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.
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 1⁄4 inch (6.4 mm) in total thickness.
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.
|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
|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
|ASTM C 557|
|Testing gypsum and gypsum products||ASTM C 22; C 472;
|Glass mat gypsum substrate||ASTM C 1177|
|Glass mat gypsum backing panel||ASTM C 1178|
|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|
|ASTM C 35; C 897
ASTM C 35
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 955|
|Steel screws||ASTM C 1002;C 954|
|Welded wire lath||ASTM C 933|
|Woven wire plaster base||ASTM C 1032|
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.
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.
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.
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.
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.
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.
For SI: 1 inch = 25.4 mm, 1 plf = 14.6 N/m.
|MATERIAL||THICKNESS OF MATERIAL
|SPACING OF FRAMING
(plf of ceiling)
|MIMIMUM FASTENER SIZE|
|5d cooler or wallboard nail;
1⅝ -inch long; 0.086-inch shank;
15/64 - inch headc
|5d cooler or wallboard nail;
1⅝ -inch long; 0.086-inch shank;
15/64 - inch headc
- Values are not cumulative with other horizontal diaphragm values and are for short-term loading due to wind or seismic loading. Values shall be reduced 25 percent for normal loading.
- Values shall be reduced 50 percent in Seismic Categories D, E and F.
- 11/4 -inch, No. 6 Type S or W screws are permitted to be substituted for the listed nails.
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.
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.
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.
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.
Wire backing is not required under expanded metal lath or paperbacked wire fabric lath.
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.
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.
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 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.
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.
|COAT||MINIMUM PERIOD MOIST
|First||48 hoursa||48 hoursb|
|Second||48 hours||7 daysc|
- 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.
- Twenty-four-hour minimum interval between coats of interior cement plaster. For alternate method of application, see Section 2512.8.
- Finish coat plaster is permitted to be applied to interior portland cement base coats after a 48-hour period.
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.
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).