• CHAPTER25
    GYPSUM BOARD, GYPSUM PANEL PRODUCTS AND PLASTER 

    User note: Code change proposals to this chapter will be considered by the IBC – Structural Code
    Development Committee during the 2016 (Group B) Code Development Cycle. See explanation on page iv.

    SECTION2501
    GENERAL

    2501.1 Scope.

    Provisions of this chapter shall govern the materials, design, construction and quality of gypsum board, gypsum panel products, lath, gypsum plaster, cement plaster and reinforced gypsum concrete.

    2501.2 Performance.

    Lathing, plastering, gypsum board and gypsum panel product construction shall be done in the manner and with the materials specified in this chapter and, when required for fire protection, shall also comply with the provisions of Chapter 7.

    2501.3 Other materials.

    Other approved wall or ceiling coverings shall be permitted to be installed in accordance with the recommendations of the manufacturer and the conditions of approval.

    SECTION2502
    DEFINITIONS

    2502.1 Definitions.

    The following terms are defined in Chapter 2:

    CEMENT PLASTER.

    EXTERIOR SURFACES.

    GYPSUM BOARD.

    GYPSUM PANEL PRODUCTS.

    GYPSUM PLASTER.

    GYPSUM VENEER PLASTER.

    INTERIOR SURFACES.

    WEATHER-EXPOSED SURFACES.

    WIRE BACKING.

    SECTION2503
    INSPECTION

    2503.1 Inspection.

    Lath, gypsum board and gypsum panel products shall be inspected in accordance with Section 110.3.5.

    SECTION2504
    VERTICAL AND HORIZONTAL ASSEMBLIES

    2504.1 Scope.

    The following requirements shall be met where construction involves gypsum board, gypsum panel products or lath and plaster in vertical and horizontal assemblies.

    2504.1.1 Wood framing.

    Wood supports for lath, gypsum board or gypsum panel products, as well as wood stripping or furring, shall be not less than 2 inches (51 mm) nominal thickness in the least dimension.

    Exception: The minimum nominal dimension of wood furring strips installed over solid backing shall be not less than 1 inch by 2 inches (25 mm by 51 mm).

    2504.1.2 Studless partitions.

    The minimum thickness of vertically erected studless solid plaster partitions of 3/8-inch (9.5 mm) and 3/4-inch (19.1 mm) rib metal lath, 1/2-inch-thick (12.7 mm) gypsum lath, gypsum board or gypsum panel product shall be 2 inches (51 mm).

    SECTION2505
    SHEAR WALL CONSTRUCTION

    2505.1 Resistance to shear (wood framing).

    Wood-frame shear walls sheathed with gypsum board, gypsum panel products or lath and plaster shall be designed and constructed in accordance with Section 2306.3 and are permitted to resist wind and seismic loads. Walls resisting seismic loads shall be subject to the limitations in Section 12.2.1 of ASCE 7.

    2505.2 Resistance to shear (steel framing).

    Cold-formed steel-frame shear walls sheathed with gypsum board or gypsum panel products and constructed in accordance with the materials and provisions of Section 2211.6 are permitted to resist wind and seismic loads. Walls resisting seismic loads shall be subject to the limitations in Section 12.2.1 of ASCE 7.

    SECTION2506
    GYPSUM BOARD AND
    GYPSUM PANEL PRODUCT MATERIALS
     

    2506.1 General.

    Gypsum board, gypsum panel products and accessories shall be identified by the manufacturer’s designation to indicate compliance with the appropriate standards referenced in this section and stored to protect such materials from the weather.

    2506.2 Standards.

    Gypsum board and gypsum panel products shall conform to the appropriate standards listed in Table 2506.2 and Chapter 35 and, where required for fire protection, shall conform to the provisions of Chapter 7.

    TABLE 2506.2

    GYPSUM BOARD AND GYPSUM PANEL PRODUCTS MATERIALS AND ACCESSORIES

    MATERIALSTANDARD
    Accessories for gypsum boardASTM C1047
    Adhesives for fastening gypsum boardASTM C557
    Cold-formed steel studs and track, structuralAISI S200 and ASTM C955, Section 8
    Cold-formed steel studs and track, nonstructuralAISI S220 and ASTM C645, Section 10
    Elastomeric joint sealantsASTM C920
    Fiber-reinforced gypsum panelsASTM C1278
    Glass mat gypsum backing panelASTM C1178
    Glass mat gypsum panel 5ASTM C1658
    Glass mat gypsum substrateASTM C1177
    Joint reinforcing tape and compoundASTM C474; C475
    Nails for gypsum boardsASTM C514, F547, F1667
    Steel screwsASTM C954; C1002
    Standard specification for gypsum boardASTM C1396
    Testing gypsum and gypsum productsASTM C22; C472; C473

    2506.2.1 Other materials.

    Metal suspension systems for acoustical and lay-in panel ceilings shall comply with ASTM C635 listed in Chapter 35 and Section 13.5.6 of ASCE 7 for installation in high seismic areas.

    SECTION2507
    LATHING AND PLASTERING 

    2507.1 General.

    Lathing and plastering materials and accessories shall be marked by the manufacturer’s designation to indicate compliance with the appropriate standards referenced in this section and stored in such a manner to protect them from the weather.

    2507.2 Standards.

    Lathing and plastering materials shall conform to the standards listed in Table 2507.2 and Chapter 35 and, where required for fire protection, shall also conform to the provisions of Chapter 7.

    TABLE 2507.2

    LATH, PLASTERING MATERIALS AND ACCESSORIES

    MATERIALSTANDARD
    Accessories for gypsum veneer baseASTM C1047
    Blended cementASTM C595
    Cold-formed steel studs and track, structuralAISI S200 and ASTM C955, Section 8
    Cold-formed steel studs and track, nonstructuralAISI S220 and ASTM C645, Section 10
    Exterior plaster bonding compoundsASTM C932
    Hydraulic cementASTM C1157; C1600
    Gypsum casting and molding plasterASTM C59
    Gypsum Keene’s cementASTM C61
    Gypsum plasterASTM C28
    Gypsum veneer plasterASTM C587
    Interior bonding compounds, gypsumASTM C631
    Lime plastersASTM C5; C206
    Masonry cementASTM C91
    Metal lathASTM C847
    Plaster aggregatesSandPerliteVermiculiteASTM C35; C897ASTM C35ASTM C35
    Plastic cementASTM C1328
    Portland cementASTM C150
    Steel screwsASTM C1002; C954
    Welded wire lathASTM C933
    Woven wire plaster baseASTM C1032

    SECTION2508
    GYPSUM CONSTRUCTION 

    2508.1 General.

    Gypsum board, gypsum panel products and gypsum plaster construction shall be of the materials listed in Tables 2506.2 and 2507.2. These materials shall be assembled and installed in compliance with the appropriate standards listed in Tables 2508.1 and 2511.1.1 and Chapter 35.

    TABLE 2508.1

    INSTALLATION OF GYPSUM CONSTRUCTION

    MATERIALSTANDARD
    Gypsum board and gypsum panel productsGA-216; ASTM C840
    Gypsum sheathing and gypsum panel productsASTM C1280
    Gypsum veneer baseASTM C844
    Interior lathing and furringASTM C841
    Steel framing for gypsum board and gypsum panel productsASTM C754; C1007

    2508.2 Limitations.

    Gypsum wallboard or gypsum plaster shall not be used in any exterior surface where such gypsum construction will be exposed directly to the weather. Gypsum wallboard shall not be used where there will be direct exposure to water or continuous high humidity conditions. Gypsum sheathing shall be installed on exterior surfaces in accordance with ASTM C1280.

    2508.2.1 Weather protection.

    Gypsum wallboard, gypsum lath or gypsum plaster shall not be installed until weather protection for the installation is provided.

    2508.3 Single-ply application.

    Edges and ends of gypsum board and gypsum panel products shall occur on the framing members, except those edges and ends that are perpendicular to the framing members. Edges and ends of gypsum board and gypsum panel products shall be in moderate contact except in concealed spaces where fire-resistance-rated construction, shear resistance or diaphragm action is not required.

    2508.3.1 Floating angles.

    Fasteners at the top and bottom plates of vertical assemblies, or the edges and ends of horizontal assemblies perpendicular to supports, and at the wall line are permitted to be omitted except on shear resisting elements or fire-resistance-rated assemblies. Fasteners shall be applied in such a manner as not to fracture the face paper with the fastener head.

    2508.4 Joint treatment.

    Gypsum board and gypsum panel product fire-resistance-rated assemblies shall have joints and fasteners treated.

    Exception: Joint and fastener treatment need not be provided where any of the following conditions occur:

    1. 1.Where the gypsum board or the gypsum panel product is to receive a decorative finish such as wood paneling, battens, acoustical finishes or any similar application that would be equivalent to joint treatment.

    2. 2.On single-layer systems where joints occur over wood framing members.

    3. 3.Square edge or tongue-and-groove edge gypsum board (V-edge), gypsum panel products, gypsum backing board or gypsum sheathing.

    4. 4.On multilayer systems where the joints of adjacent layers are offset.

    5. 5.Assemblies tested without joint treatment.

    2508.5 Horizontal gypsum board or gypsum panel product diaphragm ceilings.

    Gypsum board or gypsum panel products shall be permitted to be used on wood joists to create a horizontal diaphragm ceiling in accordance with Table 2508.5.

    TABLE 2508.5

    SHEAR CAPACITY FOR HORIZONTAL WOOD-FRAME GYPSUM BOARD DIAPHRAGM CEILING ASSEMBLIES

    MATERIALTHICKNESS OF MATERIAL (MINIMUM) (inches)SPACING OF FRAMING MEMBERS (inches)SHEAR VALUEa, b (PLF OF CEILING)MIMIMUM FASTENER SIZE
    Gypsum board or gypsum panel product1/216 o.c.905d cooler or wallboard nail; 15/8-inch long; 0.086-inch shank; 15/64-inch headc
    Gypsum board or gypsum panel product1/224 o.c.705d cooler or wallboard nail; 15/8-inch long; 0.086-inch shank; 15/64-inch headc

    For SI: 1 inch = 25.4 mm, 1 pound per foot = 14.59 N/m.

    1. a.Values are not cumulative with other horizontal diaphragm values and are for short-term wind or seismic loading. Values shall be reduced 25 percent for normal loading.

    2. b.Values shall be reduced 50 percent in Seismic Design Categories D, E and F.

    3. c.11/4-inch, No. 6 Type S or W screws are permitted to be substituted for the listed nails.

    2508.5.1 Diaphragm proportions.

    The maximum allowable diaphragm proportions shall be 11/2:1 between shear resisting elements. Rotation or cantilever conditions shall not be permitted.

    2508.5.2 Installation.

    Gypsum board or gypsum panel products used in a horizontal diaphragm ceiling shall be installed perpendicular to ceiling framing members. End joints of adjacent courses of gypsum board shall not occur on the same joist.

    2508.5.3 Blocking of perimeter edges.

    Perimeter edges shall be blocked using a wood member not less than 2-inch by 6-inch (51 mm by 152 mm) nominal dimension. Blocking material shall be installed flat over the top plate of the wall to provide a nailing surface not less than 2 inches (51 mm) in width for the attachment of the gypsum board or gypsum panel product.

    2508.5.4 Fasteners.

    Fasteners used for the attachment of gypsum board or gypsum panel products to a horizontal diaphragm ceiling shall be as defined in Table 2508.5. Fasteners shall be spaced not more than 7 inches (178 mm) on center at all supports, including perimeter blocking, and not more than 3/8 inch (9.5 mm) from the edges and ends of the gypsum board or gypsum panel product.

    2508.5.5 Lateral force restrictions.

    Gypsum board or gypsum panel products shall not be used in diaphragm ceilings to resist lateral forces imposed by masonry or concrete construction.

    SECTION2509
    SHOWERS AND WATER CLOSETS 

    2509.1 Wet areas.

    Showers and public toilet walls shall conform to Section 1210.2.

    2509.2 Base for tile.

    Materials used as a base for wall tile in tub and shower areas and wall and ceiling panels in shower areas shall be of materials listed in Table 2509.2 and installed in accordance with the manufacturer’s recommendations. Water-resistant gypsum backing board shall be used as a base for tile in water closet compartment walls when installed in accordance with GA-216 or ASTM C840 and the manufacturer’s recommendations. Regular gypsum wallboard is permitted under tile or wall panels in other wall and ceiling areas when installed in accordance with GA-216 or ASTM C840.

    TABLE 2509.2

    BACKERBOARD MATERIALS

    MATERIALSTANDARD
    Glass mat gypsum backing panelASTM C1178
    Nonasbestos fiber-cement backer boardASTM C1288 or ISO 8336, Category C
    Nonasbestos fiber-mat reinforced cementitious backer unitASTM C1325

    2509.3 Limitations.

    Water-resistant gypsum backing board shall not be used in the following locations:

    1. 1.Over a vapor retarder in shower or bathtub compartments.

    2. 2.Where there will be direct exposure to water or in areas subject to continuous high humidity.

    SECTION2510
    LATHING AND FURRING FOR CEMENT PLASTER
    (STUCCO)
     

    2510.1 General.

    Exterior and interior cement plaster and lathing shall be done with the appropriate materials listed in Table 2507.2 and Chapter 35.

    2510.2 Weather protection.

    Materials shall be stored in such a manner as to protect them from the weather.

    2510.3 Installation.

    Installation of these materials shall be in compliance with ASTM C926 and ASTM C1063.

    2510.4 Corrosion resistance.

    Metal lath and lath attachments shall be of corrosion-resistant material.

    2510.5 Backing.

    Backing or a lath shall provide sufficient rigidity to permit plaster applications.

    2510.5.1 Support of lath.

    Where lath on vertical surfaces extends between rafters or other similar projecting members, solid backing shall be installed to provide support for lath and attachments.

    2510.5.2 Use of gypsum backing board.

    Gypsum backing for cement plaster shall be in accordance with Section 2510.5.2.1 or 2510.5.2.2.

    2510.5.2.1 Gypsum board as a backing board.

    Gypsum lath or gypsum wallboard shall not be used as a backing for cement plaster.

    Exception: Gypsum lath or gypsum wallboard is permitted, with a water-resistive barrier, as a backing for self-furred metal lath or self-furred wire fabric lath and cement plaster where either of the following conditions occur:

    1. 1.On horizontal supports of ceilings or roof soffits.

    2. 2.On interior walls.

    2510.5.2.2 Gypsum sheathing backing.

    Gypsum sheathing is permitted as a backing for metal or wire fabric lath and cement plaster on walls. A water-resistive barrier shall be provided in accordance with Section 2510.6.

    2510.5.3 Backing not required.

    Wire backing is not required under expanded metal lath or paperbacked wire fabric lath.

    2510.6 Water-resistive barriers.

    Water-resistive barriers shall be installed as required in Section 1404.2 and, where applied over wood-based sheathing, shall include a water-resistive vapor-permeable barrier with a performance at least equivalent to two layers of water-resistive barrier complying with ASTM E2556, Type I. The individual layers shall be installed independently such that each layer provides a separate continuous plane and any flashing (installed in accordance with Section 1405.4) intended to drain to the water-resistive barrier is directed between the layers.

    Exception: Where the water-resistive barrier that is applied over wood-based sheathing has a water resistance equal to or greater than that of a water-resistive barrier complying with ASTM E2556, Type II and is separated from the stucco by an intervening, substantially nonwater-absorbing layer or drainage space.

    2510.7 Preparation of masonry and concrete.

    Surfaces shall be clean, free from efflorescence, sufficiently damp and rough for proper bond. If the surface is insufficiently rough, approved bonding agents or a Portland cement dash bond coat mixed in proportions of not more than two parts volume of sand to one part volume of Portland cement or plastic cement shall be applied. The dash bond coat shall be left undisturbed and shall be moist cured not less than 24 hours.

    SECTION2511
    INTERIOR PLASTER

    2511.1 General.

    Plastering gypsum plaster or cement plaster shall be not less than three coats where applied over metal lath or wire fabric lath and not less than two coats where applied over other bases permitted by this chapter.

    Exception: Gypsum veneer plaster and cement plaster specifically designed and approved for one-coat applications.

    2511.1.1 Installation.

    Installation of lathing and plaster materials shall conform to Table 2511.1.1 and Section 2507.

    TABLE 2511.1.1

    INSTALLATION OF PLASTER CONSTRUCTION

    MATERIALSTANDARD
    Cement plasterASTM C926
    Gypsum plasterASTM C842
    Gypsum veneer plasterASTM C843
    Interior lathing and furring (gypsum plaster)ASTM C841
    Lathing and furring (cement plaster)ASTM C1063
    Steel framingASTM C754; C1007

    2511.2 Limitations.

    Plaster shall not be applied directly to fiber insulation board. Cement plaster shall not be applied directly to gypsum lath or gypsum plaster except as specified in Sections 2510.5.1 and 2510.5.2.

    2511.3 Grounds.

    Where installed, grounds shall ensure the minimum thickness of plaster as set forth in ASTM C842 and ASTM C926. Plaster thickness shall be measured from the face of lath and other bases.

    2511.4 Interior masonry or concrete.

    Condition of surfaces shall be as specified in Section 2510.7. Approved specially prepared gypsum plaster designed for application to concrete surfaces or approved acoustical plaster is permitted. The total thickness of base coat plaster applied to concrete ceilings shall be as set forth in ASTM C842 or ASTM C926. Should ceiling surfaces require more than the maximum thickness permitted in ASTM C842 or ASTM C926, metal lath or wire fabric lath shall be installed on such surfaces before plastering.

    2511.5 Wet areas.

    Showers and public toilet walls shall conform to Sections 1210.2 and 1210.3. When wood frame walls and partitions are covered on the interior with cement plaster or tile of similar material and are subject to water splash, the framing shall be protected with an approved moisture barrier.

    SECTION2512
    EXTERIOR PLASTER 

    2512.1 General.

    Plastering with cement plaster shall be not less than three coats when applied over metal lath or wire fabric lath or gypsum board backing as specified in Section 2510.5 and shall be not less than two coats when applied over masonry or concrete. If the plaster surface is to be completely covered by veneer or other facing material, or is completely concealed by another wall, plaster application need only be two coats, provided the total thickness is as set forth in ASTM C926.

    2512.1.1 On-grade floor slab.

    On wood frame or steel stud construction with an on-grade concrete floor slab system, exterior plaster shall be applied in such a manner as to cover, but not to extend below, the lath and paper. The application of lath, paper and flashing or drip screeds shall comply with ASTM C1063.

    2512.1.2 Weep screeds.

    A minimum 0.019-inch (0.48 mm) (No. 26 galvanized sheet gage), corrosion-resistant weep screed with a minimum vertical attachment flange of 31/2 inches (89 mm) shall be provided at or below the foundation plate line on exterior stud walls in accordance with ASTM C926. The weep screed shall be placed a minimum of 4 inches (102 mm) above the earth or 2 inches (51 mm) above paved areas and be of a type that will allow trapped water to drain to the exterior of the building. The water-resistive barrier shall lap the attachment flange. The exterior lath shall cover and terminate on the attachment flange of the weep screed.

    2512.2 Plasticity agents.

    Only approved plasticity agents and approved amounts thereof shall be added to Portland cement or blended cements. When plastic cement or masonry cement is used, no additional lime or plasticizers shall be added. Hydrated lime or the equivalent amount of lime putty used as a plasticizer is permitted to be added to cement plaster or cement and lime plaster in an amount not to exceed that set forth in ASTM C926.

    2512.3 Limitations.

    Gypsum plaster shall not be used on exterior surfaces.

    2512.4 Cement plaster.

    Plaster coats shall be protected from freezing for a period of not less than 24 hours after set has occurred. Plaster shall be applied when the ambient temperature is higher than 40°F (4°C), unless provisions are made to keep cement plaster work above 40°F (4°C) during application and 48 hours thereafter.

    2512.5 Second-coat application.

    The second coat shall be brought out to proper thickness, rodded and floated sufficiently rough to provide adequate bond for the finish coat. The second coat shall have no variation greater than 1/4 inch (6.4 mm) in any direction under a 5-foot (1524 mm) straight edge.

    2512.6 Curing and interval.

    First and second coats of cement plaster shall be applied and moist cured as set forth in ASTM C926 and Table 2512.6.

    TABLE 2512.6

    CEMENT PLASTERS

    COATMINIMUM PERIOD MOIST CURINGMINIMUM INTERVAL BETWEEN COATS
    First48 hoursa48 hoursb
    Second48 hours7 daysc
    FinishNote c
    1. a.The first two coats shall be as required for the first coats of exterior plaster, except that the moist-curing time period between the first and second coats shall be not less than 24 hours. Moist curing shall not be required where job and weather conditions are favorable to the retention of moisture in the cement plaster for the required time period.

    2. b.Twenty-four-hour minimum interval between coats of interior cement plaster. For alternative method of application, see Section 2512.8.

    3. c.Finish coat plaster is permitted to be applied to interior cement plaster base coats after a 48-hour period.

    2512.7 Application to solid backings.

    Where applied over gypsum backing as specified in Section 2510.5 or directly to unit masonry surfaces, the second coat is permitted to be applied as soon as the first coat has attained sufficient hardness.

    2512.8 Alternate method of application.

    The second coat is permitted to be applied as soon as the first coat has attained sufficient rigidity to receive the second coat.

    2512.8.1 Admixtures.

    When using this method of application, calcium aluminate cement up to 15 percent of the weight of the Portland cement is permitted to be added to the mix.

    2512.8.2 Curing.

    Curing of the first coat is permitted to be omitted and the second coat shall be cured as set forth in ASTM C926 and Table 2512.6.

    2512.9 Finish coats.

    Cement plaster finish coats shall be applied over base coats that have been in place for the time periods set forth in ASTM C926. The third or finish coat shall be applied with sufficient material and pressure to bond and to cover the brown coat and shall be of sufficient thickness to conceal the brown coat.

    SECTION2513
    EXPOSED AGGREGATE PLASTER

    2513.1 General.

    Exposed natural or integrally colored aggregate is permitted to be partially embedded in a natural or colored bedding coat of cement plaster or gypsum plaster, subject to the provisions of this section.

    2513.2 Aggregate.

    The aggregate shall be applied manually or mechanically and shall consist of marble chips, pebbles or similar durable, moderately hard (three or more on the Mohs hardness scale), nonreactive materials.

    2513.3 Bedding coat proportions.

    The bedding coat for interior or exterior surfaces shall be composed of one part Portland cement and one part Type S lime; or one part blended cement and one part Type S lime; or masonry cement; or plastic cement and a maximum of three parts of graded white or natural sand by volume. The bedding coat for interior surfaces shall be composed of 100 pounds (45.4 kg) of neat gypsum plaster and a maximum of 200 pounds (90.8 kg) of graded white sand. A factory-prepared bedding coat for interior or exterior use is permitted. The bedding coat for exterior surfaces shall have a minimum compressive strength of 1,000 pounds per square inch (psi) (6895 kPa).

    2513.4 Application.

    The bedding coat is permitted to be applied directly over the first (scratch) coat of plaster, provided the ultimate overall thickness is a minimum of 7/8 inch (22 mm), including lath. Over concrete or masonry surfaces, the overall thickness shall be a minimum of 1/2 inch (12.7 mm).

    2513.5 Bases.

    Exposed aggregate plaster is permitted to be applied over concrete, masonry, cement plaster base coats or gypsum plaster base coats installed in accordance with Section 2511 or 2512.

    2513.6 Preparation of masonry and concrete.

    Masonry and concrete surfaces shall be prepared in accordance with the provisions of Section 2510.7.

    2513.7 Curing of base coats.

    Cement plaster base coats shall be cured in accordance with ASTM C926. Cement plaster bedding coats shall retain sufficient moisture for hydration (hardening) for 24 hours minimum or, where necessary, shall be kept damp for 24 hours by light water spraying.

    SECTION2514
    REINFORCED GYPSUM CONCRETE

    2514.1 General.

    Reinforced gypsum concrete shall comply with the requirements of ASTM C317 and ASTM C956.

    2514.2 Minimum thickness.

    The minimum thickness of reinforced gypsum concrete shall be 2 inches (51 mm) except the minimum required thickness shall be reduced to 11/2 inches (38 mm), provided the following conditions are satisfied:

    1. 1.The overall thickness, including the formboard, is not less than 2 inches (51 mm).

    2. 2.The clear span of the gypsum concrete between supports does not exceed 33 inches (838 mm).

    3. 3.Diaphragm action is not required.

    4. 4.The design live load does not exceed 40 pounds per square foot (psf) (1915 Pa).