PAINTS AS PROTECTIVE Protection is one of the few properties of coatings of paint on wood that can be measured quantitatively and strictly objectively during the whole period of life of the coating. There are, nevertheless, few data on the subject in the literature. f o r most practical uses of house paint, protection, of itself, is of minor importance, but the experiments described in this paper indicate that significant technical knowledge of the behavior of paints during exposure to the weather can be gained by measuring the changes taking place in their protective power.
f.L. BROWNE Forest Products Laboratory, Madison, Wie
exchange of nioistorc between wood and its environment.. If there should prove to he a relation between protection and maintenanco of integrity by coatings, measurement of the effectiveness against moisture movement would greatly aid the paint technologist in evaluating the durability of house paints. In certain uses of paints--for example in millpriming and back-priming-protectinn itself i s of dominant interest.. Possible future developments in the use of wood, such as plyvood for exterior exposure, may increase the number of places in which protection by coatings is of real iniportance. T h e first part of this study has already been published (4,6 ) . The previous papers reported the effectiveness of ninety-three priming paints (tests of gronp A), of the ninetytlirce priming paints followed by two coats of white load in linseed oil (tests of group H), and of three-cnat paint jobs in which ihe second and third coats were similar to the primers in cirmposition (tests of group C ) . All tests were repeated on southern yellow pine, Ilouglils fir, norther11 white pine, and redwood. The initial effect.iveness and the effectiveness after exposure to the weather for 6 months at 45" facing south a t Madison, Wis., were reported. Exposure of the 896 speciinens of groups 13 and C was continued, and tests for effectiveness were made a t intervals of 6 months. This paper reports the results with groups B and C up to a total exposure of 3 years, by which time many of the coatings had lost n a r l y all nrotcct,ive value.
@T
HE customary methods of testing exterior house paints for durability on wood consider only the changes in appearance and integrity of the coatings t.hat. are apparent to the eye during the period of exposure. Xo accoiriit is taken of changes in the degree of protertion afforded the \ ~ o o dagainst wvoorl weathering. Such preoccupation with appearance and integrity is fully justified because protection, as a rule, is of minor importance. For the most part appearance aud illtegrity must be judged by personal inspections that snffer from the difficulties inherent in subjective methods of messurement. Protection, on the other hand, can be measnred quantitatively by objective methods (5, r, 11) since it depends upon the effectiveness of the contings in retanling the
3
SERIES 200, GROW.C,SPECIMENS 201 TO 216
(IN
3
3
3
ORDER,LEFTTo RIGHT);209 TO 212 EXPOSED TO THE WEATXEB Doua~.\s FIR. SPECTMENE 201 AT LEm, UNPAINTED
798
COATINGS FOR WOOD Variation in Effectiveness with Length of Exposure to the Weather For details of t h e experiniental procedure, the layout of the tests, t h e coniposition of t h e paints, a n d t h e spreading rates with which t h e paints were applied, reference should be made to t h e earlier publication (4). Reviewing briefly, each group of tesis is further subdivided into seven series known, respectively, as the IM) series, 200series, etc. For each series four sets of wood specimens were provided, one set of each kind of wood. Each set consisted of sixteen specimens carefully matched for reasonable uniformity in weight, grain, and rate of absorption of moisture. Ono sperimen of each set was left unpa.int,ed, one painied with white lead in linseed oil, and one painted wit,h white lead in a Bakelite resin paint oil, leaving thirteen specimens ior experimental paints related in such a way t b t particular1 close comparisons between bhem were passible. Repetition o?the two contml paints in each series made it possible to gage t.he precision of the testing procedure and to make more reliable comparisons between paints in different series. The unpainted control specimens were used to determine for each series the moisture absorbed from dirmu air by the wood
kmained in a robm kept a t 05 per cent'relstive humidihy while the painted specimens were being exposcd. The effectiveness of the coatings against moisture movement %-as determined before expusure to the weather and after aach interval of 6 months during exposure by hanging the specimens in a mom kept a t 65 per cent relntive humidity and 80" F. (27" C . ) until equilibrium moisture content was approximated. As a rule the specimens were approximately in equilibrium when tiiken from the exposure racks unleis t,lrey were removed irnrne-
FOR
24 MONTES,OTHERSPECIMENS EXPOSED36 MONTWS. TOP Row, SOUTHERN Y~mornPINE; BOTTOM Row,
CoxmoL SPECIMENS NOTEXPOSED TO TEE
WXiATHEn
i99
INDUSTRIAL AND ENGINEERING CHEMISTRY
800
VOL. 28, NO. 7
~
TABLEI. AVERAGEEFFECTIVENESS OF COATINGS AGAINST MOISTURE MOVEMENT AT INTERVALS DURING E X P O S U R ~ Reference NO.
102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 203
~
202 204 205 206 207 208 209 210 211 212 213 214 215 216 302 303 304 305 306 307 308 309 310 311 312 313 314 315 316
Description of Primer for Group B and of All Three Coats f o r Group C White lead in linseed oil White lead in Bakelite oil Aluminum paints: Paste A1 in varnish A Paste AI Bakelite varnish 2 Ib. podder varnish 4 1 Ib. powder’ varnish A 2 lb. powder’ Bakelite varnish 1 Ib. powder: Bakelite varnish 2 Ib. powder in: 75-gal. ester gum varnish 33-gal. ester gum varnish Glyceryl-phthalate varnish Shellac-castor oil Raw linseed oil Kettle-bodied linseed oil Nitrocellulose lacquer White lead in Bakelite oil White pigments in linseed oil: Basic-carbonate white lead Basic-sulfate white !ead 35% leaded zinc oxide Mixt. of 204 and 207 Zinc oxide, lead-free Antimony oxide Titanium dioxide Titanium-barium pigment Zinc sulfide Lithopone Mixt of 202 207 404 Mixt’ of 210’ 207’ 404 Mixt’ of 212’ 205’ 404 405 Mixt: of 202: 207: 404: much 407 White lead in linseed oil White lead in Bakelite oil Colored pi ments in linseed oil: Iron oxi8e red 99% Fez08 Spanish oxide,’85% FezOs Venetian red 40 FeeOs Venetian red: 9 z F e z O s Iron oxide yellow 92 0 FezOrHzO Yellow ocher, 18-54 ZFepOs Chrome yellow, lemon Chrome yellow, orange Prussian blue Lampblack Graphite Red lead Litharge
-
Eo
3 s
72 84
80 87
Group B , Primer Plus Two Coats of White Lead Paint Av. effectiveness ratinga 7 En E24 Ea0 Ess EFnd SP Series 100 32 28 73 71 62 43 52 56 34 84 82 83 70 70
85
90 88 80 91 84
88 91 89 84 91 86
84 88 86 76 88 82
84 87 86 76 89 82
82 80 80 70 84 73
74 70 73 55 73 56
76 76 77 59 76 63
67 62 66 38 61 42
36 30
36
36 35 32
34
86 91 86 87 82 84 86
88 92 86 86 86 87 88
83 87 86 55 81 82 53
80 84 86
74 77 78
63 62 67
67 70 69
36 24
aci
76
65
12
..
..
..
66 72
36 27 30 12
70
48 49 52 23 50
..
20
p 12+
F2-
79
86
Series 200 79 82
81
66
64
49
32
68 69 72 72 73 68 68 68 68 67 72 69 70 70
78 79 81 81 83 81 78 76 76 77 82 81 79 79
71 68 71 74 74 69 71 66 70 67 69 67 69 69
38 38 43 43 45 52 43 39 45 42 38 38 35 36
46
52 50 48 51 51
.. .. .. ..
8 7 14 14 17 36 18 10 22 17 4 7 0 2
28 30 24 24 21
71 80
77 85
60 57 55 58 Series 300 71 68 81 82
59 54 61 59 61 66 57 55 61 59 56 55 52 52 60 79
39 66
41 65
11 50
28 30
70 69 69 72 68 70 69 69 69 71 75 72 83
77 76 76 77 75 76 75 79 76 77 80 82 89
71 72 71 75 70 73 73 73 72 71 76 76 82
69 70 67 66 67 71 71 71 71 73 75 62 66
61 62 55 53 58 61 62 61 59 63 65 37 43
44 60 54
18 51 39 30 44 46 53 53 41 49 47 6 1
F F F F F F F
-
EM
82
70 71 70 70 68 72 72 72 73 73 75 71 73 Series 400 71 73 80 79
80
..
.. .. .. ..
51
56 58 61 61 55 60 61 39 42
8 59 41 38 68 76 White lead in linseed oil 80 64 60 40 80 85 White lead in Bakelite oil Transparent pigments in linseed oil! 34 71 73 69 51 .. 68 77 Asbestine (MgSiOa) 404 19 74 73 65 45 79 71 Silica 405 8 71 70 55 38 68 76 Barytes (BaSOa) 406 16 70 69 57 38 60 78 Blanc fixe (BaSOd 407 24 72 75 66 46 .. 68 77 China clay 408 14 72 73 60 41 68 76 English chalk (CaCOa) 409 Aluminum and granular pigments: 33 76 76 73 61 53 73 80 AI and white lead 114 and 202 410 21 79 75 65 51 48 75 83 A1 and red lead 1114 and 315 411 9 72 65 57 42 75 83 AI lead sinc l i 4 and 213 412 27 76 73 66 51 75 83 Al’and h n 0 , i 1 4 and 207 413 52 76 77 77 71 63 80 74 A1 and FezOa 114 and 304 414 36 75 75 72 63 54 72 79 A1 and asbesiine 114 and 404 415 40 81 83 80 70 60 85 80 AI, lead, Bakelit;, 108 and 203 416 5 Eo,Ea, etc. = average effectiveness rating on four woods determined a t the age in months indicated by the subscript. Egnd = average effeotlveness ratin calculated for the exposed faces a t the last time of test (in series 200, group B, a t unexposed backs taken from Table I1 ifrecorded there, otherwise assumed equal t o Ea. 402 403
P+
P+
P+
F-
36 36 36 30 21 21 21 21
Integrityb DF WP 26 34
T-
F F
F
F F F F F F
F F F F F F
F F F
F F F
F F
F
32
F
F
24 24 24 24 24 36 36 36 P+ 36 21 21 21 21
T-
FP+ P+
F-
F
..
F F
F F F F F
F
24 24 24 24
24 24 24 24
30
F F
F
F F F
F F F F F F F
F F F F F F F
F
F
F F F
30
F-
F
30
F-
F-
30
F-
30
F
F F F
F
30
F
30
27 30
P+ P+ F
+ ;
27 27
36
P+
F F
;-
..
.. .. .. .. .. ..
.. .. .. .. ..
..
.. .. .. ..
F F
F F
20 28
24 27
.. ..
27 24 24
24 24
F F P+
F F F
.
12
24 24 24
.... .. I
12
24 24 24
30 30
RI)
..
.. ..
F
F P+
.. 24 24 30
F”-
F-
..
24 24
F F F
age 30 months); effectiveness of
(Concluded on page 802)
exposure to direct sunlight. It is therefore reasonable to suppose that the effectiveness of the coatings on the backs of the specimens remained approximately the aame as it was initially. If that assumption is correct, the changes in effectiveness of the exposed faces were just twice the changes recorded in Table I, and the effectiveness of the exposed face of a specimen a t any time, E:, can be comguted from the formula : E; = 2 ET - Eo where ET and Eoare the ratings recorded in Table I for T and 0 months, respectively. T o test the validity of the assumption that the effectiveness
of the unexposed backs of the painted specimens remained relatively unchanged, certain specimens a t the conclusion of the exposure test were painted on the exposed faces with three coats of aluminum paint. These specimens, together with their unpainted controls were seasoned in 65 per cent relative humidity and tested for effectiveness in the usual way with the results recorded in the third and seventh columns of Table 11. The fourth and eighth columns give the calculated effectiveness of the coatings on the backs of the specimens, assuming that the freshly applied aluminum paint on the faces was 90 per cent effective. In most cases the effectiveness of the old coating on the backs of the specimens agrees satisfactorily with the effectiveness of the entire coating ini-
JULY, 1936
INDUSTRIAL AND ENGINEERING CHEMISTRY
T O WEATHER AT
45”
7
-.
Eo
E6
75 92
85 95
92 94 94 89 95 90
94 95 95 91 96 93
FACING SOUTH,
801
AKD SCMMARY O F VISUAL OBSERVATIONS O F DETERIORATION OF COATINGS Group C, Three Coats of Paint of Kind Described Cpalk- Check- CfackIntegritybAv. effectiveness ratinga E& ingC ingc ingc SP DF WP RD Eia Ezr E30 E38 Eiz Series 100 FF 25 6 12 28 32 41 67 49 75 72 *‘ P+ G G G 84 12 90 88 94 92 93 88 86 91 82 91 85 87 93
90 98 93 92 77 89 43
93 97 95 90 85 92 55
70 75 85 38
89
93
92
89
89 91 92 82 91 85
--
89 91 92 82 92 85
87 90 89 75 90 80
80 86 82 59 85 68
76 82 79 .. 48 61 69 23 Series 200 87 12
87 91 91
83 88 87
83 90 86
75 85
77 86
70 83
69 79
92
91
87
88
65 59 66 62 63 62 40 46 44 38 70 81 56 58
47 44 50 47 49 55
49 45 47 45 47 54
54 70 35 42
51 62 41 44
87 93 89 ,.
..
..
..
..
..
..
73 69 72 75 76 68 63 64 65 55 74 70 73 73
79 78 80 81 82 74 66 68 69 55 82 79 82 80
75 75 78 80 80 65 48 55 56 47
77 7s 77
75 68 75 74 73 68 45 53 48 39 78 77 66 69
6!3 86
76 90
76 90
71 89
62 88
38 84
37 81
56 53 45 62 53 52 56 62 58 58 64 57 60
63 55 55 65 66 58 71 73 65 60 67 78 70
58 51 54 62 60 54 60 71 62 56 64 78 58
61 52 56 63 65 55 64 74 65 61 66 81 54
60 55 56 60 56 54 61 72 61 56 62 67 50
50 39 42 51 46 42 57 68 54 50 56 53 28
45 37 36 48 41 42 55 65 47 47 50 47 19
57 88
76 91
70 88
67 93
54 89
41 74
49 84
55 69 60 60 55 59
59 70 64 63 59 64
49 59 43 46 41 37
43 55 34 41 47 31
30 40 32 32 36 27
.. ..
.. ..
so
.. .. .. ..
.. .. .. ..
.. ..
86 90 88 74 90 79
.. .. .. ..
.. .. .. ..
25 21 22 15 19 40 _.
.. .. .. ..
..
..
.. .. .. .. .. .. .. ..
G
*’ ’.
F G
.. .. .
I
..
.. .. .. .... ..
.. .. .. .. .. ....
6 6 6 6 12
12
6
6 17 6 28 6 23 6 21 28 12 54 6 7 6 15 6 Series 300 4 6 76 12
36 6 18 36 18 36 18 22 18 12 Series 400 6 31 12 80 5 11 4 4 15 -5
..
6 6 6 6 6 6
.. ..
.. .. .... ..
.. ..
*. ..
12 18 24
..
12
18 12
*.
..
30 30
12
.. .. .. .... ..
18
.. .. .. .. .. .. ..
.. ..
..
.. 12
-.
G G
FG G
G G G
G G G
G G
G G
G G
.. ..
110 111 112 113 114 115 116
36
G-
G
G
203
28 28
28 36
F
F F F F F G
G
34 G 12 12
G 12 6
..
12
36
&3+ 36
F+ FP+
F F+ FF-
202 204 205 206 207 208 209 210 211 212 213 214 215 216
34
30
F
F G
F G
302 303
G G
G G
G G
G
304
G F+ -
GF+
$
