SD'33
O
I)
s~
U. S. Depart nest of Agriculture, Forest Servic e
rn° FOREST PRODUCTS LABORATOR Y
In cooperation with the University of Wisconsi n
MADISON, WISCONSIN
EFFECT OF ALUMINUM PRIMING PAINT ON TH E
DURABILITY OF HOUSE PAINTS ON WOO D
By F. L. BROWN E
Senior Chemis t
FOR PUBLICATIO N
October, 193 3
EFFECT OF ALUMINUM PRIMING PAINT O N
THE DURABILITY OF HOUSE PAINTS ON WOO D
By
L
F . L . BROWNE, Senior Chemis t
Forest Products Laborator y
In painting exposed metal it has long been customary t o
apply special priming (first-coat) paints, that is, paints in whic h
the pignertsdiffer from those used in the paint applied in subsequen t
coats . In painting exterior woodwork, on the other hand, the usw 1 .
practice is to apply priming and succeeding coats of paint havir . ; the
same composition with respect to pigments, though differing in th e
amount of liquids and in the proportions of non-volatile and volatil e
liquids . Special priming paints for wood have been proposed from tim e
to time by technologists and others . Until recently none of them _ia s
achieved extensive use with the possible exception of the once popula r
yellow ochre primer, the advantage of which was initial cheapnes s
rather than excellence . At present there is a renewed interest i n
special priming paints for wood, and several kinds of them are no w
on the market . Of the new special primers aluminum paint probabl y
is the most widely used and the best (9, 10, 11) .
As a special primer aluminum paint affords improved protection of the wood against changes in moisture content and improved durability of succeeding coats of conventional house paints . The writer ha s
IForest Service, U . S . Department of Agriculture, maintained at Madison ,
Wis ., in cooperation with the University of Wisconsin .
R1015
S
s
recently reported tests of aluminum priming paint from the point o f
view of protection against moisture movement (7) . The present pape r
deals solely with the effect of aluminum priming paint on the durabilit y
of house paints on wood as determined by test fence exposures following ,
in general, testing methods that are described elsewhere (6) . In al l
cases the test panels were rated for appearance and integrity of th e
coating and for maintenance of protection against wood weathering, i n
accordance with the general method for evaluating paint service adopte d
by the Forest Products Laboratory (11-) . For the present purpose, however ,
only the integrity and durability of the coatings need be reported .
Ordinarily the appearance of coatings (largely a matter of color an d
cleanness) is not affected by the use of aluminum priming paint, and th e
contribution made by aluminum priming to the maintenance of protectio n
against wood weathering is revealed most clearly by the special test s
of moisture movement (7) .
In an earlier publication (3) the writer reported tests o f
special priming paints on seven species of wood . In those tests th e
substitution of aluminum paint for the customary white paint prime r
increased the durability of succeeding coats of white lead paint fro m
44 to 48 months and of lead and zinc paint from 42 to 49 months on
the average, although the aluminum priming paint used was seriousl y
faulty in certain respects that will be discussed later . Th e
increase in durability of paints applied over the aluminum prime r
was greatest on those woods that usually hold paint least satisfac torily and was effected by marked retardation in the flaking of th e
coatings from the bands of summerwood after age bad made the coating s
brittle (2, 5) . The beneficial effect of the aluminum primer becam e
all the more marked after the coatings passed the point at which goo d
practice calls for repainting and entered the "period of paint neglect, "
because the coatings over aluminum primer after such neglect offere d
much more satisfactory surfaces for repainting than the coatings ove r
the white primers .
Many paint technologists have been reluctant to admit th e
merits of aluminum priming paint . For that reason it has been deeme d
necessary to repeat the earlier experiments several times and to buil d
up unusually extensive data on the subject . The later tests thoroughl y
confirm the earlier findings . Nearly 200 test areas have been prime d
with aluminum paint as a base for coatings of white paint in tests b y
the Forest Products Laboratory ; almost without exception the aluminu m
primer materially prolonged the life of the coating and in no case di d
it shorten the life .
General Procedur e
•
In tests in which comparison of aluminum priming paint wit h
the customary white priming paint was the principal objective the tw o
painting procedures were followed on neighboring areas of the same tes t
x1015
O
panel so that the comparison could be made on identical boards . As a
further precaution each test panel was made of three, four, or fiv e
boards . In certain other experiments for which pertinent data ar e
shown, the principle of "matched specimens" does not apply, but th e
number of boards painted was large enough to accomplish fair compariso n
through the principle of averages .
Some technologists have attributed the beneficial effect o f
aluminum priming paint to the varnish or bodied oil vehicle with whic h
aluminum paint is made rather than to the aluminum pigment (15, 16) .
For that reason some of the experiments included tests in which thes e
vehicles were used with the white paints as primers or in which th e
clear vehicles without any pigment were applied as primers . Some test s
also included special priming paints in which aluminum powder was use d
in admixture with other pigments .
All test panels were exposed facing south . Some were place d
on the test fences in the vertical position, as on the side of a house ,
while others were placed at a sl ope of 45 degrees . Paint fails mor e
rapidly on inclined than on vertical panels (17) ; the degree to whic h
failure is accelerated by the inclined position can be gaged fro m
tests involving concurrent exposure in both positions .
Most of the tests were made at Madison, Pis ., but some o f
them were repeated at stations representing distinctly differen t
climatic conditions .
Composition of Paint s
Raw linseed oil and liquid paint drier of the same brands ,
though from several different shipments, were used throughout thes e
experiments . Examination of a typical shipment of the linseed oi l
revealed an acid number of 5.5 mg. KOH per g . and an iodine numbe r
(Wijs) of 178 .0 .
The paints and their various mixes are listed below with a
system of symbols that will represent them in the subsequent discussion .
Aluminum priming paint s
Aluminum paints are designated by the letter A :
Al
•
R1015
Aluminum powder, standard varnish grade, 2 pounds (0 .91 kg . )
Long-oil spar varnish,
1 gallon (3 .78 1 . )
The varnish was a commercial aluminum vehicle of 80-gallo n
length in oil and presumally made chiefly of ester gum, tun g
oil, and thinners . It contained 52 percent non-volatile b y
weight .
-3-
Aluminum powder, standard varnish grade, 2 pounds (0 .91 kg . )
1 gallon (3 .78 1 . )
Bodied linseed oil vehicle,
The bodied linseed oil was made by heating varnish makers '
linseed oil at 300° C . for 2 .5 hours, adding lead and manganes e
paint drier, continuing the heating for 0 .5 hour longer, cool ing, and thinning with mineral spirits until the non-volatil e
content of the mixture was 60 percent by weight .
A2
I
Aluminum powder, standard varnish grade, 1 .5 pounds (0 .68 kg . "
1 gallon (3 .78 1 . )
Long-oil spar varnish,
The varnish was the same one used in paint A l .
A3
Aluminum powder, standard varnish grade , 2 pounds (0 .91 kg . )
1 gallon (3 .75 1 .)
Synthetic drying oil,
The synthetic drying oil was a commercial aluminum vehicl e
of the glycerol-phthalic acid type, "for use under U . S . Patent s
1,108,329, 1,108,330, and 1,119,592 . x"
A
Other special priming paint s
Special priming paints or priming liquids are designate d
by the letters SP :
O
Red lead ,
Zinc dust ,
Aluminum powder ,
Raw linseed oil,
Boiled linseed oil ,
Turpentine ,
Drier,
93
pounds
(1+2 .1 kg . )
pounds
(
7 .7 kg . )
17
8 .5 pounds
( 3 .85 kg . )
5 .15 gallons (19 .1 1 . )
1 .)
1 .06 gallons ( 4
1 .06 gallons ( 1+
1 .)
.25 gallon (0 .95 1 . )
SP
-2
Red lead,
Aluminum powder,
Linseed oil,
Turpentine,
Drier,
93
pounds
8
pounds
2 .65 gallons
1 .75 gallons
.125 gallon
(12 .1 kg . )
( 3 .63 kg. )
(10
1 .)
( 6 .62 1 . )
( .147 1 . }
SP
-3
Basic carbonate whit e
lead,
Aluminum powder,
Linseed oil,
Turpentine,
Drier,
85
pounds
3
pounds
1 .68 gallons
1 .85 gallons
.125 gallon
(38 .6 kg . )
( 1 .36 kg. )
(17 .7 1 . )
( 7
1.)
( .47 1 . )
SPA
The bodied linseed oil vehicle for aluminum paint A2 withou t
aluminum or other pigment .
SP
The varnish vehicle for aluminum paints Al and A3 without
aluminum or other pigmen t
5
R101 5
•
White paint s
White paints are designated by the letters L for pure whit e
lead paints, LZ for paints containing white lead and zinc oxide, an d
TZ for paints containing titanium pigment and zinc oxide :
I
Ll
(Paste paint)
L2
(Paste paint)
Zl
(Paste paint)
LZ
(Paste paint)
TZ l
(Paste paint)
TZ 2
(Paste paint)
(Prepared
paint)
R101 5
Basic carbonate white lead,
Linseed oil,
Unit weight for mixing,
Basic carbonate white lead,
Linseed oil,
Unit weight for mixing,
Basic carbonate white lead,
Zinc oxide, lead-free,
Magnesium silicate,
Linseed oil,
Unit weight for mixing,
Pounds
(Kg. )
92
(11 .7)
( 3 .63 )
(1 1.5 .4 )
8
100
15
100
(20 . 11.)
(10 .2 )
( 3 . 11. )
22 .5
7.5
2.5
(11 .3 )
100
1-2 .6
Titanox B,
Zinc oxide, lead-free,
Magnesium silicate,
Linseed oil,
Unit weight for mixing,
29.1
16 .0
Basic carbonate white lead,
Zinc oxide, lead-free,.
Magnesium silicate,
Total pigments,
Linseed oil,
Turpentine,
Drier,
Total liquids,
(11.5 .1{.)
11-5
Basic carbonate white lead,
Zinc oxide, lead-free,
Magnesiumasilicate,
Linseed oil,
Unit weight for mixing,
Titanox B,
Zinc oxide, lead-free,
Magnesium silicate,
Linseed oil,
Unit weight for mixing,
(38.6)
( 6 .8)
85
(19.3 )
( 9.6)
( 3 .2)
( 6 .8)
(39 )
21 .3
7 .1
15
s6!
(13 .3)
( 7.25 )
( 3 .63)
( 6 .8)
(31 )
8.0
15
- r .1E
33 .0
16 .5
5.5
15
(15)
( 7.1}8)
( 2 .)+9)
( 6.8)
(31 .7)
70
Percent by weigh t
60
30
10
61
90
5
36
.
Percent by weigh t
•
LZ~
(Prepared
paint)
LZ5
(Prepared
paint)
(Prepared
paint)
T Z3
(Prepared
paint)
Basic carbonate white lead ,
Zinc oxide, lead free,
Magnesium silicate,
Total pigments,
Linseed oil,
Turpentine,
Drier ,
Total liquids,
Basic carbonate white lead,
Zinc oxide, lead-free,
Magnesium silicate,
Total pigments,
Linseed oil,
Turpentine,
Drier ,
Total liquids,
Basic carbonate white lead,
Zinc oxide, lead-free,
Magnesium silicate,
Total pigments,
Linseed oil,
Turpentine,
Drier ,
Total liquids,
Titanox B,
Zinc oxide, lead-free,
Magnesium silicate,
Total pigments,
Linseed oil,
Turpentine,
Drier ,
Total liquids,
6o
30
10
66
90
5
34
55
35
10
66
90
5
34
1+ 5
140
15
66
90
5
34
55
35
10
66
90
5
3'+
Mixes of white paints for applicatio n
Mixes for priming coat are designated by letters a, ax (fo r
repainting), and av (containing varnish or bodied oil), mixes fo r
intermediate coat by b, and mixes for final coat by c . In the mixin g
formulas below, the quantities of liquids in gallons are added to th e
unit weight of paste paint stated in the paint formulas or (in the
case of the smaller quantities shown, as 6 to ay, etc .) to 1 gallo n
(3 .7 g 1 .) of prepared paint :
a0
4
linseed oil,
2
turpentine, l / g drier .
al
3 .5
linseed oil,
2
turpentine, 1A drier .
81015
-6-
O
3
a3
2 .75 linseed oil, 1 .85 turpentine, 1/8 drier .
a
2
a5
1 .5 linseed oil, 2
a6
1/ g
a7
1/2 turpentine .
ag
1/14 turpentine .
a9
0 .31 mineral spirits . '
avl
-2
4
linseed oil, 2
linseed oil, 2 mineral spirits,,l/S drier .
linseed oil,
turpentine, 1/8 drier .
l/4 tur pentine .
bodied oil vehicle (see
k),
2 turpentine, 1/8 drier .
3 .5 bodied oil Vehicle (seek) ; 2 turpentine, 1/ 14. drier .
av 3
1 .5 spar varnish (see A1), 2 turpentine, 1/8 drier .
av
1 .5 linseed oil, 1/2 spar varnish (see A1 ), 2 turpentine, 1/ 8
drier .
0 ,.16 spar varnish (see Ai ), 0.15 mineral spirits .
av
av7
2 .75 linseed oil, 16 spar varnish (see A1 ), 1.85 turpentine ,
1/8 drier .
.1
turpentine .
2 spar varnish (see A1 ), 1/ g linseed oil, 1/1
arl
1 .6 linseed oil,
arm
1 :25 linseed oil, 2 turpentine, 1/ g drier .
ar3
1/ g linseed oil, IA .drier . . .
b0
1 .5 linseed oil, 1 .5 turpentine, 1/ g drier .
bl
2 .62 linseed oil, 1 .25 turpentine, 1/8 drier .
b2
1/2 linseed oil, 1 .5 turpentine, i/8 drier .
b3
0 .141 linseed oil, 1 .39 turpentine, 1/8 drier .
b
1/ g turpentine .
b5
1/5 turpentine .
co
3 .5 linseed oil, 1/ g turpentine, 1/8 drier .
av
O
turpentine, 1/ g drier .
a2
R1015
2 turpentine, i/8 drier .
-7-
cl
3
c2
2 .62 linseed oil, 0 .22 turpentine, 0.22 drier .
-c 3
2 .5 linseed oil, 1/g turpentine, 1 / g drier .
c4
2 0 25 linseed oil, 1 / g turpentine, l/8 drier .
-c 5
The prepared paint without any addition .
linseed oil, 1/8 mineral spirits, 1/ g drier .
Tests on Western Larc h
A, series of tests was begun in 1927 at Madison, Wis ., t o
study the painting characteristics of western larch, a heavy softwoo d
which contains mach summerwood and is therefore difficult to pain t
durably (2) . For that reason some of the painting procedures teste d
were based on aluminum priming paint . Each panel contained fiv e
boards of commercial 4-inch (actual width 9 cm .) strip flooring. Test s
on panels of flat-grain boards and on panels of edge-grain boards wer e
made in duplicate with panels in the vertical and inclined positions .
After 26 months and again after 52 months of exposure most of th e
inclined panels were repainted with white paints . In repainting, an y
loosened shreds of old coating were removed with a putty knife an d
the surface was brushed with a painte rt s duster before applying fres h
paint .
In table 1 the painting procedures tested are indicated ,
together with the durability of the resulting coatings .
Two-coat as well as three-coat painting of new wood was in cluded in the tests . The two-coat work was accomplished by omittin g
the intermediate coat of the customary three-coat job and by applyin g
the final coat somewhat thicker . Later experience has proved tha t
proper procedure in two-coat painting calls for priming- and final coat mixes that are richer in pigments than the mixes used in conventional three-coat painting . For that reason the data of table 1
should not be taken as a measure of the relative durability of two-coa t
and three-coat painting by experienced painters . Two-coat painting i n
which the priming coat is aluminum paint and the final coat is whit e
or tinted white paint is often impracticable because one coat of whit e
paint usually fails to hide the color of the aluminum primer satisfac torily . If the final coat is gray, however, or a tint in which a
component of gray is desirable, two-coat painting over aluminum prime r
may give good results in the hands of a skillful painter .
In this series of tests coatings over aluminum primer alway s
proved distinctly more durable than the corresponding coatings over a
white primer, whether the white primer was mixed with linseed oil i n
R1015
-8-
410
Table 1 .---Painting procedures and durability of the coatingstested on
western larc h
:;
::
::
Initial painting
procedure
Durabilit y
of initial
coatin g
on
: :Repainting pro-- : : Durability o f
: : cedure at age : :
repainted
: : 26 months and : :
coatin g
: n,t age 52 months : : applied at ag e
------ -..
: :
Priming : Second : Third : :Vertical :Inclined : :
coat : coat : coat : : panels : panels : :
._
On flat-grain boards ;
L
' -lam
-1:-1-0
-1 av3 :
-1-0
: -I-0
'L b
1
1 25
Z1 av3
:L1-0
L 6 a7
:LZ6
Al
: -65
a
7
L1a5
Ll av3
;•
LZ c
c
LZag
:LZb 4
LZag
:LZ25
2g
25
. .
35+
'
19
::
: :
LZ6c5
:LZ 6c5
52
First :Second : : 26
coat : coat : :months :month s
19
26+
35+
•
•
: :
L l arl
:-l-° 0
L
1 ~0
: L1 cO
::
• :L ar
1 1
'L c
, 1~
:L c
-1-0
..
16
. .
9
::
1
: :L L
23
:L 1-0
larl
16
25
•
''
. :Months :Month s
L ar
. .
• : LZ ar3
19
20
20
20
26+
21 +
21
20
21
21 +
26+
:
21 +
26+
:
21 +
: :
:LZ c S
P .
"LZ
-°5
:
:-c5
Al
31
35+
:-1cO
-41
. ,
: : Months : Months ; :
::
31
21
: : .L arl
••
l
' L s-0
_
::
;LZ
c
.-4-5
13
9
31
19
13
:
••
13
23
: :LZ ar3
:LZ c S
26+
:
21 +
35+
19
: :LZar3
:LZ 25 : :
19
:
21 +
31
16
• :LZar
:L
I
Z c5
19
:
21+
35
•
::
(continued)
81015
-9-
i
Table 1 .--Painting procedures and durability of the coatings tested o n
western larch (continued)
::
::
::
Initial painting
procedure
: :Repainting pro- : : Durability o f
repainted
: : cedure at age : :
coating
: : 26 months and : :
:a,t age 52 months : : applied at ag e
Durability
of initial
coating
on
- ------------------------------------ - -----------------------------Priming : Second : Third : :Vertical :Inclined : : First :Second : : 26
:
52
coat : coat : coat : : panels : panels : : coat : coat : :months : months
.
.
On edge-grain boards :
L 1 a5
L 1av3
Al
:L
-1-0
:-1-0
: L1-0
:L1 c O
L1-0
;_
.
.1a5
L a
Al
. L1-0
v -I--3
a7
. . Months
Months
..
:
..
..
35+
..
..
.-l-0
:1415
LZ6 b 5
k7 :L6
c
-5
31
. .
.
.
5
. :L1 arl
•L 1 20
26+
25
. . Ll =
ar
'L c
: Ll c O
21i-
25
31
19
: Ll arl
25
13
: :L1 arl
35
23
: :L arl
:L1c0
:L 1 cO
25
13
35+
23
. .LZ4ar3
19
9
19
:
Lla5
L l av3
:LZc
35+
: LZ6 c 5
31
13
Al
. LZ
35+
23
1144
LZ 4 ag
:LZb 4
62_
5
:L_Zc S
.
: :Months :
..
.
..
:
25
1
. :Ll arl
35+
: L1.0
•
.
:
21 +
::
26+
:
21 +
.•
••
26+
.
21+
26+
:
21 +
..
26+
:
21 +
:LZ cS ••
26 +
.
21+
: Ll-O
1:
..
. : L_Z ar3
Month s
; LZc S
26+
21+
26+
18
0 0
; LZc S
•.
35+
35
.
20
: LZ 44ar3
19
. . L_Z1ar3
: LZ 42.5 . .
0L--4-5
::
26+
:
Footnote :
+ following a rating for durability indicates that the coating wa s
still considered serviceable when the panel was either repainted o r
removed from the test at the age indicated . Coatings on incline d
panels for which the durability is rated less than 26 months passe d
through a period of "paint neglect" represented by the differenc e
between 26 months and the recorded durability in months .
R1015
--10 -
21+
the customary manner or with a vehicle containing some of th e
varnish used in the aluminum paint (13, 16) . The increase i n
durability caused by aluminum primer was greatest for lead and zin c
paint Imo, which proved very low in durability when applied in ,the
customary manner . On flat-grain inclined panels three coats of pain t
LZ6 lasted only 9 months, but substitution of aluminum for whit e
priming paint increased the durability to 23 months .
The beneficial effect of initial aluminum priming continue d
after the inclined panels were repainted twice . At the time this i s
written, by far the best panels of the series are those initiall y
primed with aluminum paint . Presumably the continued good effect i s
due to the fact that aluminum priming not only prolongs the serviceabl e
life of coatings but retards the flaking from summerwood if the sur faces become paint-neglected .
Tests on Southern Yellow Pin e
A series of tests begun in 19 2g had for its primary objec t
the study of the effect on paint maintenance of impregnation of woo d
with zinc chloride wood preservative, but incidentally the tests pro vided data on aluminum priming paint under three kinds of white paint
on southern yellow pine both with and without zinc chloride . There
were 90 test panels, each panel made up of three boards . The panel s
were divided into 9 groups of 10 panels each, one grou p. for each o f
9 paints or painting procedures . Of the 10 panels in each group, 2
were made of boards containing no injected chemical, 3 with board s
impregnated with approximately 0.75 pounds of zinc chloride per cubi c
foot (12 kg. per cu . m .), 3 with 1,5 pounds of zinc chloride per cubi c
foot, and 2 with 1 .5 pounds per cubic foot of a mixture of 2 parts b y
weight of zinc chloride and 1 part sodium dichromate .
All of the painting was done in two-coat work followin g
procedures indicated in table 2 . Each of the three white paints was
applied according to the customary practice, using the white pain t
for the priming coat, each paint was applied over aluminum primer ,
and each paint was applied over a white paint priming coat in whic h
some varnish had been mixed .
The panels were exposed at Madison, Wis ., late in Octobe r
192 g . In January 1931 many of the panels were r epainted with tw o
coats of white paint as indicated in table 2 .
Table 2 reports average results . All coatings failed mor e
rapidly on wood containing zinc chloride than they did on untreate d
wood, but not sufficiently so to preclude the use of zinc chlorid e
•
R1015
-11-
Table 2 .--Painting proceduresand durability of the coatings
on southern yellow pin e
Initial painting: : Initial coating : :
Repainting
procedure
: :
::
procedure
Rating for : :
Priming: Second-: : 'e'" integrity at : :Priming Second
:
coat : coat : :bility: 26 months : : coat : coat
.....:
..- .
:
: :Months :
On untreated southern yellow pine :
: .L a
L c
• . 23
Bad
1124
, Llcl
2
L av4
, 24 • Bad
: : L2a
.
r2 :122 2
;Ll c
gl
c
•• -- ' Goo d
• :~ar2 : 2_4
3
• Ll 1
2
A,,
: : 42 : Goo d
: :(not repainted)
3
Lc
LZ 5a9 ' L7 5 c 5
26
Poo r
" LZ2 ar2 LZ2 c4
•: : LZ 2ar 2 ;LZ 2 c4
23
Bad
LZ
A3
A5
TZ3a9
Tz3-9 .
Tz3$v 5
A3
Aj
: LZ5cj
:Lc
:
5
:TZ3 c5
.-3-5
; 3 5
TZ cS
s.: mz3 o 5
: : Repainted coating
::
:.
: Rating fo r
Dura_ :integrity a t
'°
: :bility : 5g month s
, u
:
: :Months :
::
32+ : Poor +
::
27
::
::
,
5-5' 55
::
35
Fai r
: Fai r
Goo d
::
46
Goo d
••
--
Goo d
••
--
: Fai r
''
46
Fai r
: : L 2-2 .LZ2-4
: :(not repainted) : :
TZ 2 ar 2
TZ2c4
: TZ c
,-3-5
: TZ3 .5
Tz3
. TZ c
--5
3
A3
•
Tz
3-5
; Tz3 c 5
•
: Poo r
32+ : Fair
32
▪ Poo r
20
: Bad
32+
Poor +
▪
: : 32+ : Poor +
:
::
: : (not repainted) : :
32+ Poor +
:TZ2ar2
:TZ2~4
. :TZ2ar2 •TZ 2c4
32+ : Poor +
212 southern yellow pine impregnated with zinc chloride:
: : 1 g : Bad
: :1-2
:L2 cl,
:
L1N :L12 1
L1av4 ,
16
Bad
. .-2ar2
:
Llcl
:L2c4
A3
• , 30 Good
: :(not repainted.) .
: Ll c1
:
: : -- : Goo d
:• 'L2ar 2 ' L2 c4
A3
Ll cl
LZ
: : 23 : Bad
:LZ5c-5
:
▪:LZ 2ar 2 :LZ2 2 4
LZ av : LZ r c~
: .ZZ 2a-r2 :LZ 2
:
--5--5
>
A3
:LZ c_5
:(not repainted) :
Jr
:LZ5 -,5
:
: :LZ 2ar2 LZ2 c4
TZ3 a 9
-T Z3a9
teste d
: 16
: Ba d
: 12
Ba d
.
: 29
: 17
:
• Poo r
:▪ Bad
16
Bad
19
Poo r
: : 2q
: Poo r
. . 27
: Poo r
: : (not repainted )
▪ . TZ2ar2 TZ2 c4
: • 31
Poo r
:
:
: :(not repainted) : :
:2 2ar2 ' TZ2c
. : TZOr2
TZ2
Footnote :
+ following a rating for durability indicates that the coating was stil l
considered serviceable when last inspected . The rating "Poor +" means
that the integrity was not considered quite poor enough at the last inspection to require repainting .
R1015
-12 -
•
treated wood where painting is required . The relative durability o f
the different coatings was much the same on treated and untreated wood .
On wood impregnated with the mixture of zinc chloride and sodium dichro mate (not reported in able 2) the coatings proved at least as durable a s
they did on untreated wood, the relative durability of the differen t
coatings again falling in the same order .
As in the tests on western larch, aluminum priming-coat paint adde d
materially to the durability of white lead paint and of lead and zin c
paint, and the benefit of the aluminum primer continued after the panel s
had been repainted with white paints . When first painted, one final coat
of the white paints failed to hide the color of the aluminum completely ;
as time passed, however, the coatings began to chalk, and their opacit y
increased enough to hide the aluminum color satisfactorily . The repainte d
coatings showed no sign of the aluminum color at any time ,
Addition of varnish to the priming coat of the white paints prove d
slightly deleterious on the whole (13 ) 16), just as was the case in th e
tests on western larch ,
Titanox and zinc paint T Z3 proved outstandingly durable, so muc h
so that it made little difference whether it was applied over aluminu m
or over white priming paint, Paint T Z2 applied in repazt :ting did not las t
quite as long as in first painting but proved more dural e than eithe r
.repain_ed white lead or lead and zinc . The outstanding"". ; good result s
with paint T Z3 are attributed to the high volume of pigment, 31 percent ,
in the coating after evaporation of the volatile thinner, and to th e
moderate addition of liquid in the priming-coat mixtur e * Paints tha t
contain no white lead, however, are subject to serious disadvantage s
that make it unwise to recommend them for general use by painters . Paint s
containing titanium pigment, white lead, and zinc oxide in suitable propor tions prove nearly as satisfactory as properly ap -plied titanium and zin c
paints and are much less subject to damage from painters' blunders .
Tests on Douglas Fi r
A detailed study of the painting characteristics of Douglas fi r
was begun at Madison, Wis ., in June 1929, from which data on aluminu m
priming paint have been obtained as a secondary objective„ Five types of
commercial Douglas fir lumber were tested, each type in flat-grain an d
in edge-grain boards, making in all 10 classifications of wood . Seve n
test panels for vertical exposure and seven for inclined exposure wer e
made from boards of each of the 10 classes . Each panel contained thre e
boards . Vertical panels were divided into two test areas, inclined panel s
provided only one test area each . Of the seven vertical panels belongin g
to one classification of wood three panels were primed on their left- hand areas with white lead paint Lia0 and on their right hand areas ,
81015
-13-
S
respectively, with aluminum paint A2 ,
white lead paint L1av1 (contain -
ing some of the bodied oil vehicle of t
e
A ,), and the bodied oil vehicl e
without pigment, S P)4 ; the second- and third-coat paints on these thre e
panels were white lead paints
L1-0 and L120 .
Three more panels wer e
painted analogously with lead and zinc paint L Z 1 in place of white lead
paint L 1 . The seventh panel was primed on both areas with aluminu m
paint Al , after which the left-hand area received white lead pain t
L 1 b and the right-hand area lead and zinc paint LZ ib 1 and LZ1 c2 .
0
Six of the seven inclined panels of each classification of wood wer e
painted with three coats of white paint and the seventh with aluminum
paint Al and two coats of lead and zinc paint .
The results appear in table 3 . By far the most durable coat ings were obtained when the priming coat was aluminum paint, whethe r
Al or 12 0 After )47 months the coatings over aluminum primer on most o f
the vertical panels were still serviceable and rated "fair" in intkgrity .
The improvement in durability must be attributed chiefly to the actio n
of the aluminum pigment in the primer . The white primers containin g
bodied linseed oil and the clear bodied oil primer, although superio r
to the ordinary white paint primers, proved much less satisfactor y
t1an the aluminum primers .
Tests on Ponderosa Pine at Tucson and Fresn o
Aluminum priming paint was included in some tests of paintin g
ponderosa pine started at Fresno, Calif,, and at Tucson, Ariz ., in 1929.
The test panels consisted of three boards of commercial 6-inch (actua l
filth 1)4 cm .) bevel siding forming a panel area of 16 by 72 inche s
(41 by 180 cm .), which was marked off into three test areas of 16 by
24 inches (41 by 60 cm.) . Only those test areas that were primed wit h
aluminum paint and the neighboring areas on which a white paint prime r
was applied are considered here .
The painting procedures and results appear in table 4. In
every case the use of aluminum priming paint materially increased th e
drrability of the coating .
Tests Begun in 1930at Five Station s
•
In 1930 a series of tests of special priming paints wa s
begun at Madison, Wis ., Sayville, N . Y ., Washington, D . C ., Fargo ,
N . D ., and Fresno, Calif . Present concern is only with those primer s
that contained aluminum or the varnish vehicle used with aluminum ,
R1015
-14-
Table 3 .--Painting procedures and durability of the coatings teste d
on Douglas fi r
Painting procedure
: :Durability of coatings
------------------------------------------ --------- -----------Priming coat on one area of :
:
::
Average
; : Average
vertical panels or on entire :
for 1 0
;
Second
:
Third,
.
for
10
area of inclined panels
coat
.
coat
.
.
vertical
inclined
------------------ ,
panels
panel s
•:
Left-hand areaeRight-hand area :
--
..
.1-0
:L llo
: Llc
-o
Lb 0
.-I -O
. 11 120
L1
Ll avl
1'1.20
SP
Al
LZlal
A2
LZl al
LZ l 2
ZZla.l
L1b0
. L1 c0
::
, L1 b0
'L c
L 0 :12120
L1~ X1-0
LZ c
:1Z-113a
1-2
LZlbl
: LZ1 c2
LZlbl
: LZlcc
BP
Zb l
l
:A. 12.1
A
26
39
g
31
14 0
1r7+
,
1}2
2
g
47+ :
••
3g
25
1 F3
LZ1c2 . .
c
30
35
••
.
:L Z c : :
1 2
LZl2
Month s
47+ .
3
' 1
.
g
..
••
:LZ b
:
3
=-1l c0
: LZb1
Months
29
41
1}2
47
35
Footnote :
+ following a rating for durability indicates that the coatings
were still consicered serviceable when last inspected .
R1015
.
•-15 .
S
Table )4.---Painting procedures and durability of the coatings tested
on ponderosa pin e
Painting procedure
..
Durability of coatings a t
------------------------- ---------------------------------------- Fresno,-Calif
•
Priming ▪ Second : Third
Tucson.
...
coat
coat
Ariz . : Vertical panels : Inclined panel s
coat
. : Months :
L 2 a~
: L 2b 2
Al
:Z 2b 2
L7.2a2LZ
b
:
=°1
T" .!
'2
~v
:
:
TZ
TZ
2 c3
:L c
3
c3
2b2
'LZ
: 2.23
lb2
. TZ1~3
: Tz1 c3
lb2
30
..
..
46
:
25
46
Months
Months
28
21
36+
29
28
:
36+
23
29
24
25
23
46
46
26
Footnote :
+ following a rating for durability indicates that the coating
was still considered serviceable when the panel was removed fro m
the fence .
81015
-16 -
O
The test panels were made of four boards of commercia l
6-inch (actual width 14 cm .) bevel siding, comprising one boar d
each of redwood, northern white pine, Douglas fir, and souther n
yellow pine . The panels were 18 by 72 inches (46 by 180 cm .) i n
size and were marked off into three test areas each 18 by 24 inche s
(46 by 60 cm.) . The middle area was primed in each case with a whit e
paint and the end areas with special priming paints, after which tw o
coats of white paint were applied over the entire panel . The value
of a special primer is therefore determined by comparing the coatin g
on the appropriate end area with the coating on the middle area o f
the same panel . The panels were exposed in the vertical positio n
facing south . For the most part the coatings on boards of redwoo d
and northern white pine were still in serviceable condition at th e
last inspection, so'that significant comparisons could not be draw n
as to those woods, but failure by flaking of the coatings from summer wood was progressing on boards of Douglas fir and southern yellow pine .
For that reason the results reported in table 5 refer only to th e
latter woods . The data for the three areas of each panel appea r
coaeecutively in table 5 ; of the three lines of data 1'or each panel ,
compa.re the top and bottom lines with the midd . o line .
Of the special priming procedures reported in table 5 only
tie aluminum priming consistently proved superior to the customar y
tiay m' e priming paints . Of the three primers containing aluminum i n
e . . unction with granular pigments (SP l' SP2' and SP . ;, the two i n
-htch red lead was the principal pigment (S P1 and SPA ) usually prove d
Ire erior `to the customary white primer . Primer SP3 , in which whit e
_Lead was the principal pigment ) usually proved somewhat better than th e
customary white primer but not as consistently nor as markedly superio r
as did the aluminum primer (A l ) . The primer of clear varnish (SP 5 ) and
the white primers containing varnish usually proved superior to th e
customary white primers from the point of view of coatin g
integrity, but they were not as consistently or as markedly so as the
aieminum primer (13, 16) ; and in addition they led to coarse and conspiouous fissures in the coatings . Over the primer of clear varnis h
the fissures in the coating of lead and zinc paint were strikingl y
apparent at a distance of 50 feet . Even these fissures were not considered sufficient cause for judging the coatings unserviceable, althorgh such large ones might well be so regarded, The fissures tha t
d e aeloped in the different coatings over aluminum primer, on the othe r
were similar in all respects and were no more conspicuous tha n
he fissures in the coatings over the customary white primers .
Glycerol-Phtha.lic Acid Vehicle for Aluminum Prime r
•
One test was begun in 1930 with an aluminum priming pain t
made with a commercial synthetic drying oil of the glycerol-phthali c
x1015
-17-,
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acid type . One panel of the four woods chosen for the tests describe d
in the preceding section was exposed at Madison in the inclined position .
The aluminum primer, A4 , was applied on one area of this panel and a
white priming paint very similar in composition to paint T Z3 a3 was applie d
on the neighboring area . Subsequent coats of white paints similar t o
T Z3b 2 and T Z3 c)4 were applied over both primers . The durability of th e
coating over the aluminum primer was 31 months as compared with 2 0
months over the white primer . The durability of three coats of a com mercial white paint made with glycerol-phthalic acid drying oil vehicl e
was also tested on a
by the manufacturer of the aluminum paint,
k,
third area of the same test panel and found to be 20 months .
Fissures in White Paints over Aluminum Prime r
Coatings of white paint on wood eventually develop fissure s
after the coatings become brittle with age . The significance o f
fissures is not yet fully understood . They give no reliable basi s
for predicting the relative durability of coatings : because some very
druable paints exhibit well defined fissures relatively early in ser vice: whereas other paints show no fissures until they are on th e
verge of rapid failure . In linseed oil paints the development o f
fissures is markedly affected by the nature of the white pigments .
Pure white lead paint, for example ; displays fissures that have a
characteristically reticulate pattern . Addition of zinc oxide t o
white lead paint changes the pattern ; the fissures appear first a s
lines parallel to the direction of the last strokes of the pain t
brush ; later the pattern becomes reticulate but remains easily dis tinguishable from the fissures in pure white lead paint . The develop ment of fissures of these kinds, which are presumed to be superficial
until late in the life of the coating, is commonly called checkin g
(12, 18 ) 0 The writer distinguishes between reticulate and paralle l
checking as to form and believes that both types result from interna l
stresses within the coating that are not affected in any way b y
expansion and contraction of the wood under the coating . Fissure s
of another kin d) however, probably result from stresses applied to the
coating by movement of the wood beneath it . Such fissures ar e
usually relatively long openings that pass entirely through the coat ing at their first appearance . Development of such fissures is calle d
cracking . Cracking rarely occurs in a pattern that is uniforml y
characteristic of the pigment composition of the paint .
The checking fissures in coatings of any given pigmen t
composition form characteristic patterns, but their spacing varie s
widely according to circumstances . With white lead paint, for exampl e)
when the pigment volume in the final coat is less than that in th e
intermediate coat ) the dimensions of the reticulate meshes are smal l
R1015
-20-
O
and the checking is inconspicuous ; but if final and intermediat e
coats are reversed, the dimensions of the meshes become larger an d
the checking more conspicuous .
In tests started in 1925 and previously reported (3), coating s
of white lead paint and of a lead and zinc paint developed coarse r
checking when applied over aluminum primer than when applied over whit e
priming paint . The checking was sufficiently pronounced to make th e
coatings appear grayish in color daring much of the life in service .
On the other hand, in all the tests so far reported in this paper ,
fissures in the coatings of white paint were essentially equivalen t
in all respects, whether the paints were applied over aluminum prime r
or over customary white primers . The coarse and conspicuous checking
and the tendency to give white paints a gray color over aluminu m
primer in the 1925 tests did not appear in any of the later tests .
This difference in behavior was attributed mainly to the fact tha t
the aluminum primer used in the earlier test was not entirel y
hardened when the next coat of paint was applied .
To determine the validity of this explanation, a series o f
tests was started in 1931 . The test panels, which were of the kin d
used for the tests noticed in the preceding section, were exposed i n
the inclined position at Madison . Four test areas were primed wit h
aluminum paint Al and covered by coats of white lead paint L2b3 and
L 2 2 4; the time intervals between application of A l and 1 2b3 wer e
6, 12, 24, and 336 hours, respectively, for the four areas . In 6
hours the primer was barely hard enough to permit application of mor e
paint, but in 24 hours it was thoroughly hard . The interval betwee n
applications L b and L c4was 72 hours in all cases . Four more area s
-2-3
were painted in the same way except that primer A2 was used instea d
of .A1 . Eight more areas were painted in the same way as the firs t
eight except that lead and zinc paint L Z 2 replaced white lead pain t
L 2 , and a further group of eight areas were similarly painted wit h
paint T Z2 . Finally, three areas were painted, re spectively, with eac h
of the three white paints over white primers L2 a3 , L
a3 , and T Z2a3 .
In the coatings of white lead pain t' finely reticulate checking was first observed at 10 months exposure and was then well develope d
on all areas, whether primed with white or with aluminum paint an d
regardless of the time allowed for the aluminum primer to harden . Th e
subsequent development of the checking was the same on all white lead
areas .
0
In the coatings of lead and zinc paint parallel checkin g
was observed at 10 months over the white primer in an early stag e
of development . At 17 months parallel checking was well develope d
-21-
•
in LZ coatings over both white and aluminum primers, but it wa s
inconspicuous and similar on all areas, and it did not seriousl y
affect the appearance of the coatings . At still later stages th e
checking gradually became coarsely reticulate in pattern ; until at
29 months it was as conspicuous as it had been in the 1925 tests )
and the white paint appeared gray over the aluminum primers . Th e
checking became conspicuous slightly faster over primer A 2 ) mad e
with bodied oil, than over A1 , made with varnish) but the time allowe d
for the primers to harden had no effect on the conspicuousness of th e
checking . Since the coating over the white primer was judged unser viceable because of flaking from summerwood after 18 months, wherea s
the coatings were still rated as serviceable over the aluminum primer s
after 31 months, despite the checkin g) the aluminum primers ha d
already contributed notably to the durability of the coatings befor e
the checking became conspicuous . In the 1925 tests such was no t
the case, the checking over aluminum primer having became conspicuou s
at much earlier stages .
In the coatings of titanox and zinc paint checkin g
never appeared, but cracking was observed at 17 months . At that tim e
it was well developed over aluminum primer A2 , made with bodied oil ,
partially developed over the white primer) and barely started ove r
primer A1 , made with varnish . It became well developed over the whit e
primer at 22 months and over primer Al at 29 months . Even when well ,
developed, however, the cracking did not cause the white paint to appea r
gray . There was no relation between cracking and the time allowed fo r
the primers to harden 0
The durability of the white paints over white primers i n
these tests was 22 months for white lead paint, 18 months for lead an d
zinc paint, and 20 months for titanox and zinc paint . Over aluminum
primers the coatings of all three paints were still serviceable after 3 1
months, although disintegration over the bands of the summerwood had begun .
These experiments make it necessary to find some othe r
explanation for the early appearance of conspicuous checking ove r
aluminum primer in the 1925 tests . Reconsideration suggests that i t
may have resulted from the use of an excessive amount of aluminum powde r
in the aluminum primer in 1925) when the amount used was 20 ) 3 pounds pe r
gallon . The current recommendation of 2 pounds of aluminum powder pe r
gallon of vehicle may be regarded as the maximum permissible .
Aluminum Primer and Paint Scaling
Confusion has arisen about the bearing of aluminum priming upo n
the moisture-blistering and subsequent scaling (1, 14) of house paints {g) ,
The fact that aluminum primers increase the resistance of coatings t o
•
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moisture movement has led painters and house owners to assume tha t
it should prove helpful in minimizing the defects in question . On
the other hand many paint technologists assume that coatings are m o
susceptible to moisture-blistering the greater their resistance t o
moisture movement, inasmuch as the harmful moisture nearly alway s
operates from the back of the painted boards . The mechanism o f
moisture-blistering, however, is by no means completely understood ,
nor do the facts thus far available permit acceptance of eithe r
of the above assumptions .
Tests by a method recently described by the writer
(6 )
indicate that white lead paint applied with a priming coat also o f
white lead is more resistant to peeling and scaling as a result o f
moisture-blistering than other kinds of house paint . If the whit e
lead paint is applied over aluminum primer instead of white lea d
primer, the danger of serious damage by moisture acting behind the
boards is undoubtedly increased . Lead and zinc paints applied in th e
customary manner are more sensitive than white lead paint to scalin g
following blistering, and substitution of ordinary aluminum prime r
for white primer does not materially improve their bereavior unde r
the conditions in question . On the other hand ; the w-,:iter finds that
aluminum primer made with aluminum powder of standard lining grad e
instead of standard varnish grade makes lead and zinc paints some what more resistant to faulty moisture conditions .
White paints of the classification containi :g no white lead
at all are the most sensitive to scaling following mo'sture-blister ing . The resistance of such paints is found to be definitel y
increased by applying them over ordinary aluminum primer .
The write r t s experiments also indicate that back-priming o f
exterior woodwork with aluminum paint does not reduce the chance s
of blistering and scaling when moisture gets behind the boards .
Back-priming may, however, protect woods that contain water soluble colored materials against discoloration by wacer tha t
temporarily finds its way behind bevel siding and then seeps out
between the overlapping boards to run down over .the paint .
Acknowledgmen t
Acknowledgment is made of the assistance of C . E. Hrubesky i n
supervision of the tests on western larch, of Don Brouse in supervisio n
of the tests on Douglas fir and in the making of inspections, and o f
the following organizations in providing test fences for some of th e
experiments : U . S . Bureau of Standards, North Dakota Agricultura l
College, National Lead Company, W . P . Fuller Company, and Souther n
Pacific Railroad .
•
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-23-
Reference s
1 . Browne, F . L ., Proc . Scientific Section, Amer . Paint & Varnish
Mfrs . Assoc ., Circ . 317 : 180 (1927) .
2.
Browne, F . L ., Federation of Paint & Varnish Production Clubs ,
Official Digest No . 95: 106 (1930) .
3. Browne, F . L ., Ind . Eng. Chem. 22 : 81+7 (1930) .
4 . Browne, F . L ., Proc . Amer . Soc . Testing Materials, 3011 : 852
(1930) .
5. Browne, F . L ., Ind . Eng . Chem . 23 : 290 (1931) .
6. Browne, F . L ., J . Chem . Education, 10 : 529 (1933) .
77 . Browne, F . L ., Ind . Eng . Chem . 25 : 835 (1933) .
8. Edwards, J . D ., Paint, Oil, Chem . Rev . g8 : No . 13, p . 10 (1929) .
9.
Edwards, J . D . and Wray, R . I ., Ind . Eng . Chem . 17 : 639 (1925) ;
1 9 : 975 (1927) .
10 . Edwards, J . D . and Wray, R . I ., Federation of Paint & Varnis h
Production Clubs, Official Digest No . 122, p . 1 5
(1933) .
11 . Gardner, H . A ., Proc . Scientific Section, Amer . Paint & Varnish
Mfrs . Assoc ., Circ . 412 : 181 (1932) .
12 .
Gardner, H . A ., Proc . Scientific Section, Amer . Paint & Varnish
Mfrs . Assoc . Circ . 1428 : 107 (1933) .
13 . Gardner H . A . and Hart, L . P ., Proc . Scientific Section, Amer .
Paint & Varnish "Mfrs . Assoc ., Circs . 374 (1931) ;
1+06 (1932) ; 1422 (1932) .
14 .
Hartwig . O . R ., Prods Scientific Section, Amer . Paint & Varnish
Mfrs . Assoc ., Circ . 355 : 711.2 ( 1 930%
150 Nelson, H . A ., Amer . Paint J ., April 27, 1931 ) p . 20 .
16 . Schmutz, F . C ., Palmer, F . C ., and Kittleberger, W . W., Ind
. Eng.
Chem . 22: 8 55 (1930) 0
17. Walker, P . H., Ind . Eng. Chem . 16 : 528 (1924) .
l g . Sub-Committee XVI, Committee D-1, Proc . Amer
. Soc . Testing
Materials, 191 : 381 (1919) .
R1015
«24-
•
Aluminum priming retards crumbling of white lead paint on western larc h
The three panels in the upper row were primed respectively ,
reading from left to right, with white lead paint, white lead pain t
containing varnish, and al»minum paint and then finished with tw o
coats of white lead paint . The photographs were taken after 2 5
months exposure in the inclined position at Madison, CTis,, At age
26 months all three panels were repainted with two coats of whit e
lead paint ; the photographs in the lower row show the repainte d
coatings after 24 months additional exposure .
•
white lead paint on southern yellow pin e
The panels in the upper row were painted with two coat s
of white lead paint, those in the lower row with one coat o f
aluminum paint and one coat of white lead paint . In each row th e
left-hand panel was made of untreated wood, the midtle pane l
of wood treated with zinc chloride, and the rft ght-nani panel o f
wood treated with a mixture of zinc chloride and sodiu m
dichromate . The panels were exposed in the incline positio n
at Madison, Wis . The coatings were 26 months old wnen photo graphed .
•
Aluminum priming retards flaking of lea d
and zinc paint on Douglas fi r
The left-hand area was painted with three coats of lea d
and zinc paint, the right-hand area with one coat of a] .uminum
paint made with bodied linseed oil vehicle and two coats o f
lead and zinc paint . The panel was exposed in the vertical posi tion at Madison, Wis ., and was photographed when the coating s
were 46 months old.
S
•
Aluminum priming retards flaking of titanox an d
zinc paint on ponderosa pin e
The left--hand area was paintdd with three coats of titano x
and zinc paint, the right-hand area with one coat of aluminu m
paint and two coats of titanox and zinc paint . The panel was
exposed in the vertical position at Tucson, Ariz ., and was
photographed when the coatings were 1 .6 months old .
•
Checking of lead and zinc paint over three different primer s
Upper left -- Three coats of lead and zinc paint .
Upper right -- Aluminum primer and two coats of lead an d
zinc paint .
Lower view -- Bodied linseed oil (,vit ?hoi t pigment) and
two coats of lead and zinc paint .
The upper views were taken at Fargo : N. D ., on vertical
panels at age 32 months and the lower view at Fresno, Calif ., at
the same age, but they are all representative of the result s
obtained at all stations and on all woods on which the test s
were made .
Moist
failure over aluminum and over
a white
prime r
- These coatings were only 9 months old when photographed .
After 6 weeks initial exposure the panels had been placed on a
laboratory „blistering box" for 3 weeks, after which they were
,
' exposed again on the test fence . The upper panel was primed
with aluminum primer and the lower panel with a commercial whit e
. primer advertised as particularly resistant to failure under thes e
conditions . Both panels were finished with two coats of a lea d
and zinc paint . The cure for paint failure of this kind lie s
in keeping the sidewalls of houses dry, not in the applicatio n
of special primers .
L
I