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Designation: C 840 02

Standard Specication forApplication and Finishing of Gypsum Board 1

This standard is issued under the xed designation C 840; the number immediately following the designation indicates the year of original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon ( e ) indicates an editorial change since the last revision or reapproval.

This standard has been approved for use by agencies of the Department of Defense.

1. Scope1.1 This specication covers the minimum requirements for

the methods of application and nishing of gypsum board,including related items and accessories.

1.2 Details of construction for a specic assembly toachieve the required re resistance shall be obtained fromreports of re-resistance tests, engineering evaluations, or

listings from recognized re testing laboratories.1.2.1 Where this specication is more stringent (size orthickness of framing: size and spacing of fasteners) than there-rated construction, this specication shall govern.

1.3 Where sound control is required for a gypsum boardassembly, details of construction shall be in accordance withreports of acoustical tests of assemblies that have met therequired acoustical values.

1.4 Unheated spaces above gypsum board ceilings shall beproperly ventilated (seeAppendix X2).

1.5 The various application systems are located in thefollowing sections:I Application of Single-Ply Gypsum Board to Wood Framing

Members8

II Application of Two-Ply Gypsum Board to Wood FramingMembers 9

III Application of Gypsum Board by Adhesive Nail-On toWood Framing Members

10

IV Semi-Solid Gypsum Board Partitions 11V Solid Gypsum Board Partitions 12VI Application of Gypsum Board with Adhesives to Interior

Masonry or Concrete Walls13

VII Application of Gypsum Board to Rigid Foam Insulation 14VIII Application of Gypsum Board to Steel Framing and Furring 15IX Arches and Bending Radii 16X Application of Gypsum Board to Receive Tile by

Adhesive Application17

XI Exterior Application of Gypsum Wallboard andExterior Gypsum Soffit Board

18

XII Floating Interior Angles 19XIII Control (Expansion) Joints 20XIV Foil-Backed Gypsum Board 21

The values stated in inch-pound units are to be regarded asthe standard. The SI (metric) values given in parentheses areapproximate and are provided for information purposes only.

1.6 The text of this specication references notes andfootnotes which provide explanatory material. These notes andfootnotes (excluding those in tables and gures) shall not beconsidered as requirements of the specication.

1.7 The following precautionary caveat pertains only toSections 6-23. This standard does not purport to address all of the safety concerns, if any, associated with its use. It is theresponsibility of the user of this standard to establish appro- priate safety and health practices and determine the applica-bility of regulatory limitations prior to use.

1.7.1 For specic precautionary statements, see 4.1.1, 4.1.2and 22.5.

2. Referenced Documents2.1 ASTM Standards:C 11 Terminology Relating to Gypsum and Related Build-

ing Materials and Systems 2

C 36/C 36M Specication for Gypsum Wallboard2

C 442/C 442M Specication for Gypsum Backing Board,Gypsum Coreboard, and Gypsum Shaftliner Board 2

C 475 Specication for Joint Compound and Joint Tape forFinishing Gypsum Board 2

C 514 Specication for Nails for the Application of Gyp-sum Board 2

C 557 Specication for Adhesives for Fastening GypsumWallboard to Wood Framing 3

C 630/C 630M Specication for Water-Resistant GypsumBacking Board 2

C 645 Specication for Nonstructural Steel Framing Mem-bers 2

C 754 Specication for Installation of Steel Framing Mem-bers to Receive Screw-Attached Gypsum Panel Products 2

C 931/C 931M Specication for Exterior Gypsum SoffitBoard 2

1 This specication is under the jurisdiction of ASTM Committee C11 onGypsum and Related Building Materials and Systems and is the direct responsibilityof Subcommittee C11.03 on Specications for the Application of Gypsum and OtherProducts in Assemblies.

Current edition approved Dec. 10, 2002. Published February 2003. Originallyapproved in 1979. Last previous edition approved in 2001 as C 84001.

2 Annual Book of ASTM Standards , Vol 04.01.3 Annual Book of ASTM Standards , Vol 15.06.

1

Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.

NOTICE: This standard has either been superceded and replaced by a new version or discontinued.Contact ASTM International (www.astm.org) for the latest information.

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C 954 Specication for Steel Drill Screws for the Applica-tion of Gypsum Panel Products or Metal Plaster Bases toSteel Studs from 0.033 in. (0.84 mm) to 0.112 in. (2.84mm) in Thickness 2

C 1002 Specication for Steel Self-Piercing TappingScrews for the Application of Gypsum Panel Products orMetal Plaster Bases to Wood Studs or Steel Studs 2

C 1007 Specication for the Installation of Load Bearing(Transverse and Axial) Steel Studs and Related Accesso-ries 2

C 1047 Specication for Accessories for Gypsum Wall-board and Gypsum Veneer Base 2

C 1395/C 1395M Specication for Gypsum Ceiling Board 2

2.2 U.S. Department of Commerce Publication:PS20 American Softwood Lumber Standard 4

2.3 ANSI Standard:ANSI A 136.1 Organic Adhesives for Installation of Ce-

ramic Tile, Type I and Type II 5

3. Terminology

3.1 Denitions Denitions shall be in accordance withTerminology C 11.3.2 Descriptions of Terms Specic to This Standard:3.2.1 all-purpose compound , na compound formulated

and manufactured to serve as a taping or nishing compound,or both.

3.2.2 critical lighting , na condition where interior sur-faces are ooded by natural or articial lighting at an obliqueangle.

3.2.3 decoration , npaint (including primers), texture,coatings, and coverings such as wallpaper and sheet plasticmaterials designed to conceal or protect the surface of thegypsum board (see Appendix X3).

3.2.4 dry type , na compound in powder form to be mixedwith water before use.

3.2.5 drying type , na compound that hardens by theevaporation of the vehicle used to make the paste.

3.2.6 drywall primer , na paint material specically for-mulated to ll the pores and minimize the suction differencebetween gypsum board surface paper and the compound usedon nished joints, angles, fastener heads and accessories andover skim coatings.

3.2.7 face panel , noutside ply of multiple layer gypsumboard assemblies.

3.2.8 nished wallboard , nwallboard that has had the joints taped, has had the joints, fastener heads, and anges of accessories concealed with joint compound, and has beensanded to prepare the surface to receive job applied decoration.

3.2.9 nishing , nthe preparation of gypsum board sur-faces to receive the eld application of decoration.

3.2.10 nishing compound (sometimes called topping compound) , na compound used for successive coats over thetaping or all-purpose compound that provides a smooth andlevel surface for the application of decoration.

3.2.11 nishing of accessories , nthe application of com-pound to anges of accessories to create a monolithic surface.

3.2.12 ange , nthat part of an accessory extending overthe face of the gypsum wallboard intended to become a part of the monolithic plane of the prepared surface.

3.2.13 framing member , nthat portion of the framing,furring, and blocking to which the gypsum board is attached.

3.2.14 harden , va condition reached when the compoundhas lost its plasticity to an arbitrary degree, measured inresistance to penetration or deformation.

3.2.15 joint photographing , na condition where the n-ished joint areas visible after nal decoration.

3.2.16 joint tape , na strip of material designed to beembedded in compound to reinforce joints, cracks, or othersmall openings in or between gypsum boards.

3.2.17 joint treatment , napplication of joint tape andcompound to the joint between gypsum boards.

3.2.18 laminating compound , na compound (abrasive)used to adhere gypsum board to gypsum board or othermonolithic materials.

3.2.19 parallel or vertical application , n gypsum boardapplied with the edges parallel to the framing member to whichit is attached.

3.2.20 perpendicular or horizontal application , ngypsumboard application with the edges applied at right angles to theframing member to which it is attached.

3.2.21 ready-mix type , na factory-prepared compoundready to be used without the addition of water.

3.2.22 required , adj pertaining to a mandatory obligationimposed by a force outside this standard, such as a buildingcode, project specication, contract, or purchase order.

3.2.23 setting type , na compound that hardens by achemical reaction and increases in straight through drying.

3.2.24 skim coat , na thin coat of skim coat compoundapplied over the nished wallboard surface.

3.2.25 skim coat compound , njoint compound, or a com-pound specically formulated and manufactured for use as askim coat.

3.2.26 specied , adj pertaining to a mandatory require-ment of this standard or a referenced requirement (see 3.2.20).

3.2.27 spotting fastener heads , nthe application of com-pound to cover the fastener head to create a monolithic surface.

3.2.28 taping compound (sometimes called embedding compound) , na compound used for embedding and bonding jointtape and for the rst coat over the heads of fasteners andanges of accessories.

3.2.29 taping of joints , nthe application of compound and

joint reinforcing tape to the joints between adjoining gypsumboards.

3.2.30 treated joint , na joint between gypsum boards thathas been covered with joint tape and joint compound asspecied in 22.3.2.

3.2.30.1 Discussion Strip moldings or similar devicesshall be permitted.

4. Environmental Conditions4.1 Application of Gypsum Board, Joint Treatment Materi-

als, and Adhesives Room temperature shall be maintained atnot less than 40F (4C) during application of gypsum board

4 Available from U.S. Government Printing Office, Washington, DC 20402.5 Available from American National Standards Institute, 11 West 42nd Street,

13th Floor, New York, NY 10036.

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except when adhesive is used for the attachment of gypsumboard. For the bonding of adhesive, joint treatment, texturing,and decoration, the room temperature shall be maintained atnot less than 50F (10C) for 48 h prior to application andcontinuously thereafter until completely dry.

4.1.1 When a temporary heat source is used, the temperatureshall not exceed 95F (35C) in any given room or area.

4.1.2 Adequate ventilation shall be maintained in the work-ing area during installation and curing period.

4.2 Gypsum board shall be protected from direct exposureto rain, snow, sunlight, or other excessive weather conditions.

NOTE 1Where manufacturers recommendations differ from theabove, follow their recommendations.

4.3 Ready-mixed joint compounds shall be protected fromfreezing, exposure to extreme heat, and direct sunlight.

5. Materials and Manufacture

5.1 Gypsum Boards A family of gypsum sheet products asdened in Terminology C 11.

5.1.1 Type X (Special Fire-Resistant) Gypsum Wallboard,Gypsum Backing Board, Water-Resistant Gypsum Backing Board, or Exterior Gypsum Sofft Board Gypsum board thatprovides a greater degree of re resistance than regular gypsumboard as dened in Specications C 36/C 36M, C 442/ C 442M, C 630 and C 931.

5.1.2 Foil-Backed Gypsum Wallboard or Gypsum Backing Board Regular or Type X gypsum board with foil laminatedto the back surface. The foil is a vapor retarder.

5.1.3 Predecorated Gypsum Board Gypsum board with adecorative wall covering or coating applied in-plant by thegypsum board manufacturer.

5.2 Gypsum Wallboard See SpecicationC 36/C 36M.5.3 Gypsum Backing Board and Coreboard See Speci-

cation C 442/C 442M.5.4 Water-Resistant Gypsum Backing Board See Speci-

cation C 630.5.5 Exterior Gypsum Sofft Board See Specication C 931.5.6 Gypsum Ceiling Board See Specication C 1395/

C 1395M.5.7 Finishing Materials :5.7.1 Compounds Taping compound, nishing compound,

and all-purpose compound shall meet the requirements of Specication C 475.

5.7.2 Mix compounds in accordance with the manufactur-ers directions.

5.7.3 Joint Tape See Specication C 475.5.8 Fasteners :5.8.1 Nails See Specication C 514.5.8.2 Screws :5.8.2.1 See Specication C 1002 for screws for fastening

gypsum board to wood members, steel members less than 0.03in thickness, and to gypsum board.

5.8.2.2 See Specication C 754 and Specication C 954 forscrews for fastening gypsum board to steel members from0.033 to 0.112 in. in thickness.

5.8.3 Staples No. 16 USS gage attened galvanized wirestaples with 7 16 -in. (11.1-mm) wide crown outside measure-ment. Length of legs according to the following tables. Legsshall have divergent points.

NOTE 2Use only for the base ply of two-ply gypsum board applica-tion.

Length of Legs, Thickness of Gypsum Boar d,in. mm in. mm

7 8 22.2 1 4 6.41 25.4 3 8 9.51 1 8 28.6 1 2 12.71 1 4 31.8 5 8 15.9

5.9 Adhesives :5.9.1 Fastening Gypsum Board to Wood Framing See

Specication C 557.5.9.2 Fastening Gypsum Board to Steel Framing As

specied by the manufacturer.5.9.3 Laminating Gypsum Board to Gypsum Board

Laminating compounds, taping compound, or adhesive shall beas specied by the manufacturer.

NOTE 3Adhesives for the installation of ceramic tile, see AppendixX4.

5.10 Framing Members :5.10.1 Wood framing members shall conform to PS20,

American Softwood Lumber Standards. The surface to whichabutting edges or ends are attached shall be not less than 1 1 2in. (38.1 mm) wide. For internal corners or angles, the bearingsurface shall not be less than 3 4 in. (19.1 mm).

5.10.2 Steel Studs, Furring Channels, and Runners, Non-Load BearingSee Specication C 645.

5.10.3 Gypsum Studs SpecicationC 36/C 36M orC 442/ C 442M, not less than 1 in. (25.4 mm) thick by 6 in. (152 mm)wide. Studs shall be either solid or laminated.

5.11 Accessories See Specication C 1047.5.12 Water Water shall be clean, fresh, and potable (suit-

able for domestic consumption).5.13 Face Panels Face panels shall be 1 2 in. (12.7 mm),

5 8 in. (15.9 mm), or multiple laminations of regular or Type Xgypsum board.

5.14 Core Board Core board shall be 3 4 in. (19.1 mm) or1 in. (25.4 mm) either single thickness or multiple layers to therequired thickness.

6. Substrate, Surface Preparation6.1 The attachment surface of any framing member shall not

vary more than 1 8 in. (3.2 mm) from the plane of the faces of adjacent framing members.

6.2 Wood framing shall be as straight and true as possible.Wood framing shall be securely attached following acceptableengineering practices and as required for the intended design.

NOTE 4For installation of wood framing, see Appendix X5.

6.3 Metal framing members shall be of the proper size anddesign for their intended use and shall be installed in accor-dance with Specications C 754 or C 1007 as required.

6.4 Masonry or concrete walls shall be dry, free of dust, oil,or form release agents, protrusions or voids, or foreign matterthat inhibit bond for adhesively applied gypsum board.

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6.5 All framing members and substrate shall be installed sothat after the gypsum board has been applied, the nishedsurface will be in an even plane.

6.6 Gypsum board shall be kept free of any dirt, oil, or otherforeign matter that cause a lack of bond. Foreign matter shallbe removed.

6.7 All dents or gouges on the face of the gypsum board

shall be brought up to a smooth level plane with the surface of the board.

6.8 Mechanical fasteners shall be set below the plane of thesurface of the board.

6.9 All joints shall be true and even.6.10 All gypsum board shall be tight against the framing

member or substrate.6.11 Deection at design load of horizontal (ceiling) fram-

ing members supporting gypsum board shall be not more thanL/240 of the span.

7. Application of Gypsum Board

7.1 General :7.1.1 Method of Cutting and Installation Gypsum board

shall be cut by scoring and breaking or by sawing, workingfrom the face side. When cutting by scoring, the face papershall be cut with a sharp knife or other suitable tool. Gypsumboard shall be broken by snapping the gypsum board in thereverse direction, or cut the back paper with a knife or suitabletool.

7.1.2 Cut edges and ends of the gypsum board shall besmoothed to obtain neat joints when installed. Holes for pipes,xtures, or other small openings shall be scored on the back and the face in outline before removal or cut out with a saw orspecial tool designed for this purpose. Where gypsum boardmeets projecting surfaces, it shall be scribed and cut neatly.

7.1.3 When gypsum board is to be applied to both ceilingand walls, the gypsum board shall be applied rst to the ceilingand then to the walls.

7.1.4 Where used at edges or ends, fasteners shall be spacednot more than 1 in. (25 mm) from edges and not less than 3 8 in.(9.5 mm) from edges and ends of gypsum board (except whereoating angles are used). Perimeter fastening into the partitionplate or sole at the top and bottom shall not be required exceptwhere the re ratings, structural performance, or other specialconditions require such fastening. While driving the fasteners,the gypsum board shall be held in rm contact with theunderlying support. Application of fasteners shall proceed fromthe center or eld of the gypsum board to the ends and edges.

7.1.5 Nails shall be driven with the heads slightly below thesurface of the gypsum board, avoiding damage to the face andcore of the board, such as breaking the paper or fracturing thecore.

7.1.6 Screws shall be driven to provide screwhead penetra-tion just below the gypsum board surface without breaking thesurface paper of the gypsum board or stripping the framingmember around the screw shank.

7.1.7 Staples shall be driven with the crown parallel to theframing members, in such a manner that the crown bearstightly against the gypsum board without cutting into the facepaper.

7.1.7.1 Staple attachment shall be restricted to the base pliesonly of gypsum board in a multi-ply system.

7.1.8 The gypsum board shall be kept tight against theframing.

7.1.9 The external corners shall be protected with a metalcorner bead or other suitable type of corner protection that shallbe attached to supporting construction with fasteners or a

crimping tool nominally 6 in. (152 mm) on centers (see Section3 and Fig. 1).

7.2 Gypsum board shall not be used where it will beexposed to temperatures more than 125F (52C) for extendedperiods of time.

7.3 Gypsum board joints shall be located so that no jointwill align with the edge of an opening unless control joints areto be installed at these locations.

7.4 Joints shall be staggered, and joints on opposite sides of a partition shall not occur on the same stud.

7.5 Gypsum board used in building construction shall be notless than 8 in. (203 mm) from the nished grade in fullyweather and water protected siding systems, and not less than

12 in. (305 mm) from the ground within properly drained andventilated crawl spaces. Where ground moisture or humidity isextreme and/or continuous, the crawl space ground surfaceshall be covered with a vapor barrier.

8. System I: Application of Single-Ply Gypsum Board toWood Framing Members

8.1 The maximum spacing for framing members for single-ply gypsum board assembly shall not exceed those shown inTable 1.

8.1.1 The 1 4 -in. (6.4-mm) thick gypsum board shall not beused in single-ply applications on either walls or ceilings.

8.2 In single-ply installation, all ends and edges of gypsumboard shall occur over framing members or other solid backingexcept where treated joints occur at right angles to framing orfurring members.

8.3 End joints shall be staggered and joints on oppositesides of a partition shall be arranged to occur on alternateframing members.

8.4 Length of nails shall be as shown in Table 2.8.4.1 Where a specic degree of re resistance is required

for gypsum board assemblies, nails of the same length, shank diameter, and head bearing area, as those described in the retest report, shall be used.

8.4.2 Single Nailing Nails shall be spaced a maximum of 7 in. (177.8 mm) on centers on ceilings, and a maximum of 8in. (203.2 mm) on centers on walls (see Fig. 2).

8.4.3 Double Nailing Nails shall be spaced as shown inFig. 3 and driven as follows:

8.4.3.1 Starting at the center of the gypsum board, nailsshall be applied as shown in solid dots in row 1, then rows 2and 2A, 3 and 3A, 4 and 4A, always nailing from center toedges of sheet. The gypsum board shall be kept tight againstthe framing.

8.4.3.2 Second nails, shown by circles, shall be applied inthe same manner as the rst nails, also starting at row 1.

8.4.3.3 As an alternative procedure, the second nail shall beapplied immediately after all nails in each row are driven inaccordance with 8.4.3.2.

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8.4.3.4 Single nailing shall be used on the perimeter of thegypsum board, unless otherwise specied.

8.4.3.5 Nails shall be inspected for compliance with 7.1.5after the second nails have been set.

8.5 Spacing of Screws Screws shall be spaced not morethan 12 in. (304.8 mm) on centers along framing members forceilings and 16 in. (406.4 mm) on centers for walls where theframing members are 16 in. on centers. Screws shall be spacednot more than 12 in. on centers along framing members for

ceilings and walls where the framing members are 24 in. (609.6mm) on centers.

8.5.1 When using a combination of fasteners consisting of nails along the perimeter and screws in the eld of the gypsumboard, the spacing between a nail and an adjacent screw shallbe not more than the spacing specied for screws in 8.5.

9. System II: Application of Two-Ply Gypsum Board toWood Framing Members

9.1 The maximum spacings for framing members for two-ply gypsum board assemblies shall not exceed those shown inTables 3 and 4.

NOTE 1All dimensions are in inch-pound units.FIG. 1 Accessories

TABLE 1 Maximum Framing Spacing for Single-PlyConstruction A

Single-Ply Gypsum BoardThickness, in. (mm) Application

B Maximum Framing

Members On CentersSpacing, in. (mm)

Ceilings: 3 8 (9.5) C perpendicular 16 (406.4)1 2 (12.7) parallel 16 (406.4)5 8 (15.9) parallel 16 (406.4)1 2 (12.7) perpendicular 24 (609.6)5 8 (15.9) perpendicular 24 (609.6)

Sidewalls: 3 8 (9.5) perpendicular or parallel 16 (406.4)1 2 (12.7) perpendicular 24 (609.6)

or or5 8 (15.9) parallel

A Gypsum board ceilings to receive hand or spray-applied water-based texturematerial shall be applied perpendicular to framing and shall be either (i) 1 2 in. (12.7mm) Gypsum Ceiling Board (see Specication C 1395/C 1395M) applied to

framing not more than 24 in. (610 mm) on center, or (ii) other gypsum boards notless than 1 2 in. (12.7 mm) thick for 16 in. (406 mm) on center framing and not lessthan 5 8 in. (15.9 mm) thick for 24 in. (610 mm) on center framing.

B Nails for gypsum board applied over existing surfaces shall have a at headand diamond point, and shall penetrate not less than 7 8 in. (22.2 mm), nor morethan 1 1 4 in. (31.8 mm) into the framing member.

C 3 8 -in. (9.5-mm) single-ply gypsum board shall not be applied to ceilings wherethe gypsum board supports insulation.

TABLE 2 Nail Lengths for Single-Ply Gypsum Board Assembly

Gypsum Board Thickness,in. (mm) Minimum Nail Length, in. (mm)

Application of gypsum boardover existing surfaces:

Flat or concave head, diamond or needle pointof such length as to provide not less than 7 8

in. (22.2 mm) nor more than 1 1 4 in. (31.8mm) penetration into the following framing members:

3 8 (9.5) 1 1 4 (31.8)1 2 (12.7) 1 3 8 (34.9)5 8 (15.9) 1 1 2 (38.1)

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NOTE 5See Section 2 for adhesive application method.

9.2 The base ply of gypsum board shall be applied withnails, screws, or staples of the size and type required inSections 5, 7, and 8. Fastener lengths for 1 4 -in. (6.4-mm) thick gypsum board shall be of sufficient length to penetrate woodframing members not less than 7 8 in. (22.2 mm) for nails or 5 8in. (15.9 mm) for screws.

9.2.1 Base layer end joints parallel to and on the same sideof framing members shall be staggered between alternatecourses of gypsum board and from base layer joints on theopposite side of the framing members.

9.2.2 Base layer edge joints parallel to framing membersshall be staggered on opposite sides of the framing members.

9.3 When adhesive is not used between the plies, the twoplies of gypsum board shall be applied as indicated in Tables 3and 5. The face ply shall be applied with the number of nailsor screws required for normal single-ply application. Nailsused for the face ply shall be long enough to penetrate not lessthan 7 8 in. (22.2 mm) into wood framing members. Screwlength shall be long enough to penetrate not less than 5 8 in.(15.9 mm) into wood framing. Face ply joints that are parallelto framing shall fall over framing members and be offset fromthe base ply joints when two plies of gypsum board areparallel.

9.4 When an adhesive is used between the plies, the twoplies shall be applied as indicated in Table 4. If the two pliesare applied in parallel direction, the joints of the face ply shallbe offset from the base ply.

9.4.1 Joints in the face ply need not occur over the framingmembers. The adhesive used between the two plies of gypsumboard shall be uniformly applied over the back surface of theface ply of the gypsum board before it is erected or to the facesurface of the base ply. The face ply of gypsum board shall beplaced in position and fastened with nails or screws to holdgypsum board in place until the adhesive develops a bond.

FIG. 2 Single Nailing

FIG. 3 Double Nailing

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9.4.2 Permanent fasteners shall be used around the perim-eter 12 in. (304.8 mm) on centers and 16 in. (406.4 mm) oncenters along framing members for the face ply of gypsumboard applied on ceilings.

9.4.3 In place of nails and screws, the face ply of gypsumboard applied on walls shall be held in position by shoring withprops and headers, or other temporary support to ensure apressure for bonding. Permanent fasteners shall be used on top

and bottom of wall not more than 16 in. (406 mm) on centers.Nails or screws used to hold the gypsum board face ply shallbe left in place and nished in the same manner as forsingle-ply gypsum board application (see Section 10).

9.5 Base layer joints and fasteners shall not be required tobe taped or nished. Face layer joints and fasteners inmulti-layer systems shall not be required to be nished unlessrequired for appearance or decoration or as required for reresistance.

10. System III: Application of Gypsum Board byAdhesive Nail-on to Wood Framing Members

10.1 Except as herein modied, application shall be inconformance with Section 8.

10.2 Surfaces of gypsum board and framing to receive theadhesive shall be free of dust, dirt, grease, or any other foreignmatter that cause bond loss. Foreign matter shall be removed.

10.3 A bead of adhesive 3 8 in. (9.5 mm) in diameter shall beapplied to the face of all wood framing members, except plates,that support the gypsum board. The adhesive shall be spread toan average width of 3 4 in. (19 mm) and an average thickness of 1 16 in. (1.6 mm). See Fig. 4 for application patterns.

TABLE 3 Maximum Framing Spacing for Two-Ply Assemblies, Fasteners Only, No Adhesive Between Plies A

Gypsum Board Thickness,in. (mm) Application Direction

Maximum On CentersSpacing of Framing,

in. (mm)Base Ply Face Ply Base Ply Face Ply

Ceilings: 1 4 (6.4) 3 8 (9.5) or 1 2 (12.7) perpendicular perpendicular 16 (406.6)3 8 (9.5) 3 8 (9.5) or 1 2 (12.7) perpendicular perpendicular 16 (406.6)1 2 (12.7) 3 8 (9.5) or 1 2 (12.7) parallel perpendicular 16 (406.6)1 2 (12.7) 1 2 (12.7) or 5 8 (15.9) perpendicular perpendicular 24 (609.6)5 8 (15.9) B 1 2 (12.7) or 5 8 (15.9) perpendicular perpendicular 24 (609.6)

Walls: 1 4 (6.4) 1 4 (6.4) or 3 8 (9.5) or 1 2 (12.7) perpendicular or parallel perpendicular or parallel 16 (406.6)3 8 (9.5) 1 4 (6.4) or 3 8 (9.5) perpendicular or parallel perpendicular or parallel 16 (406.6)1 2 (12.7) 1 4 (6.4) or 3 8 (9.5) or 1 2 (12.7) perpendicular or parallel perpendicular or parallel 24 (609.6)5 8 (15.9) 1 4 (6.4) or 3 8 (9.5) or 1 2 (12.7) or 5 8 (15.9) perpendicular or parallel perpendicular or parallel 24 (609.6)A Gypsum board ceilings to receive hand or spray-applied water-based texture material shall be applied perpendicular to framing and shall be either (i) 1 2 in. (12.7 mm)

Gypsum Ceiling Board (see Specication C 1395/C 1395M) applied to framing not more than 24 in. (610 mm) on center, or (ii) other gypsum boards not less than 1 2 in.(12.7 mm) thick for 16 in. (406 mm) on center framing and not less than 5 8 in. (15.9 mm) thick for 24 in. (610 mm) on center framing.

B 5 8 -in. (15.9-mm) board shall be permitted to be applied perpendicularly at 16 in. (406 mm) spacing.

TABLE 4 Maximum Framing Spacing for Two-Ply Assembly Fasteners with Adhesive Between Plies A

Gypsum Board Thickness,in. (mm) Application Direction

Maximum OnCenters Spacing ofFraming, in. (mm)Base Ply Face Ply Base Ply Face Ply

Ceilings: 1 4 (6.4) 1 4 (6.4) or 3 8 (9.5) or 1 2 (12.7) perpendicular perpendicular 16 (406.6)3 8 (9.5) 1 4 (6.4) or 3 8 (9.5) or 1 2 (12.7) perpendicular perpendicular 16 (406.6)1 2 (12.7) 1 4 (6.4) or 3 8 (9.5) or 1 2 (12.7) parallel perpendicular 16 (406.6)1 2 (12.7) 1 4 (6.4) or 1 2 (12.7) or 5 8 (15.9) perpendicular perpendicular 24 (609.6)5 8 (15.9) 1 4 (6.4) or 1 2 (12.7) or 5 8 (15.9) perpendicular perpendicular 24 (609.6)

Walls: 1 4 (6.4) 1 4 (6.4) or 3 8 (9.5) or 1 2 (12.7) perpendicular or parallel perpendicular or parallel 16 (406.6)3 8 (9.5) 1 4 (6.4) or 3 8 (9.5) perpendicular or parallel perpendicular or parallel 16 (406.6)1 2 (12.7) 1 4 (6.4) or 3 8 (9.5) or 1 2 (12.7) perpendicular or parallel perpendicular or parallel 24 (609.6)5 8 (15.9) 1 4 (6.4) or 1 2 (12.7) or 5 8 (15.9) perpendicular or parallel perpendicular or parallel 24 (609.6)A Adhesive between plies shall be dried or cured prior to joint treatment application.

TABLE 5 Fastener Spacing, Base-Ply of Two-Ply System, in.(mm) On Centers

Nails Screws StaplesNo adhesive between plies 24 (609.6) 24 (609.6) 16 (406.4)

Adhesive between plies See 9.3 See 9.3 7 (177.8)

FIG. 4 Adhesive Application Patterns

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10.3.1 Where a joining of two adjacent pieces of gypsumboard occurs on a framing member, two parallel beads of adhesive shall be applied, one near each edge of the framingmember.

10.4 Adhesive shall be applied to no greater area than canbe covered with gypsum board within the open time.

NOTE 6Open time is the time period available for working withcertain adhesives before they set in accordance with the adhesivemanufacturers specication.

10.5 Fastener Spacing :10.5.1 If the properties of the adhesive ensure bridging

between the gypsum board and the wood framing, nailing shallnot be required in the eld of the board for walls. In such cases,perimeter nailing, 16 in. (406.4 mm) on centers, shall berequired.

10.5.2 When the properties of the adhesive are such thatthere is no positive bridging between the gypsum board and thewood framing, either temporary eld nailing or temporarybracing shall be used to ensure contact between the gypsumboard, the adhesive, and the wood framing, until the adhesivedevelops a bond.

10.5.3 Unless specied otherwise by the adhesive manufac-turer, fastener spacing shall be in accordance with Table 6.

11. System IV: Semi-Solid Gypsum Board Partitions11.1 Installation :11.1.1 Runners or studs shall be installed where required to

provide support at exterior walls, partition junctions, terminals,external corners, door frames and at other locations.

11.1.2 The gypsum board face panels and studs shall bepositioned vertically.

11.1.3 The gypsum studs shall be laminated to face panelsnot more than 24 in. (609.6 mm) on centers and located at face

panel vertical joints and at vertical centerline of panel.11.1.4 Gypsum studs shall be laminated to face panels prior

to erection or as erection of partition proceeds. A starter facepanel shall be erected vertically at an intersecting wall. Thestarter panel shall be plumb and secured to the oor, theceiling, and the vertical runners.

11.1.5 The next face panel adjacent to the starter panel shallbe erected by butting its edge and end rmly to the starter paneland the ceiling. Erection of the face panels shall continue bylaminating exposed faces of gypsum studs as work progresses.

11.1.6 Openings in partitions for doors and electrical outletsshall be carefully and accurately marked and cut.

11.1.7 Laminating compounds or adhesives shall be of a

consistency and volume that will cover approximately three-fourths of the stud surface after lamination.11.1.8 Type G screws shall be used to ensure a continuous

bond between face panels and studs, and shall be spaced notmore than 36 in. (914 mm) on centers.

11.1.9 Openings or changes in direction of partitions shallbe reinforced with additional studs laminated in place at thefollowing locations:

11.1.9.1 External Corners Between the face panels in thecorner opposite vertical runners.

11.1.9.2 Abutting Walls Between the face panels of apartition to reinforce junction of an abutting wall.

11.1.9.3 Door Openings Locate a vertical stud within 3in. (76.2 mm) of door frame for reinforcement, and place a studhorizontally over the door header.

12. System V: Solid Gypsum Board Partitions

12.1 Non-load bearing solid partition consisting of gypsumcoreboard faced on each side with gypsum board panels.

12.2 Installation :12.2.1 Floor and ceiling runners shall be installed according

to the layout and shall be secured not more than 24 in. (610mm) on centers. Vertical runners shall be installed wherespecied in 11.1.1.

12.2.2 For partitions located parallel to and between ceiling

members, steel or wood blocking not more than 24 in. (609.6mm) on centers shall be provided to fasten ceiling runners priorto erection of ceiling.

12.2.3 Face panels shall be attached to runners at not morethan 24 in. (609.6 mm) on centers.

12.2.4 Coreboard shall be installed prior to the installationof the face panel. Coreboard shall be attached not more than 24in. (610 mm) on centers to the steel angles when steel anglesare used as runners. When steel channels are used as runners tosecure coreboard, attachment shall not be required.

NOTE 7Combinations of wood and steel channels or angles will varythe installation procedure.

12.2.5 The adhesive shall be applied to the back surface of the face panels or the face of the coreboard as described fortwo-ply gypsum board construction (see Section 9).

12.2.6 The face panels shall be laminated to the core withsufficient pressure to ensure bonding. The joints of the facepanels and core shall be staggered. To ensure the bond betweenface panels and core, fasteners shall be permitted.

13. System VI: Application of Gypsum Board withAdhesive to Interior Masonry or Concrete Walls

13.1 When applying gypsum board to monolithic concrete,brick, or concrete block, the adhesive shall be applied directlyto the back of the gypsum board or on the wall in continuous

beads not more than 12 in. (304.8 mm) on centers or daubsspaced not more than 12 in. (304.8 mm) on centers each way.13.1.1 Beads shall be not less than 3 8 in. (9.6 mm) in

diameter to provide a continuous bond between the gypsumboard and the wall surface.

TABLE 6 Fastener Spacing with Adhesive or Mastic Application and Supplemental Fastening

Framing MemberSpacing, in. (mm)

On Centers

Ceilings, in. Partitions Load Bearing,in.Partitions Nonload

Bearing, in.Nail Screw Nail Screw Nail Screw

16 (406.4) 16 16 16 24 24 2424 (609.6) 12 16 12 16 16 24

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NOTE 10This will necessitate furring out from the framing members

the thickness of the gypsum board to be used ( 1 2 or 5 8 in. (12.7 or 15.9mm)) less the thickness of the lip, on each wall abutting a tub receptor orsubpan.

17.2 Blocking or Backing :17.2.1 Where framing is spaced more than 16 in. (406 mm)

o.c., blocking or backing shall be provided 3 4 1 1 4 in. (2030mm) above the top of the tub or receptor and at gypsum boardhorizontal joints in the area to receive tile.

17.2.2 Interior angles shall be framed or blocked to providesolid backing for interior corners.

17.2.3 Blocking, headers, or supports shall be provided tosupport the tub and other plumbing xtures and to receive soapdishes, grab bars, towel racks, and similar items.

17.3 General :17.3.1 Water-resistant gypsum backing board shall be used

as a base for adhesive application of ceramic or plastic wall tilein wet areas such as tub and shower enclosures. Either regulargypsum board or water-resistant gypsum backing board shallbe used as a base for tile in other areas. Water-resistant gypsumbacking board and regular gypsum board shall not be used in

extremely critical areas such as saunas, steam rooms, or gangshower rooms. Foil-backed gypsum board shall not be used asa base for tub or shower enclosures. Water-resistant gypsumboard used as a base for tile or wall panels in tub and showerenclosures shall not be applied directly over a vapor retarder.

17.3.1.1 Gypsum board shall not be used where there willbe direct exposure to water or continuous high humidityconditions such as are found in saunas, steam rooms, gangshower rooms, or indoor pools.

17.3.1.2 Foil-backed gypsum board shall not be used as abase for tub or shower enclosures.

17.3.1.3 Water-resistant gypsum backing board used as abase for tile or wall panels in tub and shower enclosures shallnot be applied directly over a vapor retarder.

17.3.1.4 Ceiling framing spacing for water-resistant gypsumbacking board 1 2 in. (12.7 mm) thick applied to ceilings shallbe not more than 12 in. (305 mm) on centers.

17.3.1.5 Ceiling framing spacing for water-resistant gypsumbacking board 5 8 in. (15.9 mm) thick applied to ceilings shallbe not more than 16 in. (406 mm) on centers.

NOTE 11Asphalt-impregnated felt is not considered a vapor retarder.

17.3.2 All multiple plies of gypsum board in wet areas shallbe attached with mechanical fasteners.

FIG. 5 Application of Gypsum Board at Bathtub Where WR BoardWill Receive Ceramic Tile or Other Protective Covering

FIG. 6 Adhesive Application of Gypsum Board at Shower WhereWR Board Will Receive Ceramic Tile or Other Protective

Covering

FIG. 7 Adhesive Application of Tile Over Gypsum Board

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17.3.3 Waterproof receptors, pans, or sub-pans shall have anupstanding lip or ange that shall be a minimum of 1 in. (25.4mm) higher than the water dam or threshold contained in theentry way to the shower.

17.4 Installation :17.4.1 Water-resistant gypsum backing board shall be ap-

plied with the factory edge spaced not less than 1 4 in. (6.4 mm)

above the lip of the receptor, tub, or sub-pan. Shower pans,receptors, or tubs shall be installed prior to the erection of thewater-resistant gypsum backing board.

17.4.2 Water-resistant gypsum backing board shall be at-tached by nails or screws spaced not more than 8 in. (203.2mm) on centers. When ceramic tile more than 3 8 in. (9.5 mm)thick is to be applied, the nail or screw spacing shall be notmore than 4 in. (101.6 mm) on centers.

17.4.3 Where treatment of water-resistant gypsum backingboard joints under tile in wet areas (tub and shower enclosures)is required, the compound and application thereof, shall be asrequired by the joint compound manufacturer for this specicuse, or shall be protected from penetration of moisture or water

(see X4.2).17.4.4 All cut edges and openings around pipes and xturesshall be caulked ush with water-resistant exible sealant.

17.4.5 Certain re or sound-rated gypsum board assembliesrequire the installation of an additional layer of water-resistantgypsum backing board (see Fig. 7). A 1 4 in. (6.4 mm) clearanceshall be maintained between the wallboard and tub rim, orshower base, as shown in Figs. 6 and 7.

NOTE 12For installation of ceramic tile to gypsum boards, see X4.3.

18. System XI: Exterior Application of GypsumWallboard and Exterior Gypsum Soffit Board

18.1 Where gypsum wallboard or exterior gypsum soffit

board is used for ceilings of carports, open walkways, porches,and soffits of eaves that are horizontal or inclined downwardaway from the building, the gypsum board shall be either 1 2 or5 8 in. (12.7 or 15.9 mm) in thickness. Framing shall be notmore than 16 in. (406 mm) on centers for 1 2 -in. (12.7-mm)thick gypsum board and not more than 24 in. (610 mm) oncenters for 5 8 -in. (15.9-mm) thick gypsum board. The gypsumboard shall be installed perpendicularly in accordance with theforegoing specications except as herein modied.

18.2 Suitable facia and molding shall be provided aroundthe perimeter to protect the gypsum wallboard and exteriorgypsum soffit board from direct exposure to water. Unlessprotected by metal or other water stops, the edges of the

gypsum wallboard and exterior gypsum soffit board shall beplaced not less than 1 4 in. (6.4 mm) away from abuttingvertical surfaces. (See Figs. 8-10.) Joints and fastener headsshall be treated as specied in X3.6.

18.3 Exposed surface of gypsum board and exterior gypsumsoffit board shall be treated as specied in X3.6.

18.4 Adequate ventilation shall be provided for the spaceimmediately above installations (see Appendix X2).

19. System XII: Floating Interior Angles19.1 Gypsum board shall be applied to ceiling rst. (See

Figs. 11-13.)

19.1.1 The oating angle method of application minimizesthe possibility of fastener popping in areas adjacent to the walland ceiling intersections for single-ply or two-ply applicationsof gypsum board to wood framing.

19.2 Ceilings The rst fastener into each ceiling framingmember framed perpendicular to the intersection shall belocated 7 in. (117.8 mm) out from the wall intersection forsingle nailing, and 11 to 12 in. (279.4 to 304.8 mm) for doublenailing, or screw application.

19.3 Walls Gypsum board shall be applied on walls so asto provide support for the oated edges of the ceiling gypsumboard. The top fastener into each vertical framing member shallbe located 8 in. (203.2 mm) down from the ceiling intersectionfor single nailing, and 11 to 12 in. (279.4 to 304.8 mm) fordouble nailing, or screw application. (See Figs. 11 and 12.) Atwall vertical angles, the over-lapping board shall be applied soas to bring the back of the underlying board into rm contact

with the face of the framing member behind it. Fasteners shallbe omitted from the underlying board at the intersection. (SeeFig. 13.)

20. System XIII: Control (Expansion) Joints20.1 Control (expansion) joints shall be installed in ceilings

exceeding 2500 ft 2 (232 m 2 ) in area and in partition, wall andwall furring runs exceeding 30 ft (9.1 m). The distance shallnot be more than 50 ft (15.2 m) between ceiling control(expansion) joints in either direction. A control (expansion) joint shall be installed where ceiling framing or furring changesdirection. The distance between control (expansion) joints in

FIG. 8 Frame Wall

FIG. 9 Masonry Wall

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of 3 1 2 in. (89 mm) beyond both sides of the center of the jointtape. The compound shall be drawn down to a level plane.After the compound has dried, the surface shall be sanded (see22.5) or wiped with a dampened sponge to eliminate high spotsand excessive compound.

22.4.1.1 Coats of non-setting type compounds shall bethoroughly dry before sanding or the application of additional

coats.22.4.1.2 Additional coats of compounds shall be applied

over setting-type compound either after it has set or, after it hasset and dried.

22.4.2 Additional coats of nishing compound shall beapplied with tools that will feather the material not less than 6in. (152 mm) beyond both sides of the center of the joint tape.The compound shall be drawn down to a level plane, leaving amonolithic surface.

NOTE 13A smooth surface is achieved by lightly sanding or wipingthe joint compound with a dampened sponge. Do not raise the nap of thepaper of the gypsum board (see 22.5). See Appendix X3.

22.4.3 Fastener heads shall be covered (spotted) with suc-cessive coats of joint compound. The rst coat shall be tapingor all-purpose compound; the additional coats shall be nishingor all-purpose compound.

22.4.4 All cut-outs shall be back lled with the compoundused for taping and nishing so there is no opening larger than1 4 in. (6 mm) between the gypsum board and the penetratingelement.

22.4.5 Accessories shall be nished with successive coats of joint compound. This surface, when completed, shall be ushwith the surface of the gypsum board. The rst coat over theanges shall be taping or all-purpose compound; the additionalcoats shall be nishing or all-purpose compound.

22.4.6 The skim coat of joint compound or a materialmanufactured especially for this purpose shall be applied to theentire surface where Level 5 is required.

22.4.7 All tools and containers shall be kept clean and freefrom foreign materials.

22.4.8 Only potable water shall be used for mixing powdercompounds or to thin premixed materials.

22.5 Approved protective respirators shall be worn whenmixing dry compound or sanding.

22.6 Levels of Finish :

NOTE 14The required level or extent of nishing of gypsum wall-board joints, fastener heads and overall surface can vary with the locationin a structure and the intended type of decoration. This section describes

various levels of nishing, that is, number of applications of jointcompound, sanding or other nishing techniques; the recommendations of manufacturers may vary from what is specied herein and as such are notpart of these specications. The relationship of levels of nishing withlocation and intended decoration is described in Appendix X8.

22.6.1 Level 0 :22.6.1.1 No taping, nishing or corner beads are required.22.6.2 Level 1 :22.6.2.1 All joints and interior angles shall have tape

embedded in joint compound. Surface shall be free of excess joint compound. Tool marks and ridges shall be acceptable.

22.6.3 Level 2 :

22.6.3.1 All joints and interior angles shall have tapeembedded in joint compound and shall be immediately wipedwith a joint knife or trowel leaving a thin coating of jointcompound over all joints and interior angles. Fastener headsand accessories shall be covered with a coat of joint compound.Surface shall be free of excess joint compound. Tool marks andridges are acceptable.

22.6.3.2 Joint compound applied over the body of the tapeat the time of tape embedment shall be considered a separatecoat of joint compound and shall satisfy the conditions of thislevel.

22.6.4 Level 3 :22.6.4.1 All joints and interior angles shall have tape

embedded in joint compound and shall be immediately wipedwith a joint knife or trowel leaving a thin coating of jointcompound over all joints and interior angles. One additionalcoat of joint compound shall be applied over all joints andinterior angles. Fastener heads and accessories shall be coveredwith two separate coats of joint compound. All joint com-pounds shall be smooth and free of tool marks and ridges (see

22.4.1.1). The prepared surface shall be covered with a drywallprimer prior to the application of the nal decoration.22.6.5 Level 4 :22.6.5.1 All joints and interior angles shall have tape

embedded in joint compound and shall be immediately wipedwith a joint knife or trowel leaving a thin coating of jointcompound over all joints and interior angles. Two separatecoats of joint compound shall be applied over all at joints.One separate coat of joint compound shall be applied overinterior angles. Fastener heads and accessories shall be coveredwith three separate coats of joint compound. All joint com-pounds shall be smooth and free of tool marks and ridges (see22.4.1). The prepared surface shall be covered with a drywallprimer prior to the application of the nal decoration.

22.6.6 Level 5 :22.6.6.1 All joints and interior angles shall have tape

embedded in joint compound and shall be immediately wipedwith a joint knife or trowel leaving a thin coating of jointcompound over all joints and interior angles. Two separatecoats of joint compound shall be applied over all at joints.One separate coat of joint compound shall be applied overinterior angles. Fastener heads and accessories shall be coveredwith three separate coats of joint compound. A thin skim coatof joint compound shall be trowel-applied to the entire surface.Excess compound is immediately sheared off, leaving a lm of skim coating compound completely covering the paper. As analternate to a skim coat, a material manufactured especially for

this purpose shall be applied. The surface shall be smooth andfree of toll marks and ridges (see 22.4.1.1).

23. Delivery, Identication, Handling, and Storage23.1 All materials shall be delivered in the original factory

sealed, unopened packages, containers, or bundles bearing thebrand name, applicable standard designation, and the name of the manufacturer, or the supplier for whom the product ismanufactured.

23.2 All materials shall be kept dry. Where gypsum board isstored outside, it shall be off the ground, properly supported ona level platform and fully protected from the weather or direct

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sunlight exposure. Adequate ventilation shall be provided toprevent condensation.

23.3 Gypsum board shall be neatly stacked at, not on itsend or edge, to prevent toppling, sagging or damage to theends, edges, and surfaces.

NOTE 15Gypsum board stacked on edge or end is unstable andpresents a serious hazard in the workplace should it accidentally topple.

23.4 Ready mixed and dry compounds which have beenmixed with water shall be stored at temperatures abovefreezing or temperatures specied by the manufacturer.

24. Keywords

24.1 ceiling; gypsum; wallboard; walls

APPENDIXES

(Nonmandatory Information)

X1. GENERAL INFORMATION

INTRODUCTION

These Appendixes give general information and also suggestions for inclusions to be madeelsewhere by the specier. They are not a part of this specication.

X1.1 Scaffolding shall be constructed and maintained instrict conformity with applicable laws and ordinances.

X1.2 This work shall be properly coordinated with thework of other trades.

X1.3 Gypsum board shall be protected from the elements of weather before, during, and after application.

X2. VENTILATION ABOVE GYPSUM BOARD CEILINGS

X2.1 Adequate ventilation of attics or similar unheatedspaces above gypsum board systems is essential to the perfor-mance of these systems and shall be designed and provided by

others per ASHRAE Fundamentals Handbook or applicablebuilding code.

X3. JOB APPLIED DECORATION

X3.1 Prolonged exposure of gypsum board to sunlight maycause problems in decoration.

X3.2 With the joints and fastener head depressions treatedas specied in Section 10, interior walls of gypsum board maybe decorated in any of the popular variety of nishes, such astexture or stipple, at paint or at enamel paint, wall paper, orvinyl wall coverings.

X3.3 Because the porosity and texture of the gypsum boarddiffers from that of the joint treatment, the surface shall beprimed and sealed as may be required for the subsequent nishcoats.

X3.4 In rooms where high humidity may be encountered,such as the kitchen, bath, or utility room, a at or semiglossenamel nish is recommended.

X3.5 Care should be exercised in the selection of primerand sealer paints to make sure they will perform satisfactorily,and fulll the following functions:

X3.5.1 Equalize variations of suction over the entire sur-face.

X3.5.2 Provide a bonding surface or tooth for the paint tobe applied.

X3.5.3 Avoid nap raising.

X3.6 Before applying the sealer, remove all loose dirt anddust by brushing with a soft brush or by rubbing with a drycloth. Be sure the joint treatment is thoroughly dry before anyapplication of sealer or paint.

X3.7 In applying primers or sealers, apply sufficient quan-tity to assure that the surface is completely covered. Follow themanufacturers printed directions and do not over thin. It isgood practice to tint the sealer to approximately the shade of the nish coat. This will lead to better results in the nished job.

X3.8 In all cases where deep tones are to be used in thenish paint, best results will be achieved if the surface is rstsealed. More than one coat of sealer may be necessary. Eachcoat must be thoroughly dry before applying another.

X3.9 Under normal atmospheric conditions, a waitingperiod of 12 to 18 h after application of primer-sealer should be

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observed before decoration is applied. In rainy, humid, andcold weather, a longer waiting period; sometimes as long as 36to 48 h; may be necessary to make certain the sealer coat isabsolutely dry.

X3.10 Exposed surfaces of gypsum board, as specied inSection 10 shall be painted with not less than two coats of

exterior paint.

X3.11 Where semi-gloss or high-gloss paints are requiredor where severe lighting conditions occur, and prior to theapplication of a primer, a skim coat shall be applied to theentire surface of the wallboard, including the taped joints,covered fasteners, and accessories, to reduce the absorptionand texture difference between the joint compound and the faceof the wallboard.

X4. APPLICATION OF SURFACING MATERIALS AND CAULKING

X4.1 Caulk all cut edges and openings around pipes andxtures ush with waterproof, nonhardening caulking com-pound or Type I adhesive complying with ANSI A 136.1.

X4.2 Wall tile shall be used in combination with adhesiveto protect the gypsum board and any water sensitive materialsif present (such as joint compound) from penetration of moisture or water. Responsibility for performance of com-

pleted installation shall rest with the surface materials manu-facturer or with the tile applicator.

X4.3 For application of ceramic, plastic, or metal wall tile,or plastic nished rigid wall panels, or other types of surfacingmaterials over gypsum board in wet or dry areas, the recom-mendations of the manufacturer of tile, wall panel, or othersurfacing materials shall be followed.

X4.4 Apply the surfacing material down to the top surfaceor edge of the nished shower oor, return, or tub, or install soas to overlap the top lip of receptor, sub-pan, or tub. It shallcompletely cover the following areas:

X4.4.1 Over Tubs without Showerheads Six in. (152.4

mm) above the rim of the tub.X4.4.2 Over Tubs with Showerheads A minimum of 5 ft

(1.52 m) above the rim or 6 in. (152.4 mm) above the height of the showerhead, whichever is higher.

X4.4.3 Shower Stalls A minimum of 6 ft (1.83 m) abovethe shower dam or 6 in. (152.4 mm) above the showerhead,whichever is higher.

X4.4.4 All gypsum board window sills and jambs in showeror tub enclosures shall be covered to a like height.

X4.4.5 The surfacing material shall be applied to the fullspecied height for a distance of at least 4 in. (101.6 mm)

beyond the external face of the tub or receptor. Areas beyondan exterior corner are excluded.

X4.5 Where plastic nished rigid wall panels are used as asurfacing material, the following precautions shall be taken:

X4.5.1 The type and shape of moldings recommended bythe manufacturer of the surfacing material shall be used.Recommended tub moldings shall be used at the base wherethe surfacing materials abut the tub, shower, oor, or curb.Such moldings shall be set in waterproof, nonhardeningcaulking compound.

X4.5.2 Joints shall be lled in such a manner as to leave no

voids for water penetrations.X4.5.3 A bead of adhesive shall be applied as a dam

between the back surface of the nishing material and the tubor receptor to prevent any leakage of water at the joint.

X5. WOOD FRAMING REQUIREMENTS

X5.1 The following requirements should be included in theproject specications for framing and furring and are essentialto provide a proper base to receive the gypsum board.

X5.2 All framing members to which gypsum board will befastened shall be straight and true. Framing shall be inalignment and spaced not to exceed the maximum spacingsshown in Table 1. Framing, bridging, and furring membersshall be the proper grade for the intended use and members 2by 4 in. nominal size or larger shall bear the grade mark of arecognized inspection agency. Framing, bridging, and furringshall be adequate to meet the design, or code loading, or both.Where there is an applicable local code, the framing shall be inaccordance with the Manual for House Framing by theNational Lumber Manufacturers. Supports shall be provided asnecessary for the support of xtures.

X5.3 When gypsum board is nailed to wood cross furringon ceilings, these furring members shall have a minimum crosssection of 1 1 2 by 1 1 2 in. (38.1 by 38.1 mm) actual size and bespaced in accordance with 9.2 and 9.3. Where screw applica-tion is used, the furring member may be 3 4 in. by 21 2 in. (19.1by 63.5 mm) actual size.

X5.4 Where wood furring is used over masonry or con-crete, fasteners should be of a length that does not come intocontact with the masonry surface.

X5.5 Insulating blankets or anges of blankets shall not beapplied over framing members that are to receive gypsumboard.

X5.6 Foil-backed gypsum board may be used where avapor retarder is required.

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X6. PRECAUTIONS TO MINIMIZE POTENTIAL OF SAGGING

X6.1 Ensure framing spacing is adequate for thickness of board to be used. Ensure board is applied perpendicular toframing.

X6.2 Determine that excessive weight of insulation will notbe added.

X6.3 Control the relative humidity within the structure byproviding adequate ventilation before, during, and after boardapplication. Watch for pouring of basement oors after boardapplication.

X6.4 In cold weather, maintain inside temperature between50F (10C) and 70F (20C). Where portable heaters are used,make sure to remove the extra humidity they produce.

X6.5 Ensure the gypsum board is thoroughly dry and at

ambient temperature before application.

X6.6 Ensure joint treatment is thoroughly dry beforeapplying any decoration.

X6.7 Ensure that primer and paint coats are dry before theapplication of successive coats.

X6.8 Where hand or spray-applied water-based texturenishes are to be used on gypsum board ceilings under thisspecication either (i) 1 2 in. (12.7 mm) Gypsum Ceiling Board(see Specication C 1395/C 1395M) shall be used perpendicu-lar to framing not more than 24 in. (610 mm) on center, or (ii)other gypsum boards shall be used perpendicular to framingand board thickness shall be not less than 1 2 in. (12.7 mm)thick for 16 in. (406 mm) on center framing and not less than5 8 in. (15.9 mm) thick for 24 in. (610 mm) on center framing.

X7. ELECTRIC RADIANT HEATING SYSTEMS FOR GYPSUM BOARD CEILINGS

X7.1 The application of gypsum board under this speci-cation shall be performed in accordance with Specication C840, except as herein modied.

X7.2 Gypsum boards shall have no less thickness than thatspecied for perpendicular application for the ceiling framingspacing. Both layers shall be applied perpendicularly to fram-ing members. Attachment shall be as required in Section 9.

X7.3 Electric heating cables shall be securely attached togypsum board in accordance with the recommendations of thecable manufacturer and the National Electrical Code by othertrades.

X7.4 Cables shall be parallel to and between framingmembers with at least 1 1 4 -in. (31.8-mm) clearance from centerof framing member on each side so that at least 2 1 2 -in.(63.5-mm) wide unobstructed strip is provided under eachframing member.

X7.5 Cables shall cross framing members only at ends of ceiling 4 to 6 in. (101.6 to 152.4 mm) from the wall. Thereshall be at least a 4 in. (101.6 mm) space completely around theperimeter of each ceiling that is clear of cables. Cables shall be

kept at least 8 in. (203.2 mm) clear of all openings.X7.6 All inspections and testing of the heating system shall

be completed before application of the noninsulating ller.

X7.7 Under no operating conditions shall the gypsum boardcore be exposed to a temperature exceeding 125F (51.7C)unless otherwise specically recommended by the gypsumboard manufacturer.

X7.8 Complete embedding of the heating cable is neces-sary. The area between the heating cables shall be lled with anonshrinking, noninsulating ller that shall be leveled.

X7.9 If a face layer of gypsum board is to be applied thenthe nails or screws around the perimeter of the ceilings shall bespaced 8 to 10 in. (203.2 to 254.0 mm) away from the wall toprevent striking the heating elements where they cross theframing members.

X7.9.1 All joints and heads of fasteners shall be nished inaccordance with the recommendations of the gypsum boardmanufacturer. Allow a minimum of one week with good dryingconditions and two weeks in cold conditions before operatingthe heating system.

X7.10 If gypsum board is not used as a nish, a specialspray texture for radiant heat ceilings may be applied.

X7.11 Design Data:X7.11.1 It is the responsibility of the architect to prepare

and correlate complete plans and specications.X7.11.2 It is the responsibility of the heating engineer to

properly design the radiant heating system to work effectivelywith these materials.

X7.11.3 The data in Table X7.1 are recommended for use incalculating the heat transmission coefficient ( U ) for gypsumboard constructions.

X7.12 Decoration:

TABLE X7.1 Thermal Conductivity Values

Thickness, in.(mm) Conductance C Resistance R I/C

Btu/h ft2 F W/m 2 k F h ft 2 /Btu k m2 /w3 8 (9.5) 3.10 17.6 0.32 0.057

1 2 (12.7) 2.22 12.6 0.45 0.0795 8 (15.9) 1.78 10.1 0.56 0.0991 (25.4) 1.20 6.8 0.83 0.147

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