TECHNICAL INFORMATION ON BUILDING MATERIALS

TIBM - 17

FOR USE IN THE DESIGN OF LOW-COST HOUSING

*****

THE NATIONAL BUREAU OF STANDARDS

UNITED STATES DEPARTMENT OF COMMERCE

WASHINGTON, D. C.

May 25. 1936,

CORROSION OF METALS USED IN

HOUSE CONSTRUCTION

Atmospheric Corrosion of Galvanized Ferrous Sheet Metals.

Technical Information on Building Materials No. 10 of this series

entitled, "Atmospheric Corrosion of Ferrous Metals" , summari ze s outdoor

weathering tests conducted by the American Society for Testing Materials to ascertain the durability of hare steel and iron sheets when

exuosed to rural, seacoastal, and industrial atmosuheres. Useful information was obtained on the relative corrosive action of the three

types of atmosuheres, and on the life that might be expected in such

locations from bare l6 and 22-gage steel and iron sheets made of metal

with and without added cooper.

The present uaper (TIBM-17) deals with steel and iron sheets

urovided with a urotective coating. This generally consists of zinc

lead, tin or lead-tin alloy. In addition, the sheets are often painted. These various urotective measures greatly urolong the useful life

of the sheets, particularly when they are used for uarts of buildings

exposed in locations having severely corrosive atmospheres.

Properties of Metal Coatings.

Since zinc in a coating corrodes faster than iron, a .zinc coating will protect the base metal on which it is applied against corrosion even if there are occasional thin spots, holes or scratches in

the coating. At such places, if the base metal is exposed, corrosion

of the base metal will not occur until the area of the spot of exposed

05283 6-Z - 1 -
> ' + ‘.1 ; .
iron is considerably increased. On the other hand if there are discontinuities in coatings of lead* tin -or lead-tin alloy, ( terne alloy),

the base metal, if exposed, .corrodes faster than the coating and may

perforate if corrosion continues. Because of this tendency to delay

perforation of the base metal at thin places or discontinuities, zinc

coatings, ordinarily referred to as galvanizing, have a very general

application and usefulness. One practical result of the difference in

action between zinc coatings and those of lead, tin or terne, is that

painting of a zinc coated sheet for preservation can be delayed considerably longer, if need be, than can the painting of the other types of

metal coatings. In most cases lead, tin or terne coated sheets are painted when installed especially for outdoor ,use.

In order to evaluate zinc coatings of different commercial thicknesses under various conditions of outdoor exposure, the American Society

for Testing Materials, started an investigation, in. 1926 on the outdoor

weathering of zinc coated (hot-dip galvanized) iron and steel sheets.

Details of American Society for Testing Materials Test.

The base metals were l6 and 22-gage sheets made from steels and

irons with and without added copper, these being similar in type to

those studied in the atmosuheric test of bare metals. The sheets were coated by the hot-dip galvanized process with, respectively, 2.5, 2.0,

1.5, 1.25, and 0.75 ounces of zinc uer square foot of sheet. After’

galvanizing, the sheets were corrugated and cut into 26" x 30" specimens

which were exposed on racks at the different test sites. These locations

were: Brunot Island in the Ohio "River near Pittsburgh, Pennsylvania and

Altoona, Pennsylvania, typifying severely corrosive industrial atmospheres

Sandy Hook, Hew Jersey (foggy, seacoast atmosphere possibly with some industrial-contamination); Key West, Florida (tropical seacoast atmosphere);

and State College, Pennsylvania (rural atmosphere). Inspections were made

at least twice a year and a coating was considered to have failed when

the base metal itself rusted at one or more spots.

Results of Test.

The inspections reported to the Society in 1935 show that at Key

West, Florida there have been no coating failures after 8.7^ years

exposure and at State College, Pennsylvania only one coating failure

(0.75 ounce coating) after 8 t ^>l years. The results at Brunot Island,

Altoona, Pennsylvania and Sandy Hook, New Jersey are summarized in

Table I. Inspect ions of the corroded sheets are being continued to determine the time of perforation. Hence, any conclusions now as to the

complete life of the galvanized sheets at the different locations must

2
be based on the assumption that the life of galvanized sheets is the life

of the coating plus the life of the base metal. It is nrobable that the

life of the galvanized sheets is not less than this, and may be more, but

a definite statement on this point based on the results of the test itself

cannot be made at this time.

C one lus ions

.

1. The industrial atmospheres were very destructive to all weights

of zinc coatings. The foggy contaminated seacoast atmosphere was also

severe in its action.

2. The tropical marine atmosphere and especially the rural atmosphere were very mildly corrosive to all the weights of zinc coatings

te sted.

Recommendations.

I'rom the standnoint of low-maintenance cost it is suggested:

1. At the industrial locations, painting for preservation outdoors

of galvanized sheets carrying 0.75 to 1,5 ounces zinc per square foot of

sheet should be done a few months after installation and in no case delayed later than three years. If the service permits using sheets with

coatings of 2.0 to 2.5 ounces zinc per square foot of sheet, painting

should not be delayed later than about the fifth year.

2. At places with atmospheres like Sandy Hook, painting for preservation outdoors of galvanized sheets may be done after one year and

should not be delayed later than six years aftep installation if the

coating weight is 1.25 ounces zinc per square foot of sheet. If 2.0 to

2.5 ounce coating is used, painting should not be delayed later than

nine years after installation.

3. In rural locations like State College, painting for preservation of galvanized sheets with light coatings (l ounce per square foot

of sheet) may be done the first year but should not be delayed later

than nine years after installation. If the heavier coatings are used,

painting can be done much later.

4 . The paint coat at the various locations must be maintained

in good condition.

- 3 -
I £ 1 n | I 1 O CO £ •rH £ r: I cd i 1 1 P rH o 1 ED

cd

CO 0 0 ft * £ K-1 I CO MO OC OC 1 CO r— c— md f— rH oc •H ft ft ft

O

p 1 £ • H £ I rH CO ITNftf- i—1 1—1 1 co ift E- ocft CO 1 E cr— - MO CO C— 0 o -P •rH • • • • « • • • • 0 o 0 0 • • I • » 0 1 > cd • m iftft- hft rft CM 1 ft ft rft cm CM rH 1 P CO CO 1 r— mo ft 0 <d o © £ P i o «m | 0 I 1 O o

•H £ o £ i £1 1 0 t 1 rd 1—1 £ i ft 1 1 0 O CO CO •H o i o 1 1 £ 0 E • P

CO •rH i -P 1 1 CO p £ <d 0 £

CO 0 i «m 1 £ 1 'TP o -P 0 £

Eh 0 1 Q nP | O 1 ft 1 •H

ED CO

© ft 0 t cd 0 1 CO £ ED p £ •H ft o o o o o o o o o O o o b E ft ft o o p £ 1 £ «M •H 0 1 >D • • • • • • ( E 0 • • • • | o ! • • • • CO •H CD o -P Eh o o o O o o -P o o o o o o CO 1 ft ft o o o P 1 O cd o o o O O O 1 o o o o o O 1 I 1 ft OM O O

ft CO £ o -P 1 1 1—1 1—1 1—1 1 1 1—1 1—1 «m 1—1 f—1 1—1 1—1

rH i—1

ft 1—1 1—1 X 0 1 CD o 0 I 0 1 i p

0H pH ft •rH

O •H 1 -p 1 £ 1 i £ £ £ -P 0 O o 1 CO 1 ft i o 0H £ rH

•d t «d 1 EH i ft p s £ •rH p -p 1 CO I V—H 1 1—1 i CO o (1) £ P ED v-/ 0 CO •H ! CD CD £ 1 1 i O 0 0 £ o ft «M 1 • •H PJ CO CO CO CO ft- £ O CO CO CO CO CO ft £ £ CO

r co ft- •H o l 6 o •H -p | rH i—1 1—t 1—1

rH i—1 1 P 1—1 i—1 1—1 1—1

rH rH 1 o O s—If—Ip

CO £ 0 0 • CO •* £ £

CO i is

O 1 0 i £ 1 ©

ED £ o ft np £ £ Cd t i £ 1 0

•rH o

** 1—1 ft

p •H i ft i *s—

1 ft 0 £ ED CO o CD i £ t 1 o o E «H £ £ E

<J) 1 c •H ft i • 1 P o *d CO 0 £ 0) ! £ cd CO -p 1 p i ft I •H fti CD -P -P CO p CM CO CO CO CO ft O CO CO CO CO CO P O CO CO CO CO ft

tSJ -p 1 ft cd CD 0 1 •rH 1 1 1 1 1—1 1—I i—1 rH ! •» rH rH 1—1 1—1 1 1 rH 1 w 1 1 1—1 1—1 1—1 1—If

—1 E o 0 EH ft 0 0

<H 1 £ o ft i £ 1 O o is 1 CO £ o o 0 ! o 1 0

0) 0 p 0

«H 1 £ 1 rH I in

•H

ft 1 CD Tj P I -P 1 b -P

CO • £ 0 0 Stf) ED 0 1 cd ED 0 0 e t: n r: | 0 fc r: 2: c Zz j 0

FQ £ 1 1 ft ft o ft l CO w i CO i ft CO • £ -P J-H i—1 t o cd Cm i ft i £ o +3 O o o • t I 1 o o i i o £ • « • • ft 1 £ o £ P i •p i -p O £ £ P P <+H V 1 •H ft • i • i • • rH 1 1 co ft E Sr c 2: ~ ft = is cr1 ft 1 CD CO i CO i CO 0 CD 0H “

rs *

&H

J P o N l b3 i ft Csj CO o o o o 1 to Lft Lft 1 LT. Lft 1 o Lft Lft <H CO LPi Lft o Lft cm r

imno Lft CM r— ft LTMft!

O LTM CM 1

1 o 0 • • • • « • | • • * • • • | • • • • £ CM CM CM rH rH O CJ CM CM rH rH o CM CM CM i—l i—I o 1 CO ft 1 i CO o •* •* £ 1 CD •rH 0 1 0 i 0 0 £ ft tUD ED in t Eh 0 = Zz s: e 1 0 E sr zz Zr rr | 0 O CD ED ED I •H

ft Tj£ mA CM CM CM t CM CM MD CM CM CM CM i CM 1 MO CM CM CM CM CM 1 Eh 0 rH OJ CM CM CM CM 1 rH CM CM CM CM CM 1 rH CM CM CM CM CM 1

*Coatin^

on

one

sheet

out

of

18

not

yet

failed.