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/61_Fourth Progress Report

PRIMING-COAT REDUCTIONS FOR PAINTING N W DSURFACES

A Joint Project o f

Northwestern Paint and. Varnish Production Clu bMinnesota chapter of the International Associa-

tion of Master Painters and Decorator sPaint, Oil and Varnish Club of the Twin Citie sRetail m4!!emie -Ae .r,w rir of the Twin Cities

with the assistance o f

Forest Products Laboratory, Forest Service ,U .S . Department of Agricultur e

By F . L . Brown eFor the St . Paul Test Fence Comm tte .

W . J . Philippbar, Chairman- 'L . P . Warren

T . J . MacMahonS . O . SorensonJ . M . OlsenPeter GydesenM. H . Sim eF . L . Browne

•

1

PRIMING-COAT REDUCTIONS FOR PAINTIN G

NEW WOOD SURFACES

By

F . L . Brownefor the Test Fence Committee-

The principal object of this study is to discove rthe optimum priming-coat reduction in applying common hous epaints to softwoods and to determine whether the primin gcoat should be reduced differently according to the natur eof the softwood painted . The experiments were described i ndetail in a first progress report published in American Pain tand Varnish Manufacturers Association, Scientific Section ,Circular 404; 596 (1031) . A second progress report appearedin Federation of Paint and Varnish Production Clubs, OfficialDigest No. 121, 1068 (1932) and a third report in AmericanPaint and Varnish Manufacturers Association, Scientifi cSection, Circular 445, 454 (1933) : Oil,Paint and DrugReporter 124, 68 (Nov . 16, 1933) ; Paint, Oil and Chemica lReview 95, 67 (Nov . 2, 1933) .

•

Four woods and three paints were used in th eexperiments on priming-coat reduction . The woods were Norwaypine, northern white pine, western red cedar, and redwood .The paints were white linseed oil house paints that differedonly in the nature of the pigments ; in one the pigment wasentirely basic carbonate white lead, in the second the pigmen tcontained 60 percent by weight basic carbonate white lead ,30 percent lead-free zinc oxide, and 10 percent magnesiu msilicate, and the pigment of the third contained 60 percenttitanox B, 30 percent lead-free zinc oxide, and 10 percentmagnesium silicate . All three paints were made in the for mof semi-pastes one gallon of which consisted of 0 .435 gallo n

. J . Philippbar, Chairman, L . P . Warren, T . J . MacMahon ,S . O . Sorenson, J . I . Olsen, Peter Gydesen, M . H . Sime ,F . L . Browne .

•

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of pigment and 0 .555 gallon of linseed oil . For the variou spriming coats these paste paints were thinned with linsee doil, turpentine, and paint drier as indicated in table 1 .Some of the painting was done in two-coat work and some i nthree-coat work . For the final coat in two-coat paintingthe paste paints were thinned with 0 .655 gallon of linsee doil, 0 .036 gallon of turpentine, and 0 .036 gallon of drie rper gallon of paste paint, making paint of 26 .4 percentpigment volume . For three-coat work the second coat wa smade by mixing 1 gallon of paste paint, 0 .218 gallon oflinseed oil, 0 .437 gallon of turpentine, and 0 .036 gallon o fdrier, making paint of 35 .9 percent pigment volume ; for th ethird coat the mixtures were 1 gallon of paste paint, 0 .946gallon of linseed oil, 0 .036 gallon of turpentine, and 0 .03 6gallon of drier, uaaking paint of 22 .4 percent pigm-en-t volurn:e. .

Panels were attached to both sides of test fences ,providing both northern and southern expo•sura-s . 14e panelswere made of boards of bevel siding 12 feet long +o tha tgroups of 6 matched test areas each 2 feet hang were providedon which six variations in priming-coat reduction were testedon the same boards . In table 1' the 6 priming praaadure :stested on _subdivisions of the same boards are groro :p dtogether . Priming reduetiltOR 1-3 was re!p.e .ted on each s•e tof boards in order to reveal .differences due to characterij=tics of the boards in dif14;cLt panels of the same wood. ariato furnish z basis for oor Nr'.ng priming pro.oedutes•' e !tedon different panels .

Since the third progress report was written tber ehave been two formal inspections of t1;e fence, one in Jun eand the other in October 1934 . At the last ii spect'a )n th ecoatings were 38 months old . The writer also inspedted 'Wefence in August 1934 in company with a group of visitingpaint technologists but records were not made at that tiia e::At 38 months the coatings on the south side of the fenc ewere failing in integrity sufficiently to re v , e, .!!: disttiiitc tdifferences caused by the variations in. pruning-coatreduction . ; On the north side of the fence, h! wever ,coatings remained intact except for cexfta.in J gcal ca

' '•moisture failure mentioned in the third progri,se repo

-The present report is concerned chiefly witly i4,e trend sdurability of the coatings on the s .out- side of 'tie fenwt=;

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. 1 1

S Effect of Priming-Coat Reductio n

Table 1 ree ordlt the rat i - of the coatings i nintegrity at age 38 maonttt, the ieJ0 4ii7 in months of thos ecoatings that had become unserViceable,send were in the perio dof paint neglect, and an arbitrary estimate of the du abilit yof those coatings that still remained serviceable The restimated durabilities are based on the assumption thatcoatings rated Poor plus at the last inspection will remai nserviceable 3 months longer, those rated Fair minus 6 monthslonger, and those rated Fair 9 months longer. The estimateddurabilities calculated in this way greatly facilitat ediscussion of the results but they are far from accurat epredictions of future behavior . Less than one-third of th edurabilities recorded in table 1, however] are estimated i nthis way and for that reason the relative Merits of th evarious priming procedures are as clearly revealed as theywill be when the tests have continued until all of th ecoatings are unserviceable . •

In table 1 the priming-coat reductions nu b,erAd 1=1 ,1-4, '4, 1-4, and 1-5 were mixtures in whioh. the c.otc.en-tration of pigment is suitable for three-cat paintiog 4ranging from 17 .2 to 23 .2 percent by volume of the mixtur e(including volatile) . Reduction-s numbered 2-1 ) 2-2, and.2-3 had a higher concentration of pigment, 24 .1 to 26 . 3percmi, suitable for two-coat painting . Among the reduction sof series 1 the best results were obtained with 1-1, in whichno turpentine was used, and the tendency was for th edurability to decrease as the turpentine was increased andthe linseed oil decreased in the priming coat . Th edifference in results with primers 1-1, 1 .2 ; and 1-3 ,however, was so small that they may well be cons .derod equall yserviceable : Reductions 1-4 and 1-5 were on the whole dis-tinctly inferior although on redwood-1-4 wa . Still provingnearly as good as 1-3, Threductions of series 2 wheal.used in two-coat work revealed a definite superiority o fthe reduction 2-1 ; made with linseed oil and no turpent,i-n eover those in which there was linseed oil and turpent-U14 4Of the two reductions of series 2 used for three-eoO vwa-rk ,the one containing more oil and less turpentine prove dsomewhat superior .

It should be noted that, in three-coat work ,reduction 2-2 was slightly superior to 1-3 in the case•"s- o fwhite lead and titanox and zinc paint and slightly inf :ri:orin the case of lead and zinc paint . In other words ,

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reductions 2-2 and 1-3 on the whole proved about equall yserviceable. The pigment volume in 1-3 was 22 .3 percent(of the non-volatile and the ratio of linseed oil t oturpentine by volume was about 2 .6. In 2-2 the pigment volum ewas 30 .2 percent and the ratio of oil to turpentine 3 .4.Reduction 1-4, which was inferior to 1-3 with all paints, ha da pigment volume of 29 .4 but a ratio of oil to turpentine o fonly 1 .4. It seems, therefore, that the ratio of oil t oturpentine is more significant, at least within the range o fdesirable reductions, than is the pigment volume . Apparentlya good primer should have at least 2-1/2 times as much linsee doil as turpentine and it is questionable whether there nee dbe any turpentine in the primer at all . The pigment volum ein a good primer for three-coat painting presumably may b eanywhere in the range of 20 to 30 percent but for two-coa tpainting practical considerations require that the pigmentvolume be in the upper portion of this range .

Reductions for Different Woods

The notion has long prevailed that the optimu mpriming-coat reduction differs according to the kind . of woodpainted. There is no published evidence in support of such abelief and its soundness may well be doubted in view of thecontradictory recommendations often made when writers try t ogive specific priming-coat formulas for different woods .The data of table I suggest the same optimum priming-coa treduction for all woods, namely, reduction with linseed oi land little or no turpentine . The results are not at al lconsistent with the view that the reduction for red ceda ror redwood should differ from the reduction for white pin eor Norway pine . It should be recognized, however, that th epresent experiments were concerned principally with th eproportions of linseed oil and. turpentine in the primingcoat and did not cover possible variations in pigment concen-tration as adequately as could be desired . Further researchmay show that for woods like redwood and red cedar, whic habsorb paint oils quickly, a slightly lower pigment concen-tration may be advisable in order to avoid unduly lo wspreading rates and difficulty with painters' laps than i sappropriate for such woods as Norway pine, southern yello wpine, and Douglas fir . Nevertheless the present indicationsare that a single recommendation for reducing priming coat sfor all kinds of woods is entirely practical and probabl yadvisable . The "easily paintable" woods probably differ fro mthe "difficultly paintable" ones chiefly in degree o fsensitiveness to departure from the optimum reduction, tha t

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-4-

is, less damage to the serviceableness of the coating may b eexpected if the painter fails to use the optimum reduction i npainting redwood than will result when painting Norway pine .

Order of Failure on the Four Wood s

The order of failure of the three paints on the fou rkinds of wood is indicated in table 2, which records in eac hcase the average durability for all priming-coat reductionsof the white paint . Certain physical properties of the board sof each of these woods were reported in table 1 of the thirdprogress report . On cedar, white pine, and Norway pine theaverage curability of the three paints was inversely proportionalto the average density of the boards of those species . Thedurability on redwood, however, was about as great as it wason red cedar although the density of the boards was nearl ythe same as the density of the white pine . These results ar eentirely in accord with results previously reported by th eForest Products Laboratory (Federation of Paint and VarnishProduction Clubs, Official Digest No . 95, p . 106 (1930) ) .

Table 2 .--Order of failure of paints on the four wood s

:Average durability in months of coatings of-:Density :: of

:'mite mead : Lead and :Titanox : Average: wood : paint

:zinc paint :and zinc : for all: paint : 3 paint s

:Lbs .per :Ift . ::cu .

Redwood : 26 .2

. 38 .4 39 .3

: 38 .8

: 38 . 8Red

cedar . . . : 21 .5

. 38 .8 37 .4

: 40 .6 38 . 9White pine . . : 26 .8

. 35 .5 33 .6

: 30 .5

. 33 . 2Norway pine . : 28 .9

. 30 .0 36 .5

. 24 .3

. 30 .3

Kind_ o fwood

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The relative behavior of the white lead paint, lea dand zinc paint, and titanox and zinc paint during the firs ttwo years of exposure was described in detail in the thir dprogress report . Since that time all throe paints have bee nchalking freely enough on the south side of the fence t odislodge most of the remaining dirt and the white lead andlead and zinc paints at 38 months were nearly as clean andwhite as the titanox and zinc paint . On the north side of th efence the titanox and zinc paint still remained almost a sclean and white as it was on the south side, the lead an dzinc paint had thrown off most of the dirt previousl yaccumulated and was only slightly more gray than the titanoxand zinc paint, but the white lead paint still retained muc hdirt, was very spotted in discoloration, and was still rate dBad in appearance .

On the south side of the fence at the last inspectio nthe characteristic reticulate checking of white lead paintwas readily visible on close examination without a magnifyin gglass. The checking was then undoubtedly deep. The lead andzinc paint was likewise checking visibly and the checking wa sgradually becoming reticulate . The titanox and zinc paintremained free from checking .

Disintegration of the white lead paint proceededentirely by crumbling . The lead and zinc paint and the titanoxand zinc paint disintegrated by slitting or cracking followe dby curling and flaking . Chalking of the titanox and zin cpaint had reduced the thickness of the film enough to impai rthe opacity observably although very close inspection wa snecessary to disclose that fact . There had, however, been nowashing of the chalk over the black identification numberswith which the test areas were marked .

The extent to which disintegration of the three paintshad gone after 38 months may be seen by referring again t otable 2 . On redwood and red cedar they were provingpractically equal in durability but on white pine and Norwa ypine the titanox and zinc paint had disintegrated earlier tha nthe other two paints . As a result there was a greate rvariation in durability on different woods with the titano xand zinc paint than with either of the other two paints .

As was pointed out in the third progress report ,there was more difference in durability between any one of th epaints on the four woods than there was between that of that

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1 - , three paints on any one wood . It is also true that the rwas more difference in durability between the best and t eworst priming-coat reduction with any one paint than ther ewas between tlat

he thre•j paints on redwood r e p .cedar ,11 - -% or white

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With the white lead paint and the titanox and zincpaint the best two-coat job (priming-coat reduction 2-1 }

• proved equal or superior in durability on the whole to th e- hest three-coat job (with white primer) applied on the sam e

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boards

With the lead and zinc paint the best two-coat job.r was slighly inferior to the best three-coat job on the s 'boards except on red cedar, where it was better . Table 3

y I'm - - the first progress report recorded the total amounts o f%

paint applied in the two-coat and three-coat jobs and s wed__• - that, by reason of the higher pigment concentrations and

lower spreading rates followed in the two-coat painting ,

▪ 1 - roughly similar total quantities of paint were applied i n_ two-coat and three-coat jobs, It is evident that two-coat-painting when done in the manner followed in these experiment s

' - is thoroughly practicable and gives coatings that closel y% approach good three-coat work in durability and prove die -

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- white paint . On all woods except white pine the coatings o f

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all three paints over aluminum primer were still rated Fai r ,-

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minus or better in integrity at the last inspection and i nall cases except that of lead and zinc paint on white pi n

0:1 •• the coating over aluminum primer was rated as high or highe r1

in integrity than the best coating over a white primer o nthe same boards. On 10 out of 12 panels the coating over ,

-- aluminum primer had the highest rating, on 1 panel it s.%

rating (Fair minus) was equalled only by white priming-coa _{

reduction 1-1, and on 1 panel it was distinctly superior t o- - reductions 1-4 and 1-5 but inferior to reductions 1-1, 1-2 ,

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and 1-3. On the last panel, however, failure was confined t otwo of the four boards which developed loose grain toward th e

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aluminum primer in these tests tended to hold the coating sintact longer than any of the priming-coat reductions of th ewhite paint .

Failure of the coatings in integrity took plac eunusually rapidly on the St . Paul test fence . Coatings o fthe white paints used should be expected to remain service -able in the Lake States region for at least 4 years on suc hwoods as red cedar, redwood, and white pine, yet th efailures took place in less than 4 years . The coatings o fwhite lead paint and of lead and zinc paint applied wit hpriming-coat reduction 1-3 as recorded in table 1 ma yreasonably be compared with certain tests by the Forest

HProducts Laboratory in which the same paints were appliedwith very similar reductions and on some of the same kinds o fwood at Fargo, N . P ., and at Madison, Wis ., in 1930. Table 3records data suitable for comparing the results with thos eat St . Paul .

The reason for faster disintegration of the paint sat St . Paul is unknown but the fact that there is unmistak-able evidence of some moisture failure on the north sid eof the fence, as pointed out in the third progress report ,suggests that moisture getting into the fence at some tim emay have hastened disintegration on the south side eve nthough the moisture conditions were not severe enough t oresult in typical blistering or other developments clearl yrecognizable as moisture failures . It has been reported t othe test fence committee that at one time during the winte rof 1932-33 snow drifted against the fence to the extent o fpractically covering one side . This snow was not shovele daway and there is a possibility that entrance of moistur ewithin the fence took place when it melted .

Miscellaneous Tests on Units 7 and8

In addition to the main portion of the test fenc ethere were two units added for the purpose of trying th eeffect of special primers made with white pigments in th e

Unusually Early Failure of the Paint%

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81045

•

Bakelite varnish used as a vehicle for the aluminum prime ron units 1 to 6 and for trying the recommendations fo rthinning white lead paint made by the National Lead Compan yand the Eagle-Picher Lead Company and certain paints suggeste dby the New Jersey Zinc Company and the Titanium Pigment sCompany. The condition of these paints with respect t ointegrity of the coatings at the last inspection is recorde din table 4 .

Of the special primers made with white pigments i nBakelite varnish the one made with zinc oxide gave distinctl yinferior results . The ones made with white lead and titano xwere better but by no means so good as the aluminum primerreported in table 1 . The type of failure of the white leadpaint over these priers was not the same as that of whitelead paint over white lead primer or over aluminum primer bu ttook the form of flaking as distinguished from crumblin gover the bands of summerwood .

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