Provisions of this chapter shall govern the materials, design, construction and quality of gypsum board, lath, gypsum plaster and cement plaster.
Other approved wall or ceiling coverings shall be permitted to be installed in accordance with the recommendations of the manufacturer and the approval of the commissioner.
The following words and terms shall, for the purposes of this chapter and as used elsewhere in this code, have the meanings shown herein.
CEMENT PLASTER. A mixture of portland or blended cement, portland cement or blended cement and hydrated lime, masonry cement or plastic cement and aggregate and other approved materials as specified in this code.
EXTERIOR SURFACES. Weather-exposed surfaces.
GYPSUM BOARD. Gypsum wallboard, gypsum sheathing, gypsum base for gypsum veneer plaster, exterior gypsum soffit board, predecorated gypsum board or water-resistant gypsum backing board complying with the standards listed in Tables 2506.2, 2507.2 and Chapter 35.
GYPSUM PLASTER. A mixture of calcined gypsum or calcined gypsum and lime and aggregate and other approved materials as specified in this code.
GYPSUM VENEER PLASTER. Gypsum plaster applied to an approved base in one or more coats normally not exceeding 1 inch (6.4 mm) in total thickness.
INTERIOR SURFACES. Surfaces other than weather-exposed surfaces.
WEATHER-EXPOSED SURFACES. Surfaces of walls, ceilings, floors, roofs, soffits and similar surfaces exposed to the weather except the following:
1. Ceilings and roof soffits enclosed by walls, fascia, bulkheads or beams that extend a minimum of 12 inches (305 mm) below such ceiling or roof soffits.
2. Walls or portions of walls beneath an unenclosed roof area, where located a horizontal distance from an open exterior opening equal to at least twice the height of the opening.
3. Ceiling and roof soffits located a minimum horizontal distance of 10 feet (3048 mm) from the outer edges of the ceiling or roof soffits.
WIRE BACKING. Horizontal strands of tautened wire attached to surfaces of vertical supports which, when covered with the building paper, provide a backing for cement plaster.
The following requirements shall be met where construction involves gypsum board, lath and plaster in vertical and horizontal assemblies.
Wood supports for lath or gypsum board, as well as wood stripping or furring, shall not be 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 not be less than 1 inch by 2 inches (25 mm by 51 mm).
The minimum thickness of vertically erected studless solid plaster partitions of 3 / 8 -inch (9.5 mm) and 3 -inch (19.1 mm) rib metal lath or 1 / 2 -inch-thick (12.7 mm) long-length gypsum lath and gypsum board partitions shall be 2 inches (51 mm).
Cold-formed steel framed shear walls sheathed with gypsum board and constructed in accordance with the materials and provisions of Sections 2211.1, 2211.2, 2211.2.1 and 2184.108.40.206 are permitted to resist wind and seismic loads. Walls resisting seismic loads shall be subject to the limitations in Section 1617.6.
Gypsum board materials 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.
Metal suspension systems for acoustical and lay-in panel ceilings shall conform with Section 803.9.
Gypsum Board Materials and Accessories
|Accessories for gypsum board||ASTM C 1047|
|Gypsum sheathing||ASTM C 79|
|Gypsum wallboard||ASTM C 36|
|Joint reinforcing tape and compound||ASTM C 474; C 475|
|Nails for gypsum boards||ASTM C 514, F 547, F 1667|
|Steel screws||ASTM C 954; C 1002|
|Steel studs, nonload bearing||ASTM C 645|
|Steel studs, load bearing||ASTM C 955|
|Water-resistant gypsum backing board||ASTM C 630|
|Exterior soffit board||ASTM C 931|
|Fiber-reinforced gypsum panels||ASTM C 1278|
|Gypsum backing board and gypsum shaftliner|
|ASTM C 442|
|Gypsum ceiling board||ASTM C 1395|
|Standard specification for gypsum board||ASTM C 1396|
|Predecorated gypsum board||ASTM C 960|
|Adhesives for fastening gypsum wallboard||ASTM C 557|
|Testing gypsum and gypsum products||ASTM C 22; C 472; C 473|
|Glass mat gypsum substrate||ASTM C 1177|
|Glass mat gypsum backing panel||ASTM C 1178|
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.
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.
Lath, Plastering Materials and Accessories
|Accessories for gypsum veneer base||ASTM C 1047|
|Exterior plaster bonding compounds||ASTM C 932|
|Gypsum base for veneer plasters||ASTM C 588|
|Gypsum casting and molding plaster||ASTM C 59|
|Gypsum Keene's cement||ASTM C 61|
|Gypsum lath||ASTM C 37|
|Gypsum plaster||ASTM C 28|
|Gypsum veneer plaster||ASTM C 587|
|Interior bonding compounds, gypsum||ASTM C 631|
|Lime plasters||ASTM C 5; C 206|
|Masonry cement||ASTM C 91|
|Metal lath||ASTM C 847|
| Sand||ASTM C 35; C 897|
| Perlite||ASTM C 35|
| Vermiculite||ASTM C 35|
|Plastic cement||ASTM C 1328|
|Blended cement||ASTM C 595|
|Portland cement||ASTM C 150|
|Steel studs and track||ASTM C 645; C 995|
|Steel screws||ASTM C 1002; C 954|
|Welded wire lath||ASTM C 933|
|Woven wire plaster base||ASTM C 1032|
Gypsum board 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, and Chapter 35.
Installation of Gypsum Construction
|Gypsum sheathing||ASTM C 1280|
|Gypsum veneer base||ASTM C 844|
|Gypsum board||GA-216; ASTM C 840|
|Interior bathing and furring||ASTM C 841|
|Steel framing for gypsum boards||ASTM C 754; C 1007|
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 C 1280.
Gypsum wallboard, gypsum lath or gypsum plaster shall not be installed until weather protection for the installation is provided.
Edges and ends of gypsum board shall occur on the framing members, except those edges and ends that are perpendicular to the framing members. Edges and ends of gypsum board shall be in moderate contact except in concealed spaces where fire-resistance-rated construction, shear resistance or diaphragm action is not required.
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.
Gypsum board 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. Where the gypsum board 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. On single-layer systems where joints occur over wood framing members.
3. Square edge or tongue-and-groove edge gypsum board (V-edge), gypsum backing board or gypsum sheathing.
4. On multilayer systems where the joints of adjacent layers are offset from one to another.
5. Assemblies tested without joint treatment.
Gypsum board shall be permitted to be used on wood joists to create a horizontal diaphragm ceiling in accordance with Table 2508.5.
The maximum allowable diaphragm proportions shall be 1 1 / 2 :1 between shear resisting elements. Rotation or cantilever conditions shall not be permitted.
Gypsum board 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.
All 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.
Fasteners used for the attachment of gypsum board 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 (o.c.) 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.
Gypsum board shall not be used in diaphragm ceilings to resist lateral forces imposed by masonry or concrete construction.
When gypsum board is used as a base for tile or wall panels for tubs, shower or water closet compartment walls, water-resistant gypsum backing board shall be used as a substrate. 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 C 840.
Water-resistant gypsum backing board shall not be used in the following locations:
1. Over a vapor retarder in shower or bathtub compartments.
2. Where there will be direct exposure to water or in areas subject to continuous high humidity.
3. On ceilings where frame spacing exceeds 12 inches (305 mm) o.c. for 1/2-inch-thick (12.7 mm) water-resistant gypsum backing board and more than 16 inches (406 mm) o.c. for 5/8-inch-thick (15.9 mm) water-resistant gypsum backing board.
Materials shall be stored in such a manner as to protect such materials from the weather.
Installation of these materials shall be in compliance with ASTM C 926 and ASTM C 1063.
Metal lath and lath attachments shall be of corrosion-resistant material.
Backing or a lath shall provide sufficient rigidity to permit plaster applications.
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.
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 weather-resistant 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. On horizontal supports of ceilings or roof soffits.
2. On interior walls.
Gypsum sheathing is permitted as a backing for metal or wire fabric lath and cement plaster on walls. A weather-resistant barrier shall be provided in accordance with Section 2510.6.
Wire backing is not required under expanded metal lath or paperbacked wire fabric lath.
Weather-resistant barriers shall be installed as required in Section 1404.2 and, where applied over wood-based sheathing, shall include a weather-resistant vapor-permeable barrier with a performance at least equivalent to two layers of Grade D paper.
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.
Plastering gypsum plaster or cement plaster shall not be 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.
Installation of Plaster Construction
|Gypsum plaster||ASTM C 842|
|Gypsum veneer plaster||ASTM C 843|
|Interior lathing and furring (gypsum plaster)||ASTM C 841|
|Lathing and furring (cement plaster)||ASTM C 1063|
|Portland cement plaster||ASTM C 926|
|Steel framing||ASTM C 754; C 1007|
Where installed, grounds shall ensure the minimum thickness of plaster as set forth in ASTM C 842 and ASTM C 926. Plaster thickness shall be measured from the face of lath and other bases.
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 C 842 or ASTM C 926. Should ceiling surfaces require more than the maximum thickness permitted in ASTM C 842 or ASTM C 926, metal lath or wire fabric lath shall be installed on such surfaces before plastering.
Plastering with cement plaster shall not be less than three coats where applied over metal lath or wire fabric lath and not less than two coats where applied over masonry, concrete or gypsum board backing as specified in Section 2510.5. 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 be only two coats, provided the total thickness is as set forth in ASTM C 926.
On wood framed 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 C 1063.
A minimum 0.019-inch (0.48 mm) (No. 26 galvanized sheet gage), corrosion-resistant weep screed with a minimum vertical attachment flange of 3 1 / 2 inches (89 mm) shall be provided at or below the foundation plate line on exterior stud walls in accordance with ASTM C 926. 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 weather-resistant barrier shall lap the attachment flange. The exterior lath shall cover and terminate on the attachment flange of the weep screed.
Only approved plasticity agents and approved amounts thereof shall be added to portland cement. 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 C 926.
Gypsum plaster shall not be used on exterior surfaces.
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.
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.
First and second coats of cement plaster shall be applied and moist cured as set forth in ASTM C 926 and Table 2512.6.
|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 not be 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.|
|b. ||Twenty-four-hour minimum interval between coats of interior cement plaster. For alternate method of application, see Section 2512.8.|
|c. ||Finish coat plaster is permitted to be applied to interior portland cement base coats after a 48-hour period.|
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.
The second coat is permitted to be applied as soon as the first coat has attained sufficiently rigidity to receive the second coat.
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.
Curing of the first coat is permitted to be omitted and the second coat shall be cured as set forth in ASTM C 926 and Table 2512.6.
Cement plaster finish coats shall be applied over base coats that have been in place for the time periods set forth in ASTM C 926. 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.
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.
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.
The bedding coat for interior or exterior surfaces shall be composed of one-part portland cement, one-part Type S lime 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).
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).
Masonry and concrete surfaces shall be prepared in accordance with the provisions of Section 2510.7.
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.