FZGI~HFI 1. FLAKING STANDARDS
House Paints Effect of Climate, Wood Types, and Priming Practices JOHNMAHSHALL, J. W. ILIFF,AND H. H. YOUNG,E. I. du Pont de Nernours & C o m p a n y , Inc., Wilmington, Del. HIS paper sUUlNlariZes a number of observations made
T
parative performance of various types of wood as regards during the past several years in connection with the paint-holding properties. general study of the painting of wood, with the particuThe study in question was initiated largely as a result of lar objective of developing priming systems that would tcnd an observation on the part of the writers t h a t in the Southto level out the differencesknown previously to exist between west practically every house constructed of "novelty siding" woods of the tvDe of Donalas fir and yellow pine on the one w5s showing pronounced flaking failure of paint over the hand, and cedar.and whitepine on the-other. Unfortunately summerwood; tliis was demonstrated by an actual count of this principal objective has not been attained; to date no priming system has been A large m a w of evidence shows that extremes of climate represented devised which makes Douglas fir and yellow by Florida and by dry-climate exposures may yield diametrically op pine approach cedar or white pine in paintposite results as regards the effect of composition on paint durability. holding properties. The study, however, I n general, it appears that valid conclusions as to durability of paint had from the first included a variety of tests designed to throw some light on the factors on wood cannot be drawn from indioidual series of exposures inmlving affecting the validity of conclusions to be single-panel tests of each paint, since the digerences in paint perforobtained from the normal exposure study of I I W L C ~ due to variations of wood, even in a single species, may be greater wood painting. in magnitude than the diferences introduced by the maximum variaThe conclusions reached in these tests may tions in composition met in normal practice in the high-quality paint he helpful to other workers in the field; and in a number of respects very useful wholefild. eale amplification has been obtained of the No valid basis appears f r o m the studies in question f o r stating that results previously reported by Browne of the material diference in performance is giuen by the use of aluminum Forest Products Laboratory,' on the comBrowne, F. L,,"Painting Characteristics oi Woods. 3rd Progreep Rent.." p. 24. Forest Produota Lab., Nav. 29. 1820; Pioc.. Wood Poinfing Conf.,D. 3 (act.. 1829). I
priming as compared with simple oil rednctwn of topcoat material. Sereml general corzGlusions are drawn as to details of the exposure testing of paints. 1A7
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Yo]. 27, No. 2
It is evident that in some localities at least the housebuilder does not have even an optional choice of the most satisfactory grades of siding material. The eneral effect roduced by Douglas fir and yellow pine on paint 18e bears no refationship to the type of paint used on the buildings, since an all-inclusive count of the t'ype mentioned in the foregoing must necessarily cover all the grades and types of paint used in the locality. In the relatively dry climate of the Southwest, flaking failure on these two lumbers must take place promptly after the application of the paint, since the count in uestion must of necessity have included houses having a relativiy short paint age. The southwestern climate, as represented by the localities west of Kansas City, must constitute an exceptionally severe problem in wood painting, and tests in this locality might give accelerated results of value.
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I I I AMARJLLO
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The du Pont Company already had exposure stations located near Miami, Fla., and Wilmington, Del. Arrangements were made for an additional test station a t Canyon, Texas, a few miles from ilmarillo, and a comprehensive series of exposures was started with the general objectives stated in the foregoing. This series covered a systematic crosssectioning of a number of different paint compositions and wood priming systems, and six different lumber types. Included also were comparative series of exposures a t the three test locations, comparisons of south vertical and south 45" exposure, together with the other detailed studies that will be briefly mentioned later. In all, several thoucand panels were involved. 41
FIGURE2. COMPARISON OF CLIMATIC EFFECTSON
FENCE
THE
45'
several hundred houses in Amarillo, Texas, and in Oklahoma City, which showed that 95 per cent of the novelty siding houses in these cities were showing sufficient flaking failure to be readily observable from a passing automobile; in the case of houses constructed with beveled siding, only 25 per cent showed this degree of failure. Inquiry at the local lumber yards in both cities revealed that the novelty siding construction was confined exclusively to Douglas fir and yellow pine, whereas the beveled siding used in these districts was either western yellow pine (Pinus ponderosa) or red cedar. In dmarillo i t was learned that a t the moment the only lumbers available for sale for siding purposes consisted of Douglas fir and western yellow pine. In Oklahoma City only Arkansas yellow pine and western yellow pine were available. At neither point could purchases be made of red cedar or of white pine siding materials. Browne in his publications of 1926 and 1929 had pointed out the inferior paint durability of finishes used over Douglas fir 'and yellow pine, but the observation mentioned in the foregoing indicated that the paint manufacturers of the country were faced with a much more severe problem than that previously indicated by Browne; the following conclusions seemed warranted :
RESULTSON THE 45 ', UNBACKED PANELS FIGURE 3. AMARILLO
It is obvious that no complete r6surn6 of this study is either desirable or possible. However, certain groups of results have general interest. PROCEDURE FOLLOWED IN MAKING OBSERVATIONS From the standpoint of the householder, particularly in the Southwest, the principal criterion of paint performance is obviously the speed with which bare wood is exposed. I n the
TABLE I. PAINT TYPESSTUDIED PIQMEKTATION
DESCRIPTIOX
1
2 3
4
5 6
TiOn 26%; BaSO4.75% b
Basiccarbonate white lead Lithopone 100 .. 55
50
...
... ...
....
.. 33 43
Lead-free .4m. Titanox process Ba ZnO
.... ..
..
20
..
.... .. ..
30
40
ZnO based on5% leaded zinc
35% leaded Bine
..
...
.. .. ..
100
30 35
...
...
...
...
Natibnal Lead Cornpany'reoommended reductions (3.5 gallons of oil per 100 pounds of paste in the topcoat).
Extender
.. 15 15
..
17 17
VEHICLE Linseed oil Linseed oil L+eed oil Linseed-oil-modified glycery 1 phthalate resin Linseed oil Linseed oil
February. 1935
I N D U S T R I A L A N D E N G I N E E R I N G C H E 41 I S T R Y
NOVEMBEL3,7937
FIGURE4.
D.4ILY &rAXIMCM AND RIINIMUM TEMPERATURES FROM NOVEMBER 8 TO 23, 1931
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backs and ends by a two-coat application of a high-grade lead-zinc paint. In Figure 2 results are illustrated on four of the paints. Each curve represents the life history of the paint as shown by the average observations from twelve panels. Table I gives the details of composition of the paints included in Figure 2, together with other paints discussed later in this paper. In Miami paint 4 shows definite superiority over the other types and the white lead in oil (paint 1) shows the poorest results. In Amarillo, on the other hand, the white lead paint shows decidedly the best results for the first 18 months a t least, while paint 4 shows inferior results. It is difficult to believe that paint 3, which lies close to paint 2 in the Miami test, properly belongs in the position given by the Amarillo test, and this may be one of the inconsistencies referred to earlier. On the other hand, the explanation may lie in the fact that this particular group of results deals exclusively with panels protected a t the back. Some color is lent to this possibility by the evidence given in Figure 3 which compares the same four paints at Amarillo on unbacked panels. In this case paints 1, 2, and 3 are grouped quite closely together, whereas paint 4 shows definite inferiority.
judging of panels, therefore, ratings were exclusively on the basis of amount of exposed wood, and an arbitrary scale was established, as shown in Figure 1, in which perfect, integrity of film, from the standpoint of wood exposure, was given a rating of zero with an ascending scale for increased percentages of exposure. This system is open to the many criticisms that can properly be directed a t arbitrary scales of the type, but the system has apparently, a t least, achieved comparable results. The work was originally set u p to provide individual series for the demonstration of i n d i v i d u a l p o i n t s . Early in the study, however, i t became apparent that valid conclusions could not be drawn from any individual series since the difference between panels of the same wood, even though carefully selected, frequently overshadowed in their effect the maximum variations introduced in the way of paint composition or primer practice. It b e c a m e n e c e s s a r y , therefore, to generalize much more broadly than had been intended a t first; conclusions were drawn as t o type of wood, for example, from the average observations, of all the paints used over the given wood type. Even FIGURE5. COMPARISONOF 45" AND VERTICAL SOUTHERN EXPOSURES AT with this method of 1,reatment all concluAMARILLO sions are not wholly clean cut, as will be illustrated later in the paper. I t is believed, however, that the I n Wilmington (Figure 2) there seems to have been no conclusions are as sound as it is possible to obtain in a study significant difference in performance exhibited by paints 1 to of the painting of wood. 4 on the backed panels. This procedure emphasizes what appears to bt. one of the It is worth while to examine the possible causes for the remost important outcomes of this work; namely, in the field versal in results exhibited by the Miami and Amarillo staof wood painting, conclusions are only to be considered valid tions and the intermediate position apparently occupied when supported by a large volume of carefully averaged by Wilmington. Figure 4 gives the maximum and minievidence. m u m temperature records of t h e COMPARISON OF U. S. W e a t h e r CLIMATIC CONB u r e a u f o r their DITIONS stations nearest This comparison the three du Pont was made by means t e s t localities, of laboratory panels covering a 2-week painted with three p e r i o d in Kovemcoats; the first was b e r , 1931. T h i s thinned with oil and period r e p r e s e n t s e x p o s e d a t 45' a s o m e w h a t exsouth at each point, a g g e r a t e d condiIn t h i s s e r i e s all tion which recurs, panels were, as far h o w e v e r , several as possible, selected times a year. A e d g e - g r a i n wood, s i m i l a r difference p r o t e c t e d a t the FIGURE6. COMPARISON OF THREE PRIMARY SYSTEMS AT AMARILLO in temperature
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Vol. 21, No. 2 MAX.A v . HUMIDITY VARIATION For 1 For year month 1933
MAX. RECORDED HUUIDITY VARIATION Daily for 2-Week 2 weeke period
P
%
%
%
%
32 43 43
36 68 70
22 25 32
34 35 44
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Miami Philadelphia Amarillo
3
Here, again, Amarillo shows large and rapid variations in humidity as compared with the other test localities. There is no way of knowing exactly what opposing forces are produced in wood and in a paint film by the normal differences that occur in temperature and in humidity because of the large number of variables entailed. It seems reasonable to assume, however, that with these two dissimilar types of material the reversal of results in the exDosure tests a t the several stations must be l i n k e d - d i r e c t l y t o t h e climatic differences. The following conclusions seem justified from these data:
uz
f
tl
0
3
5
1 2
NoNrnd- ~
13 21 ~ - ~ . - A M A ~ I I L O
FIGURE7. OIL REDUCTION us. ALUMINUM PRIMING
M i a m i exposure favors the less flexible, hard 6lm types which g e n e r a l l y receive a better relative rating in any series a t Miami than other exposure stations. At Amarillo, on the other hand, the less flexible, hard film type quickly fails; this type g e n e r a l l y receives a lower relative rating in any series at Amarillo than at the other stations. In the vicinity of Wilmington, intermediate results are secured and film hardness appears to have less effect on ultimate film integrity. T a k i n g t h e c o u n t r y a s a whole, n o one t e s t l o c a l i t y c a n be acce ted as a criterion of paint performance. For exampi, it is u n s o u n d p r a c t i c e t o base the general marketing of a paint for wood upon r e s u l t s of F l o r i d a t e s t s , e v e n p e r h a p s when supp l e m e n t e d b y t e s t s i n a c l i m a t e such as that of Wilmington. Results on backed panels may be completely misFIGURE8. COMPARISON OF WOOD TYPES AT AMARILLO leading as compared with results on unbacked panela, since paint failure may depend more on the speed with variations mag be noted from the record of maximum and which dimensional changes take place in the wood from the effect of temperature and humidity, than on any other one factor. minimum monthly temperatures for the same period. The extent of temperature variations a t the three points is as follows: MAXIMUM TEMPERATURE VARIATIONVARIATION 2-week 1-month F O R ENTIRE Daily period period YEAR F. O F. F. F. 16 16 43 54 Miami 20 34 50 81 Philadelphia 31 59 72 92 Amarillo
Amarillo appears to be subject to variations between day and night temperature about twice those occurring at Miami; Philadelphia is closer to Miami in this respect than to Amarillo and this relationship apparently maintains throughout the year. Apparently, therefore, a paint film a t Amarillo is subject to more frequent and extreme flexing than a t the other two stations. Atmospheric moisture has a plasticizing effect on a paint film, and wood itself tends to expand and contract with changes in atmospheric moisture. It is probable, therefore, that differences in relative humidity play an important part i n the degree of strain placed on the paint film by the flexing produced by temperature, in that this factor affects the relative expansion and contraction of the wood as compared with the paint film. The following tabulation gives details taken from the Weather Bureau's records of relative humidity corresponding in dates to the t e m p e r a t u r e data given in the foregoing:
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FIGURE9. COMPARISON OF LUMBER TYPESON BACKED PANELS
February, 1935
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It is not known which type of exposure most closely parallels the results to be obtained from the unbacked siding used in normal house construction. Unbacked panels fail on the average more rapidly than backed panels; this point may be significant in connection with the current discussions of mill-priming and back-priming of lumber to be used in new construction. The relatlonship of results from the two types of panels, however, varies considerably with type of paint.
panels. It is probable that the reversal of results noted between the 45" and south vertical exposure is again linked with wood variations which are not smoothed out even by the large number of panels considered. This may be another outstanding example of the inconsistency of results which are to be evpected in the study of mood painting. A more valuable comparison of aluminum priming with oil reduction may be given by Figure 7, which is a wholesale COMPARISON OF SOUTH 45" WITH SOUTHVERTICAL EXPOSUREaverage of the results from five topcoat paints, applied over six woods; each curve is thus established b y the average There has been a general tradition in the industry to the results from one hundred twenty panels. There appears to effect that south 45" exposure causes paint failure about be some superiority for aluminum priming, but it is certainly twice as rapidly as south vertical. This may apply as renot of sufficient magnitude t o represent a real advantage. gards chalking but seems not to apply as regards film integCOhlPARATIVE PAINT PERFORMAKCE ON VARKOUs
TYPESOF
LUMBER The lumber types studied were white pine, red cedar, western yellow pine, Douglas fir "novelty," Arkansas yellow pine "novelty," and long-leaf southern pine beveled siding. Figure 8 illustrates the results obtained from this series on the Amarillo fences, using 45" exposure of unbacked siding. I n general, the order of results obtained compares favorably with that previously published by Browne, although the writers place white pine as definitely superior to red cedar, whereas Browne concluded that red cedar is the better of the two. I I I I I I 21 30 33 36 Each of the curves in this chart was established by means of M O N T H ~ ~ X P O S W ~ /~ LM ~/ N EG- T O N the average results of five different types of high-grade orthoFIGURE10. LABOR 4TORY-PAINTED US. FIELD-PAINTED dox paints, including white lead in oil, lead-zinc mixed paints, PANELSAT WILMINGTON and lithopone-zinc mixed paints. Each curve represents the rity and degree of exposure to bare wood. Figure 5 compares average life history of forty-four panels. I n the case of the white pine, red cedar, the two types of exposure a t Amarillo for each of the five beveled siding materials-namely, types of paint, with one priming system and five types of western yellow pine, and long-leaf southern yellow pinewood used under each paint. Each curve represents the half of the panels were, as far as possible, edge-grain and the average life history of twenty field-painted, unbacked panels. other half flat-grain. I n each set of tests the paints fail in approximately the same order. Here, however, similarity ceases, since it is impossible to fix any time relationship for equivalent degrees of failure with any given paint. This point is illustrated further b y Figure 6 which makes a direct comparison of a high-grade lithopone paint over three types of priming, using field-painted, unbacked panels. As far as fdm integrity is concerned, there is no direct correlation between time and degree of failure for the two types of exposure. OL
VALUESOF ALUMINUM PRIMING On Figure 6 a comparison is given on both the south vertical and 45' fences at Amarillo of three systems of painting:
A. Three coats applied directly from the package without reduction. B. The f i s t coat reduced with one quart of linseed oil per gallon and the last two coats reduced with turpentine only. C . Lumber primed with an aluminum paint having as a vehicle a long-oil spar varnish of the type normally recommended for wood.
As previously mentioned, a high-grade lithopone paint (paint 6) was used for topcoats. On the 45" fences the aluminum primer seems t o give the best results, the normal oil reduction being close to it; but, as would be expected, the results of three-coat application with no oil reduction have been definitely inferior. On the vertical fences, however, for some unknown reason the aluminum-primed panels gave an average result distinctly inferior to either the oil reduction or the unreduced paint. This result is contrary to those obtained by Browne and described in several recent publications, but i t is felt that the results cannot be disregarded in view of the fact that each of the curves in question is established by the average of twenty
FIGURE11. EFFECTOF WEATHERINQ OF WOOD Figure 9 gives a comparison of 45" exposures of backed panels at the three test locations, each curve being established by the average results from five different paints. The data on the wood types in this series are more in accord with Browne's findings, which were understood to have been obtained on backed panels also. This suggests a possible interesting difference in the behavior of red cedar when protected and unprotected a t the back. It is felt, however, that the results as a whole constitute a confirmation of Browne's previous findings and emphasize strongly the desirability of having available to the ultimate consumer a t least the types represented by white pine and red cedar. Even western yellow pine does not wholly satisfy the needs of the situation as indicated by Figure 8.
LABORATORY-PAINTED US. FIELD-PAINTED
PANELS
Figure 10 compares, on both south 45" and vertical fences a t Wilmington, a lithopone paint applied in the laboratory
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to the difference in painting practice as regards the exposed surface.
VOl. 27, No. 2
RECEIVED September 21, 1934. Presented before the Division of Paint and Varnish Chemistry at t h e 88th Meeting of the American Chemical Society, Cleveland, Ohio, September 10 t o 14, 1934.
Spontaneous Ignition of Petroleum Fractions P. J. WIEZEVICH, J. M. WHITELEY,AND L. B. TURNER, Standard Oil Development Company, Elizabeth, N. J.
V
A R I 0 US investigators (510" C.) none of the oils could Spontaneous ignition temperatures of various have published data on be made to i g n i t e e i t h e r on fractions from different crudes were determined. the spontaneous ignition the bare open plate, or when A minimum value is noted in the kerosene and temperatures (or auto-ignition dropped on a thin mat of asbesfuel oil range, while a rapid rise takes place in temperatures) of a number of tos. L i g h t fractions such as the lubricating oil range. W h e n compared acpure compounds and petroleum gasoline would immediately form a ball, similar to that of a drop products. These observations cording to boiling point, both Pennsylvania and are of value in determining the of water on a hot stove, and Colombian crude fractions show similar sponexplosion and fire hazards inthen g r a d u a l l y distill away. taneous ignition temperature curves. volved in the numerous comHeavier oils volatilized off (probExperiments with heated open plates and closed mercial processes e m p l o y i n g ably with simultaneous crackcontainers heated with oxygen under pressure such products. ing) , the vapors being diluted Hersey ( I S ) reported some with the air so quickly that no are described. Oxygen is exceedingly dangerous i n t e r e s t i n g results on the exexplosive mixture resulted. in many cases, leading to detonations as well as F r o m t h e s e observations i t plosive effects of mineral and the burning of metal lines. The presence of can be concluded that hot survegetable oils when subjected to nitrogen, steam, or other similar diluents greatly faces u p to 950" F., open to the oxygen pressure, stating that the reduces the explosion hazard. air, do n o t p r e s e n t a serious critical temperature for linseed fire hazard when sprayed with oil lies between 60" and 120" C. The spontaneous ignition temperature is a s m a l l a m o u n t s of o i l . The a t 2500 pounds per square inch relaticely simple melhod f o r indicating the strucdangerous conditions would exist (170 atmospheres) oxygen presture of hydrocarbons. For the same number of sure. Bridgeman and Marvin where the surfaces were enclosed carbon atoms, the decrease in spontaneous ignior partly enclosed, or where they (6),a s w e l l as M a s s o n a n d tion temperature falls roughly in the order: arowere contacted with considerable Hamilton ( l 7 ) ,have given sponamounts of oil, sufficient to form taneous ignition of various pure matics, alkylated aromatics, naphthenes, alkylated inflammable mixtures. Temcompounds and fuels ( 9 , 9 A , 16, naphthenes, straight-chain parafins, branchedperatures above red heat might 21,22). The effect of pressure on chain parufins, and unsaturated aliphatics. c a u s e i g n i t i o n of even small this property has been discussed quantities of oil. b y various investigators (7, 15, 1;). A number ofvalues for petroleum products have been EXPERIMENTS IN CLOSEDIGNITIOK APPARATUS determined by the A. S. T. M. method and a standard apparatus has been devised ( 2 ) . In this connection, it might be emphasized that the results Araki and Otsu (3) have recently shown that the spon- with various methods described in the literature are only of a taneous ignition of gasoline is somewhat lowered b y the addi- relative nature, comparison between them often being very tion of lubricating oils and even more so than when castor difficult. oil is added. The apparatus employed in the closed chamber runs was a The effect of knock suppressors and inducers has also been gas-heated Thompson bomb (21) and a somewhat modified studied (4,11, $0). Comparative data between air and oxy- Moore apparatus (18). The device is shown in Figure 1: gen are likewise available (8, 10, 14, 25). A represents a container cut from 4-inch (10.2-cm.) steel shafting. B, the ignition block, is also of mild steel and is made reEXPERIMENTS WITH OPEN HEATED PLATES movable to facilitate cleaning; if s. I. T. (spontaneous ignition During the study of auto-ignition temperatures of petro- temperature) is to be determined on othermaterials, this block may inexpensively replaced by a similar piece of the desired maleum fractions, a few tests were made with a heated plate. be terial. The temperature of the igniting surface is recorded by a Oil was dropped on a n open heated plate upon which a ther- thermocouple placed in well C. For most purposes an iron-conmocouple was welded. A t temperatures u p to 950" F. stantan couple will suffice. A hole IS provided in cover D (made
