ASTM_D_7787_-_D_7787M_-_13.pdf

Designation:D7787/D7787M13Standard Practice forSelecting Wood Substrates for Weathering Evaluations ofArchitectural Coatings1This standard is issued under the fixed designation D7787/D7787M;the number immediately following the designation indicates theyear of original adoption or,in the case of revision,the year of last revision.A number in parentheses indicates the year of lastreapproval.A superscript epsilon()indicates an editorial change since the last revision or reapproval.1.Scope1.1 This practice offers guidelines for selecting wood orwood composite substrates for the evaluation of specificweathering performance characteristics of architectural coat-ings such as exterior paints,primers,and deck finishes.1.2 Procedures include selecting wood species and choosingindividual wood test panels through visual examination of thewood characteristics.1.3 This practice is intended to cover the most commonlyemployed wood substrates used in weathering studies ofarchitectural coatings.It is not intended to serve as a compre-hensive guide for all wood species that may be employed forthe purpose of evaluating weathering performance character-istics of architectural coatings.1.4 The values stated in either SI units or inch-pound unitsare to be regarded separately as standard.The values stated ineach system may not be exact equivalents;therefore,eachsystem shall be used independently of the other.Combiningvalues from the two systems may result in non-conformancewith the standard.1.5 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:2D4214 Test Methods for Evaluating the Degree of Chalkingof Exterior Paint FilmsG147 Practice for Conditioning and Handling of Nonmetal-lic Materials for Natural and Artificial Weathering Tests3.Terminology3.1 Definitions:3.1.1 weathering performance characteristic,nan attri-bute displayed by a coating after a period of exposure to naturalsunlight,UV light,moisture,varying temperatures or otherenvironmental elements.3.1.1.1 DiscussionWeathering performance characteris-tics may include film integrity attributes such as checking,cracking,peeling,flaking,erosion,chalking;appearance attri-butes such as gloss or color retention;or resistance to dirtpickup,mildew,or algal defacement.3.1.2 wood condition factor,nan attribute of a wood panelthat indicates its state prior to being used in a coatingsperformance evaluation.3.1.2.1 DiscussionWood condition factors may includeduration of time since the panel was milled,chemical pre-treatments,or exposure to environmental elements prior tobeing coated.3.1.3 wood panel,na thin,flat substrate material com-posed of any species of wood or wood composite.4.Summary of Practice4.1 The experimenter first determines the critical weather-ing performance characteristics of the architectural coatingbeing tested and determines the species and lumber grade of awood or wood composite that is similar to the in-serviceapplication of the wood that is to be studied.4.2 Wood species are selected based on the weatheringperformance characteristics of interest and the species that willlikely be used for the studied application.4.3 Individual test panels are selected based on visualobservation of the following features:(a)growth patterns(rateof growth,%latewood,grain,etc.),(b)grain orientation,(c)characteristic feature(knots,checks,glue lines,etc.),and(d)color characteristics frequently associated with heartwood orsapwood of the wood and the type of wood extractives of thein service wood.Selection should be done using quantitative orqualitative criteria to ensure the best substrate representationfor the test series.When evaluating multiple coating sampleson the same board,in selecting the board,care must be takento assure that the areas designated for each paint sample1This practice is under the jurisdiction of ASTM Committee D01 on Paint andRelated Coatings,Materials,and Applications and is the direct responsibility ofSubcommittee D01.42 on Architectural Coatings.Current edition approved June 1,2013.Published August 2013.DOI:10.1520/D7787_D7787M-13.2For 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.Copyright ASTM International,100 Barr Harbor Drive,PO Box C700,West Conshohocken,PA 19428-2959.United States1 contain similar characteristic features mentioned above toinsure proper comparison of coating durability.5.Significance and Use5.1 Natural weathering tests can take several years andaccelerated weathering evaluations often run for cycles requir-ing several weeks or months before obtaining useful data.Correlating wood panels selectio