ASTM C842-05(2015)

Standard Specification for Application of Interior Gypsum Plaster

ABSTRACT
This specification covers the minimum requirements for full-thickness interior gypsum plastering on gypsum, metal, masonry, or monolithic concrete bases designed or prepared to receive gypsum plaster. Gypsum plaster applied to the interior side of exterior walls of masonry or concrete shall be isolated from the exterior wall. Gypsum plasters shall not be used in exterior locations or interior wet areas. Plasters and other cementitious materials shall be kept dry until used; they shall be stored off the ground, under cover, and away from walls with condensation and other damp surfaces. Metal products shall be protected, while stored, against rusting. The surface preparations of plasters are presented in details. All plaster mixing shall be done by mechanical means unless hand mixing is specified. Plaster shall be applied by hand or machine as specified.
SCOPE
1.1 This specification covers the minimum requirements for full-thickness (in accordance with Table 1) interior gypsum plastering on gypsum, metal, masonry, or monolithic concrete bases designed or prepared to receive gypsum plaster.  (A) Base coat plastering of the same proportions as specified for unit masonry is not prohibited from being used over plain or reinforced monolithic concrete, provided the surface is first covered with a metal plaster base or first coated with a bonding compound.(B) Finish coat plaster applied direct to a bonding compound over vertical monolithic concrete shall be not more than 3/16 in. (4.8 mm) in thickness. Where more than 3/16 in. of finish coat is required to bring such vertical surface to a true plane, a base coat of plaster shall first be applied to the bonding compound.(C) Where horizontal or vertical monolithic concrete surfaces require more than 3/8 in. (9.5 mm) or 5/8 in. (15.9 mm) of plaster, respectively, to produce required lines or surfaces, metal plaster base shall be attached to the concrete before application of plaster. Where concrete surface requires the application of more than 1 in. (25.4 mm) of plaster to produce required lines or surfaces, lath shall be applied over furring secured to the concrete.
† Typo corrected editorially October 2010.  
1.1.1 Gypsum plaster applied to the interior side of exterior walls of masonry or concrete shall be isolated from the exterior wall.  
1.2 Gypsum plasters shall not be used in exterior locations or interior “wet” areas.  
Note 1: To secure desirable results, this specification should be coordinated with the provisions of Specification C841. General information concerning full thickness gypsum plastering is contained in Annex A2, Annex A3, and Annex A4.  
1.3 Details of construction for a specific assembly to achieve the required fire resistance shall be obtained from reports of fire-resistance tests, engineering evaluations, or listings from recognized fire testing laboratories.  
1.4 Details of construction to achieve required sound control shall be obtained from reports of tests conducted at recognized sound testing laboratories in accordance with the applicable sound tests of Test Methods E90, C423, or E492.  
1.5 The values stated in inch-pound units are to be regarded as the standard. The SI (metric) values given in parentheses are approximate and are provided for information purposes only.  
1.6 The text of this standard references notes and footnotes which provide explanatory material. These notes and footnotes (excluding those in tables and figures) shall not be considered as requirements of the standard.

General Information

• Status: Historical
• Publication Date: 30-Sep-2015
• ICS: 91.100.10 - Cement. Gypsum. Lime. Mortar
• Technical Committee: C11 - Gypsum and Related Building Materials and Systems
• Drafting Committee: C11.03 - Specifications for the Application of Gypsum and Other Products in Assemblies

Standards Content (Sample)

NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
Contact ASTM International (www.astm.org) for the latest information
Designation:C842 −05 (Reapproved 2015)
Standard Specification for
Application of Interior Gypsum Plaster
This standard is issued under the fixed designation C842; 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. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope C11 Terminology Relating to Gypsum and Related Building
Materials and Systems
1.1 This specification covers the minimum requirements for
C28/C28M Specification for Gypsum Plasters
full-thickness (in accordance with Table 1) interior gypsum
C35 Specification for Inorganic Aggregates for Use in Gyp-
plastering on gypsum, metal, masonry, or monolithic concrete
sum Plaster
bases designed or prepared to receive gypsum plaster.
C59/C59M Specification for Gypsum Casting Plaster and
1.1.1 Gypsum plaster applied to the interior side of exterior
Gypsum Molding Plaster
wallsofmasonryorconcreteshallbeisolatedfromtheexterior
C61/C61M Specification for Gypsum Keene’s Cement
wall.
C206 Specification for Finishing Hydrated Lime
1.2 Gypsum plasters shall not be used in exterior locations
C423 Test Method for SoundAbsorption and SoundAbsorp-
or interior “wet” areas.
tion Coefficients by the Reverberation Room Method
NOTE 1—To secure desirable results, this specification should be C631 Specification for Bonding Compounds for Interior
coordinated with the provisions of Specification C841. General informa-
Gypsum Plastering
tion concerning full thickness gypsum plastering is contained in Annex
C841 Specification for Installation of Interior Lathing and
A2, Annex A3, and Annex A4.
Furring
1.3 Details of construction for a specific assembly to
C1489 Specification for Lime Putty for Structural Purposes
achieve the required fire resistance shall be obtained from
E90 Test Method for Laboratory Measurement of Airborne
reports of fire-resistance tests, engineering evaluations, or
Sound Transmission Loss of Building Partitions and
listings from recognized fire testing laboratories.
Elements
1.4 Details of construction to achieve required sound con- E492 Test Method for Laboratory Measurement of Impact
trol shall be obtained from reports of tests conducted at Sound Transmission Through Floor-Ceiling Assemblies
recognized sound testing laboratories in accordance with the Using the Tapping Machine
applicable sound tests of Test Methods E90, C423,or E492.
3. Terminology
1.5 The values stated in inch-pound units are to be regarded
3.1 Definitions:
as the standard.The SI (metric) values given in parentheses are
3.1.1 Definitions shall be in accordance with Terminology
approximate and are provided for information purposes only.
C11.
1.6 The text of this standard references notes and footnotes
3.2 Definitions of Terms Specific to This Standard:
which provide explanatory material. These notes and footnotes
3.2.1 catfaces, n—blemishes or rough depressions in the
(excluding those in tables and figures) shall not be considered
finish coat.
as requirements of the standard.
3.2.2 coat, n—a thickness or layer of plaster applied over a
surface in a single application.
2. Referenced Documents
3.2.2.1 basecoat,n—thesumofthescratchandbrowncoats
2.1 ASTM Standards:
or the total coats in place prior to application of finish coats.
C5 Specification for Quicklime for Structural Purposes
3.2.2.2 brown coat, n—the second coat of plaster applied in
This specification is under the jurisdiction of ASTM Committee C11 on
three-coat work.
GypsumandRelatedBuildingMaterialsandSystemsandisthedirectresponsibility
3.2.2.3 finish coat, n—the last coat of plaster applied in
ofSubcommitteeC11.03onSpecificationsfortheApplicationofGypsumandOther
Products in Assemblies. either two-coat or three-coat work.
Current edition approved Oct. 1, 2015. Published October 2015. Originally
ε1 3.2.2.4 scratch coat, n—the first coat of plaster applied over
approved in 1976. Last previous edition approved in 2010 as C842– 05 (2010) .
a lath or other substrate.
DOI: 10.1520/C0842-05R15.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
3.2.2.5 three-coat work, n—plaster applied in three succes-
contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM
sive coats, leaving time between coats for setting or drying, or
Standards volume information, refer to the standard’s Document Summary page on
the ASTM website. both, of the plaster.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
C842−05 (2015)
3.2.2.6 two-coat work, n—scratch and brown coats applied or uneven heat or cold on the plaster, and maintained until the
from the same mix with no time allowed for setting of the permanent HVAC system is activated.
scratch coat before the brown coat is applied.
NOTE 2—The requirement should minimize the possibility of plaster
3.2.3 gypsum ready mixed plaster, n—calcined gypsum cracking due to structural movements caused by thermal changes from
outdoor temperature extremes during construction.
plaster, mixed at the mill with a mineral aggregate, designed to
function as a base coat to receive various finish coats.
6.2 Ventilation—Sufficient ventilation shall be provided to
removeexcesswatergivenoffthroughthedryingprocess.(See
3.2.4 metal bases, n—expanded metal, welded or woven
Appendix X2 for provisions for ventilating underside of roofs
wire, or punched sheet metal plaster bases.
and glazed buildings with and without operable windows.)
3.2.5 smooth-trowel finish, n—a finish resulting from steel
troweling.
7. Materials
3.2.6 texture finish, n—a finish resulting from (1) trowel
7.1 Gypsum Plasters—The following plasters shall conform
applicationfollowedbyfloatingortexturingofthesurfacewith
to Specification C28/C28M:
any of a variety of tools using a minimum of water or (2)
7.1.1 Ready mixed.
machine application which is or is not hand textured.
7.1.2 Neat.
7.1.3 Wood-fibered.
7.1.4 Gauging for finish coat.
TABLE 1 Thickness of Plaster
Thickness of Plaster Including Finish 7.2 Gypsum Casting and Molding Plasters—Specification
Plaster Base
Coat, in. (mm)
C5, C59/C59M.
Metal plaster base ⁄8 (16) min
1 7.3 Gypsum Keene’s Cement—Specification C61/C61M.
All other types of plaster base ⁄2 (13) min
Unit masonry ⁄8 (16) min
7.4 Lime:
A
Monolithic concrete surfaces:
BC
Vertical ⁄8 (16) min 7.4.1 Finishing Hydrated Lime—Specification C206, Type
C †
1 5
Horizontal ⁄8 (3) to ⁄8 (16 )
S.
A
Base coat plastering of the same proportions as specified for unit masonry is not
7.4.2 Quicklime for Structural Purposes—Specification C5.
prohibited from being used over plain or reinforced monolithic concrete, provided
7.4.3 Lime Putty for Structural Purposes—Specification
the surface is first covered with a metal plaster base or first coated with a bonding
C1489.
compound.
B
Finish coat plaster applied direct to a bonding compound over vertical monolithic
7.5 Lime Putty—Lime putty exceeding 8 weight % of
concrete shall be not more than ⁄16 in. (4.8 mm) in thickness. Where more
than ⁄16 in. of finish coat is required to bring such vertical surface to a true plane, unhydrated magnesium oxide shall not be used for finish coat
a base coat of plaster shall first be applied to the bonding compound.
plaster.
C
Where horizontal or vertical monolithic concrete surfaces require more
3 5
than ⁄8 in. (9.5 mm) or ⁄8 in. (15.9 mm) of plaster, respectively, to produce
7.6 Aggregates:
required lines or surfaces, metal plaster base shall be attached to the concrete
7.6.1 Aggregates for Base Coat Plaster—Specification C35.
before application of plaster. Where concrete surface requires the application of
more than 1 in. (25.4 mm) of plaster to produce required lines or surfaces, lath 7.6.2 Aggregates for Finish Coat Plasters—Specification
shall be applied over furring secured to the concrete.
C35, except that gradation shall be within the limits specified
†
Typo corrected editorially October 2010.
in Table 2.
7.6.3 Sand for job mixed lime putty-gypsum gauged, sand
float finish (see 9.6.6.1) shall be graded within the limits
specified in Table 3.
4. Delivery of Materials
7.7 Water—Water used in mixing and finishing plaster shall
4.1 All manufactured materials shall be delivered in the
be potable, and free of such amounts of mineral or organic
original packages, containers, or bundles bearing the brand
substances that affect the set, the plaster, or any metal in the
name and manufacturer (or supplier) identification.
system.
5. Protection of Materials
NOTE 3—Water containing salt or alum, or water in which tools have
5.1 Plasters and other cementitious materials shall be kept
been washed, accelerates the “set” and may cause efflorescence. Water
from stagnant pools and wells frequently contain organic or vegetable
dry until used; they shall be stored off the ground, under cover,
matter which may retard the “set,” cause staining, or interfere with the
and away from walls with condensation and other damp
bond.
surfaces. Metal products shall be protected, while stored,
7.8 Bonding Compounds—Specification C631.
against rusting.
6. Environmental Conditions
TABLE 2 Aggregate for Finish Coat Plasters, Percentage
Retained on Each Sieve, Cumulative
6.1 Temperatures—Where the ambient outdoor temperature
Perlite, Natural and Manufactured Sand
at the building site is less than 55 °F (13 °C), a temperature of
Sieve Size Volume,% Weight, %
not less than 55 °F (13 °C) and not more than 80 °F (27 °C)
max min max min
shall be maintained continuously inside the building for a No. 20 (850 µm) 0 . 0 .
No. 30 (600 µm) 10 . 0.5 .
period of not less than one week prior to the application of
No. 100 (150 µm) 100 40 100 40
plaster (Note 2). Temporary heat shall be evenly distributed,
No. 200 (75 µm) 100 70 100 70
using deflective or protective screens to prevent concentrated
C842−05 (2015)
TABLE 3 Sand for Job-Mixed Lime Putty-Gypsum Gaged Sand
9.1.3 All tools shall be kept clean.
Float Finish, Percent Retained on Each Sieve by Weight,
9.1.4 The setting time shall be not more than 4 h.
Cumulative
9.2 Hand Mixing—see Annex A3.1.
Sieve Size max min
No. 16 (1.18 mm) 0 0
9.3 MechanicalMixing—Inaccordancewithmanufacturer’s
No. 30 (600 µm) 50 20
printed directions. See Annex A3.2.
No. 50 (300 µm) 70 50
No. 100 (150 µm) 100 80
9.4 Base Coat Proportions:
9.4.1 Gypsum Neat Plaster—Proportions of sand, perlite, or
vermiculite aggregate to 100 lb (45.4 kg) of gypsum neat
plaster shall be not more than those specified in Table 4. (See
8. Surface Preparation
A2.3 for equivalent measure for aggregates.)
8.1 Substrates—Surfaces of substrates for the application of
9.4.2 Gypsum Ready Mixed Plaster—Shall be used with the
gypsum plaster shall be free of materials that will inhibit bond
addition of water only.
or adhesion, shall be straight, plumb, level, square, and true to
9.4.3 Gypsum Wood-Fibered Plaster—Proportion of damp,
required plan angles and curves. See A2.5. loose sand or perlite or vermiculite shall be not more than 1 ft
8.1.1 All accessories shall be securely attached to the
(0.028 m ) to 100 lb (45.4 kg) of gypsum wood-fibered plaster.
substrate and be installed to accommodate embedment of
9.5 Preparation of Lime Putty:
flanges.
9.5.1 Lime putty shall be prepared from Type S hydrated
8.1.2 Gypsum and Metal Lath—Shall have been installed in
lime or pulverized quicklime, in accordance with the manufac-
compliance with Specification C841.
turer’s printed directions.
8.2 Conditioning of Surfaces—All depressions in masonry
9.5.2 Hydrated Lime—Type S lime shall only be used after
and concrete surfaces deeper than ⁄8 in. (3.2 mm) shall be
soaking for the time period required in accordance with the
brought flush to the surface with compatible materials prior to
manufacturer’s printed directions.
plaster application. Fins or protrusions extending more
9.6 Finish Coat Proportions:
than ⁄16 in. (1.6 mm) from the surface shall be removed.
9.6.1 Finish coats shall be either ready mixed or job mixed
Protrusions less than ⁄16 in. (1.6 mm) shall be feathered out
in accordance with Table 5 and Table 6.
with compatible materials prior to plaster application.
9.6.1.1 Wherethicknessofthefinishcoatismorethan ⁄8 in.
8.2.1 Masonry—All masonry surfaces shall be wetted im-
(3.2 mm), the proportion of the gypsum gauging plaster shall
mediately prior to the plaster application. No free water shall
be increased to minimize shrinkage type cracks.
remain visible on the substrate surface.
9.6.2 Troweled Finishes of lime putty gauged with gypsum
8.2.1.1 Wherethesurfaceistoosmoothtoprovidemechani-
gauging plaster or ready mixed gypsum plaster shall be
cal key, the surface shall be roughened or bonding compound
proportioned in accordance with Table 5.
shall be used. (See Annex A2.5 and A2.6.)
9.6.2.1 Where finish in9.6.2 is to be applied over base coats
8.2.1.2 Where bond cannot be obtained over the entire
containing perlite or vermiculite, the addition of not less
surface by the methods specified in 8.2.1.1, self-furring metal
3 3 3 3
than ⁄2 ft (0.014 m ) or not more than 1 ft (0.028 m)offine
lath shall be used in accordance with Specification C841.
aggregate meeting the sieve analysis of Table 2 shall be added
8.2.2 Monolithic concrete—bonding compounds shall be
to the mix.
used prior to plastering all monolithic concrete surfaces. (See
9.6.3 Troweled finishes of lime putty gauged with gypsum
A2.6.)
Keene’s cement shall be specified as medium or hard and shall
8.2.3 Grounds, beads, and screeds shall be installed prior to
be proportioned in accordance with Table 5.
the plastering as modified herein.
9.6.3.1 When finish in 9.6.3 is mechanically mixed, the
8.3 Grouting:
water shall be placed in the mixer first, then the lime, the fine
8.3.1 Metal bases for solid partitions shall be grouted with
aggregate (if used), and finally the gypsum Keene’s cement.
gypsum plaster leaving ⁄4 in. (6.4 mm) below the top edge of
9.6.4 Troweledfinishesofgypsumreadymixedplastershall
the base, and be formed with a center groove so that the lath
be mixed in accordance with Table 5.
extends ⁄4 in. (19 mm) below the top edge of the base, or
9.6.5 Float finishes of lime putty gauged with gypsum
plaster grout shall be placed after installation of lath.
gauging plaster shall be proportioned in accordance with Table
8.3.2 MetalFrames—Hollowdoorandwindowframesshall
5.
be filled with gypsum plaster grout.
9.6.5.1 When finish in 9.6.6 is to be mixed with sand, the
sand shall be graded within the limits shown for basecoats in
9. Mix Design
Specification C35 except that all of the sand shall pass a No. 8
9.1 Mixing, General—All plaster
...

This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version. Because
it may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current version
of the standard as published by ASTM is to be considered the official document.
´1
Designation: C842 − 05 (Reapproved 2010) C842 − 05 (Reapproved 2015)
Standard Specification for
Application of Interior Gypsum Plaster
This standard is issued under the fixed designation C842; 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. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
ε NOTE—Typos were corrected editorially in Table 1 and 9.6.2.1 in October 2010.
1. Scope
1.1 This specification covers the minimum requirements for full-thickness (in accordance with Table 1) interior gypsum
plastering on gypsum, metal, masonry, or monolithic concrete bases designed or prepared to receive gypsum plaster.
1.1.1 Gypsum plaster applied to the interior side of exterior walls of masonry or concrete shall be isolated from the exterior wall.
1.2 Gypsum plasters shall not be used in exterior locations or interior “wet” areas.
NOTE 1—To secure desirable results, this specification should be coordinated with the provisions of Specification C841. General information
concerning full thickness gypsum plastering is contained in Annex A2, Annex A3, and Annex A4.
1.3 Details of construction for a specific assembly to achieve the required fire resistance shall be obtained from reports of
fire-resistance tests, engineering evaluations, or listings from recognized fire testing laboratories.
1.4 Details of construction to achieve required sound control shall be obtained from reports of tests conducted at recognized
sound testing laboratories in accordance with the applicable sound tests of Test Methods E90, C423, or E492.
1.5 The values stated in inch-pound units are to be regarded as the standard. The SI (metric) values given in parentheses are
approximate and are provided for information purposes only.
1.6 The text of this standard references notes and footnotes which provide explanatory material. These notes and footnotes
(excluding those in tables and figures) shall not be considered as requirements of the standard.
2. Referenced Documents
2.1 ASTM Standards:
C5 Specification for Quicklime for Structural Purposes
C11 Terminology Relating to Gypsum and Related Building Materials and Systems
C28/C28M Specification for Gypsum Plasters
C35 Specification for Inorganic Aggregates for Use in Gypsum Plaster
C59/C59M Specification for Gypsum Casting Plaster and Gypsum Molding Plaster
C61/C61M Specification for Gypsum Keene’s Cement
C206 Specification for Finishing Hydrated Lime
C423 Test Method for Sound Absorption and Sound Absorption Coefficients by the Reverberation Room Method
C631 Specification for Bonding Compounds for Interior Gypsum Plastering
C841 Specification for Installation of Interior Lathing and Furring
C1489 Specification for Lime Putty for Structural Purposes
E90 Test Method for Laboratory Measurement of Airborne Sound Transmission Loss of Building Partitions and Elements
E492 Test Method for Laboratory Measurement of Impact Sound Transmission Through Floor-Ceiling Assemblies Using the
Tapping Machine
3. Terminology
3.1 Definitions:
3.1.1 Definitions shall be in accordance with Terminology C11.
This specification is under the jurisdiction of ASTM Committee C11 on Gypsum and Related Building Materials and Systems and is the direct responsibility of
Subcommittee C11.03 on Specifications for the Application of Gypsum and Other Products in Assemblies.
Current edition approved Oct. 1, 2010Oct. 1, 2015. Published December 2010October 2015. Originally approved in 1976. Last previous edition approved in 20052010
ε1
as C842–05.– 05 (2010) . DOI: 10.1520/C0842-05R10e1.10.1520/C0842-05R15.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM Standards
volume information, refer to the standard’s Document Summary page on the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
C842 − 05 (2015)
3.2 Definitions of Terms Specific to This Standard:
3.2.1 catfaces, n—blemishes or rough depressions in the finish coat.
3.2.2 coat, n—a thickness or layer of plaster applied over a surface in a single application.
3.2.2.1 base coat, n—the sum of the scratch and brown coats or the total coats in place prior to application of finish coats.
3.2.2.2 brown coat, n—the second coat of plaster applied in three-coat work.
3.2.2.3 finish coat, n—the last coat of plaster applied in either two-coat or three-coat work.
3.2.2.4 scratch coat, n—the first coat of plaster applied over a lath or other substrate.
3.2.2.5 three-coat work, n—plaster applied in three successive coats, leaving time between coats for setting or drying, or both,
of the plaster.
3.2.2.6 two-coat work, n—scratch and brown coats applied from the same mix with no time allowed for setting of the scratch
coat before the brown coat is applied.
3.2.3 gypsum ready mixed plaster, n—calcined gypsum plaster, mixed at the mill with a mineral aggregate, designed to function
as a base coat to receive various finish coats.
3.2.4 metal bases, n—expanded metal, welded or woven wire, or punched sheet metal plaster bases.
3.2.5 smooth-trowel finish, n—a finish resulting from steel troweling.
3.2.6 texture finish, n—a finish resulting from (1) trowel application followed by floating or texturing of the surface with any
of a variety of tools using a minimum of water or (2) machine application which is or is not hand textured.
TABLE 1 Thickness of Plaster
Thickness of Plaster Including Finish
Plaster Base
Coat, in. (mm)
Metal plaster base ⁄8 (16) min
All other types of plaster base ⁄2 (13) min
Unit masonry ⁄8 (16) min
A
Monolithic concrete surfaces:
BC
Vertical ⁄8 (16) min
C †
1 5
Horizontal ⁄8 (3) to ⁄8 (16 )
A
Base coat plastering of the same proportions as specified for unit masonry is not
prohibited from being used over plain or reinforced monolithic concrete, provided
the surface is first covered with a metal plaster base or first coated with a bonding
compound.
B
Finish coat plaster applied direct to a bonding compound over vertical monolithic
concrete shall be not more than ⁄16 in. (4.8 mm) in thickness. Where more
than ⁄16 in. of finish coat is required to bring such vertical surface to a true plane,
a base coat of plaster shall first be applied to the bonding compound.
C
Where horizontal or vertical monolithic concrete surfaces require more
3 5
than ⁄8 in. (9.5 mm) or ⁄8 in. (15.9 mm) of plaster, respectively, to produce
required lines or surfaces, metal plaster base shall be attached to the concrete
before application of plaster. Where concrete surface requires the application of
more than 1 in. (25.4 mm) of plaster to produce required lines or surfaces, lath
shall be applied over furring secured to the concrete.
†
Typo corrected editorially October 2010.
4. Delivery of Materials
4.1 All manufactured materials shall be delivered in the original packages, containers, or bundles bearing the brand name and
manufacturer (or supplier) identification.
5. Protection of Materials
5.1 Plasters and other cementitious materials shall be kept dry until used; they shall be stored off the ground, under cover, and
away from walls with condensation and other damp surfaces. Metal products shall be protected, while stored, against rusting.
6. Environmental Conditions
6.1 Temperatures—Where the ambient outdoor temperature at the building site is less than 55 °F (13 °C), a temperature of not
less than 55 °F (13 °C) and not more than 80 °F (27 °C) shall be maintained continuously inside the building for a period of not
less than one week prior to the application of plaster (Note 2). Temporary heat shall be evenly distributed, using deflective or
protective screens to prevent concentrated or uneven heat or cold on the plaster, and maintained until the permanent HVAC system
is activated.
NOTE 2—The requirement should minimize the possibility of plaster cracking due to structural movements caused by thermal changes from outdoor
temperature extremes during construction.
C842 − 05 (2015)
6.2 Ventilation—Sufficient ventilation shall be provided to remove excess water given off through the drying process. (See
Appendix X2 for provisions for ventilating underside of roofs and glazed buildings with and without operable windows.)
7. Materials
7.1 Gypsum Plasters—The following plasters shall conform to Specification C28/C28M:
7.1.1 Ready mixed.
7.1.2 Neat.
7.1.3 Wood-fibered.
7.1.4 Gauging for finish coat.
7.2 Gypsum Casting and Molding Plasters—Specification C5, C59/C59M.
7.3 Gypsum Keene’s Cement—Specification C61/C61M.
7.4 Lime:
7.4.1 Finishing Hydrated Lime—Specification C206, Type S.
7.4.2 Quicklime for Structural Purposes—Specification C5.
7.4.3 Lime Putty for Structural Purposes—Specification C1489.
7.5 Lime Putty—Lime putty exceeding 8 weight % of unhydrated magnesium oxide shall not be used for finish coat plaster.
7.6 Aggregates:
7.6.1 Aggregates for Base Coat Plaster—Specification C35.
7.6.2 Aggregates for Finish Coat Plasters—Specification C35, except that gradation shall be within the limits specified in Table
2.
7.6.3 Sand for job mixed lime putty-gypsum gauged, sand float finish (see 9.6.6.1) shall be graded within the limits specified
in Table 3.
7.7 Water—Water used in mixing and finishing plaster shall be potable, and free of such amounts of mineral or organic
substances that affect the set, the plaster, or any metal in the system.
NOTE 3—Water containing salt or alum, or water in which tools have been washed, accelerates the “set” and may cause efflorescence. Water from
stagnant pools and wells frequently contain organic or vegetable matter which may retard the “set,” cause staining, or interfere with the bond.
7.8 Bonding Compounds—Specification C631.
8. Surface Preparation
8.1 Substrates—Surfaces of substrates for the application of gypsum plaster shall be free of materials that will inhibit bond or
adhesion, shall be straight, plumb, level, square, and true to required plan angles and curves. See A2.5.
8.1.1 All accessories shall be securely attached to the substrate and be installed to accommodate embedment of flanges.
8.1.2 Gypsum and Metal Lath—Shall have been installed in compliance with Specification C841.
8.2 Conditioning of Surfaces—All depressions in masonry and concrete surfaces deeper than ⁄8 in. (3.2 mm) shall be brought
flush to the surface with compatible materials prior to plaster application. Fins or protrusions extending more than ⁄16 in. (1.6 mm)
from the surface shall be removed. Protrusions less than ⁄16 in. (1.6 mm) shall be feathered out with compatible materials prior
to plaster application.
8.2.1 Masonry—All masonry surfaces shall be wetted immediately prior to the plaster application. No free water shall remain
visible on the substrate surface.
8.2.1.1 Where the surface is too smooth to provide mechanical key, the surface shall be roughened or bonding compound shall
be used. (See Annex A2.5 and A2.6.)
8.2.1.2 Where bond cannot be obtained over the entire surface by the methods specified in 8.2.1.1, self-furring metal lath shall
be used in accordance with Specification C841.
8.2.2 Monolithic concrete—bonding compounds shall be used prior to plastering all monolithic concrete surfaces. (See A2.6.)
8.2.3 Grounds, beads, and screeds shall be installed prior to the plastering as modified herein.
8.3 Grouting:
TABLE 2 Aggregate for Finish Coat Plasters, Percentage
Retained on Each Sieve, Cumulative
Perlite, Natural and Manufactured Sand
Sieve Size Volume,% Weight, %
max min max min
No. 20 (850 μm) 0 . 0 .
No. 30 (600 μm) 10 . 0.5 .
No. 100 (150 μm) 100 40 100 40
No. 200 (75 μm) 100 70 100 70
C842 − 05 (2015)
TABLE 3 Sand for Job-Mixed Lime Putty-Gypsum Gaged Sand
Float Finish, Percent Retained on Each Sieve by Weight,
Cumulative
Sieve Size max min
No. 16 (1.18 mm) 0 0
No. 30 (600 μm) 50 20
No. 50 (300 μm) 70 50
No. 100 (150 μm) 100 80
8.3.1 Metal bases for solid partitions shall be grouted with gypsum plaster leaving ⁄4 in. (6.4 mm) below the top edge of the
base, and be formed with a center groove so that the lath extends ⁄4 in. (19 mm) below the top edge of the base, or plaster grout
shall be placed after installation of lath.
8.3.2 Metal Frames—Hollow door and window frames shall be filled with gypsum plaster grout.
9. Mix Design
9.1 Mixing, General—All plaster mixing shall be done by mechanical means unless hand mixing is specified.
9.1.1 Retempered, partially set, frozen, caked or lumpy material shall not be used.
9.1.2 Each batch shall be mixed separately and mixers shall be free of all set and hardened materials prior to mixing each batch.
9.1.3 All tools shall be kept clean.
9.1.4 The setting time shall be not more than 4 h.
9.2 Hand Mixing—see Annex A3.1.
9.3 Mechanical Mixing—In accordance with manufacturer’s printed directions. See Annex A3.2.
9.4 Base Coat Proportions:
9.4.1 Gypsum Neat Plaster—Proportions of sand, perlite, or vermiculite aggregate to 100 lb (45.4 kg) of gypsum neat plaster
shall be not more than those specified in Table 4. (See A2.3 for equivalent measure for aggregates.)
9.4.2 Gypsum Ready Mixed Plaster—Shall be used with the addition of water only.
A
TABLE 4 Base Coat Proportions
B
Aggregates
C
Plaster Base Sand Perlite or Vermiculite
3 3 3 3
By Volume, ft (m ), Damp and Loose By Weight, lb (kg), Damp and Loose By Volume, ft (m )
Over Gypsum Lath
Two-coat work:
Base coat 2 ⁄2 (0.071) 250 (113) 2 (0.06)
Three-coat work:
Scratch coat 2 (0.056) 200 (91) 2 (0.06)
Brown coat 3 (0.085) 300 (136) 2 (0.06)
or
Scratch and 2 ⁄2 (0.071) 250 (113) .
brown coats
Over Metal Lath
Three-coat work:
Scratch coat 2 (0.056) 200 (91) 2 (0.06)
Brown coat 3 (0.085) 300 (136) 2 (0.06)
or
Scratch and 2 ⁄2 (0.071) 250 (113) .
brown coats
Over Unit Masonry (Note 6)
Two-coat work:
Base coat 3 (0.085) 300 (136) 3 (0.085)
Three-coat work:
Scratch coat 3 (0.085) 300 (136) 3 (0.085)
Brown coat 3 (0.085) 300 (136) 3 (0.085)
D
Over Monolithic Concrete
For base coat proportions applicable to monolithic concrete, see 10.2.1.
A
The proportions in Table 3 are applicable for both hand and machine application of plaster. See plaster manufacturer’s instructions for application of machine-applied
plaster.
B
Use of an accurate devic
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