1、Designation: D7787/D7787M 13Standard 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
2、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 evaluatio
3、n 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
4、 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
5、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
6、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. Ref
7、erenced 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 characterist
8、ic, 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
9、, 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 con
10、dition 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
11、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
12、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,
13、 (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 substrat
14、e 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, a
15、nd 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 service
16、astm.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 States1contain similar characteristic features mentioned above toi
17、nsure 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 selection with desired weatherin
18、gperformance characteristics assists a coatings experimenter inmaximizing information in the desired time frame.5.2 Because of the long time spans required for exposuretesting, it is critical to plan a reliable experiment whilecontrolling as many variables as possible. For this reason,selection of e
19、xperimental panels made from representativewood species or composites, grades of lumber and surfacetypes that are expected to be painted is very important.5.3 This practice may be used for any types of exteriorarchitectural coating intended for use on wood or woodcomposite substrate such as exterior
20、 house paints, primers,wood stains, or waterproofers.6. Procedure6.1 Determine Critical Weathering Performance Character-istics:6.1.1 The determination of critical weathering performancecharacteristics is at the discretion of the experimenter depend-ing on the performance indicators of interest for
21、the coatingsystem being evaluated.6.1.2 Weathering characteristics typically of interest mayinclude:6.1.2.1 Film deterioration factors such as cracking, peeling,flaking, chalking, or blistering.6.1.2.2 Ability of coating to adhere to wood or woodcomposite surface over extended periods as the substra
22、teexpands and contracts due to moisture, or thermal influences,or both.6.1.2.3 Visual appearance factors such as color or glossretention.6.1.2.4 Extractive bleeding or other paint discoloration as-sociated with the wood substrate.6.1.2.5 Resistance to fungal or algal defacement.6.1.2.6 Resistance to
23、 dirt pick-up.6.2 Select wood characteristics for the experiment that willprovide the most relevant results for the exposure experimentin the desired timeframe. Wood features and wood conditionfactors (as defined in 3.1.2) together with coating formulationand application method, including dry film t
24、hickness or cov-erage spread rate will determine the speed and extent ofexhibited weathering performance characteristics.6.2.1 Pre-weathering of wood substrates affects the weath-ering performance of coatings. Significant changes in theweathering results of coatings may be observed from periods ofpr
25、e-weathering as short as one week. For this reason, adequatepre-weathering of panels is required if paint is to be appliedsometime after wood installation on the structure.6.2.2 Different types of wood chemical or thermaltreatments, composite glue lines or type of binder used mayimpact a coatings pe
26、rformance or longevity.6.3 Select Wood Species (younger than 60 years old):6.3.1 Southern Yellow Pine (Pinus spp.)This wood type isamong the most commonly employed wood substrates forweathering tests due to its availability and low dimensionalstability. It includes species such as shortleaf, slash,
27、loblolly,and longleaf. Pine is often selected where film deteriorationcharacteristics such as cracking, checking, and flaking arerequired. Pine boards tend to flex and expand more than otherwood species in varying environmental conditions. Specificfeatures of pine species are resin pockets and bleed
28、ing resin.For this reason, pine lumber used in a majority of architecturalapplications such as siding or trim boards must be kiln dried ata high temperature to set the resin.6.3.2 CedarThe term “Cedar” is a general term that can beapplied for True Cedar (Cedrus spp.) but is also used forWestern Redc
29、edar (Thuja plicata) and Eastern Redcedar (Ju-niperus virginiana). Cedars generally will give a more dimen-sionally sound surface than Pine species. Film durabilityfailures will normally take longer over cedar than pine. Cedarpanels can be used to assess gloss and color retention, and itcan be used
30、to observe tannin stain-blocking resistance.6.3.3 Redwood (Sequoia sempervirens)Generally selectedfor its heavy tannin content to observe stainblocking effective-ness of architectural primers or topcoats.6.3.4 Pressure Treated PineIncludes various chemicallytreated wood. Pressure treated lumber is g
31、enerally used forstudying weathering effects of deck finishes, wood stains andwaterproofing coatings. Pressure-treated pine is often selectedto study erosion or film deterioration of waterproofingcoatings, and long-term water repellent characteristics.6.3.5 Engineered Wood Trim (EWT) and SidingInclu
32、desmanufactured wood products composed of wood segments,flakes, particles, or fiber-based composites, or combinationsthereof. Use of EWT and siding now command a significantshare of the wood cladding market. Thus, it is critical toevaluate these products in any general architectural finishperformanc
33、e evaluation.6.4 Selection of Wood Test Panels for Natural Weathering:NOTE 1The techniques described for selection of wood test panelsmay be applied to any wood species and are not limited to the specieslisted previously.NOTE 2Supplementary information related to wood structure andfeatures affecting
34、 paint performance can be found in relevant literature,including publications.36.4.1 Panel ThicknessAlthough the exact size of the woodtest panel is not critical, natural weathering exposures aretypically performed on boards 0.9 to 1.2 m 3 to 4 ft in length,13 to 20 cm 5 to 8 in. wide, and 0.6 to 2.
35、5 cm 14 to 1 in. inthickness. Boards with thickness greater than or smaller thanthese dimensions may affect the standard dimensional stabilityof a substrate, so it is recommended to use boards within 0.6cm 14 in. variance within the same study for consistency. Ifthe paint is designed for machine app
36、lication, it is recom-mended to prepare the samples for testing using the same type3Williams, R. S., Wood Handbook, Wood as and Engineering Material 2010,Chapter 16, “Finishing of Wood,” (http:/www.fpl.fs.fed.us/documnts/fplgtr/fplgtr190/chapter_16.pdf).D7787/D7787M 132of coaters and drying conditio
37、ns as will be set up for produc-tion. In this case, panels should be of a size that they can beaccommodated on the coater line. Coated samples could laterbe cut to the required size for testing.6.4.2 Moisture ContentThe panels selected should repli-cate the in-service applications of the wood. If th
38、e in-serviceapplication calls for dry wood, kiln dried pine boards processedunder the appropriate conditions to set up resin should be usedas is usually recommended for architectural applications.However, if the in-service wood is not likely to be kiln dried,then the panels should not be kiln dried.
39、 Panels that areselected should have the same moisture content that the coatingmanufacturer indicates is acceptable for the application. If thecoating manufacturer requires dry wood, the wood should bedried to their specifications. If on the other hand the coatingmanufacturers product is intended to
40、 be applied over greenwood, the panel should not be dry (less than 20 % MC). Greenlumber panels can be stored tightly wrapped in polyethylenefilm and frozen for a prolonged period of time. Before use,wrapped panels should be left on a bench for thawing andwarming to room temperature as long as requi
41、red. These greenpanels should be used as soon as possible.6.4.3 Wood FeaturesPanels should be made from woodgrades designated for a wide range of architectural applica-tions. They should contain both heartwood and sapwood inadequate proportions and features such as knots, checks,segments of juvenile
42、 wood, bark, and pockets of resin andother features as accepted by grading.6.4.4 Wood GrainsPanels of the same wood speciesshould have a versatile grain density and ratio of latewood toearlywood as would be expected to be seen in wood architec-tural applications. Grain structure is related to wood d
43、ensityand its dimensional stability. Wood surfaces frequently containannual ring patterns that can be classified as edge-grain,flat-grain or mixed. Paint performance is different on theedge-grain (vertical-grain or quarter-sawn) than on a flat-grain(slash-grain or plain-sawn) board surface due to di
44、fferentdimensional stability. Reduced adhesion of the paint to anexposed late wood surface is usually seen due to an exposedlate wood surface. If a flat-grain wood surface is expected to bepresent in the targeted architectural application, as it frequentlyis, it must be adequately represented in the
45、 panels selected forpaint testing.6.4.5 Wood Surface FinishDepending on the sawing andfinishing equipment used, and the desired architecturalappearance, the wood surface could be finished from verysmooth to rough sawn. There is a known difference in paintdurability on smooth versus rough wood with p
46、aint usuallylasting longer on the rough sawn wood surface. For this reason,panels used for testing should have the surface milled as it isexpected to be used in the targeted architectural application. Ifa variety of wood milling with different degrees of roughnessare expected to be encountered, pane
47、ls with extremely smoothand rough surfaces should be selected for testing.6.4.6 Wood CompositesIn the case of engineered woodproducts, attention has to be paid to the following: (a) forfinger joint products, all types of glue lines must be representedfor different wood segments with respect to grain
48、 density andorientation on both sides of the glue line, (b) for woodcomposite panels, the side designed by the manufacturer forexterior exposure must be identified, and (c) certain types ofwood composites (for example, wood plastic composites) mayrequire special surface treatment to achieve sufficie
49、nt paintadhesion.6.4.7 Panel GroupingWood panels for evaluation within asingle test series should be grouped based on similar charac-teristics relative to the features of the selected wood species(this applies to the presence or absence of knots, or knots ofcertain size or type, resin pockets, heartwood or sapwood,fragments of bark or juvenile wood etc.), grain density, grainsurface pattern (flat-grains and edge-grains or pitch and barkside), milling variations (smooth and rough) and moisturecontent. In many cases, groups of panels may contain severalsim
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