1、Designation: C28/C28M 10Standard 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 in parentheses indi
2、cates 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 Department of Defense.1. Scope1.1 This specification covers gypsum mill-mixed plaster,gypsum neat plaster, gypsum
3、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 in brackets. The value
4、s 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 references notes and f
5、ootnoteswhich 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 theresponsibility of the
6、 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 Specification for Gypsu
7、mC35 Specification for Inorganic Aggregates for Use inGypsum PlasterC471M Test Methods for Chemical Analysis of Gypsumand Gypsum Products (Metric)C472 Test Methods for Physical Testing of Gypsum, Gyp-sum Plasters and Gypsum ConcreteC778 Specification for SandC842 Specification for Application of Int
8、erior GypsumPlasterE11 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 calcinedgypsum plaster designed t
9、o be mixed with lime putty for thefinish coat.3.2.2 gypsum neat plaster, ncalcined gypsum mixed atthe mill 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 on the job.3.2.3 gypsum m
10、ill-mixed plaster, ncalcined gypsum plas-ter, 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 workingproperties.3.2.4 gypsum
11、 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 Perlite Aggregate, Specifi
12、cation C35.1This specification is under the jurisdiction of ASTM Committee C11 onGypsum and Related Building Materials and Systems and is the direct responsibilityof Subcommittee C11.01 on Specifications and Test Methods for Gypsum Products.Current edition approved Oct. 1, 2010. Published November 2
13、010. Originallyapproved in 1920. Last previous edition approved in 2005 as C28/C28M00(2005).DOI: 10.1520/C0028_C0028M-10.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refe
14、r to the standards Document Summary page onthe ASTM website.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.4.4 Sand Aggregate, Specification C35.4.5 Ottawa Sand, Specification C778 for 2030 sand.4.6 Wood Fiber, non staining wood fib
15、er.5. 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 may be made byusing
16、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 in accordance withTe
17、st 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 of gypsum plasters
18、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 time of not more than
19、 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 least 1 % of the pa
20、ckages, 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 than 7 lb 3.2 kg. Th
21、is 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 informationshall be legibly
22、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 supplier as part of the pur
23、chaseagreement.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 specification.11. Certifi
24、cation11.1 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; neat plaster; plaste
25、r; 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 TimeACompressive StrengthBnot less thanft3m3hours psi MPaMill-Mixed Plaster
26、 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 16C750D5.2Wood Fibered Plaste
27、r 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 weight of Ottawa sand.DWhe
28、n 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 102APPENDIX(Nonmandatory Information)X1. DETERMINATION OF AGGREGATE CONTENT OF MILL-MIXED PLASTERINTRODUCTIONThe
29、 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 approximate purity ofthe gypsum plas
30、ter 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 This appendix covers mechanical
31、 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.X1.2.2 Interferences:X1.2.2.
32、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 of the aggregate, andhigher v
33、alues 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 sample to 60.1 g.X1.2.4.2 Sieve
34、 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, weigh eachportion to the near
35、est 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 Weight Ratio Calculate and repor
36、t the weightratio as pounds of aggregate/100 lb 45 kg of plaster per EqX1.1.WR5wawp3 100 (X1.1)where:WR= weight ratio, lbs of aggregate/100 lb 45 kg ofplaster,wa= weight of aggregate, g, and,wp= weight of plaster, g.X1.2.5.2 Volume Ratio Calculate and report the volumeratio as cubic feet of aggregat
37、e/100 lb 45 kg of plaster per EqX1.2.VR5vawp3 1.60 (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 of this test method because
38、 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 Interferences:X1.3.2.1 It is as
39、sumed 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 calculated amounts ofaggregate an
40、d plaster. If possible, obtain the approximatepurity of the plaster from the manufacturer. This informationwill greatly increase the accuracy of the results.C28/C28M 103X1.3.2.2 In the volume calculation it is assumed that thevolume of the insoluble material in the plaster is insignificantcompared t
41、o the volume of the aggregate. This is usually thecase.X1.3.3 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)dissolve250 g of ammonium acetate (NH4C
42、2H3O2) 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-Lbeaker.Add 600 to 700 mLof (NH4C2H3O2) solution thatis slightly alkaline to litmu
43、s paper. If acidic, add a few mL of(NH4OH) (1:59) to the stock (NH4C2H3O2) solution to renderit slightly alkaline prior to the addition of the test sample.X1.3.5.2 Warm the suspension to a temperature of 70 6 5Cand stir continuously for 20 to 30 min. Filter the warmsuspension through a small Buchner
44、 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 anadditional 100 mL of warm (NH4C2H3O2)
45、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 EqX1.3.WR5w12w12 w2pw12 w2p3 100 (X1.3)
46、where:WR= weight ratio, lbs of aggregate/100 lb 45 kg ofplaster,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 0.9(90 %) as an estimate.X1.3.6.2 Vo
47、lume Ratio Calculate the volume ratio ascubic feet of aggregate/100 lb 45 kg of plaster per Eq X1.4.VR5v1w12 w2p3 1.6 (X1.4)where:VR= volume ratio, cubic feet of aggregate/100 lb 45 kgof plaster,v1= volume of insoluble residue retained on filter, mL,w1= weight of original specimen, g,w2= weight of i
48、nsoluble 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 of this test method because of the
49、 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 must be reviewed every five years andi
