ASTM_D_5795_-_95_2008.pdf

Designation:D579595(Reapproved 2008)Standard Test Method forDetermination of Liquid Water Absorption of CoatedHardboard and Other Composite Wood Products Via“Cobb Ring”Apparatus1This standard is issued under the fixed designation D5795;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 indicates the year of last reapproval.Asuperscript epsilon()indicates an editorial change since the last revision or reapproval.1.Scope1.1 This test method is intended to serve as a means formeasurement of liquid water that passes through a wetted paintfilm,and which is subsequently absorbed and retained by theunderlying wood substrate.Alternative techniques for the useof the“Cobb Ring”apparatus are described.1.2 The values stated in SI units are to be regarded as thestandard.The values given in parentheses are for informationonly.1.3 This standard does not purport to address all of thesafety concerns,if any,associated with its use.It is theresponsibility 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:2D1193 Specification for Reagent WaterE177 Practice for Use of the Terms Precision and Bias inASTM Test MethodsE691 Practice for Conducting an Interlaboratory Study toDetermine the Precision of a Test Method3.Terminology3.1 Definitions of Terms Specific to This Standard:3.1.1 Cobb unit(C.U.),nThe weight of distilled waterabsorbed by the underlying wood substrate in grams per 645cm2(100 in.2)of surface area(discounting additional areascontributed by texturing or grooves)per 24-h time period.3.1.2 Cobb unit(C.U.)factor,na dimensionless math-ematical term which,for a given ring size,may be multipliedtimes the weight change after 24 h to calculate the Cobb unitvalue.3.1.2.1 DiscussionThe C.U.factor is calculated as fol-lows:C.U.Factor5100Arearing!5100pr2(1)where:r=radiusFor example,for 101.6-mm(4-in.)inside diameter ring.orC.U.Factor51003.142!2510012.565 7.96(2)3.1.3 composite wood products,nboards or other struc-tured or decorative materials manufactured from wood fibers,flakes or strands and various resin binders.3.1.3.1 DiscussionOne example is hardboard.3.1.4 hardboarda generic term for a panel manufacturedprimarily from interfelted lignocellulose fibers consolidatedunder heat and pressures in a hot press to density of at least 31lbs(13.95 kg)per cubic foot(cubic metre).34.Summary of Test Method4.1 Suitable size rings of metal or plastic are adhered orclamped to the flat,coated surface of composite wood panels tobe tested.4.2 The assembly is equilibrated at a constant temperatureand humidity and weighed.4.3 The weighed assembly is placed on horizontal4surfacein a controlled temperature and humidity room or environmen-tal chamber.Water is placed in the ring and left in contact withthe board face for 24 h.1This test method is under the jurisdiction of ASTM Committee D01 on Paintand Related Coatings,Materials,and Applications and is the direct responsibility ofSubcommittee D01.52 on Factory Coated Wood Products.Current edition approved June 1,2008.Published June 2008.Originallyapproved in 1995.Last previous edition approved in 2000 as D5795-95(2000).DOI:10.1520/D5795-95R08.2For referenced ASTM standards,visit the ASTM website,www.astm.org,orcontact ASTM Customer Service at serviceastm.org.For Annual Book of ASTMStandards volume information,refer to the standards Document Summary page onthe ASTM website.3“Todays Hardboard,”American Hardboard Association,1210 W.NorthwestHighway,Palatine,IL 60067.4The specification of a solid,continuous horizontal surface or a discontinuous(wire rack,expanded metal,etc.)is required.Surface must be consistent fromlaboratory to laboratory since this can influence the rate of evaporation of moistureand,thus,retention of moisture and Cobb values.Copyright ASTM International,100 Barr Harbor Drive,PO Box C700,West Conshohocken,PA 19428-2959.United States1 4.4 After 24 h the remaining water is removed from the ring,the assembly blotted dry and reweighed.4.5 The increase in weight of the assembly due to wateruptake is calculated by simple subtraction and then convertedto Cobb units through the use of the C.U.factor(see 3.1.2).5.Significance and Use5.1 This test method provides a simple quantitative measureof water absorption by coated composite wood products.Although primarily used to evaluate factory-primed compositewood products,this test method may be of service for otherwood substrates and coating systems.5.2 This test method has demonstrated utility for compositewood siding products ranging in thickness from approximately6.35 to 25.4 mm(14to 1 in.).Extension of this test method towood substrates of other types and thickness may be useful.5.3 Conditioning of substrate,coated sample preparation,application method,dry film thickness,cure conditions,