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<4 PAINT TESTING MANUAL PHYSICAL AND CHEMICAL EXAMINATION PAINTS, VARNISHES, LACQUERS AND COLORS By HENRY A. GARDNER, D. Sc. AND GEORGE G. SWARD, M.S. TWELFTH EDITION MARCH, 1962 Distributed By GARDNER LABORATORY, INC. P. O. Box 5728 Beihesda 14, Maryland, U.S.A. i 26f> posure tests, and the divergence of opinions regarding the durability of | paints.** For example, some technolo gists consider a paint to have failed as soon as a few cracks appear; others, realizing that repainting as a rule is not done until an appreciable portion of the surface is bare, evaluate their tests accordingly. Table 135, prepared by F. L. Browne,0 . shows how observers may differ in their ideas regarding paint failures. For example, a degree of failure may be rated as 4, 7, 8, slight, or complete, depending on the observer (see also Table 137). It seems worth while to have a set of illustrations showing definite types of failures, such as blistering, which could be rated as Slight, Definite, and Bad. Such illustrations in the form of drawings are Used by the Sub-Tropical Testing Service, Miami, Florida, in its reports of inspection. Cooperative work in committees of the American Society for Testing Materials and of the Federation of Paint and Varnish Production Clubs resulted in adoption of standard photo graphic illustrations for blistering, checking, cracking, erosion, flaking, | rusting (on iron) and blistering and chalking. Modern photography has simplified ^ pictorial records. Standard cartridges -of 35-millimeter film may be used when many pictures are made at one time. Cut film may be more economical for occasional pictures. Some people use color film exclusively. When de veloped, it may be used directly for projection on screens. Negatives for black-white reproduction may be made from colored slides. Often this round about way gives more details of check ing and cracking than photographing directly on black-white film.* Stereo pictures and pocket viewers deserve consideration for some purposes. Browne Method of Rating 4- Paint Tests This is a graphical method primarily for tests on wood. A typical Browne **Symposium on Paint and Paint Materials. ASTM Regional Meeting, Philadelphia, Pa., March, 1935. F. L. Browne. Procedure Used by the Forest Products Laboratory for Evaluating Paint Service on Wood. Proc. ASTM 30, Part II, 852-70 (1930). *F. L. Browne. Personal communication, 1958. EXPOSURE TESTING Figure 468. Enlargements or Close-ups Supplement Ordinary Photographs. (Courtesy of F. L. Browne) EXPOSURE TESTING 267 record sheet is shown in Figure 469. According to Browne, the records of \ inspections at Forest Products Laborai tory, throughout the history of a test panel will be collected on this form. The ratings for appearance, integrity, and protection will be plotted graph ically against the age of the coating, following the method devised by the E. I. du Pont de Nemours and Co. and the Grasselli Chemical Co. ``Beneath the graph for appearance,. spaces are provided for five qualities: gloss, hiding, color, cleanliness, and uniformity. The first two have the same meaning given them by Sub committee XVI*. Color is the quality corresponding to the defect usually called fading. Cleanliness means free dom from discoloration with dirt. Uni formity describes the even or spotty distribution of dirt and of fading. "Beneath the graph for integrity are spaces for seven defects: chalking, checking, crumbling, cracking, slitting, flaking, scaling. Checking includes not only the fine, reticulate fissures now generally known by that term but also fine parallel fissures that are not demonstrably through to the wood . when first seen. Fissures, which were once called checks, retain that desigv nation even though ultimately they open wide enough for the microscope to reveal the wood through them. The inspector should indicate whether checks are reticulate or parallel, micro scopic or visible, and whether the wood can be seen through them. Crumbling is the ultimate development of checking, in which pieces of coating outlined by checks fall off bodily, leaving the wood bare. Parallel checks, of course, become reticulate before they result in crumbling. Cracking refers to fissures through which bare wood can be seen when the defect is first observed, but at the edges of which the coating does not curl promptly, as it does in slitting, which has already been defined. Cracks to begin with are much longer fissures than checks; they tend to lie generally parallel to each other but may be either approximately parallel or at right angles to the grain of the wood, and they are often curved at the ends giv ing them roughly an ogee shape. They look much like rents caused by an *Comm. on Definitions. Proc. ASTM 19 Part I, 384 (1919). RECORD OF INSPECTIONS Symbols; tt, good; F, fair; p, uoor; 3, bad (descriptive of qualities); O.none; T,' trace; S, slight; V, marked; TO, very marked (descrip tive of defects), Under checking JJ, parallel; 0, reticulate; checking visible without magnification if symbol is encircled. P2mi 3 c* fo JbO JbO JO o JbO jg JvOD jo>0 JnOD JsOo CO JO to J<O> c< NS N fO nS 'ros ro GOOD o >- fH 4 ggg Ps (S 3 o iair PDOR EM) *--) f--J S i--, '-'V ; Chalking Checking g Curling w.O T S M 5 M VM __ ; ::::o;;q. ;ti; w. $; @ ... p ..o t s s )) .in, ..................................9. .9 . .9.. X. -f) . M.. .ft ft. <S Crumbling....................................................................................................................... S Flaking .........................................................9..T. . T . S .. 5. .4. .ft . .tfl. Scaling ......................................................................................................................?.. PROTECTION REMARKS; K aKeetfca; that. 4k- JuefoW Am IT/nunJSat. CxajJuU.ar it> ~ Jlteib t&tc Ac vuli&'tfef Ay 3 8 'W0X&V. JWaii CAao 4> Atruym. Ac SUiX&VuL MiW 41 'Wtok&A: Sftn*. weed cltehkwc^- * A&v Aa 3 a+uC 4 Figure 469. Browne Exposure Test Record. [Courtesy of F. L. Browne) external force of tension upon the coat ing. Long cracks may result in scaling, which is defined as disintegration of the coating in pieces large enough to lay bare springwood as well as summerwood. Shorter cracks result in flak ing, in which the pieces of separated coating are smaller and at first lay bare summerwood only. Breaking off of the curled edges of coating at slits is also flaking." "If the ratings for the indexes of serviceableness at successive inspec tions or of corresponding panels at widely separated stations are to be compared with each other it is essential that the scales of ratings be defined in reasonably permanent fashion. The scales consist of four ratings only, good, fair, poor, and bad. Obviously much finer distinctions can often be drawn among the members of a group of panels being observed side by side, but the finer distinctions cannot be detected if the observations are sep arated in time or in space. A scale with too many degrees is therefore illusory. "Appearance.--In appearance, the rating good permits a moderate depar ture from the original cleanliness and color provided that the appearance re mains sensibly uniform and is still pleasing. Moderate but somewhat ir regular change in cleanliness or in color, or fairly marked but uniform change in either quality calls for a rat ing of fair. Marked irregularity in ceanliness or color, somewhat displeas- 268 EXPOSURE TESTING ing color, or marked though uniform change reqi ires a rating of poof. Very | irregular cleanliness or color, displeas ing color, or very marked though uni form departure from the original ap pearance is rated bad. "Integrity.--The integrity of the coating is rated good if no bare wood can be seen through checks, cracks, slits, crumbling, flaking, or scaling of the coating. If there is any bare wood at all the rating must be lower than good. The rating is fair if the micro scope is necessary to reveal the bare wood, or if the bare wood is visible to the unaided eye but the breaks in the coating are few in number and the coating is still intact over considerable areas of the panel. The rating is poor if bare wood, visible to the unaided eye, is observable in all parts of the panel or if some of the bare areas are ' conspicuous. Conspicuous bare areas in many parts of the panel require a rating of bad. "Coatings are rated for integrity only over areas of clear lumber. Fissures or fractures over knots, pitch pockets, or pitch streaks are recorded separately as supplementary information. Simi larly, disintegration of the coating near the ends of boards, especially if near end checks in the wood, are given little consideration. "This scale reaches the rating "bad" while most of the original coating still remains in place. With further weath ering the coating would slough off more completely, but there is no point in continuing the test after the coating has become clearly unserviceable on the score of bad integrity. "Protection.--In protection the coat ing is rated good if there is no evidence of Wood weathering in any part of the panel where the coating is still intact. A few small wood cheeks- requiring careful examination to detect call for a rating of fair. Such checks may not be observable at all if the surface of the panel has recently become, moist from dew or rain, hence inspections are best made during dry weather and not too early in the day. The .rating is poor if there are small wood checks in all parts of the panel, if some of the checks are-conspicuous, or if cup ping of the board has begun. Nu merous conspicuous wood checks, marked cupping or loosening at nail fastenings requires a" rating of bad.- Ra r e l MAttAlAC _ acmes ex bq s u be PIS BIND. \ 11 rtCHCNT vot_ i! I 24 IT 30 33 3 14 17 30 33 36 DIRT COLLECTION IT 30 33 36 ABRASIVE STREAK fit CRACK TAILORS EDGE MONTHS * 2 3 4 S 6 7 B 9 IO It 12 | MltOCW BLISTERING REELING SCALING CURBING 8ARCWOOO REPAINT MISCMEOLNLTAHNSEOUS 11 i ~T~ j Figure 470. Du Pont Exposure Test Records, Printed on cards, 4x6 inch. Top, front side; bottom, obverse side. (Courtesy of du Pont Co.) "The ratings for integrity and pro tection do not depend upon the total area of bare wood or the total num ber of wood, checks as much as they do upon the uniformity in distribution of the defects and. their conspicuous ness. Defining the ratings in this way gains the important advantage of minimizing the variations in coating behavior, caused by difference between boards in density, proportion of summerwood, width of annual rings', and angle at. which the rings meet the sur face." Figures 470 and 471 show the forms used by the du Pont Company and by Pratt & Lambert, respectively. The du Pont form is on a card about 4 by 6 inches, each side containing half of the form. The Pratt & Lambert form is printed on a sheet about 8 by 11 inches. This form contains two columns in case duplicate panels are tested or where two kinds of wood are used, or`where one coat and two coats of material are under test. Societies for Paint Technology Method of Rating Paint Tests A survey of schemes for reporting paint tests revealed some 50 terms to name 10 or 12 phenomena.* Many of the terms for rating exposure tests have been accepted by the Federation of Societies for Paint Technology and the ASTM substantially as defined by the New York Club. "General Appearance is the complete impression conveyed when the panel is viewed at a distance of ten feet before any detailed inspection has been made. This quality is measured purely in terms of satisfactory or unsatisfactory appeal to the observer and should be rated on the record sheet good, fair, poor." (New York Club). *New York' Paint and Varnish Production Club. A Code for Designating and Evaluating Exposure Tests on Paint, Varnish and Lacquer Coatings. Scientific Section Circ. 404, 563 (Dec. 1934). EXPOSURE TESTING 269 "Discoloration is an alteration in the original color of a panel. The extent o which this change is manifest should )ie denoted by the ratings slight, defi nite, bad, together with an indication of the color and trend of the change. Emphasis must be placed on the in clusiveness of this definition. Every alteration in the original color is im plied, e. g., yellowing, darkening, fad ing, mottling, bronzing, dirt collections, mold growth, etc." (New York Club). "Gloss is that property of a panel that makes possible a description as mirror-like, flat, or some intermediate degree of luster. The determination should be made on an unwashed, un polished or otherwise unmodified film. Gloss should be rated in terms of ex cellent, fair, eggshell, flat." (New York Club). "Checking is that phenomenon mani fested in paint films by slight breaks in the film that do not penetrate to the underlying surface. The break should be called a creek if the under lying surface is visible. Where preci sion is necessary in evaluating a paint film, checking may be described both as visible (as seep with the naked eye) 'sas microscopic (as observed under a Jjagnification of 10 diameters)." -> "Three types of checking are recog nized under this definition: "Irregular pattern type. Checking in which the breaks develop in the surface of the film in no definite pat tern." "Line type. Checking in which the breaks in the surface of the film are generally arranged in parallel lines, usually either horizontally or vertically, over the surface of the film. These breaks often follow the line of-brush marks." Crowfoot Type. Checking in which the breaks in the surface of the film form in a definite three-prong pattern with the breaks running from a center and forming an angle of about 120 deg. between the prongs." (ASTM, Societies for Paint Technology). "Checking is that phenomenon manifested in paint films by slight breaks in the film that do not penetrate to the underlying surface. The break should be called a crack3 if the under lying surface is visible. Where preeiNn is necessary in evaluating a paint checking may be described as visible (as seen with the naked eye) ,Color Pratt & Lambert-Inc. Laboratory Serviceability Test Record (Sheet No. 2) MWlUliaMflt Test No. fit-303 Panel No. 1 Date Exposed OCT 7 1932 General Appearance Checking Cracking Blistering Scaling Gloss Chalking Erosion Color Change Dirt Collection Rusting Wood Checking Warping 5&SBPlft OO O VC c F P VP N VS s M B VB N S M B N S M B N 5 M B vcG f P VP ft N S M B S M B N VS s M 8 VB N S M B N S M B N S M B 22SE * sz 1=1 ..... * lime in Months Figure 471. Pratt & Lambert Exposure Test Record. (Courtesy of Pratt & Lambert Co.) Table 136. Terms In Use for Designating Types of Failures of Organic Coatings (New York Club) ( most widely used terms) Adherence of Weathered Coating Advanced Erosion Advanced Map Checking Alligatoring Bad Grain Checking Blistering Bridging Bubble Blister Chalking Change in Color Checking Coarse Shrinkage Color Change Condition for Repainting Corrosion Cracking Crumbling Cupping Darkening Dirt Collection Dirt Retention Discoloration Dulling Erosion Expansion Exudation Fading Failure of Wood Flaking Fine Scaling General Appearance General Condition Good Condition Gloss Grain Checking Grain Cracks Heavy Rust Hiding Power Integrity of Weathered Coat Iridescence Leather Checking Lifting Loss in Gloss Map Checking Medium Erosion Microscopic Checking Morocco Leather Checks Peeling Pock Marks Rusting Scaling Shrinkage Slitting Sun-blistering Sun-craters Switch Checks Warping Wrinkling 270 or as microscopic (as observed under "A. a magnification of 10 diameters)." j "Three types of checking are recog nized : "Irregular Pattern Type. Checking in which the breaks develop in the sur face of the film in no definite pattern. "Line Type. Checking in which the breaks in the surface of the film are generally arranged in parallel lines, usually either horizontally or vertically, over the surface of the film. These breaks often follow the line of brush marks. "Crowfoot Type. Checking in which the breaks in the surface of the film form in a definite three-prong pattern with the breaks running from a center and forming an angle of about 120 deg. between the prongs." (ASTM, Societies for Paint Technology). "Chalking is that phenomenon mani fested in paint films by the presence of loose removable powder, evolved from the film itself, at or just beneath the surface. Chalking may be detected by rubbing the film with the fingertip." (ASTM, Societies for Paint Tech nology). "Cracking is that phenomenon mani- k tested in paint films by a break extendV ing through to the surface painted. Where this is difficult to determine, the break should be called a crack only if the underlying surface is visible. The use of a magnification of 10 diameters is recommended in cases where it is difficult to differentiate be tween cracking and checking. "Three types of cracking are recog nized : "Irregular Pattern Type.--Cracking in which the breaks in the film are in no definite pattern. "Line Type.--Cracking in which the breaks in the film are generally ar ranged in parallel lines, usually either horizontally or vertically, over the sur face of the film. These breaks often follow the line of brush marks. "Sigmoid Type.--Cracking in which the breaks in the film form a pattern consisting of curves meeting and inter secting, usually on a relatively large scale." (ASTM, Societies for Paint Technology). "Flaking (scaling) is that phenome non manifested in paint films by the ? actual detachment of pieces of the film itself either from its substrate or from paint previously applied. Flaking EXPOSURE TESTING ennui,wwoccor Ttm MMCITD ft. EXPOSURE RECORD 1 --------------- MINT NO. fIGMCNT t o t ho. couin____ we. | k h p. I v p h t il x CHALKING CHECKING PCC- Afc--s--sitgiit a--a cr-- Figure 472. Exposure Test Record of Societies for Point Technology. Adopted also by ASTM. Figure 473. Paint Film on a Typical Soft Wood. Top, transverse section showing both spring and summer wood. Bottom, radial section through a band of summer wood. Black areas are paint. In the actual specimen, the wood is stained green and the linseed oil is'stained red. Although not visible in the photograph, under the micro scope, the red transparent oil can be seen to penetrate the summer wood to the bottom edge of both views. In the spring wood, the oil has penetrated only a few cavities near top of upper view. (Courtesy of F. L. Browne) EXPOSURE TESTING 271 staling) is generally preceded by _ cracking or checking and is the result T|of loss of adhesion, usually due to / stress-strain factors coming into play. "In techncial literature, a distinction is sometimes made between flaking and scaling. In most cases, however, flak ing and scaling refer to the same phenomenon. In some instances, the term flaking is used to describe the de tachment of pieces of film less than J4 in. in size, and scaling, the detach ment of pieces over l/A in. in size. In other instances, the term flaking is used to describe the detachment of pieces of film from the immediate undercoat (intercoat failure) and scal ing the detachment of pieces from the base (complete failure). It should be kept in mind that the flakes may vary widely in size and shape from those illustrated by the reference standards in Fig 1, varying from a fraction of an inch to several inches in size." "Peeling should be considered as an aggravated form of flaking (scaling) and not as a different type of failure. It is frequently due to a moisture condition and when this is evident it should be taken into consideration in V any evaluation." (ASTM, Societies Jj for Paint Technology). "Erosion is that phenomenon mani fested in paint films by the wearing away of the finish to expose the sub strate. The degree of failure is de pendent on the amount of substrate visible. Erosion occurs as the result of chalking." (ASTM Societies for Paint Technology). The qualities general appearance, discoloration and gloss should be summarized in the term appearance; cheeping, cracking, etc., in the term integrity; the protection offered to the painted surface is deduced from the discoloration. These three collective qualities are then rated as good, fair, poor or bad. In most cases only three degrees of a quality are recognized. Browne usually recognizes four, while others recognize as many as six de grees in some cases. The ASTM and the Federation of Societies for Paint Technology recom mend the form shown in Figure 472 for recording results of exposure tests. It is based on the original form designed by the New York Club. In a group of methods for rating resistance to chalking, checking, crack Figure 474. Red Cedar Stains on Paint. Water-soluble stain in wood is dissolved by water originating in wet plaster. Solution migrates to surface of paint and leaves paint stained when the water evaporates. (Courtesy of F. L. Browne) Figure 475. Redwood Stains on Paint. See Figure 473 for explanation. (Courtesy of J. R. MacGregor) ing, erosion and flaking, the ASTM recognizes 10 degrees of development of the phenomena. It recommends rat ing by comparison with photographs of steps S, 6, 4, and 2. No photographs are needed for step 10 (no develop ment) and step 0 (complete develop ment). Steps intermediate between those illustrated may be used if de sired, hut are rarely necessary. The methods are: D 714 Blistering D 659 Chalking D 660 Checking D 661 Cracking D 662 Erosion D 772 Flaking (Scaling) An approximate relation between numerical and descriptive ratings is given in Table 137 (see also Table 135). Table 137. Numerical vs. Descriptive ___ Ratings_ Appearance. Film Failures ____ Jfolor, Gloss~(Chalking, etc.) 10 9*!) 7) 6) 5f Perfect Good Intermediate Absent Slight Failure intermediate 3) 2 r Poor i .i 0 Poorest Degree Conceivable Bad Failure Complete Failure