2H2O) resulting
    primarily from an industrial process. 
  • Tapered edge, n—an edge formation of gypsum board which
    provides a shallow depression at the paper-bound edge to
    receive joint reinforcement. Also known as a recessed edge. 
  • Taping compound, n—(sometimes called embedding compound) a compound specifically formulated and manufactured for use in embedding of joint reinforcing tape at
    gypsum board joints.
    temper, v—to mix or restore to a workable consistency. 
  • Texture finish, n—any applied decorative finish other than
    smooth.
    three-coat work, n—plaster applied in three successive coats
    with time between coats for setting or drying, or both.
    topping compound—see finishing compound. 
  • Veneer plaster, n—a calcined gypsum plaster formulated to be
    applied in thin coats. (C587)
    vermiculite aggregate, n—a micaceous mineral that expands
    with heat. (C35)
    wallboard—see gypsum wallboard. 
  • water absorption, n—the amount of water absorbed by a
    material under specified test conditions commonly expressed
    as weight percent of the test specimen. 
  • water-repellent paper, n—gypsum board paper surfacing
    which has been formulated or treated to resist water penetration. 
  • water-resistant core, n—a gypsum board specially formulated
    to resist water penetration.
    water vapor transmission (WVT), n—the rate of water vapor
    flow, under steady specified conditions, through a unit area
    of a material, between its two parallel surfaces and normal to
    the surfaces. Metric unit of measurement is 1 g/24 h·m2
    . See
    permeability,permeance, perm. 
  • Wood-fibered plaster, n—a calcined gypsum plaster containing shredded or ground wood fiber added during manufacture.

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