gypsum board and plaster - mcgraw-hill educationbooks.mcgraw-hill.com/engineering/pdfs/pdf_withcx/25...

T. PATTERSON: Illustrated 2006 Building Code Handbook 1685

25Gypsum Board and Plaster

Hoyt Street Properties. Portland Oregon. (partial elevlation)

Ankrom Moisan Associated Architects. Portland, Oregon.


2502 Definitions

2502.1 Definitions (part 1 of 2)

• Cement plaster

� One of the following mixtures:

Portland cement, aggregate, other approved materials.

Portland cement, hydrated lime, aggregate, other approved materials.

Blended cement, aggregate, or other approved materials.

Blended cement, hydrated lime, aggregate, other approved materials.

Masonry cement, aggregate, other approved materials.

Plastic cement, aggregate, other approved materials.

� Other approved materials are as specified in the code.

• Exterior surfaces

� Surfaces exposed to the weather.

• Gypsum board

� Any of the following:

Gypsum wallboard.

Gypsum sheathing.

Gypsum veneer plaster base.

Exterior gypsum soffit board.

Predecorated gypsum board.

Water-resistant gypsum backing board.


Note: The following are cited as listing standards governing gypsum board:

IBC Table 2506.2, “Gypsum Board Materials and Accessories.”

IBC Table 2507.2, “Lath, Plastering Materials and Accessories.”

Chapter 35, “Referenced Standards.”

• Gypsum plaster

� Any of the following:

Calcined gypsum.

A mixture of the following:

Calcined gypsum.

Lime.

Aggregate.

Other approved materials.

• Gypsum veneer plaster

� Gypsum plaster as follows:

Applied to an approved base.

Applied in 1 or more layers.

Usually ≤1/4" thick.

• Interior surfaces

� Surfaces not exposed to the weather.


2502 Definitions

2502.1 Definitions (part 2 of 2)

• Weather-exposed surfaces

� The following surfaces are not included:

Ceilings and roof soffit surfaces as follows:

Enclosed by the following components that extend ≥ 12" below such surfaces:

Walls.

Fascia.

Bulkheads.

Beams.

Walls or parts of walls under a roof as follows:

In an area that is not enclosed.

Set back from the roof edge as follows:

A distance ≥ 2 × the height of the open space under the roof edge.

Parts of ceilings and roof soffits located as follows:

A horizontal distance ≥ 10' from the outer edges of the following:

The ceiling or roof soffit.

� Otherwise, the following surfaces where exposed to the weather are included:

Walls.

Ceilings.

Floors.

Roofs.


Soffits.

Similar surfaces.

• Wire backing

� Horizontal strands of wire as follows:

Attached to surfaces of vertical supports.

Wire is taut.

Covered with building paper.

Serves as a backing for cement plaster.


Fig. 2502.1. Conditions of exposure conditions for ceilings, soffits, and walls.

X

s

ee fi

g. (

b)

12” m

in

NOT EXPOSEDto WEATHER

OPEN PORCH

BUILDINGINTERIOR

SECTION

(a)

ROOF OVERHANG

ROOF OVERHANG

EXPOSED to WEATHER

NOT EXPOSED to WEATHER

PORCH AREA

min 2X see fig. (a)

EXPOSED to WEATHER

< 2X see fig. (a)

< 2X see fig. (a)

PLAN

(b)

BUILDING

< 12”

EXPOSED to WEATHER

NOT EXPOSED to WEATHER

10’

OPENPORCH

BUILDING INTERIOR

SECTION

(c)

••••

••

•

•

•

•••

• •

•

•

• ••

•

•••• •

• •


2504 Vertical and Horizontal Assemblies

2504.1.1 Wood framing

• The wood supports for the following be ≥ 2" in any dimension:

� Lath.

� Gypsum board.

• Wood stripping or furring is governed as follows:

� Where applied to solid backing the following size is required:

≥ 1"× 2".

� Otherwise, the following size is required:

≥ 2" in any dimension.

2504.1.2 Studless partitions

• The required thicknesses of the following vertical studless partitions are ≥ 2":

� Solid plaster on the following:

3/8" rib metal lath.

3/4" rib metal lath.

1/2" long-length gypsum lath.

� Gypsum board partitions.


2508 Gypsum Construction

2508.2 Limitations

• The following materials may not be exposed directly to the weather:

� Gypsum wallboard.

� Gypsum plaster.

• Gypsum wallboard may not be used in the following locations:

� With direct exposure to water.

� With exposure to continuous high humidity.

• Gypsum sheathing may be installed in the following location:

� On exterior surfaces.

Note: ASTM C 1280, “Standard Specification for Application of Gypsum Sheathing,” is

cited as governing gypsum sheathing.

2508.2.1 Weather protection

• Weather protection must be provided prior to the installation of the following:

� Gypsum wallboard.

� Gypsum lath.

� Gypsum plaster.

2508.3 Single-ply application

• The following parts of gypsum board must fall on framing members:


� Edges � to framing members.

� Ends � to framing members.

• The following parts of gypsum board are governed as indicated below:

� Parts:

Edges.

Ends.

� Requirements:

They need not touch adjacent panels in the following case:

In concealed spaces as follows:

Where there is no requirement for the following:

Fire-resistance-rated construction.

Shear resistance.

Diaphragm resistance.

In other locations they must be in contact with adjacent panels.



2508.3.1 Floating angles

• Where the following conditions apply, the fastening of gypsum board is governed as

indicated below:

� Conditions:

The assembly is not intended to resist shear.

The assembly does not require a fire-resistance rating.

� Requirements:

Fasteners are not required at the following locations:

Top plates of walls.

Bottom plates of walls.

Fasteners are not required at the perimeters of the following:

Ceilings.

Soffits.

• Fastener heads may not break the following:

� The face paper on the gypsum board.

2508.4 Joint treatment

• This section addresses the following details in fire-resistance-rated assemblies:

� Joints between gypsum board panels.

� Fasteners in gypsum board panels.

• The details need not be finished so as to seal them in any of the following cases:


� Where the details will have a decorative finish such as follows that would seal them:

Wood paneling.

Battens.

Acoustical finishes.

Similar applications.

� In one-layer assemblies as follows:

Where joints fall on wood framing.

� Where any of the following gypsum board products are used:

Square edge.

Tongue-and-groove (V-edge).

Backing board.

Sheathing.

� In multiple-layer assemblies as follows:

Where joints of adjacent layers are offset.

� In assemblies which were tested for fire resistance as follows:

Without the details being sealed.

• In other cases the details must be finished so as to seal them.

2508.5 Horizontal gypsum board diaphragm ceilings

• A horizontal diaphragm ceiling may be created by the following:

� Gypsum board applied wood joists.


Note: IBC Table 2508.5, “Shear Capacity for Horizontal Wood Framed Gypsum Board

Diaphragm Ceiling Assemblies,” is cited as governing these diaphragms.



2508.5.1 Diaphragm proportions

• Horizontal diaphragm ceilings must have the following proportions:

� ≤ 1-1/2:1 as defined at its edges by shear walls.

• The following conditions are not allowed for the diaphragm:

� Rotation or cantilevers.

2508.5.2. Installation

• Installation of horizontal diaphragm ceilings is governed as follows:

� Gypsum board must be applied � to the joists.

� Joints between the ends of gypsum board panels have the following requirement:

Adjacent courses must have end joints on different joists.

2508.5.3 Blocking of perimeter edges

• Blocking of horizontal diaphragm ceilings are governed as follows:

� The perimeter of the gypsum board ceiling must be blocked as follows:

With wood ≥ 2"× 6" as follows:

Installed with the wider dimension horizontal in the following location:

Over the wall top plate as follows:

To provide a nailing surface for the gypsum board ≥ 2" wide.


2508.5.4 Fasteners

• Fasteners in horizontal diaphragm ceilings have the following requirements:

� Gypsum board must be secured in the following manner:

Fasteners must be spaced ≤ 7" oc as follows:

At all supports and perimeter blocking.

Fasteners must be located ≤ 3/8" from the following:

Edge of the gypsum board as applicable.

End of the gypsum board as applicable.

Note: IBC Table 2508.5, “Shear Capacity for Horizontal Wood Framed Gypsum Board

Diaphragm Ceiling Assemblies,” is cited as governing the fasteners.

2508.5.5 Lateral force restrictions

• A gypsum board diaphragm may not be used to resist forces from the following:

� Masonry or concrete construction.


2509 Gypsum Board in Showers and Water Closets

2509.2 Base for tile

• One or more of the following materials must be installed according to manufacturer’s

recommendations in the locations listed below:

� Materials.

Cement fiber backing board.

Cement backing board.

Glass mat gypsum backing board.

� Locations

Behind wall tile in tub and shower areas.

Behind wall and ceiling panels in shower areas.

Note: The following are cited as governing the backing boards listed above:

ASTM C 1288, “Standard Specification for Discrete Non-Asbestos Fiber-Cement

Interior Substrate Sheets.”

ASTM C 1325, “Standard Specification for Non-Asbestos Fiber-Mat Reinforced

Cement Interior Substrate Sheets.”

ASTM C 1178, “Standard Specification for Glass Mat Water-Resistant Gypsum

Backing Panel.”Manufacturer recommendations.

• Water-resistant gypsum backing board must be installed as follows:

� Behind wall tile in WC compartments.


� According to manufacturer’s recommendations.

• Standard gypsum wallboard is allowed in the following locations:

� Behind tile or panels on walls or ceilings.

Note: Either of the following is cited as governing the water-resistant gypsum backing

board and the gypsum wallboard listed above:

GA-216, “Application and Finishing of Gypsum Board.”

ASTM C 840, “Standard Specification for Application and Finishing of Gypsum

Board.”

2509.3 Limitations

• This section addresses water-resistant gypsum backing board.

• Such boards may not be used as follows:

� Over a vapor retarder in the following areas:

Bathtub compartments.

Shower compartments.

� In any of the following areas:

Those directly exposed to water.

Those exposed to continuous high humidity.

• Such boards 1/2" thick may not be used as follows:

� On ceilings where supports are > 12" on center.

• Such boards 5/8" thick may not be used as follows:

� On ceilings where supports are 16" on center.


2510 Lathing and Furring for Cement Plaster (Stucco)

2510.5.1 Support of lath

• Solid backing is required for lath and attachments as follows:

� Where lath on a vertical surface extends between the following:

Rafters or similar projections.

2510.5.2.1 Use of gypsum board as a backing board

• Use of the following materials as backing board must meet the requirements listed below:

� Materials:

Gypsum lath or wallboard.

� Requirements:

Such materials may be used as a backing for cement plaster as follows:

Where the following materials are used in the locations indicated below:

Materials:

Water-resistive barrier between lath and sheathing.

One of the following types of lath:

Self-furred metal lath.

Self-furred wire fabric lath.

Locations:

On horizontal supports of ceilings or roof soffits.

On interior walls.

Such materials may not be used as backing for cement plaster in other cases.


2510.5.2.2 Use of gypsum sheathing backing

• Gypsum sheathing may be used as a backing for cement plaster where the following are used:

� Water-resistive barrier between lath and sheathing.

� Metal or wire fabric lath.

Note: 2510.6, “Water-resistive barriers,” is cited as governing such barriers.

2510.5.3 Backing not required

• Wire backing is not required behind the following:

� Expanded metal lath.

� Paperbacked wire fabric lath.

2510.6 Water-resistive barriers

• This section does not govern weather-resistant barriers with all the following characteristics:

� Where applied over wood-based sheathing.

� With a water resistance ≥ that of 60-minute Grade D paper.

� Where separated from the stucco by one of the following:

A layer that does not absorb water.

A drainage space.

• Water-resistive barriers installed over wood-based sheathing require the following:

� A weather-resistive vapor permeable barrier that performs as follows must be included:

Performance to be ≥ 2 layers of Grade D paper.

� Water-resistive barriers are to be installed as specified elsewhere in the code.


Note: 1404.2, “Water-resistive barrier,” is cited as governing such barriers.


2511 Interior Plaster

2511.2 Limitations

• Plaster may not be applied directly to the following:

� Fiber insulation board.

• Cement plaster applied to the following materials is governed as indicated below:

� Materials:

Gypsum lath.

Gypsum plaster.

� Requirements:

Such materials must be protected by a water-resistive barrier.

Direct application to such materials is not permitted.

Note: The following are cited as sources of applicable requirements, a partial summary of

which is provided above:

2510.5.1, “Support of lath.”

2510.5.2, “Use of gypsum backing board.”

2511.3 Grounds

• Where used, grounds must establish the required thickness for plaster.

• Plaster thickness is measured from the following:

� Face of lath.

� Face of other bases as applicable.


Note: The following are cited as governing the required thickness of plaster:

ASTM C 842, “Standard Specification for Application of Interior Gypsum Plaster.”

ASTM C 926, “Standard Specification for Application of Portland Cement-Based

Plaster.”

2511.5 Wet areas

• Showers and public toilets require the following wall surfaces:

� Smooth.

� Nonabsorbent.

Note: The following are cited as sources of applicable requirements, a partial summary of

which is provided above:

1210.2, “Walls.”

1210.3, “Showers.”

• Wood framing must be protected with an approved moisture barrier as follows:

� Where the interior of walls and partitions have all of the following characteristics:

Covered with one of the following materials:

Cement plaster.

Tile of similar material.

Subject to splashed water.


2512 Exterior Plaster

2512.1 General

• Cement plaster is required to be applied as follows:

� In ≥ 3 coats as follows:

Where applied over any of the following:

Metal lath.

Wire fabric lath.

� In ≥ 2 coats as follows:

Where applied over any of the following:

Masonry.

Concrete.

Gypsym board.

Where both the following conditions exist:

The plaster is of adequate thickness.

Where the plaster is covered by any of the following:

A veneer.

Other facing material.

A second wall.

Note: 2510.5, “Backing,” is cited as governing the backing for cement plaster.

ASTM C 926, “Standard Specification for Application of Portland Cement Based

Plaster,” is cited as reporting the thickness of the plaster, which is adequate for the

purpose noted above.


2512.1.1 On-grade floor slab

• On the following assemblies, exterior plaster is governed as indicated below:

� Assemblies:

Wood framing on a concrete slab-on-grade.

Steel framing on a concrete slab-on-grade.

� Requirements:

The plaster must cover the lath and paper.

The plaster may not extend below the lath and paper.

� The installation of the following components must also comply with standards other than

the code:

Lath.

Paper.

Flashing.

Drip screeds.

Note: ASTM C 1063, “Standard Specification for Installation of Lathing and Furring to

Receive Interior and Exterior Portland Cement-Based Plaster,” is cited as governing

the components listed above.

2512.1.2 Weep screeds

• Weep screeds are required for exterior cement plaster as follows:

� Screeds must drain trapped water to the exterior.

� Screed requirements are shown in the detail on the next page.


Note: ASTM C 926, “Standard Specification for Application of Portland Cement-Based

Plaster,” is cited as governing weep screeds.


Fig. 2512.1.2. Cement plaster weep screed requirements.

CEMENTPLASTER

EXTERIORSTUD WALL

≥ 26 ga GALVANIZEDWEEP SCREED

Lath covers screed flange

Weatherbarrierlaps screedflange

2" minabovepavingsurface

4" min aboveexposedearth

3-1/

2” m

in

•

•

••

•

•••

••

•

•


2512.2 Plasticity agents

• The following substances may not be added to the stucco mixtures indicated below:

� Substances:

Lime.

Plasticizers.

� Mixtures:

With plastic cement.

With masonry cement.

• In other cases plasticity agents may be added to stucco mixtures as follows:

� Where approved.

� In quantities that are approved.

• The following plasticizers may be added to the stucco mixtures indicated below:

� Plasticizers:

Hydrated lime.

Lime putty.

� Mixtures:

Cement plaster.

Cement lime plaster.

Note: ASTM C 926, “Standard Specification for Application of Portland Cement-Based

Plaster,” is cited as governing the amounts of the plasticizers that may be added.




2512.3 Limitations

• Gypsum plaster is not permitted as follows:

� In exterior applications.

2512.5 Second-coat application

• The second coat of exterior cement plaster is governed as follows:

� It must be applied to the required thickness.

� It must be rodded and floated to a roughness as follows:

Adequate for bonding with the finish coat.

Roughness is limited to 1/4"variation under a 5' straight edge in any direction.


Fig. 2512.5. Three-coat exterior plaster installation.

TEXTURE MUST be ADEQUATE to BOND to FINISH COAT

FIRST COAT

•

•

SECOND COAT

FINISH COAT

• •

≤ 1/4” in ANY 5’ dia CIRCLE

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