United States Gypsum Company USG  

Lath & Plaster. CSI 3-Part Specifications.




Use this guide specification to specify lath and plaster systems

by U. S. Gypsum Co. for construction of partitions, furring,

ceilings, soffits and related assemblies. Review a copy of USG

publication SA-920 before editing specification.




General and Supplementary Conditions of Contract as well as

Drawings and general provisions of Contract and Division 1

Specification section, apply to work of this section.


Extent of lath and plaster work is shown on drawings and

schedules. Types of work included are:

Preparation of masonry an monolithic concrete.

Framing for partitions, ceilings, furring, etc.

Metal lath, gypsum lath, and related components.

Full coat gypsum plaster.

Coordinate with all trades required to install work on or

into work of this section.

Related Work Specified Elsewhere

Painting - Section 09900


Do not use polyvinyl acetate primers or paints with lime-gauging

or lime-containing plaster finishes.


Insulation - Section 07200


THERMAFIBER Brand Sound Attenuation fire blankets are usually

installed as part of this section. Exterior wall insulation in

conjunction with Z-Furring Channels can also be installed as part

of this section.


Hollow Metal Doors and Frames - Section 08100


Include additional related sections as pertinent.




ASTM C-28 Standard Specification for Gypsum Plasters

ASTM C-35 Standard Specification for Inorganic

Aggregates in Gypsum Plaster

ASTM C-37 Standard Specification Gypsum Lath

ASTM C-61 Standard Specification for Gypsum Keene's


ASTM C-206 Standard Specification for Finishing

Hydrated Lime

ASTM C-631 Standard Specification for Bonding

Compounds for Interior Plastering.

ASTM C-641 Standard Specification for Zinc-Coated

(Galvanized) Carbon Steel Wire.

ASTM C-645 Standard Specification for Non-Load (Axial)

Bearing Steel Studs, Runners (Track), and

Rigid Furring Channels for Screw

Application of Gypsum Board.

ASTM C-754 Standard Specification for Installation of

Steel Framing Members to Receive Screw-

Attached Gypsum Board, Backing Board, or

Water-Resistant Backing Board.

ASTM C-841 Standard Specification for Installation of

Interior Lathing and Furring.

ASTM C-842 Standard Specification for Application of

Interior Gypsum Plaster

ASTM C-1002 Standard Specification for Steel Drill

Screws for the Application of Gypsum Board.

ASTM C-847 Standard Specification for Metal Lath

Fire-Resistance Rating: Where fire resistance rating is

required, provide materials and installation which are

identical with those of applicable assemblies tested per

ASTM E119 by fire testing laboratories acceptable to

authorities having jurisdiction.


If mock-up is required identify location at the site, size

required and if special tests will be conducted relative to same

(e.g. sound tests).


Unit Responsibility: Obtain lath and plaster materials from

a single manufacturer to ensure consistency in quality of

performance and appearance.


Product Data: Submit manufacturer's product specifications

and installation instructions for systems used.

Certificates: Submit certification of compliance with fire

and sound requirements indicated.


Copies of actual fire and sound test reports can be specified for



Samples: Furnish one standard sample of each linear or

continuous product, one standard hand sample of sheet

product, and one sample of all other components required for



Delete "Samples" paragraph if none required.

Include requirement for shop drawings if necessary.



Handling: Handle materials to avoid damage.

Delivery: Deliver materials to the jobsite in original

unopened packages, containers, or bundles bearing the brand

name and manufacturer's identification.

Storage: Store materials in dry locations with adequate

ventilation, free from water, and in such a manner to permit

easy access for inspection and handling. Remove damaged or

deteriorated materials from the site.


Protect adjacent work of other trades from moisture damage,

soiling, physical distress, etc.

In cold weather, all glazing shall be completed and the

building heated to minimum of 55F. before gypsum base and

lath installation. Temperature of building shall be

maintained in uniform range above 55F. for an adequate

period prior to application of plaster, while plastering is

being done, and until plaster is dry. When required heat

shall be supplied by ( ). Heat shall be well distributed in

all areas, with deflection or protective screens used to

prevent concentrated or irregular heat on plaster near


Ventilation shall be provided to properly dry plaster during

and subsequent to its application.



Subject to compliance with requirements, provide lath,

plaster, and all related components, as manufactured or

supplied by United States Gypsum Co.


A. Steel Studs and Runners - UNIMAST:

(158ST25) (158CR25) (212ST25) (212CR25) (358ST25)

(358CR25) (400ST25) (400CR25) (600ST25) (600CR25)

(212ST22) (212CR22) (358ST22) (358CR22) (400ST22)

(400CR22) (600ST22) (600CR22) (212ST20) (358ST20)

(358CR20) (400ST20) (400CR20) (600ST20) (362SJ20)



Additional studs available in SJ series for increased height



B. Metal Furring Materials:

(Unimast Metal Furring Channels and Clips)

(Unimast Adjustable Wall-Furring Brackets)

(Unimast Cold-Rolled Channels [3/4"][1-1/2"])

(SHEETROCK Z-Furring Channels)


For cold-rolled channels specify standard painted or galvanized



C. Utility Angles: Nominal 2"x2"x24ga., corrosion

resistant steel, lengths as required.

D. Hanger Wire: Galvanized, 8-ga.

Tie Wire: Galvanized, 18-ga.

E. Corner Bead: - Unimast - (1-A Expanded) (Double X)

F. Casing Beads: - Unimast - (#66 Expanded Flange

[1/2"][5/8"][3/4"][7/8"][1"][1-1/4"])(#66 Short Flange


G. Control Joint: (SHEETROCK Zinc Control Joint

[#50][#75][#100]) (Unimast Double-V Expansion Joint

[1/2"][3/4"]) (galv.)(zinc)

H. Screws:

SIZE: (3/8")(7/16")(1/2")(1")(1-1/4")(1-1/2")


Style: (framing - Type [S][S-12]) (drywall - Type S)

(self-drilling - Type S-12) (laminating - Type G)

Head: (bugle)(pan)(trim)(pancake)(low-profile)(mod.


Coating: (reg.)(corrosion-resistant)

I. Insulation: THERMAFIBER Sound Attenuation Fire

Blankets (1")(1-1/2")(2")(3") thick,

(16")(24")(25") wide


Specify insulation required for exterior walls for use with Z-

Furring Channels if to be installed under this Section


J. Reinforcement: - Unimast - (Cornerite) (Striplath)

K. Lath Attachment Clip: BRIDJOINT B-1 Field Clip

L. ROCKLATH Plaster Base (3/8"x16"x48") (1/2"x16"x48")

(3/8"x16"x96") (FIRECODE)


Check with local U.S. Gypsum Co. representative for availability

in particular markets.


M. Metal Lath - Unimast:

*(Junior Diamond Mesh [1.75#][2.5#][3.4#])

*(Self-Furring Diamond Mesh [2.5#][3.4#][Paper-

Backed - Grade B or D])

*(4-Mesh Z-Rib Lath [2.75#][3.4#])

*(3/8" Riblath [3.4#])


N. Basecoat Plaster:

(RED TOP Gypsum Plaster)

(RED TOP Wood Fiber Plaster)

(RED TOP Two Purpose Plaster)

(STRUCTO-BASE Gypsum Plaster)

(STRUCTO-LITE Gypsum Plaster)

O. Aggregate: (sand) (perlite). Sand for float finishes

shall be graded (white) silica sand passing a (30 mesh)

(20 mesh) screen.


Select sand passing through 30 mesh screen for finest float



P. Finish Lime: Type S (IVORY) (SNOWDRIFT)

Q. Gauging Plaster: (RED TOP Gauging) (CHAMPION

Gauging) (STAR Gauging) (STRUCTO-GAUGE Gauging) (RED

TOP Keenes Cement)


RED TOP, CHAMPION, and STAR Gauging Plasters are available in

"Quality" (aggregated) formulation for smooth trowel finish over

lightweight aggregate basecoats.


R. Grout: RED TOP Gypsum Plaster

S. Water: Potable without impurities that affect the

setting of gypsum.

T. Bonding Compound: ASTM C-631

U. Acoustical Sealant: SHEETROCK Brand Acoustical Sealant



3.01.1 Stud System Erection:

Attach steel runners at floor and ceiling to structural

elements with suitable fasteners located 2" from each

end and spaced 24" o.c. max. To suspended ceilings,

use toggle bolts or hollow wall anchors spaced 16"

o.c. max.

Position studs vertically, with open side facing in

same direction, engaging floor and ceiling runners,

spaced (24" o.c.)(16" o.c.)(as shown on drawings).Place

studs in direct contact with all door frame jambs,

abutting partitions, partition corners and existing

construction elements. Where studs are installed

directly against exterior walls install asphalt felt

strips between studs and wall surface.


24- inch stud spacing acceptable with 1/2" ROCKLATH Plaster Base.

End joints of 1/2" ROCKLATH Plaster Base must occur over stud

flanges and be secured to studs with screws.


Anchor all studs for shelf-walls and those adjacent to

door and window frames, partition intersections,

corners and free-standing furring to floor and ceiling

runners with metal-lock fastener tool or screws.

Securely anchor studs to jamb and head anchors of door

or borrowed-light frames by bolt or screw attachment.

Over metal door and borrowed-light frames, place a

horizontal cut-to-length section of runner, with a web-

flange bend at each end, and secure to strut studs with

two screws in each bent web. Position a cut-to-length

studs as necessary over door frame header.

3.01.3 ROCKLATH Plaster Base Installation:

Apply 3/8" ROCKLATH Plaster Base perpendicular to

studs, bottom course first, with face out. Position

all ends between studs. Fit ends and edges closely,

but not forced together. Stagger joints in succeeding

courses of lath. Secure 3/8" lath to studs with 1" type

S screws, 2 per stud, approximately 2-inches from lath

edges; fasten lath ends with B-1 BRIDJOINT Clips at

top, center and bottom of each end joint. Secure 1/2"

lath to studs with 1" type S screws, 3 per stud,

position lath ends over studs and secure with screws,

with joints staggered in succeeding courses.


For fire rated assemblies, UL Design U-488 (1-hr.), UL Design

U-484 (2-hr.) space screws 8" o.c. ROCKLATH FIRECODE Plaster

Base required for Design U-488. For 20 gauge studs type S-12

screws are recommended.


3.01.4 Sound Attenuation Fire Blanket Installation:

Install THERMAFIBER Sound Attenuation Fire Blankets

after ROCKLATH Plaster Base is applied to one side of

studs. Fasten to the back of the ROCKLATH Plaster Base

using five 9/16" long staples driven through paper

reinforcement strips. Three-inch thick blankets are

friction-fit; insulation equal to or 1/2" less than

stud width may be friction fit.

Creased THERMAFIBER Sound Attenuation Fire Blankets -

Insert 25" wide blankets in the stud cavity

by bowing slightly. After inserting make a vertical

cut in blanket about 1-inch deep on a centerline

between the studs with a sharp utility knife.

3.01.5 Metal Lath Application:

Place 3.4#/s.y. self-furring diamond mesh lath with

long dimension perpendicular to studs and over

previously applied ROCKLATH Plaster Base. Secure metal

lath to steel studs with 1-1/4" screws spaced 8" o.c.

Ends shall be lapped 1" and staggered in adjacent

courses and sides lapped 1/2".


Above application of metal lath is required for two-hour

partition, UL Design U-484.



3.02.1 Steel Stud System:

Align two parallel rows of floor and ceiling runners

spaced apart as shown on drawings. Attach to concrete

slabs with concrete stub nails or power-driven anchors

24" o.c.; to suspended ceilings with toggle bolts or

hollow wall anchors 16" o.c.

Position studs vertically in runners (16") (24") o.c.

with flanges in same direction, and with studs on

opposite sides of chase directly across from each


Place cross bracing made of gypsum base, minimum 12"

high by chase wall width, between rows of studs and

attach to stud webs with six 1" type S screws per

brace. Space braces 48" o.c. vertically.

Bracing of 2-1/2" steel studs may be used in place of

gypsum panels. Anchor web at each end of steel brace

to stud web with two 3/8" pan head screws. When chase

wall studs are not opposite install steel stud cross

braces 24" o.c. horizontally and securely anchor each

end to a continuous horizontal 2-1/2" runner screw-

attached to chase wall studs within the cavity

Install ROCKLATH Plaster Base per 3.01.4.

3.02.2 Channel Stud/Metal Lath System:

Secure two rows of 3/4" cold-rolled channel studs

vertically to floor and ceiling structure with

appropriate fasteners, and spaced 16" o.c. Install

horizontal 3/4" cold-rolled channel braces (at mid-

point [to 9'-0"])(at third points [to 13'-6"]) securely

wire-tied to the back flange of each vertical channel

with 18-ga. tie wire. Connect between horizontal

braces with 3/4" cold-rolled channel brackets spaced

30" o.c.


Add other partition systems, e.g. solid Metal Lath/Plaster, as

required per project


Install Metal Lath with long dimension across supports

and with end joints staggered in adjacent rows. Lap

ends of lath 1" at supports; lap side joints at least

1/2". Secure lath to furring channels with 18-ga. tie

wire. Between supports, wire tie side laps together at

intervals not exceeding 9-inches.


3.03.1 Grillage Erection:

Space 8-ga. hanger wires 48" o.c. along carrying

channels and within 6" of ends of carrying channel run.

In concrete, anchor hangers by attachment to

reinforcing steel, by loops embedded at least 2", or by

approved inserts. For steel construction wrap hanger

around or through beams or joists. Do not fasten

hangers to steel roof decks.

Install 1-1/2" carrying channels (48") (36") o.c. and

within 6" of walls, positioned for proper ceiling

height. Level and secure with hanger wire saddle-tied

along channel. Provide 1" clearance between runners

and abutting walls. At channel splices interlock

flanges, overlap ends 12" and secure each end with

double-strand 18-ga. tie wire.

Erect (3/4" cold-rolled furring channels)(metal furring

channels) at right angles to 1-1/2" carrying channels.

Space furring (13-1/2")(16")(19")(24") o.c. and within

6" of walls; secure to furring channels by wire-tieing

with double-strand 18-ga. wire. At splices nest

furring channels 8" and securely wire-tie each end with

double-strand 18-ga. wire.

At light troffers or any openings that interrupt the

carrying or furring channels, install necessary

reinforcing to insure lateral stability of grillage.

3.03.2 Lath Installation:

ROCKLATH Plaster Base Installation:

Apply ROCKLATH Plaster Base perpendicular to metal

furring channels and fasten with 1" type S screws.

Position all ends between furring channels. Fit ends

and edges closely, but not forced together; stagger end

joints in succeeding courses. Fasten ends with B-1

BRIDJOINT Clips at center and each end.


When 1/2" ROCKLATH Plaster Base is used end joints must occur

over furring channels and be screwed thereto.


Metal Lath Installation:

Apply lath with long dimension across supports and with

end joints staggered in adjacent rows. Lap ends of

Junior Diamond Mesh Lath 1" at supports and at least

1/2" between supports. Lap sides of rib lath by

nesting outside ribs. Secure lath to furring channels

with 18-ga. tie wire at intervals not exceeding 6";

securely tie end-laps at supports with 18-ga. wire.

Between supports, wire-tie side laps together at

intervals not exceeding 9-inches.


3.04.1 Direct Furring Channel Attachment:

Attach metal furring channels vertically spaced

(16")(24") o.c. to masonry or concrete surfaces with

concrete stub nails or power-driven fasteners staggered

24" on opposite flanges. On exterior walls install

asphalt felt protection strip between furring channel

and wall.

Install ROCKLATH Plaster Base per 3.01.4.

3.04.2 SHEETROCK Z-Furring Channels:

Install insulation vertically and hold in place with

SHEETROCK Z-Furring Channels spaced (16")(24") o.c.

Attach narrow flanges of furring channels to wall with

concrete stub nails or power-driven fasteners spaced

24" o.c. At exterior corners attach wide flange to

wall with short flange extending beyond corner. On

adjacent wall surface screw attach short flange of

channel to web of attached channel. Start from this

channel with standard width insulation and continue in

regular manner. At interior corners space second

channel no more than 12" from corner and cut insulation

to fit. Hold insulation in place until gypsum base is

installed with 10" long staple field-fabricated from

18-ga. tie wire inserted through slot in channel.

Install ROCKLATH Plaster Base per 3.01.4.

3.04.3 Channel Stud Furring:

Secure adjustable wall furring brackets to masonry or

concrete wall surface using appropriate

fasteners. Space brackets 36" o.c. vertically and 4'-6"

horizontally. Wire-tie plumbed horizontal 3/4" cold-

rolled furring channel to bracket and bend excess of

bracket down. Horizontal channels shall be spaced not

more than 6-inches from the floor and ceiling and not

more than 54" o.c. Wire-tie vertical 3/4" cold-rolled

channels to the horizontal members with 18-ga. tie wire

and space as required for the type of metal lath


Install metal lath with long dimension across supports

and with end joints staggered in adjacent rows. Lap

ends of lath 1" at supports and at least 1/2" between

supports. Secure lath to furring channels with 18-ga.

tie wire. Between supports, wire tie side laps

together at intervals not exceeding 9-inches.


3.05.1 Corner Bead - Reinforce all vertical and horizontal

exterior corners with corner bead secured

with suitable fasteners spaced 12" o.c. on both flanges

along entire length of bead. Vertical corners shall be

plumb; horizontal corners shall be level.

3.05.2 Casing Bead - Where assembly terminates against masonry

or other dissimilar material, and where shown on

drawings, apply metal casing beads fastened 12" o.c.

3.05.3 Control Joints - Break lath and framing behind joint

and back with suitable support. Attach Control Joint

with suitable fasteners 12" o.c. on both flanges along

entire length of joint.

3.05.4 Reinforcing - Install self-furring Diamond Mesh Lath or

Striplath over joints between dissimilar plaster bases.

Reinforce openings with Striplath stapled across

corners; install Cornerite in interior angles.


3.06.1 Plaster thickness shall be as shown on plans but in no

case shall the grounds be less than:

Metal Lath: 5/8" from face of lath

ROCKLATH Plaster Base: 1/2"

Masonry Units: 5/8"

Monolithic Concrete Ceilings: 1/8" [3/8" maximum]

Monolithic Concrete Walls: 1/8" [5/8" maximum]

3.06.2 Basecoat Plaster:

Mix basecoat plasters by hand or in a mechanical mixer

to a uniform consistency following manufacturer's

directions. Apply basecoat plaster by (hand)(machine)

in (1)(2) coats. Masonry surfaces that exhibit high

suction shall be moderately wetted immediately before

plastering. Monolithic concrete surfaces shall be

coated with a plaster bonding compound before


Basecoat Plasters - Mix Proportions

Under Smooth

Trowel Finishe

Under Texture



















































Two-Coat Work: Over ROCKLATH and unit masonry, apply

base (first) coat with sufficient material and pressure

to form good bond to base and to cover well, and then

double back to bring plaster out to grounds. Straighten

to a true surface with rod and darby without use of

additional water and leave rough to receive finish

(second) coat.

Three-Coat Work: Apply scratch (first) coat with

sufficient material and pressure to form good full keys

on metal lath, and good bond on other bases, and then

cross-rake. Apply brown (second) coat after scratch

coat has set firm and hard; bring out to grounds and

straighten to a true surface with rod and darby without

use of additional water. Leave rough to receive finish

(third) coat.

3.06.3 Grout all steel door frames in steel stud partitions

full with basecoat mortar prior to lathing.

3.06.4 Finish Coat Plaster:

Finish Coat Plaster - Mix Proportions


Finish Textur




Lime Finis

Smooth Trowel

Extremely Har

100 lbs. Gauging

100 lbs. Lime

Smooth Trowel


100 lbs. Gauging

200 lbs, Lime

Keenes Cement

Lime Finish

Smooth Trowel

200 lbs. Keenes

100 lbs. Lime

Keenes Cement

Lime/Sand Finish

Float Finish

200 lbs. Keenes

100 lbs. Lime

800 lbs. Sand

Gauging Plaster

Lime Finis

Smooth Trowe

50 lbs. Gauging

100 lbs. Lime

Gauging Plaster

Lime/Sand Finish

Float Finish

50 lbs. Gauging

100 lbs. Lime

400 lbs. Sand


Smooth Trowel Finish Coats: Scratch plaster in

thoroughly and immediately double back to fill out to a

smooth, dense surface for decoration, free of surface

blemishes and irregularities. Apply finish coat as

thin as possible; 1/16" to not more than 1/8" thick.

Trowel RED TOP Keenes Cement finishes until the

material sets.


Smooth trowel finishes are not recommended over basecoats

comprised of lightweight aggregate which are applied to metal

lath. Where lightweight aggregate basecoats are used over

masonry or ROCKLATH Plaster Base and a smooth trowel finish is

desired the finish coat should include 1/2 cu.ft. of perlite

fines or 50 lbs. of No. 1 white silica sand per 100 lbs. gauging

plaster, or "Quality" factory-aggregated gauging plaster.


Float Finishes Coats: Scratch plaster in thoroughly and

immediately double back to a true, even surface. Float

using a (shingle)(cork)(wood)(carpet)(rubber) float to

bring aggregate to the surface to produce a finish of

uniform texture free of slick spots, cat faces, and

other blemishes. Use water sparingly.

Machine-applied Spray Finishes: Apply plaster uniformly

to produce a texture approved by the Architect.


Sealant at the perimeter of all sound rated partitions with

1/4" minimum round bead. Apply sealant to the back and sides

of electrical boxes, around perimeter of electrical boxes, and

around all penetrations to prevent sound flanking.

3.08 PATCHING: Point up around trim and other work. Cut out and

patch defective and damaged plaster. Patch plaster to match

existing work on texture and finish flush and smooth.

3.09 CLEAN-UP: At the completion of the finish plaster work,

clean plaster from beads, screeds, metal base and metal

trim,leaving work ready for decoration by others. Remove

all lath and plaster rubbish, excess material, scaffolding,

tools and equipment from the building, leaving the floors

broom clean.

End of Section 09200


Copyright 1991 by U.S. Gypsum Co.

A limited license is extended to qualified design professionals

to duplicate and print this guide specification for the purpose

of incorporating products manufactured by U.S. Gypsum Co. into a

construction specification or purchase order.

Notice: We shall not be liable for incidental and consequential

damages, directly or indirectly sustained, nor for any loss

caused by application of these goods not in accordance with

current printed instructions or for other than the intended use.

Our liability is expressly limited to replacement of defective

goods. Any claim shall be deemed waived unless made in writing

to us within thirty (30) days from date it was or reasonably

should have been discovered.