BUILDING SCIENCE SERIES 38

1939 Exposure Test

of Porcelain Enamels

on Steel

30-Year Inspection
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UNITED STATES DEPARTMENT OF COMMERCE • Maurice H. Stans, SecTetary

NATIONAL BUREAU OF STANDARDS • Lewis M. Branscomb, Director

1939 Exposure Test

of Porcelain Enamels on Steel

30-Year Inspection

Margaret A. Baker

Building Research Division

Institute for Applied Technology

National Bureau of Standards

Washington, D.C. 20234

Building Science Series 38

Nat. Bur. Stand. (U.S.), Bldg. Sci. Ser. 38, 9 pages (Aug. 1971)

CODEN: BSSNB

Issued August 1971

For sale by the Superintendent of Documents, U.S. Government Office Washington, D.C 20402 (Order by SD Catalog No. C 13.29/2:38 ) , Price 25 cents

Stock Number 0303-0897
Contents

Page

1. Introduction 1

2. Materials 1

2.1. Types and Sources of Enamels 1

2.2. Description and Mounting of Enameled Panels 4

2.3. Acid Resistance of Enamels 4

2.4. Enamel Thickness 5

3. Results 5

3.1. Cleaning of Panels 5

3.2. Visual Observations 5

a. Comparison with Stored Panels 5

b. Corrosion Protection 5

3.3. Gloss Retention 6

3.4. Color Change 6

4. Discussion 7

5. Future Exposure Testing of These Enamels 7

6. Summary 7

7. References 7

Library of Congress Catalog Card Number: 70-170158
1939 Exposure Test of Porcelain Enamels on Steel

30-Year Inspection

Margaret A. Baker*

The weather resistance of 192 porcelain enameled panels representing 14 enamel types was evaluated after being exposed for 30 years at Washington, D.C. A direct correlation was found between the acid resistance and weather resistance of the enamels tested. The

porcelain enamel protected the base metal from corrosion if the initial coverage was

complete.

Similar evaluations and findings were made on 58 panels representing 13 enamel tyi)es that were added to this test in 1947.

Key words : Acid resistance ; color ; gloss ; porcelain enamel ; weather resistance.

1. Introduction

Porcelain enamels have long been used as an

exterior finish for office buildings, store fronts, and

gasoline filling stations. Porcelain enamel's popularity has depended largely on the wide variety of

colors available, ease of installation, and the pros- pect of a long maintenance-free service life. When

this exposure test was initiated in 1939, there had

been reports of porcelain enameled street signs

that had been exposed for as long as 25 years

with no apparent degradation. However, there

had also been reports of porcelain enameled in- stallations where both the gloss and color had

changed markedly after only ten years' exposure.

The goals of this test were to determine an

enamel's durability, as measured by changes in

gloss and color, and to develop accelerated tests to predict an enamel's weatherability.

A total of 864 one-foot (30.48-cm) square and

an equal number of 4 X 6-in (10.16 X 15.24-cm)

laboratory specimens were prepared by twelve

cooperating manufacturers. Of the 864 large

panels, 768 were exposed and 96 were placed in

storage for use as reference standards. Duplicate

panels of each of the 96 different enamels were

exposed at four exposure sites : Washington, D.C.

;

St. Louis, Missouri ; Lakeland, Florida ; and Atlantic City, New Jersey. These enamels have been

inspected and measured for changes in gloss and

color after 1 [1]S 7 [2], and 15 [3] years' exposure. Exposure testing was discontinued at all sites except Washington after the 15-year inspection.

The enamels at Washington were i-eturned to the

exposure racks after their 15-year inspection for an additional 15 years' exposure.

This paper is primarily a summary of the re- sults of the 30- Year Inspection of the original

•Research Associate from the Porcelain Enamel Institute at the National Bureau of Standards, Washington, D.C, 1964 to present.

' Figures in brackets indicate the literature references at the end of this paper.

96 enamels exposed at Washington, D.C. It also

includes a summary of the 23- Year Inspection of

29 enamels added to this test in 1947. A description of the original enamels and earlier exposure

data [1,2,3] will be repeated in this report since

the earlier reports are out of print.

2. Materials

2.1. Types and Sources of Enamels

The enameled panels were supplied by 12 co- operating companies who were active in the field of architectural enamels in 1939. The frits- and

various mill additions^* for preparing the enamels were supplied by 4 frit companies. Each of these

4 companies furnished the materials for each of

the 14 enamel types to the 12 fabricators who

applied the enamel to the metal panels. By this

arrangement, it was possible to introduce the two

variables of frit source and fabricator. The frits were all proprietary products for which no chemical analyses were available. It is probable that

there were at least minor variations in composition of the four enamels of any one type as supplied by the different frit companies. Likewise,

the 12 fabricators probably produced enamels of

slightly dift'erent properties from the same frit because of minor variations in the mill batch, the

milling procedure, and firing conditions. Thus,

although the investigation included nominally

only 14 enamel types, there were, in effect, 96

somewhat different enamels under study. These

enamels are listed in table 1.

- Frit is the principal ingredient used in preparing porcelain enamels. It is formed b.v melting 'Suitable raw materials and

then quenching the molten mass.

3 In the preparation of an enamel for application to sheet

iron, the enamel frit is ball-milled together with such ingredi- ents as clay, opacifler, color oxide, electrol.vte. and water. The

materials added at the mill constitute mill additions.

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In 1947, 13 additional enamel types were added

to this test program. The 4 frit companies and

the Enameled-Metals Section at the National Bureau of Standards supplied and fabricated these

additional panels. Again differences in the enamels made by the different producers probably re- sulted in 29 somewhat different enamels as indicated in table 2. The weathering results of the

enamels added to this test in 1947 are also in- cluded in this report. This is the first published

report on these 29 enamels.

2.2. Description and Methods of Mounting

Enameled Panels

The panels, which were 1-ft. (30.48-cm) square, were fabricated of 16-gage (nominally 0.057-in. or 0.15-cm) enameling grade steel and had 1-in

(2.54-cm) box-flanged edges. The flange of the

lower side had a V^-in (1.27-cm) downward ex- tension parallel to the face of the panel. Two clips

made of 1-in (2.54-cm) strap steel were welded

to the top flange so as to extend downward. The

clips and the lower flange extension fitted into

18-gage (nominally 0.048-in or 0.12-cm) galvanized-iron channels, that were firmly attached to

the supporting racks. The crevices between the

specimens were not caulked but were left open to

facilitate removal of the panels during periods of

inspection.

The supporting racks were constructed of

3/16-in (0.48-cm) thick angle iron, and after

priming, were painted periodically with aluminum paint. Each rack was constructed to support

28 of the 1-ft (30.48-cm) square panels. The

racks were placed on the roof of the Industrial

Building at the National Bureau of Standards in

Washington, D.C., and were held in place by

weights placed on the bottoms of the racks. The

racks faced south and the panels were exposed

at 45° to the horizontal.

2.3. Acid Resistance of Enamels

In 1937, the Porcelain Enamel Institute promulgated a citric acid spot test [4] to determine

the acid resistance of porcelain enamels. The

4 X 6-in (10.16 X 15.24-cm) laboratory speci- mens of the enamels included in this test were

evaluated for acid resistance by this procedure.

The acid resistance ratings for these enamels are

Table 2. Summary of initial data and gloss and color-difference after 23 years' exposure

Average Average Acid Visual Percentage Enamel Specimen Frit enamel Initial resistance weathering gloss Color change

fabricator supplier thickness specular (PEI test) rating ^ retained (NBS units)

(mils) gloss Titanium white FA 2 2 16 42.9 B B 91.8 0.52 CA 1 1 9 63.5 AA A 64.1 0.88 RA 3 3 8 59.9 A B 64.2 1.11 PA 4 4 10 62.1 A A 64.0 0.47 Acid-resistant ground coat, one coat FB 2 2 6 50.9 AA B 59.9 2.71 CB 1 1 6 53.9 AA B 58.0 1.94 RB 3 3 4 54.6 AA B 59.9 1.26 PB 4 4 5 54.2 AA C 69.4 4.23 Acid-resistant ground coat, two coat FC 2 2 8 44.3 A B 64.2 3.20 CC 1 1 8 52.6 A B 51.8 2.52 RC 3 3 5 52.8 AA B 49.9 3.46 PC 4 4 9 55.6 AA B 59.7 6.37 Regular ground coat, one coat FD 2 2 6 49.6 A c 67.4 8.81 CD 1 1 5 49.4 C D 31.9 29.16 RD 3 3 3 51.6 C D 36.1 30.40 PD 4 4 5 51.8 A C 88.6 11.19 Regular ground coat, two coat FE 2 2 7 51.1 A C 66.2 10.46 CB 1 1 7 52.4 C D 63.4 41.45 RE 3 3 5 50.7 C D 41.0 .32.33 PE 4 4 6 51.4 B C 62.9 19.64 Antimony matte FF 2 2 16 17.7 A 68.8 2.26 Titanium matte CG 1 1 11 54.9 B B 63.5 1.14 Low fired, 1300 ">F CH 1 1 10 42.9 D D 41.9 13.31 PH 4 4 9 65.2 D D 28.4 9.50 Antimony matte FK 2 _ _ 2 16 14.1 A c 67.6 10.91 Ground coat with silica added LN 5 5 4 49.1 AA B 67.8 2.18 Red, semi-gloss

PM 4 4 16 53.8 A B 60.9 4.22 A-31 NR 5 5 3 D 4.57 LH 9 52.5 AA B 53.7 1.18 ^A visual rating of A means no apparent change in the enamel's surface, B means the enamel surface is just beginning to change, C means that moderate changes have taken place in the enamel's surface, and D means severe changes have taken place

in the enamel's surface.
presented in tables 1 and 2. Enamels with AA

and A acid-resistance ratings aie considered to be acid-resistant, while the enamels with B, C,

or D ratings ai-e considered nonacid-resistant.

2.4. Enamel Thickness

The enamel thickness was nieasni-ed with a magnetic thickness gage at two locations on the

stored panels. The average of these two r'eadings

is given to the nearest mil (0.001 in or 0.025 mm)

in tables 1 and 2.

3. Results

3.1. Cleaning of Panels

At the beginning of this test, it was planned to clean the panels before each inspection with a one percent solution of trisodinm phosphate on a

soft cellulose sponge, followed by successive rins- ing with distilled water, tap water, and alcohol.

This cleaning procedure cleaned the panels aftei- 1 and 7 years' exposure but it did not clean them

at three of the 4 exposure sites after 15 years"

exposure. Therefore all the panels were scoured

with a commercial scouring agent at the beginning of the 15-year inspection.

The procedure adopted to clean the panels prior

to the 30-year inspection was a combination and

modification of the two techniques outlined above.

The panels were scoured Avith calcium carbonate

(a mild abrasive) on a sponge that had been

moistened with a one percent solution of tri- sodium phosphate. The panels were then rinsed

successively with tap w^ater, distilled water, and

alcohol. This procedure removed the visible dirt

from almost all of the panels. A few of the matte

panels retained some dirt, but the amount of dirt

retained did not appear to affect the gloss or

color measui'ements.

3.2. Visual Observations

a. Comparison with Stored Panels

Following cleaning, the exposed panels were compared with the stored panels for changes in

gloss and color. The exposed panels that did not

appear to have changed were given a visual rat- ing of A, those that showed only a slight change

were given a visual rating of B, those that

showed readily noticeable changes were given a visual rating of C, and those that showed ex- treme changes were given a visual rating of D.

These ratings foi- all enamels in the test are pre- sented in tables 1 and 2. The enamels with ^-isual ratings of either A or B should be acceptable to the user while enamels with visual ratings of C

or D would probably prompt complaints since

the changes in these enamels were readily

apparent.

Tables 3 and 4 summarize the visual ratings of

the enamels with different acid-resistance ratings.

Table 3. Comparison of vinual weathcrinf/ ratinij with

the cnamel'K acid resistance rating for enamels

exposed 30 years

Acid reslBtanee

V IMIill rating AA A B C D

A 15 3 1 0 0 B 10 10 1 1 0 C 2 3 1 8 4 D 0 1 0 12 Vi

Table 4. Comparison of visual weathcrino rating vnth

the enamel's acid resistance rating for enamels

exposed only 23 years

Visual

rating

A

B

CD

Acid resistance AA

Although there are some exceptions, the trend is for enamels with good acid resistance to have

good weather resistance as indicated by the visual

ratings.

b. Corrosion Protection

Following the visual rating, the panels were

insj^ected for evidence of corrosion on the face

of the panel. Corrosion of the base metal was

noted on the face of only one enamel (panels

A-71 and A-72) that had been exposed for 30

years. This corrosion occurred in what appeared

to be large fishscale-type spalls, '^^^len the panel was turned over, it was noted that the enamel

coverage on the back was pooi- and the back of

the panel was severely corroded. The fishscale- type fractures on the front of the panels occurred over severely corroded sections on the back of

the panels. Corrosion and spalling similar to this was observed at Atlantic City after 7 years' ex- posure and at Lakeland and St. Louis after 15

years' exposure. In the 15-year report [3] it was

hypothesized that hydrogen originating from the

action of condensed moisture on the unprotected

metal was the probable cause of this spalling.

The hydrogen diffused through the metal and

generated enough pressure to rupture the enamel on the face side of the panel. If this is indeed

true, then it is important to have good coverage on the back of the panels as well as on the front

if there is any j^ossibility of moisture, either from

occasional rain leaks or from the humidity inside

the building, contacting the back of poorly coated

panels.

Five of the enamels exposed in 1947 (23 years'

exposure) showed rust on the face of the panels.

Three of these enamels (CD, RD, and CH) were

enamels with poor acid resistance and would not

normally be considered for outdoor applications.

HoAvever, the remaining two enamels RA and FF

showed i-ust around pinhole-type defects and in- dicated a definite need for continuous coatings to be applied when the enamels ai-e to be used in

5
outdoor exposures. This hiidiug is particularly

significant when it is realized that only one of

96 of the original enamels exposed in 1939 rusted

while 5 of only 29 of the enamels exposed in 1947

rusted. This indicates that the thicker enamels

(average thickness 13 mils) originally included

in this test did a much better job of protecting

the base metal from corrosion than did the newer

enamels that had an average thickness of only

8 mils.

3.3. Gloss Retention

The 45° specular gloss was measured at four

orientations at 90° to each other near the center of each panel. This procedure varied slightly

from that used previously when the gloss was

measured at two locations on the panel. The gloss

data are expressed as the percentage of the initial gloss retained after exposure and they are pre- sented in tables 1 and 2. The initial gloss values are also reported in tables 1 and 2. It is of interest to observe how acid-resistant

and nonacid-resistant enamels weather with time.

These results are illustrated in figure 1 for the

enamels exposed in 1939. The data in figure 1

0 4 e 12 16 20 24 28 32 36 EXPOSURE TIME, yeors Figure 1. Effect of exposure time on the gloss retention of porcelain enamels on steel. indicate that the rate of gloss loss is greatest during the first 7 years' exposure for both acid and

nonacid-resistant enamels. However, the nonacidresistant enamels lose more gloss during the first seven years' exposure than the acid-resistant

enamels. The apparent increase in gloss of the

acid-resistant enamels at 15 years is probably

caused by the scouring treatment given these

enamels at that time. There are two possible ways

in which the scouring could increase the enamel's

gloss: (a) a thin film that reduced the gloss

might have been removed by scouring, or (b) the

scouring may have polished the surface.

Since this is the first inspection of the enamels

exposed in 1947, the average percentage gloss

retained for the acid-resistant and the nonacidresistant enamels is given below

Acid-resistant enamels 63.5 Nonacid-resistant enamels 51.2

Again it can be seen that the acid-resistant

enamels have better gloss retention than the nonacid-resistant enamels.

3.4. Color Change

The color-change data* in tables 1 and 2 indi- cate the color change between the stored panels

and the exposed panels. The color change was in- dicated in this way because color ditference meters

[5] were not readily available at the beginning

of this test program so it was not possible to measure the initial color values on the exposed

panels. The color change data are shown as a function of time and of acid resistance in figure 2.

ENAMELS

0 4 8 12 16 20 24 28 32 36 EXPOSURE TIME, years Figure 2. Effect of exposure time on the color retention of porcelain enamels on steel. The difference between the acid- and nonacidi-esistant enamels is more pronounced for color

difference than it is for gloss retention of these same enamels as indicated by the greater separation of the two sets of curves. The enamels appear to have lost color gradually over the entire

exposure period, but because of the lack of color- change data during the early years of exposure

any more rapid color change that may have oc- curred during this pei'iod was not observed.

Again the only color-difference data for the

enamels exposed in 1947 is after 23 years' ex- posure. These data are presented in table 2. The

average color differences for the acid- and nonacid-resistajit enamels are given below

Acid-resistant enamels 4.2 NBS units

Nonacid-resistant enamels 19.2 NBS units

It must be remembered that these are average

values and some nonacid-resistant enamels have

gloss and color i-etentions as high or higher than some of the acid-resistant enamels. This is illus-

* The color difference parameters, L (lightness-darkness),

a (red-green), and b ( vellow-blue) were measured with a color

difference meter. The color change, in NBS Units, was calcu- lated by the following formula : Color Change (AE) = V^^^H^'Aa^TAF

where L is 10 and Rd is the 45", 0° luminous daylight reflectance.

6
ACID RESISTANCE RATING, PEI lesi Figure 3. Color change after SO years' exposure -for enamels with different acid resitance ratings.

trated for color change of the enamels exposed

in 1939 in figure 3.

4. Discussion

The goals of this test are to determine the

durability of porcelain enamels on exposure to outdoor weathering, and to develop or evaluate

laboratory tests to predict this durability. The

results of this inspection indicate that, in general, the enamels with good acid resistance had

good weather resistance after 30 years' exposure

at Washington, D.C. The weather resistance was

evaluated either visually by comparison of ex- posed panels with stored panels or by measured

changes in gloss and color of the exposed jjanels.

Subsequent weathering studies [6,7] have indicated that enamels exposed at different locations

often weather at different rates. Therefore, the

weather resistance of porcelain enamels exposed

at sites other than AYashington may \'ary from

the results given in this report.

One significant finding of this inspection was

the increased percentage of enamels that failed

to protect the substrate from corrosion when the

enamels were applied in one or two coats (average total thickness 8 mils) instead of three or more coats (average total thickness 13 mils). This

indicates that extreme care must be given to the

application of porcelain enamel to assure complete

coverage of the base metal. This will be mor'e and more important as the porcelain enamel is applied in thinner coatings.

5. Future Exposure Testing of

These Enamels

In the past [1,2, and 3] these enameled panels

have been inspected and returned to the exposure

racks on the Industrial Building in Washington,

p.C. for additional exposure. Since the primary

interest in this program is to determine the durability of porcelain enamels, it has been decided

to re-expose only those enamels which received a

visual rating of either A or B, (very little change

in the porcelain enamel surface after ex2:)OSure).

These enamels will be placed on new exposure

racks at the current location of the National

Bureau of Standards, Gaithersburg, Maryland.

The next inspection of these enamels is tentatively scheduled for 1986 after a cumulative exposure

period of 45 years.

6. Summary

After 30-years' exposure at Washington, D.C,

it can be said that

:

(1) All the glossy and semimatte porcelain

enamels in this test were easy to clean. (2) The porcelain enamel protected the base

metal from corrosion if the initial cover- age on both the front and back of the panel was complete.

(3) Both the visual appearance, and the aver- age color and gloss retention coi-related

quite well with the enamel's acid resistance.

(4) The majority of enamels with good acid

resistance showed only barely percejDtable

changes in gloss and color. Similar statements can be made for the 29

enamels that were added to this test program in

1947 and have been exposed for 23 years in

Washington, D.C.

7. References

[1] Harrison, W. N., and Moore, D. G., Weather Resist- ance of Porcelain Enameled Iron Structural Units,

.1. Research, NBS 28, 735 (1942) RP1476.

[2] Harrison, W. N., and Moore, D. G., Weather Resist- ance of Porcelain Enamels Exposed for Seven Years,

J. Research, NBS 42, 43 (1949) RP 1949.

[3] Moore, D. G., and Harrison, W. N., Fifteen-Tear Exposure Test of Porcelain Enamels, NBS Building

Materials and Structures Report 148 (19.57). [4] Test for Acid Resistance of Porcelain Enamels, PEI

Bulletin T-21, Porcelain Enamel Institute, 1900 L

St., N.W., Washington, D.C. 20036, 1962.

[5] Hunter, R. S., Photoelectric Color-Difference Meter,

J. Opt. Soc. Am. 38, 661 (1948).

[6] Rushmer. M. A., and Burdick, M. D., Weather Resistance of Porcelain Enamels : Effect of Exposure

Site and Other Variables After Seven Years, Nat. Bur. Stand. (T^.S.), Bldg. Sci. Ser. 4. 16 pages (May

1966).

[7] Baker, M. A., 1964 Exposure Test of Porcelain Enamels on Aluminum, Three Year Inspection. Nat. Bur.

Stand. (U.S.), Bldg. Sci. Ser. 29. 13 pages (April

1970).

£t U. S. GOVERNMENT PRINTING OFFICE: 1 971 _^81 -321i/33 7

FORM NBS-114A (1-71) U.S. DEPT. OF COMM. BIBLIOGRAPHIC DATA

SHEET

1. PUBLICATION OR REPORT NO. NBS-BSS-38

2. Gov't Accession

No.

3. Recipient s Accession No.

4. TITLE AND SUBTITLE

1939 Exposure Test of Porcelain Enamels on Steel

30-Year Inspection

5. Publication Date August 1971

6. Performing Organization Code

7. AUTHOR(S)

M A Baker

8. Performing Organization

9. PERFORMING ORGANIZATION NAME AND ADDRESS

NATIONAL BUREAU OF STANDARDS

DEPARTMENT OF COMMERCE

WASHINGTON, D.C. 20234

10. Project/Task/Work Unit No. 4216371

11. Contract/Grant No.

12. Sponsoring Organization Name and Address Porcelain Enamel Institute

1900 L Street, N.W.

Washington, D.C. 20036

13. Type of Report & Period FiSfir^^eport

(1939-1970)

14. Sponsoring Agency Code

15. SUPPLEMENTARY NOTES

16. ABSTRACT (A 200-word or less factua 1 summary of most significant information. If document includes a significant

bibliography or literature survey, mention it here.) The weather resistance of 192 porcelain enameled panels representing 14 enamel

types was evaluated after being exposed for 30 years at Washington, D.C. A

direct correlation was found between the acid resistance and weather resistance

of the enamels tested. The porcelain enamel protected the base metal from

corrosion if the initial coverage was complete.

Similar evaluations and findings were made on 58 panels representing 13 enamel

types that were added to this test in 1947.

17. KEY WORDS (Alphabetical order, separated by semicolons)

Acid resistance; color; gloss; porcelain enamel; weather resistance.

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