ASTM C926-98a
(Specification)Standard Specification for Application of Portland Cement-Based Plaster
Standard Specification for Application of Portland Cement-Based Plaster
SCOPE
1.1 This specification covers the requirements for the application of full thickness portland cement-based plaster for exterior (stucco) and interior work.
1.2 This specification sets forth tables for proportioning of various plaster mixes and plaster thickness. Note 1-General information will be found in Annex A1. Design considerations will be found in Annex A2.
1.3 The values stated in inch-pound units are the standard. The values in parentheses are for information only.
1.4 The text of this specification references notes and footnotes that provide explanatory material. These notes and footnotes (excluding those in tables and figures) shall not be considered as requirements of the specification.
General Information
Relations
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NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.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: C 926 – 98a
Standard Specification for
Application of Portland Cement-Based Plaster
This standard is issued under the fixed designation C 926; 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 (e) indicates an editorial change since the last revision or reapproval.
1. Scope C 260 Specification forAir-EntrainingAdmixtures for Con-
crete
1.1 This specification covers the requirements for the appli-
2,3
C 595M Specification for Blended Hydraulic Cements
cation of full thickness portland cement-based plaster for
C 631 Specification for Bonding Compounds for Interior
exterior (stucco) and interior work.
Plastering
1.2 This specification sets forth tables for proportioning of
C 897 Specification for Aggregate for Job-Mixed Portland
various plaster mixes and plaster thickness.
Cement-Based Plasters
NOTE 1—General information will be found in Annex A1. Design
C 932 Specification for Surface-Applied BondingAgent for
considerations will be found in Annex A2.
Exterior Plastering
1.3 The values stated in inch-pound units are to be regarded
C 1063 Specification for Installation of Lathing and Furring
as the standard.The SI (metric) values given in parentheses are
to Receive Interior and Exterior Portland Cement-Based
approximate and are provided for information purposes only.
Plaster
1.4 The text of this specification references notes and
C 1116 Specification for Fiber-Reinforced Concrete and
footnotes that provide explanatory material. These notes and
Shotcrete
footnotes (excluding those in tables and figures) shall not be
C 1328 Specification for Plastic (Stucco) Cement
considered as requirements of the specification.
E 90 Test Method for Laboratory Measurement of
1.5 Details of construction for a specific assembly to
Airborne-Sound Transmission Loss of Building Partitions
achieve the required fire resistance shall be obtained from
E 119 Test Methods for Fire Tests of Building Construction
reports of fire-resistance tests, engineering evaluations, or
and Materials
listings from recognized fire testing laboratories.
E 492 Test Method for Laboratory Measurement of Impact
Sound Transmission Through Floor-Ceiling Assemblies
2. Referenced Documents
Using the Tapping Machine
2.1 ASTM Standards:
2.2 ANSI Standard:
C 11 Terminology Relating to Gypsum and Related Build-
A108.1 Specification for Installation of Ceramic Tile
ing Materials and Systems
3. Terminology
C 25 Test Methods for Chemical Analysis of Limestone,
Quicklime, and Hydrated Lime
3.1 Terms shall be defined as in Terminologies C 11 and
C 35 Specification for Inorganic Aggregates for Use in
C 219, except as modified herein.
Gypsum Plaster
3.2 Definitions of Terms Specific to This Standard:
C 91 Specification for Masonry Cement
3.2.1 accelerator—an admixture that will shorten the set-
C 150 Specification for Portland Cement
ting time of plaster.
C 206 Specification for Finishing Hydrated Lime
3.2.2 admixture—a material other than water, aggregate, or
C 207 Specification for Hydrated Lime for Masonry Pur-
basic cementitious material added to the batch before or during
poses
job mixing.
C 219 Terminology Relating to Hydraulic Cement
3.2.3 acid etching—the cleansing and controlled erosion of
a solid surface, using an acid wash.
This specification is under the jurisdiction of ASTM Committee C-11 on
Gypsum and Related Building Materials and Systems and is the direct responsibility
of Subcommittee C11.03 on Specifications for Application of Gypsum and Other Annual Book of ASTM Standards, Vol 04.02.
Products on Assemblies. Annual Book of ASTM Standards, Vol 04.06.
Current edition approved June 10, 1998. Published December 1998. Originally Annual Book of ASTM Standards, Vol 04.07.
published as C 926–81. Last previous edition C 926–98a. Available from American National Standards Institute, 11 W. 42nd St., 13th
Annual Book of ASTM Standards, Vol 04.01. Floor, New York, NY 10036.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
C 926
3.2.4 air entrainment—the use of an air-entraining admix- 3.2.14 fiber, natural or synthetic—an elongated fiber or
ture or air-entraining cementitious material in a plaster mix to strand admixture added to plaster mix to improve cohesiveness
yield a controlled quantity of minute (typically between 10 and or pumpability, or both.
1000 µm in diameter) disconnected air bubbles in the plaster 3.2.15 floating—act of compacting and leveling brown-coat
(see entrapped air). plaster to a reasonably true surface plane using a float tool or
3.2.5 backplaster—plaster applied to the face of metal lath the act of bringing the aggregate to the surface of finish-coat
plaster.
opposite a previously applied plaster.
3.2.16 key (also mechanical key)—plaster that physically
3.2.6 bond—the state of adhesion between plaster coats or
surrounds, penetrates, or deforms to lock onto the perforations
between plaster and plaster base.
or irregularities of the plaster base or previous coat of plaster.
3.2.7 bonding compound or agent—compounds surface ap-
3.2.17 metal plaster base—expanded metal lath, or welded
plied or integrally mixed with plaster to improve the quality of
or woven wire lath.
bond between plaster and plaster base or between plaster coats.
3.2.18 plaster—portland cement-based cementitious mix-
3.2.8 cementitious material—a material that, when mixed
ture (see stucco).
with water and with or without aggregate, provides the
3.2.19 required—pertaining to a mandatory obligation im-
plasticity and the cohesive and adhesive properties necessary
posedbyaforceoutsideofthisspecification,suchasabuilding
for placement and the formation of a rigid mass.
code, project specification, contract, or purchase order.
3.2.9 coat—a thickness of plaster applied in a single opera-
3.2.20 rustication (also “break”)—an interruption or
tion.
change in plane of a plastered surface.
3.2.9.1 basecoat—all plaster applied before the application
3.2.21 scoring (also known as “scratching”)—the grooving
of the finish coat.
of the surface of an unset plaster coat to provide a key for a
3.2.9.2 bedding coat—a plaster coat that receives aggregate
subsequent coat.
or other decorative material impinged into its surface before it
3.2.22 set—thechemicalandphysicalchangeinplasterasit
sets.
goes from a plastic, workable state to a rigid state.
3.2.9.3 brown coat—in three-coat work, the second coat,
3.2.23 stucco—portland cement-based plaster used on exte-
applied over the scratch coat. In two-coat work, brown coat
rior locations.
refers to the double-up basecoat. In either use, the brown coat
3.2.24 stucco finish—a factory-prepared, dry blend of ma-
is the coat directly beneath the finish coat.
terials for finish coat applications.
3.2.9.4 dash-bond coat—a thick wet mixture of portland
3.2.25 temper, v—to mix or restore unset plaster with water
cement and water, with or without aggregate, dashed onto the
to a workable consistency.
surface of a plaster base such as smooth monolithic concrete or
3.2.26 texture—any surface appearance as contrasted to a
concrete block surfaces to improve the mechanical key for
smooth surface.
subsequent plaster coats.
3.2.9.5 double-up coat—the brown-coat plaster applied to
4. Materials
the scratch coat plaster before the scratch-coat plaster has set.
4.1 Materials shall conform to the requirements of the
3.2.9.6 finish coat—the final layer of plaster applied over
referencedspecificationsandstandardsandtotherequirements
basecoat plaster.
specified herein.
3.2.9.7 fog coat—a light coat of cement and water, with or
4.2 Cement:
without aggregate or color pigment, applied by machine spray
4.2.1 Portland Cement—SpecificationC 150,TypeI,II,and
to improve color consistency.
III, as specified. White where specified.
3.2.9.8 scratch coat—the first coat of plaster applied to a
4.2.2 Air-Entraining Portland Cement—Specification
plaster base.
C 150, type as specified. White where specified.
3.2.9.9 skim coat—a thin finish coat applied to an existing
4.2.3 Masonry Cement—Specification C 91, Types N, S,
plaster surface or other substrate to improve appearance.
and M. White where specified.
3.2.9.10 three-coat work—application of plaster in three
4.2.4 Blended Hydraulic Cement—Specification C 595,
successive coats with time between coats for setting or drying,
Type IP, I(PM), IS, and I(SM) as specified.
or both.
4.2.5 Air-Entraining Blended Hydraulic Cement—
3.2.10 cold joint (“joining” or “jointing”)—the juncture of
Specification C 595, Type IP-A, I(PM)-A, IS-A, and I(SM)-A
fresh plaster application adjacent to set plaster, in the same
as specified.
plane.
4.2.6 Plastic Cement—Plastic Cement shall meet the re-
3.2.11 curing—the act or processes of producing a moisture
quirements of Specification C 1328, Standard Specification for
environment favorable to cement hydration, resulting in the
Plastic (Stucco) Cement.
setting or hardening of the plaster.
NOTE 2—Plastic cements are not available nationally.
3.2.12 entrapped air—unintentional air voids in the plaster
generally larger than 1 mm. 4.3 Type “S” Hydrated Lime—A hydrated lime that con-
3.2.13 factory prepared (“mill-mixed” or “ready mixed”)— tains not more than 8 % unhydrated oxides when tested in
pertaining to material combinations that have been formulated accordance with Test Methods C 25. See Specifications C 206
and dry-blended by the manufacturer, requiring only the and C 207 for a complete description of a Type “S” hydrated
addition of and mixing with water to produce plaster. lime.
C 926
4.4 Aggregates: 5.2.2.2 Application of a dash-bond coat applied forcefully
4.4.1 Sand for Base Coats—Specification C 897.Aggregate against the surface, left untroweled, undisturbed, and moist
failing to meet gradation limits in Specification C 897 shall be cured for at least 24 h, or
permitted to be used, provided the plaster made with this sand 5.2.2.3 Application of a bonding compound suitable for
has an acceptable demonstrated performance record in similar exterior or interior exposure solid surfaces in accordance with
construction and climate conditions. the manufacturer’s written directions.
4.4.2 Perlite—Specification C 35. 5.2.3 Wherebondcannotbeobtainedovertheentiresurface
4.4.3 Sand for Job-Mixed Finish Coats—Specification to receive plaster by one or more of the methods in 5.2.2, or
C 897. where total plaster thickness will exceed the total thickness
4.5 Water—Water used in mixing, application, and finishing specified in Table 1 for types of solid bases, furred or
of plaster shall be clean, fresh, suitable for domestic water self-furring metal plaster base shall be installed in accordance
consumption, and free of such amounts of mineral or organic with Specification C 1063.
substances as would affect the set, the plaster, or any metal in
6. Plaster Proportions and Mixing
the system.
6.1 Proportions:
4.6 Admixtures—See 3.2.2 and .
6.1.1 All portland cement plasters shall be mixed and
4.7 Fibers—Specification C 1116 on alkali-resistant fibers,
proportioned in accordance with the following tables and
glass fibers, nylon, polypropylene or carbon fibers.
accompanying requirements, using measuring devices of
5. Requirements for Bases to Receive Portland Cement-
known volume with successive batches proportioned alike.
Based Plaster 6.1.2 Plaster mix used shall be as designated and referenced
to Table 2.
5.1 Metal bases and accessories used to receive plaster shall
6.1.3 Base-coat proportions shall be as shown inTable 3 for
be installed in conformance with Specification C 1063, except
the mix specified from Table 2.
as otherwise specified.
6.1.3.1 Measurement of Materials—The method of measur-
NOTE 3—All metal, or PVC, or CPVC plastic members should be free
ing materials for the plaster shall be such that the specified
of deleterious amounts of rust, oil, or other foreign matter, which could
proportions are controlled and accurately maintained. The
cause bond failure or unsightly discoloration.
weights per cubic foot of the materials are considered to be as
5.2 Surfaces of solid bases to receive plaster, such as
follows:
masonry, stone, cast-in-place or precast concrete shall be
3 3
Material Weight, lb/ft (kg/m )
straight and true within ⁄4 in. in 10 ft (2.1 mm/m) and shall be
Portland cement 94 (1505)
free of form oil or other elements, which would interfere with
Blended cement Weight printed on bag
bonding. Form ties or other obstructions shall be removed or
Masonry or plastic cement Weight printed on bag
trimmed back even with the surface of the solid base.
Hydrated Lime 40 (640)
Lime Putty 80 (1280)
5.2.1 Solid surfaces shall have the suction (ability to absorb
Sand, Damp and Loose (6.1.3.2) 80 (1280) of dry sand
water) or surface roughness, or both, to provide the bond
required for the plaster. 6.1.3.2 For purposes of this specification, a weight of 80 lb
5.2.2 Smooth or nonabsorbent solid surfaces, such as cast- (1280 kg) of oven-dried sand shall be used. This is, in most
in-place or precast concrete, shall be prepared to receive cases, equivalent to one cubic foot of loose, damp sand.
portland cement plaster by one of the following methods: 6.1.4 Finish-coat proportions for job-mixed finish coats
5.2.2.1 Sandblasting, wire brushing, acid etching, or chip- shall be as specified in Table 4.
ping or a combination thereof, 6.1.5 Factory-Prepared Finish Coats—See 3.2.14.
A
TABLE 1 Nominal Plaster Thickness for Three- and Two-Coat Work, in. (mm)
Vertical Horizontal
B B
BASE 1st Coat 2nd Coat 3rd Coat Total 1st Coat 2nd Coat 3rd Coat Total
Interior/Exterior
C
Three-coat work:
3 3 1 7 1 1 1 5
Metal plaster base ⁄8 (9.5) ⁄8 (9.5) ⁄8 (3) ⁄8 (22) ⁄4 (6) ⁄4 (6) ⁄8 (3) ⁄8 (16)
Solid plaster base:
1 1 1 5
Unit masonry ⁄4 (4) ⁄4 (6) ⁄8 (3) ⁄8 (16) Use two-coat work
1 1 1 5 3
Cast-in-place or precast ⁄4 (6) ⁄4 (6) ⁄8 (3) ⁄8 (16) ⁄8 (9.5), max
concrete
1 1 1 7 1 1 1 7
Metal plaster base over solid ⁄2 (12.5) ⁄4 (6) ⁄8 (3) ⁄8 (22) ⁄2 (12.5) ⁄4 (6) ⁄8 (3) ⁄8 (22)
base
Two-coat work:
Solid plaster base:
3 1 1 3
Unit masonry ⁄8 (9.5) ⁄8 (3) ⁄2 (12.5) ⁄8 (9.5)
1 1 3 3
Cast-in-place or pre-cast ⁄4 (6) ⁄8 (3) ⁄8 (9.5) ⁄8 (9.5)
concrete
A
Exclusive of texture.
B
For solid plaster partitions, additional coats shall be applied to meet the finished thickness specified.
C
For exposed aggregate finishes, the second (brown) coat shall become the “bedding” coat and shall be of sufficient thickness to receive and hold the aggregate.
C 926
TABLE 2 Plaster Bases—Permissible Mixes
abrupt changes in the unifor
...
Questions, Comments and Discussion
Ask us and Technical Secretary will try to provide an answer. You can facilitate discussion about the standard in here.