1、Designation: C28/C28M 10 (Reapproved 2015)Standard Specification forGypsum Plasters1This standard is issued under the fixed designation C28/C28M; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last revision. A number i
2、n parentheses indicates the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.This standard has been approved for use by agencies of the U.S. Department of Defense.1. Scope1.1 This specification covers gypsum mill-mixed plaster,gypsu
3、m neat plaster, gypsum wood-fibered plaster, and gyp-sum gauging plaster.NOTE 1Specification C842 contains application procedures for inte-rior gypsum plaster.1.2 The values stated in either SI units or inch-pound unitsare to be regarded separately as standard. Within the text, theSI units are shown
4、 in brackets. The values stated in eachsystem may not be exact equivalents; therefore, each systemshall be used independently of the other. Combining valuesfrom the two systems may result in non-conformance with thestandard. This paragraph does not apply to the appendix.1.3 The text of this standard
5、 references notes and footnoteswhich provide explanatory material. These notes and footnotes(excluding those in tables and figures) shall not be consideredas requirements of the standard.1.4 This standard does not purport to address all of thesafety concerns, if any, associated with its use. It is t
6、heresponsibility 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.2. Referenced Documents2.1 ASTM Standards:2C11 Terminology Relating to Gypsum and Related BuildingMaterials and SystemsC22/C22M
7、Specification for GypsumC35 Specification for Inorganic Aggregates for Use in Gyp-sum PlasterC471M Test Methods for ChemicalAnalysis of Gypsum andGypsum Products (Metric)C472 Test Methods for Physical Testing of Gypsum, Gyp-sum Plasters and Gypsum ConcreteC778 Specification for SandC842 Specificatio
8、n for Application of Interior Gypsum Plas-terE11 Specification for Woven Wire Test Sieve Cloth and TestSieves3. Terminology3.1 DefinitionsDefinitions shall be in accordance withTerminology C11.3.2 Definitions of Terms Specific to This Standard:3.2.1 gypsum gauging plaster for finish coat, na calcine
9、dgypsum plaster designed to be mixed with lime putty for thefinish coat.3.2.2 gypsum neat plaster, ncalcined gypsum mixed at themill with other ingredients to control working quality andsetting time.3.2.2.1 DiscussionNeat plaster is either fibered or unfi-bered. The addition of aggregate is required
10、 on the job.3.2.3 gypsum mill-mixed plaster, ncalcined gypsumplaster, mixed at the mill with a mineral aggregate, designed tofunction as a base coat to receive various finish coats.3.2.3.1 DiscussionOther materials are not prohibited frombeing added to control setting time and other desirable workin
11、gproperties.3.2.4 gypsum wood-fibered plaster, na calcined gypsumplaster in which wood fiber is used as an aggregate.4. Materials4.1 Calcined GypsumCalcined gypsum shall be manufac-tured from gypsum meeting the requirements of SpecificationC22/C22M.4.2 Vermiculite Aggregate, Specification C35.4.3 Pe
12、rlite Aggregate, Specification C35.4.4 Sand Aggregate, Specification C35.4.5 Ottawa Sand, Specification C778 for 2030 sand.4.6 Wood Fiber, non staining wood fiber.1This specification is under the jurisdiction of ASTM Committee C11 onGypsum and Related Building Materials and Systems and is the direct
13、 responsibilityof Subcommittee C11.01 on Specifications and Test Methods for Gypsum Products.Current edition approved Oct. 1, 2010. Published October 2015. Originallyapproved in 1920. Last previous edition approved in 2010 as C28/C28M 10. DOI:10.1520/C0028_C0028M-10R15.2For referenced ASTM standards
14、, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 194
15、28-2959. United States15. Composition5.1 When tested in accordance with Test Methods C471M,calcined gypsum shall contain no less than 66.0 weight %CaSO412 H2O.5.2 Aggregateplasters shall contain a volume of aggregatenot more than that shown in Table 1.NOTE 2An approximation of the aggregate content
16、may be made byusing the test methods in the appendix. A more accurate method fordetermining sand in plaster is described in Test Methods C471M. TestMethods C471M requires that the original sand and plaster components beavailable separately.6. Mechanical Properties6.1 Compressive StrengthWhen tested
17、in accordance withTest Methods C472 the compressive strength shall be asspecified in Table 1.6.2 Setting TimeWhen tested in accordance with TestMethods C472 using the Vicat method, the setting time shall beas specified in Table 1.NOTE 3Setting TimeAttention is directed to conditions affecting jobset
18、 of gypsum plasters that are usually beyond the control of the producer.Materials added at the site of application such as water and aggregatesaffect job sets. In addition, the various bases with different absorptivevalues may affect job performance. The plaster may be retarded to providea setting t
19、ime of not more than 4 h. Setting times more than 2 h may resultin lower compressive strengths.6.3 Fineness of Gauging Plaster for Finish CoatWhentested in accordance with Test Method C472 100 % shall passa No. 14 1.4 mm sieve and not less than 60 % shall pass a No.100 150 m sieve.37. Sampling7.1 At
20、 least 1 % of the packages, but not less than 5packages, shall be sampled. Packages to be sampled shall beselected at random. Samples shall be taken both from the outerportion and the center of each package. The materials soobtained shall be thoroughly mixed to provide a compositesample of not less
21、than 7 lb 3.2 kg. This composite sampleshall be placed immediately in a clean, dry, airtight containerfor delivery to the laboratory.8. Packaging and Package Marking8.1 Gypsum plasters shall be dry and free of lumps, andshall be shipped in packages.8.2 When shipped for resale, the following informat
22、ionshall be legibly marked on each package or on a tag of suitablesize attached to the package:8.2.1 Name of manufacturer or seller,8.2.2 Brand name, if any, and8.2.3 Net weight of the package.9. Inspection9.1 Inspection of the gypsum plaster shall be agreed uponbetween the purchaser and the supplie
23、r as part of the purchaseagreement.10. Rejection10.1 Rejection of gypsum plaster that fails to conform to therequirements of this specification shall be reported to theproducer or supplier promptly and in writing. The notice ofrejection shall contain a statement documenting requirementsof this speci
24、fication.11. Certification11.1 When specified in the purchase agreement, a manufac-turers or suppliers report shall be furnished at the time ofshipment certifying that the product is in compliance with thisspecification.12. Keywords12.1 aggregate; gauging plaster; gypsum plaster; mill-mixedplaster;
25、neat plaster; plaster; wood fibered plaster3Detailed requirements for these sieves are given in Specification E11.TABLE 1 Composition and Physical PropertiesProduct Aggregate TypeComposition, Aggregate per 100 lbof Plaster, not more thanSetting TimeA Compressive StrengthBnot less thanft3m3hours psi
26、MPaMill-Mixed Plaster over Lath Base Vermiculite 2 0.057 112 to 8 450 3.1Perlite 2 0.057 112 to 8 600 4.1Sand 2.5 0.071 112 to 8 700 4.8Mill-Mixed Plaster over Masonry Vermiculite 3 0.085 112 to 8 325 2.2Perlite 3 0.085 112 to 8 400 2.8Sand 3 0.085 112 to 8 400 2.8Neat Plaster none . . 2 to 16C750D5
27、.2Wood Fibered Plaster none . . 112 to 8 1200 8.3Gauging Plaster none . .E1200 8.3ASetting time shall be not less than the shorter time shown nor more than the longer time shown.BCompressive strengths are as tested at the setting times specified in Test Methods C472.CWhen mixed with 3 parts by weigh
28、t of Ottawa sand.DWhen mixed with 2 parts by weight of Ottawa sand.EWhen not retarded, the setting time shall be not less than 20 nor more than 40 minutes and, when retarded, not less than 40 minutes.C28/C28M 10 (2015)2APPENDIX(Nonmandatory Information)X1. DETERMINATION OF AGGREGATE CONTENT OF MILL-
29、MIXED PLASTERINTRODUCTIONThe determination of the aggregate content of mill-mixed plaster is normally not precise. Mostgypsum plasters contain natural impurities that cannot be separated from the aggregate by eithermechanical or chemical means. A better estimate can be made by obtaining the approxim
30、ate purity ofthe gypsum plaster used in the product from the manufacturer.An accurate method for determining sand in set plaster is contained in Test Methods C471M.Separate specimens of the sand and gypsum plaster used in the mill-mixed plaster are required for TestMethods C471M.X1.1 ScopeX1.1.1 Thi
31、s appendix covers mechanical and chemical testmethods for separating the aggregate from gypsum plaster.X1.2 Mechanical SeparationX1.2.1 Significance and Use:X1.2.1.1 This test method is used to estimate the weight orvolume of aggregate contained in mill-mixed gypsum plastersby mechanical separation.
32、X1.2.2 Interferences:X1.2.2.1 It is assumed by this test method that the aggregatemeets Specification C35 and that only a minor portion of theaggregate passes through a 100-mesh 150 m sieve. To theextent that a greater portion passes the 100 mesh sieve, theresults will show lower values for volume o
33、f the aggregate, andhigher values for the weight of the gypsum plaster, thanactually in the sample.X1.2.3 Apparatus:X1.2.3.1 SieveSpecification E11, 100 mesh 150 m.X1.2.3.2 Balancewith a capacity of not less than 100 gand a precision of at least 0.1 g.X1.2.4 Procedure:X1.2.4.1 Weigh 100 g of the sam
34、ple to 60.1 g.X1.2.4.2 Sieve the 100 g specimen through the 100 mesh150 m sieve. Examine the material on the sieve to be suresmall lumps or agglomerates of plaster are not retained. Theretained portion is assumed to be aggregate. If the weight ratioof the aggregate and plaster is to be determined, w
35、eigh eachportion to the nearest 0.1 g. If the volume ratio of aggregate tothe weight of plaster is to be determined, measure the volumeof aggregate retained on the sieve to the nearest mL and weighthe material passing through the sieve to the nearest 0.1 g.X1.2.5 Calculation and Report:X1.2.5.1 Weig
36、ht Ratio Calculate and report the weightratio as pounds of aggregate/100 lb 45 kg of plaster per EqX1.1.WR5wawp3100 (X1.1)where:WR= weight ratio, lbs of aggregate/100 lb 45 kg of plaster,wa= weight of aggregate, g, and,wp= weight of plaster, g.X1.2.5.2 Volume Ratio Calculate and report the volumerat
37、io as cubic feet of aggregate/100 lb 45 kg of plaster per EqX1.2.VR5vawp31.60 (X1.2)where:R= volume ratio, cubic feet of aggregate per 100 lb ofplaster,va= volume of aggregate, mL, andwp= weight of plaster, g.X1.2.6 Precision and Bias:X1.2.6.1 It is not practical to specify the precision or thebias
38、of this test method because of the unknown variabilities inthe particle sizes of the aggregates.X1.3 Chemical SeparationX1.3.1 Significance and Use:X1.3.1.1 This test method is used to estimate the weight orvolume of aggregate contained in mill-mixed gypsum plastersby chemical separation.X1.3.2 Inte
39、rferences:X1.3.2.1 It is assumed in this test method that all of thematerial insoluble in ammonium acetate is aggregate and thesoluble material is plaster. In many cases there is a significantamount of insoluble material in the plaster. To the extent thatthis is true it will produce erroneous calcul
40、ated amounts ofaggregate and plaster. If possible, obtain the approximatepurity of the plaster from the manufacturer. This informationwill greatly increase the accuracy of the results.X1.3.2.2 In the volume calculation it is assumed that thevolume of the insoluble material in the plaster is insignif
41、icantcompared to the volume of the aggregate. This is usually thecase.C28/C28M 10 (2015)3X1.3.3 Apparatus:X1.3.3.1 Analytical Balancewith a precision of 0.001 g.X1.3.3.2 Drying Oven capable of maintaining a tempera-ture of 100 to 110C.X1.3.4 Reagents:X1.3.4.1 Ammonium Acetate Solution (250 g/L)disso
42、lve250 g of ammonium acetate (NH4C2H3O2) in water and diluteto1L.X1.3.4.2 Ammonium Hydroxide (1:59)Mix one volume ofconcentrated (NH4OH) (sp gr 0.90) with 59 volumes of water.X1.3.5 Procedure:X1.3.5.1 Accurately weigh 40 6 0.05 g of the sample intoa 1-L beaker. Add 600 to 700 mL of (NH4C2H3O2) solut
43、ionthat is slightly alkaline to litmus paper. If acidic, add a few mLof (NH4OH) (1:59) to the stock (NH4C2H3O2) solution torender it slightly alkaline prior to the addition of the testsample.X1.3.5.2 Warm the suspension to a temperature of 70 6 5Cand stir continuously for 20 to 30 min. Filter the wa
44、rmsuspension through a small Buchner funnel or Gooch cruciblein which filter paper has previously been formed, the funneland mat having been dried at 110C to a constant weight within0.01 g. Refilter the first 100 mL of the filtrate. Wash theaggregate remaining in the beaker onto the filter with anad
45、ditional 100 mL of warm (NH4C2H3O2) solution. Wash thebeaker and residue with 200 to 300 mL of water, dry the funneland aggregate at 100C to constant weight.X1.3.6 Calculation and Report:X1.3.6.1 Weight Ratio Calculate and report the weightratio as pounds of aggregate/100 lb 45 kg of plaster per EqX
46、1.3.WR5w12w12 w2pw12 w2p3100 (X1.3)where:WR= weight ratio, lbs of aggregate/100 lb 45 kg of plaster,w1= weight of original specimen, g,w2= weight of insoluble residue retained on filter, g, andp = purity of gypsum plaster expressed as a decimal (thatis, 85 % purity = 0.85). If purity is unknown use
47、0.9(90 %) as an estimate.X1.3.6.2 Volume Ratio Calculate the volume ratio ascubic feet of aggregate/100 lb 45 kg of plaster per Eq X1.4.VR5v1w12 w2p31.6 (X1.4)where:VR= volume ratio, cubic feet of aggregate/100 lb 45 kg ofplaster,v1= volume of insoluble residue retained on filter, mL,w1= weight of o
48、riginal specimen, g,w2= weight of insoluble residue retained on filter, g, andp = purity of gypsum plaster expressed as a decimal (thatis, 85 % purity = 0.85). If purity is unknown use 0.9(90 %) as an estimate.X1.3.7 Precision and Bias:X1.3.7.1 It is not practical to specify the precision or thebias
49、 of this test method because of the unknown variabilities inthe purity of the plaster.ASTM International takes no position respecting the validity of any patent rights asserted in connection with any item mentionedin this standard. Users of this standard are expressly advised that determination of the validity of any such patent rights, and the riskof infringement of such rights, are entirely their own responsibility.This standard is subject to revision at any time by the responsible technical committee and mu
