National Bureau of Standards

Library, N. W. Bidg,

AUG 1 9 1952

Atmospheric Exposure Tests of Nailed SheetMetal Building Materials

United States Department of Commerce

National Bureau of Standards

Building Materials and Structures Report 128
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BMS2 Methods of Determining the Structural Properties of Low-Cost House Constructions. 10^ BMS3 Suitability of Fiber Insulating Lath as a Plaster Base 15^ BMS4 Accelerated Aging of Fiber Building Boards 10^ BMS6 Survey of Roofing Materials in the Southeastern States 15^ BMS8 Methods of Investigation of Surface Treatment for Corrosion Protection of Steel 15^ BMS9 Structural Properties of the Insulated Steel Construction Co.'s "Frameless-Steel"

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[List continued on cover page iii]
UNITED, STATES DEPARTMENT OF COMMERCE • Charles Sawyer, Secretary NATIONAL BUREAU OF STANDARDS • A. V. Astin, Acting, Director

Atmospheric Exposure Tests of Nailed SheetMetal Building Materials

Theodore H. Orem

Building Materials and Structures Report 128

Issued March 28, 1952

For sale by the Superintendent of Documents, U. S. Government Printing Office, Washington 25, D. C.

Price 20 cents
Foreword

The atmospheric exposure tests of the nailed sheet-metal building materials reported herein were initiated to determuie the resistance of such

materials to atmospheric corrosion and to point out how improper installation

practices can cause serious corrosion.

Wliile it is not yet possible to establish the relative resistance to corrosion

of the different materials because of the short duration of the tests, the dele- terious corrosion of some of the materials that has already taken place because

of improper installation warrants reporting on this phase of the project at

this time. Classification of the materials as to their relative merit to withstand exposure to the atmosphere will be considered after definite conclusions can be drawn.

It is anticipated that the results of the tests will be of value in making

information available as to how to avoid undue maintenance costs that result from improper installation of the various building materials studied.

A. V. AsTiN, Acting Director.

Contents

Page

Foreword

1. Introduction

2. Materials

3. Description

4. Results and discussion

13

1414

1920

2123

II1

4.1 Aluminum alloys

4.2 Aluminum-coated steel 4.3 Galvanized steel 4.4 Zinc alloys

5. Conclusions

II
Atmospheric Exposure Tests of Nailed Sheet

Metal Building Materials

Theodore H. Orem

Tests of nailed metallic building sheets of aluminum, aluminum alloy, aluminum-coated

steel, galvanized steel, and zinc alloy exposed for a period of 2 years to the atmospheres of Washington, D. C, and Hampton Roads, Va., are described. The tests indicate that im- proper installation practices can cause accelerated corrosion of such materials, but which

when properly installed, may be expected to give long satisfactory service. Important

conclusions and recommendations are given regarding the installation of sheet-metal

building materials.

1. Introduction

Atmospheric corrosion tests of metals and alloys are a means by which the relative corrosion re- sistances of metallic materials in a given geographical location can be determined. Contraiy

to what wotild generally be expected, data from

atmospheric exposure tests are seldom of value in estimating the life expectancies of metals and

alloys under different conditions of exposure be- cause factors that affect the corrosion of metallic

materials in their end use are usually radically

different from those tliat contribute to failures in the ordinary atmospheric exposure test. The lat- ter tests generally are so designed that specimens

of the material are isolated completely from all other metallic or nonmetallic materials that may

accelerate their breakdown, thus making the at- mosjihere the only factor that can cause any

change in the material.

If it were possible to use a metallic building material completely isolated from other materials

that may have a corrosive effect on it, then data

obtaineci from atmospheric tests could be used

with reasonable accuracy in estimating the life expectancy of the particular material. However,

the fact that some metallic materials used in btiild- ing, particularly thin sheets used for roofing and

siding, often fail in far less time than is indicated

by the usual atmospheric exposure test data, suggests that factors other than the atmosphere

contribute to the breakdown. This premature deterioration of the material usually is caused by

contacts with dissimilar metallic materials of construction or by proximity to nonmetallic materials.

These materials may be corrosive in themselves,

or they may tend to prodtice conditions that will be corrosive to the metallic material.

In the building industry is often impractical,

if not impossible, to avoid using materials that

may accelerate the corrosion of one of the materials when they are brought into intimate contact. It is possible, however, to insulate the

materials from each other by means of paints,

mastics, waterproof papers, felts, etc., so that

corrosion will be minimized.

Lack of knowledge of the potential seriousness

of bringing metallic materials into direct contact

with materials that may cause their corrosion, or economic considerations that prevent precautions against such contacts, often result in construction in which the metallic components will

fail in a short time or require undue maintenance.

However, the simple expedient of insulating dis- similar metallic contacts provides much longer

life, with a minimmn cost for upkeep.

The present study was conducted to determine

the relative resistances to corrosion of the different

sheet materials under conditions of proper building construction and to illustrate how improper

construction can cause premature deterioration

of metallic coverings for buildings.

2. Materials

The aluminum and zinc-base alloys used in this

investigation are typical of materials available

in 1947 for use in domestic building constrviction. The aluminum alloys (table 1) are identified by the suffix A and are of two general types,

namely, (1) clad sheets (5A and 9A) having a thin cladding of aluminum or an aluminum alloy

that is anodic to the core material and thus will retard its corrosion if it is exposed, and (2) unclad,

or homogeneous, sheets, the entire cross sections

of which are of the same composition. Characteristic microstrtictures of the aluminum and

aluminum alloys used in this investigation are shown in figure 1.

1
MATERWL lA MATERIAL 2A MATERIAL 3A MATERIAL 4A MATERIAL 5A

MATERIAL 6A MATERIAL 7A MATERIAL 8A MATERIAL 9A MATERIAL lOA

Figure 1. Microstructure of aluminum base alloys. Materials 5A and 9A etched with Keller's etch ; others unetched. Photomicrographs in rolling direction at X 250.

Takle 1. Nominal corn-position of materials investigated

Specimen

Alloying elements

Cu Mn Mg Zn Cr Fe Al Balance

lA % mto % % % % %

99 min.

99 min. %

(') (') 0)

(')

(')

(') (0

{')

(') 0)

2A

3A 1.2 4A 1.2 5A cladding 1.0 5A core 1.2 1.0 2.6

2.5

6A 0. 25

7A .25 8A 99 9A cladding . .. 99 min. 9A core 2 ... ... lOA 0. 3 max.

1.0 1.0.5

.5

.5

.5

0. 7 max. 96 min. 0) IZ... .01 (2) (11

(^) «

(')

2Z

3Z

4Z

.004 6Z .004

1 Balance consists of aluminum and normal impurities. ^ Analysis unknown. ^ Balance consists of zinc and norma! impurities.
ALUMINUM COATED STEEL GALVANIZED STEEL MATERIAL IZ MATERIAL 2Z

MATERIAL 3Z MATERIAL 4Z MATERIAL 5Z , MATERIAL 6Z •

Figure 2. Microstructures of aluminum-coated steel, galvanized steel and zinc base alloys. Zinc alloys etched with solution of chromic acid and sodium sulfate ; aluminum-coated steel and galvanized steel unetched. Photographs in rolling direction at x250. The zinc alloys investigated are identified by the

suffix Z and were of two general types. One con- tained copper as an alloying constituent, and the

other contained copper and a small amount of

magnesium (table 1). Two of the materials, one

of each general type, -iZ and 6Z, were in the hotrolled condition, and four materials, IZ, 2Z, 3Z,

and 5Z, two of each general type, were cold-rolled. Spectrographic analysis of the alloys showed

the presence of magnesium in all the alloys, al- though 2Z, 3Z, and 4Z were supposed to contain no magnesium. However, 2Z had magnesium in excess of that in the alloys in which magnesium

was an added element, whereas 3Z and 4Z showed

only faint traces of this element.

In addition to the aluminum and zinc-base alloy

sheets, an aluminum-coated steel sheet having an aluminum coating between 0.0015 and 0.002 in. in thickness and a galvanized steel sheet (2

oz/ft") were investigated. I'hotomicrographs of

these two materials and the zinc-alloy sheets are shown in figure 2.

3. Description

To simulate conditions in actual building construction, the different sheet materials were nailed

to wood boards with diffei'ent types of nails that

might be used for this purpose. Each material was nailed to the boards (1) without any sealing

washer, (2) with neoprene sealing washers, and

(3) with lead sealing washers between the nail

head and the sheet. The neoprene washers used were of two different types, one, a greyish-white

molded washer commonly used for building purposes, and the other cut from neoprene sheet

impregnated with carbon black.
The lecommended practice for securing aluminum-alloy building slaeets to wood sheathing or framing is to insulate the sheets from direct contact with the wood by means of water-resistant

building paper, asphalt-impregnated felt, or paint,

in order to preclude the possibility of corrosion

due to the wood. In this investigation the speci- mens were purposely nailed directly to the wood in order to detei'mine the possible seriousness of such

a procedure.

Nails of bare steel, resin-coated steel, copper,

aluminum alloy, galvanized steel, and cadmiumplated steel were used to fasten the sheets to the

wood. As the latter two types generally are con- sidered to be suitable substitutes for ahuninum

nails for fastening aluminum sheets, it was de- sirable to obtain data regarding the length of

time such nails could be expected to give satis- factory sei'vice under different atmospheric conditions. Bare steel and resin-coated steel nails were used because these two types, particularly

the former, are known to be unsatisfactory for

this purpose, and it was desirable to emphasize

this fact. The resin-coated steel nails also were

used to determine if the film of resin would serve

as an insulating material in preventing direct contact between the nail and the aluminum. Copper

nails were used to illustrate the fact that two materials, such as aluminum and coppei', each highly

corrosion-resistant, can cause deleterious coiTosion

of the metal having the highest electronegative

potential (the aluminum) wlien the two are brought into direct contact in the presence of

moisture.

The aluminum-alloy specimens, except lA and

lOA, were attached to the boards with the galvanized nails by two methods. In one complete set of specimens the nailing was done through di'illed holes, Avhereas in the other set, nailing was by

the conventional method of driving directly

through the sheet. This was done to determine

whether driving the nail through the sheet re- moved enough of the galvanized coating to impair

the corrosion resistance of tlie nail. In the case of materials lA and lOA the galvanized nails were punched through the slieet in the upper left- hand and lower right-hand corners and were

nailed through drilled holes in the center of the

sheet. The specimens of galvanized steel and

aluminum-coated steel were fastened to the boards

with nail and washer combinations similar to those used on the aluminum specimens. These two

materials were nailed through holes drilled in the

sheets. The specimens of zinc-alloy building sheets were nailed with bare steel and galvanized steel nails only. Insufficient space on the exposure

racks prevented the use of all the different types

of nails used with the ahuninum specimens. As. the zinc-alloy and the aluminum specimens were

exposed at different times, a second set of galvanized steel sheets was exposed with the zinc-alloy

sheets for comparison purposes.

The specimens for exposure tests were mounted

on boards of basswood and yellow pine. Table 2

shows the woods to which the different materials were nailed and also the different nail and washer

combinations used with each material.

The exposure racks at the Naval Air Station,

Hampton Roads, Va., shown in figure 3, situated

directly over the water of Willoughby Bay, are appi'oximately 10 ft above mean tide level and

face in an east-southeast direction. Specimens

placed in tlie rack are inclined 45° to the horizontal. Some spray may reach the specimens during periods of high winds.

The racks at the National Bureau of Standards,,

figure 4, face directly south, and specimens placed

in them are inclined 45° to the horizontal. A

smokestack of the Bureau Power Plant is located

approximately 150 ft northeast of the exposurerack area. All specimens were inspected immediately after

removal from the racks and again after cleaning.

The aluminum, aluminum-alloy, and aluminumcoated steel specimens were cleaned with concentrated nitric acid. The galvanized-steel and

zinc-alloy specimens were cleaned with a solution

of acetic acid and ammonium chloride. Inspection of the specimens involved examination for

general corrosion from the atmosphere, galvanic

corrosion due to contact with nails of material

different from that of the sheet, corrosion due to contact with lead washers, and corrosion on the

undersurface of tlie specimens where they contact

the wood. The latter three types of corrosion are referred to in the inspection reports, tables 3, 4,

5, and 6, as "galvanic corrosion", "lead-washer

corrosion", and "undersurface corrosion", respectively. The conditions of the cut edges of the

aluminum-coated and galvanized-steel specimens

and of the nails and washers were also noted.

Figures 5 and 6 illustrate the degrees of corrosion from contact with lead washers and of undersurface corrosion, respectively, observed on the

aluminum alloys, as indicated in tables 3 and 4. Figure 7 illustrates the various degrees of undersurface corrosion observed on the aluminumcoated and galvanized-steel specimens. Corrosion

of the aluminum alloys from contact with dis- similar metal nails used without washers, listed under the cohunn "Galvanic Corrosion" on the

inspection charts, may be compared with the

pertinent degrees of corrosion caused by contact of

the sheets with lead washers, as shown in figure 5.

4
NAIL AND SEALING WASHER

COMBINATION FOR EACH SET

MATERIAL NUMBER

OF

SETS

AT

EACH

EXPOSURE

SITE

NAILED

TO

BASSWOOD

NUMBER

OF

SETS

AT

EACH

EXPOSURE

SITE

NAILED

TO

YELLOW

PINE

ALUMINUM

-NO

ALUMINUM

-

NEOPRENE

ALUMINUM

-LEAD

BARE

STEEL

-NO

BARE

STEEL-NEOPRENE

BARE

STEELLEAD

RESIN

COATED

b1

LLL-NO

RESIN

COATED

STEELNEOPR

RESIN

COATED

STEEL-LEAD

DRGALVANIZED

-NO

DRGALVANIZED

-

NEOPRENE

DRGALVANIZED

-LEAD

PNGALVANIZED

- NO

PN

-GALVANIZED

-

NEOPRENE

PN

-

GALVANIZED

-

LEAD

COPPER

-NO

COPPER

-

NEOPRENE

COPPER

-LEAD

CADMIUM

PLATED

STEELN<

CADMIUM

PLATED

STEEL

-Nl

CADMIUM

PLATED

STEEL

"LI

ALUMINUM AND

ITS ALLOYS

lA 0 5 2A 5 0 3A 5 0

4A 5 0

5A 5 0

fiA 5 0

7A 5 0

fiA 5 0

QA 5 0

QA' 0 2

IDA 0 5 • • •

17 0 5 0 5 0 5 4Z 0 5 5Z 0 5 6Z 0 5 COATED STEELS

ALUMINUM COATED 5 0 • • • • • • • •

GALVANIZED

* 0 5 • • • • • • • • •

GALVANIZED-" 0 5 • • •

I DR DENOTES THAT THE NAIL WAS DRIVEN INTO THE WOOD THROUGH A HOLE DRILLED IN THE SHEET. e PN DENOTES THAT THE NAIL WAS PUNCHED THROUGH THE SHEET AND INTO THE WOOD,

3 THESE SPECIMENS EXPOSED AT LATER DATE THAN OTHER MATERIAL 9A SPECIMENS AFTER OBSERVING

THE DELETERIOUS EFFECT OF BASSWOOD ON THE UNDERSURFACE OF THE LATTER.

4 THESE SPECIMENS EXPOSED AT SAME TIME AS ALUMINUM AND ALUMINUM ALLOY SPECIMENS. 5 THESE SPECIMENS EXPOSED AT SAME TIME AS ZINC ALLOY SPECIMENS. Table 2. Sheet-nail-ioasher comMnations for atmospheric exposure tests of nailed sheet-metal 'building materials.

5
Figure 3, Aerial view of atmospheric exposure test racks at Hampton Roads, Va. (Norfolk).
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10
CORROSION FROM LEAD WASHER CORROSION FROM LEAD WASHER CORROSION FROM LEAD WASHER

MATERIAL 5A MATERIALS lA. 2A. 3A.4A,6A,7A,8A& lOA MATERIAL 9A

MODERATE MODERATE MODERATE

SEVERE

Figure 5. Lead-ica slier corrosion ratings for alinuiiiiini-base alloys; X~Vj.

11
UNDERSURFACE CORROSION

MATERIAL 5A

UNDERSURFACE CORROSION

MATERIALS 2A,3A,4A,6A,7A&8A

UNDERSURFACE CORROSION

MATERIAL 9A

SLIGHT SLIGHT SLIGHT

MODERATE

' MODERATE MODERATE

SEVERE SEVERE

Figure 6. Vndersurface-corrosionratings for aluminiim-hase alloys.

Light-colored areas on photographs of materials 5A and 9A are areas wliere cladding has corroded away. X2%.

12
UNDERSURFACE CORROSION

(ALUMINUM COATED STEEL)

UNDERSURFACE CORROSION

(GALVANIZED STEEL)

SEVERE

FiGUEE 7. I'ndersurface-corrosion ratings for aluminum-coated steel and galvanized steel sheets. Darkened areas are exposed steel in the ease of the aluminum-coated steel and an underlaying zinc-iron alloy in the case of the galvanized steel. X2%.
The term "slight" as used in the inspection

charts has a cUial meaning, depending on whether

it pertains to (1) corrosion from tlie atmosphere

and not influenced by galvanic or contact effects, or (2) corrosion due to contacts with nails, washers, and wood. When referring to corrosion of

type ( 1 ) "slight" is used to indicate the first traces of attack on the exposed surface, which in most

instances was observable only with a microscope,

and "moderate" is distinguishable from slight

corrosion in that it refers to corrosive attack observable with the unaided eye. "Slight" corrosion, as used in the second case, generally indi- cates local attack, such as illustrated in figure 5 and usually visible to the unaided eye.

4. Results and Discussion

4.1. Aluminum Alloys

Reports of inspections made on the aluminum

and aluminum-alloy building sheets after exposure of 6 and 24 months are given in tables 3 and

4, respectively. Data obtained in oidy 24 months

of exposure are insufficient to establish an order

of merit of the different materials with respect to their resistance to atmospheric corrosion, and,

therefore, this objective of the investigation will have to be delayed until the results of the sets of

specimens on more extended exposui'e warrant a comparison. At this time it is possible tO' make

only the most general comments in regard to the

aluminum and aluminum-alloy building materials

as a group.

All the aluminum and the aluminum alloys in- vestigated were unaffected, except for discoloration and fine spotting, by exposure to the atmosphere of Washington, D. C, for a period of 24

months. There Avas no conspicuous difference in

the atmospheric corrosion resistance of any of

these materials. Discoloration of the specimens was uniform over most of the surface of the speci- mens. Most of the spotting was concentrated in an area extending from the bottom edge of the

specimens upward for a distance of approximately

in., the remaining surface being spotted to a

lesser degree. Some materials were slightly more

resistant to spotting tlian others. At Norfolk the atmospheric attack on the sur- faces of the aluminum alloys was only slightly

greater than that on the Washington specimens.

All unclad aluminum alloys exposed at Norfolk were noticeably spotted after 2 years of exposure,

and microscopic examination of the spots showed

them to be associated with superficial corrosion

of the sheets. The clad aluminum-alloy sheets,

5A and 9A, corroded in spots completely through

their cladding, and, as a consequence, the core materials had become exposed. However, there was no evidence of any attack on either of the

core materials.

The 2-year-exposure tests indicate that when

aluminum-alloy sheets are properly applied, they can be expected to give long satisfactory service

in an atmosphere such as that in Washington, D. C.

Similar exposure at Hampton Roads, Va. (Norfolk) foretells a relatively long satisfactory life for most of the materials, even though this type

of atmosphere is known to be conducive to cor- rosion of aluminum alloys. Significant corrosion

of the core of material 9A has been previously

observed only after relatively large areas of the

cladding had corroded away and, as in the present

study, insufficient cladding has thus far been re- moved, it is not possible at this time to predict the

life expectancy of this material in a coastal at- mosphere. The presently available results suggest

that all the unclad materials and the clad sheet

5A can be expected to render satisfactory service

for considerable periods under coastal atmospheric

conditions similar to those at the Norfolk exposure

site.The evaluation of the materials tested under

improper installation procedures, has revealed, as expected, that they are subject to accelerated cor- rosion when in intimate contact with materials

such as lead, steel and copper. The degree of ac- celeration varied for different materials and

atmospheres.

Unclad sheets exposed at Washington were only

mildly coi'roded at areas contacted by uncoated

steel and copper nails and lead washers. No one

material apj^eared to have superior corrosion re- sistance under these conditions. In the atmosphere of Norfolk, however, significant corrosion

of the sheets occurred at areas of contact with uncoated steel and copper nails, the degree of in- tensity of such corrosion varying from "slight"

after exposure for 3 months to "moderate" after

exposure for 24 months. Corrosion due to contact with these nails on specimens exposed at Norfolk was definitely more ])rominent than that on speci- mens exposed in Washington. During the 24- month ex])osure period there were only two

instances of j^erforation of the sheets, both occur- ring on material 3A at Norfolk after exposure for

6 months, one in the case of contact with a bare

steel nail, the second Avhere contacted by a lead

washer. However, as no perforations were ob- served in the interval between the sixth and

twenty-fourth month of exposure, the presence of

these perforations may be considered as not characteristic of the behavior of this material. It is possible that these perforations were not caused

solely by galvanic corrosion but were the result of a combination of pitting by galvanic action on

the topside of the sheet due to the particular nail and washer, and corrosion on the unclersurface of

the sheet due to contact with the wood. As will be seen later on, this material was the least re- sistant of all the unclad materials to corrosion

14
when in contact with basswood in the atmosphere

at Norfolk.

Ahhougli there was little difference in the in- tensity of corrosion on tlie dilTerent unclad materials caused by contact with dissimilar metal nails

and washers, initial corrosion occurred on some

materials earlier than it did on others. All speci- mens exposed at Norfolk had an incrustation of

gTeyish-white corrosion products, similar to that

FiGUEE 8. Incrustation of corrosion products ietween

lead washer and aluminum-alloy sheet.

shown in figure 8, between the sheet and the lead

washers after only 3 months of exposure. In the

case of materials lA and lOA this layer of corrosion products was very thin at the end of 3, 6, and

12 months of exposure and considerably heavier

after 24 months, at which time moderate pitting

occurred in these materials beneath the corrosion

products. Moderate pitting similarly was observed on most of the other unclad materials after

only 12 months of exposure. The moderate pitting that occurred on all the unclad materials,

excej)t lA and lOA, aftei- only months may be

accounted for by the fact that lA and lOA were

nailed to yelhnv pine, whereas the other matei-ials were nailed to basswood, whicli appears to accel- erate corrosicm. It is possible tliat the earlier

accelerated lead-washer corrosion of materials

nailed to basswood was enhanced by corrosive

fluids from the wood being drawn up by capillary

attraction to the interface between the aluminum

sheet and the lead washer. This condition did

not exist where materials were nailed to yellow

pine, which had no significantly corrosive effect on the aluminum alloys. It must be emphasized,

however, that the accelerated corrosion at the contact with lead washers occurred only on sheets

exposed in the coastal atmosphere and that no

such accelerated corrosion of sheets nailed to basswood was observed on Washington exposed speci- mens. This suggests that any action of the fluids in the basswood in accelerating the corrosion of

the sheets in contact with lead washers was asso- ciated with the coastal atmosphere.

The clad materials, .5A and 9A, exhibited radically different corrosion characteristics under conditions of improper installation. Material 5A

was at least equal in corrosion resistance to all the

unclad materials insofar as corrosion from contacts with bare steel and copper nails and lead

washers was concerned. On the other hand, material 9A was badly corroded from contacts with

these nails and with most lead washers exposed at Norfolk, potentially serious corrosion of the speci- mens being noted after only 6 months of exposure.

The cladding on material 5A retarded pitting of

the core material by lead washers until some time

between 12 and 24 months of exposure, the first pitting of this material due to such contacts being

noticed after 24 months of exposure. All unclacl materials exposed at Norfolk were observed to have pitted due to contact with lead washers after

only 3 to 6 months, the majority of materials be- ing pitted after only 3 months.

Figure 9 illustrates the superiority of material

5A over 9A and the unclad sheets as regards reMATERIAL 9A

12 MONTH EXPOSURE

MATERIAL 6A

12 MONTH EXPOSURE

MATERIAL 5A

12 MONTH EXPOSURE

MATERIAL 5A 24 MONTH EXPOSURE

FiGUKE 9. Corrosive effect of lead washers in contact tvitli clad and hare alUDiinum-alJoij sheets in a marine

atmosphere.

Material 6A is a bare slieet ; other slieets are clad.

15
sistance to a pitting type of corrosion. The resist- ance of material 5A to pitting is clue solely to the

sacrificial action of its cladding, so that after the

cladding was corroded away to such an extent that

it no longer could protect the core material by this electrolytic action, the core material pitted. This

depletion of the cladding occurred between the

twelfth and twenty-fourth months. The severe corrosion on material 9A is due to the low corro- sion resistance of the core material, its cladding

being capable of preventing corrosion of the core material oidy when relatively small areas of core material were exposed. Once a large area of cladding had corroded away, as in this case over the

area where contacted by the lead Avasher, the core material corrodes severely owing to the intimate

contact with the lead washer.

Where lead washers were used in conjunction

Avith mateiial 9A at Norfolk, except with galvanized steel nails, the corrosion of the sheet due to such contacts was so severe after 12 months of ex- posure that the material was considered as having

failed. Figure 10 illustrates the difference in corFiGURE 10. Corrosive effect of lead washers on material 9A in a marine atmosphere.

Sheet eom.pletely perforated where aluminum nail was used ; only cladding corroded where galvanized nail was used. A, Lead

washer-galvanized nail ; B, lead washer-aluminum nail.

rosion of material 9A due to lead washers where

aluminum-alloy and galvauized-steel nails were

used. In the latter, only the cladding has cor- roded away, and there was no significant attack on the core material, probably due to the inhibiting action of the zinc corrosion products of the

galvanized steel nail that seeps in between the lead

washer and the sheet. With respect to the corrosion on the surfaces of

aluminum alloys contacting basswood, the results obtained thus far in the Washington, D. C, at- mosphere indicate that this causes corrosion to a degree approaching that caused by contact be- tween aluminum and nails of bare steel and copl^er. However, this corrosion can be prevented by

proper insulation between the wood and metal

sheet. Materials lA and lOA, which were nailed

to yellow pine, showed no corrosion after 12

months of exposure and only the faintest corrosion on the undersurface after 24 months. However, material 2A, similar to lA, although made

by a different producer, was significantly corroded on the undersurface after only 6 months at both

exposure sites when nailed to basswood. Material

9A, which showed unusual corrosion on the undersurface after only 6 months of exposure when

nailed to basswood, did not corrode on the undersurface after 6 months when nailed to yellow pine,

as illustrated in figure 11. Further evidence that

Figure 11. Effect of 6-month contact of material 9A

%oith bassivood and yelloiv pine, respectively. Note abnormal corrosion of cladding (light areas) where con- tacted by basswood and absence of corrosion where contacted liy yellow pine. A, Yellow pine, NBS site : B, yellow pine, Norfolk

site ; C, basswood, NBS site ; D, basswood, Norfolk site. basswood was the cause of the undei'surface cor- rosion was observed in the cases of materials

nailed with aluminum nails, except when lead

washers were used. These sheets corroded even though, in the absence of lead washers, there was

no possibility of dissimilar metal-corrosion products washing between the wood and the sheet. The serious corrosion of the core material progressino- from the undersurfaces of some of the 9

A

• • • specimens is considered to be caused by both the contact with the basswood and the jjroximity of

heavy metal nails and lead washers. The corro- sion of the cladding on the undersurfaces of these

specimens exposed at Norfolk was first observed

after only 3 months. Those specimens nailed with

steel and copper nails without washers, or with

any type of nail, except galvanized nails, employing a lead washer, were considerably more cor- roded after 6 months of exposure than at the end

of 3 months. It thus appears that some condition

other than the contact with basswood was acceler- ating the corrosion on the undersurface. Serious

corrosion was observed on the core material of

only those sheets fastened with any nails (except

galvanized) employing lead washers and with

copper and steel nails without washers. From

these observations it is postulated that iron and

copper and/or lead deposited on the aluminum

undersurface from solutions of corrosion products

of the nails and washers seeping to this area set up

16
local couples with the aluminum, thus accelerating

the corrosion of the aluminum. The initial cor- rosion of the cladding is attributed to contact with

the basswood because 9A specimens similarly

nailed to yellow ])ine showed no corrosion of the

cladding after 0 months of exposure. It is of course recognized that the increased rate of cor- rosion attributed to bassAvood may be greater

under the conditions of test reported in this ])aper

than would be expected in a metal roof installation

where less moisture usually is in contact with the

vmcovered portion of the wood.

The corrosive effect of the basswood was evident

after only 3 months of exposure. At the end of

this time most of the specimens in contact with

this wood showed evidence of some corrosive at- tack. All materials, except 5A and 9A, exhibited

a pitting type of attack. Materials 5A and 9A

Avere attacked only on their claddings, with no at- tack on the core material. The cladding on material 5A had corroded away over comparatively

large areas of the specimen. Subsequent inspections after 6, 12, and 24 months of exposure re- vealed that on most matex'ials the pitting was at an

increasing rate for the first 12 months and that it slowed down during the second 12-month period.

A significant characteristic of material 5A was

revealed in this investigation, in that although

considerable areas of chickling were corroded away

after only 3 months of exposure, only the faintest

evidence of pitting was detected after 24 months.

This behavior of material 5A indicates its superiority over material 9A and the unclad materials

for use under corrosive conditions that might be

comparable to those of this test. Material 3A was very susceptible to pitting due

to contact Avith basswood in a coastal atmosphere, some specimens having perforated after only 6

months of exposure. After 24 months of exposure

all specimens of this material Avere perforated. It

is noteworthy that this material, only slightly more resistant to "undersurface corrosion" than

material 9A Avhen in contact with bassw^ood in a

coastal atmosphere, should be the most corrosion

i-esistant of all materials in this respect in the

atmosphere of Washington, D. C. A similar alloy,

4A, furnished by a different producer, corroded

considerably on the undersurface Avhen exposed at Washington but was much more resistant to this attack than material 3A when exposed at Norfolk.

The undersurface corrosion resistance of materials 2A, 6A, 7A, and 8A was intermediate to that of materials Avhich shoAved the most and the

least resistance to this type of attack. Material

TA exposed at Norfolk shoAved early indications

of potentially serious corrosion on its undersurI face, being approximately as corroded as material

! 3A after 6 months of exposure. Unlike 3A, howI ever, its rate of corrosion decreased progressiA^ely

j betAveen the sixth and twenty-fourth months.

After 12 months of exposure all specimens fas- tened with galvanized steel nails Avere noticeably

less corroded on llicii' undersurfaces than Avere specimens fastened with the other types of nails. After 24 months of exjjosure several of the speci- mens secured with galvanized nails were i)itted to the same degree as those fastened with the otlier types of nails. However, the over-all beneficial

effect of the galvanized nails in I'etarding a pitting

type of corrosion Avas still ap])arent, because in most cases the aluminum materials thus nailed were the least corroded after 24 months of

exposure.

The retardation of undersurface corrosion on

sheets fastened Avith galvanized steel nails is be- lieved to be caused by the Avashing of zinc cor- rosion protlucts from the nail into the interface

betAveen the sheet and the Avood. The increased

corrosion betAveen the tAvelfth and twenty-fourth

months on some sheets so fastened Avas caused by

an insufficiency of zinc corrosion products reaching the interface between the metal sheet and AVood

to retard corrosion of the aluminum.

Bare steel, resin-coated steel, or copper nails

should never be used in conjunction Avith alumi- num. Accelerated corrosion of aluminiun alloys

due to contact Avith these nails has been demonstrated in this investigation, particularly in the

case of material 9A. The object in using resincoated steel nails Avas to determine Avhat effect, if any, the I'esin coating Avould have in breaking

direct contact of the nail Avith the aluminum. It was apparent after the 3-month inspection period

that no beneficial effect Avhatsoever Avas to be had

from the resin coating, as the sheets fastened Avith this type of nail Avere as readily corroded because

of contact Avith the nail as were sheets fastened

Avith bare steel nails. Although an aluminum-alloy nail is the proper

one to use Avith ahmiinum-allov building sheet,

cadmium-plated and galvanized steel nails generally are considered acceptable sulistitutes for

aluminum nails, inasmuch as no corrosion of the

aluminum Avill occur so long as the coating on

these nails remains intact. Once the steel of the

nails is exposed, hoAvever, the aluminum Avill cor- rode galA'anically because of contact Avith the ex- posed steel of the nail. Cadmium has a solution

potential similar to that of these aluminum alloys

and, therefore, there is A^ery little or no galvanic

corrosion of either material when cadmium and

aluminum are in intimate contact Avith each other. Zinc Avill corrode only slightly Avhen in contact

Avith alumimnn because, while zinc has a more

electronegative potential than aluminum, the dif- ference in potential is small.

The 24-month exposure tests of the galvanized

nails in intimate contact Avith aluminum-alloy

building slieets indicated that they had lost none

of their effectiveness, although the outer zinc layer

17
on the nail heads not adjacent to the ahnninum

sheet had partially corroded away and exposed an

intermediate zinc-iron alloy layer. The remoteness of this corroded area of the nail head from

the sheet indicated that the depletion of the outer

zinc layer was due to general atmospheric corro- sion and not to galvanic effects. After exposure,

the galvanized nails driven through the aluminum

sheets were no different in appearance from those

nails driven through holes drilled in the sheets nor was there any apparent difference in the appearance of the aluminum sheets fastened by the

two methods.

The cadmium-plated steel nails darkened at joth

sites after only 3 months of exposure, and those

used in conjunction with lead w^ashers at Norfolk

were covered with a fine whitish corrosion product

during this initial period. This corrosion product was not observed on nails used with lead washers

at Washington until after 6 months of exposure.

During the interval between the time of the initial development of this corrosion product and the 24-

month inspection period, this coi'rosion product

had increased in volume and had taken on a yellowish tinge, indicating that perforation of the

plating had occurred, with consequent rusting of

the exposed steel of the nail. Only \ery faint

white corrosion products were observed on nails

used wnthout washers and with neoprene washers

after 24 months of exposure at both sites. Figure

12 illustrates the difference in appeai'ance between

Figure 12. Appearance of cadmium-plated steel nails after use tvith neoprene and lead sealing washers,

respectively. Note white corrosion products on nail used witli lead washer

on right.

tlie cadmium plate on nails used with lead and

neoj^rene washers after exposure for 6 months.

Although the cadmium plate on nails used without washers or with neoprene washers was not

noticeably perforated after 24 months of exposure,

as indicated by the absence of the yellowish dis- coloration in their corrosion products, there was

evidence of a trend toward deterioration of the

plating similar to the initial deterioration of the

plating observed on the nails used with the lead

washers.

On the basis of the presently avaihible results of

this investigation, it would be difficult to accurately estimate the life expectancy of galvanized

or cadmium-plated nails. However, the cadmium-plated nails tested, even without lead

washers, probably would not serve satisfactorily

for more than about 3 yeai's. As commercially

available cadmium-plated nails have considerably

thinner coatings than those on the nails used in

these tests, their life expectancy could be con- siderably less than those investigated. Nails

used in these tests had cadmium coatings of from

0.0008 to 0.001 in. in thickness.

The grey molded neoprene washers used in this investigation were prone to harden and crack

after prolonged exposure to sunlight. This hardening and cracking was first observed after only 3

months of exposure. Although the cracking of

the Avashers was only slight after 3 months, it be- came progressively more prominent for longer ex- posure periods, evidence of considerable checking

of this type of washer being observed after 24

months of exposure. There w^as no appreciable

difference between the appearance of washers ex- posed in Washington and Norfolk. Despite the

poor condition of the exposed surfaces of these

washers, that part of the washer sealing the hole

punched by the nail was free from cracks and

apparently unaffected otherwise.

The sealing washers cut from neoprene sheet

pigmented with carbon black showed no tendency

to harden after exposure for 24 months. There was no evidence of cracking of this type of washer

after exposure for 12 months. Figure 13 illusFiGUEE 13. Appearance of neoprene sealing washers after exposure for 1 year at Hampton Roads, Va.

Note crack-free appearance of carbon-black-filled neoprene washer on right.

trates the difference in the grey molded neoprene

washer and the washer cut from carbon-blackfilled neoprene sheet after 12 months of exposure.

Despite the superiority of the carbon-black-filled

neoprene washers, insofar as resistance to hardening and cracking was concerned, they, too, had

a tendency to crack at the areas adjacent to the

sheet after exposure for 24 months. In this in18
vestigation two cai'bon-black-filled neoprene washers were used with each nail. The bottom washer,

the one in intimate contact with the specimen, was the only one that had cracked (fig. 14). The

top washer was free from any cracking (fig. 14).

Figure 14. Crackmg of carhon-Mack-filled neoprene

sealing washers after 2-year exposure to the atmosphere.

A, Washer in normal position. Bottom waslier cradied in highly stressed, exposed area. B, Washers in expanded position. Top washer free from cracks in highly stressed, unexposed areas. Both washers were as pliable after 24 months of

exposure as they were in their original condition.

In the expanded view on the right of figure 14,

the bottom washer is removed from its normal

position to show the crack-free condition of the

top washer. Examination of these washers

showed this material to be subject to cracking on

prolonged exposure to the atmosphere only if stressed in tension and then only when exposed to gases in the atmosphere and/or sunlight (areas

adjacent to sheet, fig. 14). Thus the absence of

cracks in the top washers shown in figure 14 may

be explained by the fact that the bottom washers

protected the highly stressed areas of the top

washers from sunlight and from gases in the

atmosphere. The soft, pliable condition of the

cracked washer, however, suggests that gases in

the atmosphere, rather than sunlight, were the

cause of the cracking because sunlight would also have hardened the washers.

j 4.2. Aluminum-Coated Steel

j The results of the 6- and 24-month exposure

I tests of the aluminum-coated steel specimens are

! given in tables 5 and 6. The aluminum-coated

steel sheets showed good resistance to corrosion

I in the atmosphere of Washington, D. C, for 24

; months. There was no indication of any attack

I of the aluminum coating.

I At Norfolk very faint corrosion of the alui minum coating was noted at the end of 3 months

j of exposure. After 6 months widely scattered

< "pin-point" corrosion of the aluminum coating

, was observed. Faint specks of a i-eddish-brown

j corrosion product, indicative of perforation of

j the cladding and rusting of the underlying steel,

j were visible at the points where the aluminum

j coating had corroded. Very little progressive corI rosion of the aluminum coating was observed after

24 months of exposure.

The aliimiiiiiiii-coated steel specimens behaved

similarly to the ahimiiium-alloy s|)eciinens, insofar

as corrosion from contact with coj)per and steel nails and lead washers was concerned. All contacts with these materials, except with lead

washers on specimens exposed in Washington,

caused perforation of the aluminum cladding in

less than 24 months, the first perforations occur- ring on specimens exposed at Norfolk after only

3 months of exposure. Figure 15 is typical of the

Figure 13. Corrosion of aluminum-coated steel due to contact with lead sealing washer in a marine atmosphere. Dark area is exposed steel base.

corrosion of the aluminum coating caused by contact with a lead washer in a coastal atmosphere.

The lead washers appeared to be equally or more

harmful than bare steel and copper nails in ac- celerating the corrosion of the cladding in marine

atmospheres.

Aluminum-coated steel sheets contacted by lead

washers were only slightly corroded after 24

months of exposure in Washington, although iso- lated cases of slight corrosion were observed after

12 months of exposure. In this respect the alu- minum-coated steel was similar to the aluminum

alloys discussed above.

All aluminum-coated steel specimens were

nailed to basswood boards. As in the case of the

aluminum-alloy specimens so nailed, the contact with basswoocl caused serious corrosion on the

undersurfaces of the aluminum-coated steel specimens, the first evidence of corrosion being observed after 3 months of exposure. The speci- mens exposed at Norfolk were significantly more

corroded on their undersurfaces than were similarly nailed specimens exposed in Washington.

The most significant difference between the undersurface corrosion on the aluminum-alloy speci- mens and that on the aluminum-coated steel speci- mens occurred on those specimens fastened to basswood with galvanized steel nails. Contrary

to the results obtained on aluminum alloys, aluminum-coated steel specimens so nailed and exposed

at Norfolk were the most severely corroded, ex19
cept for those specimens fastened with copper

nails. The ahuninnm-coated steel specimens

fastened with galvanized nails exposed 24 months

in Washington were as severely corroded as any

specimens nailed with other types of nail, the

aluminum coating of the undersurface having

been completely removed and the exposed steel rusted. Specimens nailed with bare steel nails ex- hibited the least undersurface corrosion at both

exposure sites. The corrosion on specimens

fastened with aluminum nails was intermediate

between that on the most and least severely cor- roded specimens. The portions of the steel base

exposed in the severely corroded areas of the undersurfaces on the Washington specimens were found to be only superficially rusted after 24

months of exposure, whereas those on the Norfolk

specimens were rusted to the point of scaling during the interval between the twelfth and twentyfourth months.

The cut edges of the aluminum-coated steel sheets were only slightly rusted after 24 months

of exposure, the rusting on the Norfolk specimens

being slightly greater than that on the Washington specimens. This rusting was first noted after

3 months of exposure. There was evidence of

slight galvanic corrosion of the aluminum coating

immediately adjacent to the cut edges of the Norfolk specimens but not on specimens exposed at Washington.

The condition of the nails and washers used in

conjunction with the aluminum-coated specimens was approximately the same as on the aluminumalloy specimens.

4.3. Galvanized Steel

Reports of inspections made on the galvanizeclsteel specimens after exposures of 6 and 24 months

are given in tables 5 and 6. All galvanized-steel

specimens showed only slight attack of the zinc

coating after 24 months of exposure at both Norfolk and Washington.

The first evidence of attack was widely scattered

pin-point corrosion observed on the surfaces of

the specimens after 3 months of exposure. This

corrosion penetrated the outer zinc layer only and was discernible only under a microscope. This

corrosion increased with time of exposure, result- ing in a general darkening of the surface due to the elimination of the bright zinc outer layer and

exposure of tlie darker intermediate layer of zinciron alloy. Although the sj^ecimens had darkened,

the spangles were still clearly visible and the zinc

coating was apparently attacked to a depth no

deeper than that of the outer zinc layer of the

coating. The specimens exposed at Norfolk

showed slightly more attack than those at Washington.

After 3 montlis of exposure the Norfolk speci- mens were covered with a fine powdery greyishwhite corrosion product that completely obscured

the spangles. This corrosion product was less prominent on specimens withdrawn after 6, 12,

and 24 months of exposure. Specimens exposed

at the National Bureau of Standards had no observable corrosion products.

Although the corrosion on the surfaces was of

the pin-point type, there was no penetration of

the coating. This may be explained by the fact

that, as the corrosion started at pin-point nucleii over the entire surface of the specimens, an inter- mediate zinc-iron alloy layer, cathodic to the zinc

layer above it, was exposed beneath each of these

pin-point pits. Pitting of this exposed underlying

layer is prevented by the sacrificial action of the

adjacent zinc until sufficient has been removed so that it no longer is effective in preventing pitting

of the initially exposed area of the underlying

layer. When this happens a pin-point pit will start in the exposed zinc-iron alloy intermediate

layer.

There are several layers of zinc-iron alloys be- tween the zinc outer layer and the steel base metal,

eacli being progressively richer in iron than the

layers above it. As any layer is cathodic to the ones above it, the underlying one will not pit until considerable of the anodic adjacent upper layer

has corroded away. Therefore, gross areas of each

upper layer of the coating on galvanized steel will be dissipated by corrosion before the adjacent

underlying layer is attacked, with consequent little likelihood of deep-seated pitting.

The first indications of corrosion of the galvanized steel due to contacts with bare steel and copper

nails and lead washers was observed after 3 months of exposure at both sites. The rate of

corrosion due to these contacts was so slow, however, that even after 24 months of exposure this corrosion still was considered to be only slight.

All the nails, except galvanized, used in con- junction with these galvanized specimens have

lower electronegative solution potentials than

zinc, and, theoretically, they should cause cor- rosion of the galvanized coating on the galvanized

steel when the nail and the sheet are in intimate

contact. However, the solution potentials of zinc,

aluminum, and cadmium are close together and

nails of aluminum and cadmium-coated steel were

observed to have little or no corrosive effect on

the galvanized sheet. The solution potentials of

bare steel, copper, and lead are considerably dif- ferent from that of the zinc coating on the sheet,

however, and these materials will accelerate cor- rosion of galvanized steel in intimate contact with

them.

The lead washers caused some corrosion of the galvanized coatings, as shown in figure 16. This

corrosion was first noticed after 3 months of ex- posure at both sites. The rate of corrosion of the

coating was vei-y slow, and after 24 months the

20
coating was onl}' slightly more attacked than at the end of 3 months. There ^Yas no significant

diiference in intensity of corrosion on specimens

exposed at Washington and Norfolk. Corrosion

of the zinc coating due to contacts with bare steel and copper nails was about equal to that produced by contact with the lead washer, only the

outer zinc layer of the coating being attacked.

FiGUEE 16. Corrosion of gal ram '.( d sio / due to contact with a lead sealing washer.

Circular darkened area is exposed zinc-iron alloy layer.

All galvanized-steel specimens were nailed to yellow-pine boards. Except for the anomalous

behavior of three specimens at the Norfolk site secured on the 3-month-exposure panel with cadmium-plated steel, galvanized steel, and copper

nails, in which cases the undersurfaces of the

specimens were badly corroded, the contact with

wood had very little corrosive effect at either site on the undersurface of the galvanized specimens.

The cut edges of the galvanized-steel specimens

had rusted superficially after 3 months of exposure at both sites and did not differ in this respect

after 24 months.

The condition of the nails and washers used

with the galvanized-steel specimens was similar to that of these accessories used with the aluminumcoated steel and aluminum-alloy specimens.

4.4. Zinc Alloys

Results of inspections made on the zinc-alloy

! specimens after exposures for 6 and 24 months are incorporated in tables 5 and 6. All the zinc alloys investigated showed good

resistance to corrosion in the atmospheres of Norfolk and Washington, D. C. for 24 months, and

this behavior suggests that they should give satis- factory service in such atmospheres.

The galvanizecl-steel sheets exposed with the

zinc-alloy specimens for comparison purposes were

in good condition at both sites after 24 months of

exposure. The behavior of these galvanized specimens, as regards cori'osion of tlie coatings fi'om

tlie atmosphere and due to contact with bare ~1ccl nails, lead sealing wasliers, and wood, was not unlike that of the similarly nailed galvanized-steel

specimens discussed above.

Galvanic corrosion of the zinc- alloy sheets due

to contacts with bare steel nails and lead sealing

Avashers was only mild, at most, and there was no

appreciable difference in the degree of corrosion

from these sources on specimens exposed at Norfolk and Washington, respectively. Also, no one

alloy appeared to be significantly different than

any other alloy, insofar as the effect of these nails

and washers was concerned.

All the zinc alloys exhibited a pitting type of

corrosion over their entire surfaces, and after 24

months of exposure the maximum depth of the

pits varied from 0.0015 in. on materials 3Z and 5Z

to 0.001 in. on IZ, 2Z, 4Z, and 6Z. As the maximum-depth pits are aj)proximately only twice as deep after 24 months of exposure (0.0015 in.) as after 3 months (approximately 0.0007 in.), it is obvious that the rate of pitting decreases with

time. It is probable that this decreasing rate is due to the formation in the pits of zinc carbonates,

oxides, or hydroxides, or combinations of these,

which have some protective effects. Although these materials have not been exposed

sufficientlj' long to permit any conclusions as to their relative corrosive resistance, there are indications that they vary. Tlius. after each exposure

period, those materials containing the least copper, alloys 3Z and 5Z (actual analysis, in percent,

showed copper as follows: IZ, 0.89; 2Z, 1.03; 3Z,

0.46; 4Z, 0.96; 5Z ,0.45; and 6Z, 1.13), were found

to have more and slightly deeper corrosion pits

than those having the highest percentages of copper (alloys IZ, 2Z, 4Z, and 6Z)

.

Materials 3Z and 5Z, Avhich wei'e in the coldrolled condition, were slightly more corroded than

hot-rolled materials 4Z and 6Z and also slightly

less corrosion resistant than materials IZ and 2Z,

which also are cold-rolled. Since materials IZ,

2Z, 4Z, and 6Z contained approximately twice as much copper as materials 3Z and 5Z, and since

materials IZ, 2Z, 3Z, and 5Z had been similarly

rolled, it appears that the corrosion resistance of

the zinc-alloy sheets is influenced more by their

cop])er content than by their rolled condition.

The effect of magnesium content on the corrosion resistance of the zinc alloys is uncertain.

However, materials of the same copper content

and similarly containing the highest percentages

of magnesium appear to be more uniformly cor- roded than those of the lowest magnesium content. This is illustrated in the enlarged photographs of

the corroded surfaces of the six materials in figures IT and 18. Material 2Z, which has a higher magnesium content (by actual analysis) than IZ, is

21
3 MONTHS 6 MONTHS | 12 MONTHS~| [MATERIAL 1 1 EXPOSED AT

IZ WASHINGTON

IZ NORFOLK. VA;

2Z WASHINGTON

2Z NORFOLK. VA.

3Z WASHINGTON

3Z NORFOLK. VA.

4Z WASHINGTON

4Z NORFOLK. VA.

5Z WASHINGTON

5Z NORFOLK. VA.

6Z

Figure 17. Surface oppea/

WASHINGTON

6Z NORFOLK, VA.

of zinc alloiis after cxiiu.'Hire of 3. 6, and 12 months; X ITSmore evenly corroded than the hitter. Since these

materials are both in the cold-rolled condition and

contain approximately the same amount of copper,

the results suggest that the higher magnesium

content of material 2Z may be the contributing

factor in ^^romoting its more uniform corrosion.

The same can be said of materials 3Z and 5Z,

material 5Z having the higher magnesium content

of these two cold-rolled materials, which have approximately the same copper content, and materials 4Z and (iZ, material 6Z containing the most

magnesium of these two hot-rolled materials having approximately the same copjDer content. Some corrosion of the zinc alloys occurred

around the peripheries of neoj)rene washers used

with galvanized steel nails despite the retention of

continuous coatings on the nails. This corrosion

is attributed to entrapped dirt or fine cinders at those points and not to any galvanic corrosion

between the sheet and the nails, which will occur only when the steel of the nail becomes exposed

because of corrosion of its galvanized coating.

22
24 MONTHS | MATERIAL EXPOSED AT

4'

i

1

IZ

2Z

2Z

3Z

3Z

4Z

6Z

6Z

WASHINGTON

NORFOLK, VA.

WASHINGTON

NORFOLK, VA.

WASHINGTON

NORFOLK, VA.

WASHINGTON

4Z NORFOLK. VA.

5Z WASHINGTON

5Z NORFOLK. VA.

WASHINGTON

NORFOLK, VA

FiGi'KE 18. Surface appearance of zinc alloys after ex- posure for 24 months; X 17.6.

5. Conclusions

This investigation of sheet-metal materials was

initiated to determine the relative corrosion resist- ances of materials commonly used in the buildingindustry and to illustrate how improper installa- tion practices can cause premature deterioration

of materials which, when properly installed, can

be expected to give long satisfactoi'y service. The

materials investigated were nailed to wood boards

with a variety of nails and sealing washers that

might be used in the building industiT and were

exjjosed to the atmosphere of Washiiigloii, D. C,

and Noi'folk, Va., foi' a pei'iod of 2 years. Exposure for 2 years is too short a time in whicli

to draw dehnite conclusions as to tlie relative

merit of any of the materials investigated, but

warrants some conclusions and recommendations

regarding installation practices of sheet-metal

building materials.

1. Lead in intimate contact with aluniiiuini causes accelerated corrosion of the latter in a coastal atmosphere. It is recommended, therefoi e, tliat lead sealing washers not be used in con- junction with aluminum building sheets in such an atmosphere.. Because of insufficient data re- garding the corrosive effect of lead in contact with

aluminum in inland, nonindustrial atmospheres,

such as that in Washington, D. C, definite recom- mendations cannot be made at this time regarding

the advisability of using these washers under such

atmospheric conditions.

2. Aluminum and aluminum alloys in intimate

contact with certain kinds of wood may be se- riously corroded on the contacting surfaces. Tlierefore, all avoocI surfaces to be covered with

aluminum building sheets should first either be

painted properly or covered with asphalt-impregmited felt or water-resistant building paper to preclude contact of the aluminum with the wood.

3. Aluminum nails only should be used in con- junction with aluminum building materials. Serious corrosion may be caused on aluminum sheet

by securing them Avith nails of bare steel, resin- coated steel, or copper. Cadmium-plated steel nails also were found unsatisfactory for use in

conjunction Avith aluminum building sheets. Although the gah-anized steel nails AA^ere found

intact after 2 years of exposure, they shoAved some

evidence of approaching deterioration and, therefore, it is reasonable to conclude that when such

nails are used for fastening aluminum building

sheets, the sheets Avill not i-ender the maximum

expected life.

i. Sealing washers molded from neoprene pigmented with carbon black have longer life than similar Avashers Avithout carbon black, and.

although the former have been noted to crack

after 2 years of exposure to the atmosphere, they

do not become hard and brittle, as is the case of

neoprene Avashers Avithout carbon black. The

cracking of either type of neoprene Avasher does

not appear to impair their weather-proofing properties, as the cracks do not extend to those portions

in intimate contact with the sheets in the immediate Aacinity of the nail puncture.

5. The conclusions and recommendations re- garding aluminum sheet Avith respect to the use of nails, washers, and insulation against Avood

also are applicable to the aluminum-coated steel sheets.

23
6. Galvanized sheet should be secured with

aluminum-alloy or galvanized steel nails as these were the only types of those investigated that

showed no evidence of being significantly cor- roded or causing galvanic attack on the sheet.

7. Neoprene was found to be more promising

than lead for sealing washers that may contact

galvanized sheet, as there was evidence of galvanic

corrosion by lead washers but no deleterious effects by neoprene. Galvanized nails are moi'e suitable

for securing zinc-alloy sheet than bare steel nails as the latter cause accelerated corrosion of the

sheet at the area of contact. Although no aluminum-alloy nails were used with the zinc-alloy

sheets, the behavior of galvanized sheets where

contacted by aluminum-alloy nails, suggests that

this nail may be more satisfactory than galvanized

nails for use with zinc-alloy sheets. This is based on the fact that zinc in contact with aluminum will corrode at a slower rate than will zinc in contact with steel, a condition which will prevail when

the zinc coating on the galvanized nail corrodes

away under normal atmospheric exposure.

Washington, May 31, 1951.

24 V. S. GOVERNMENT PRINTING OFFICE: 1952


BUILDING MATERIALS AND STRUCTURES REPORTS

[Continued from cover page ii] BMS32 Structural Properties of Two Brick-Concrete-Block Wall Constructions and a Concrete-Block Wall Construction Sponsored by the National Concrete Masonry

Association 15^ BMS33 Plastic Calking Materials 15^ BMS34 Performance Test of Floor Coverings for Use in Low-Cost Housing: Part 1 15^ BMS36 Structural Properties of Wood-Frame Wall, Partition, Floor, and Roof Constructions With "Red Stripe" Lath Sponsored by The Weston Paper and Manufacturing

Co lOi BMS38 Structural Properties of Two "Dunstone" Wall Constructions Sponsored by the W. E. Dunn Manufacturing Co 10^ BMS39 Structural Properties of a Wall Construction of "Pfeifer Units" Sponsored by the Wisconsin Units Co 10^ BMS42 Structural Properties of Wood-Frame Wall and Partition Construction with "Celotex"

Insulating Boards Sponsored by The Celotex Corporation 15f5 BMS43 Performance Test of Floor Coverings for Use in Low-Cost Housing: Part 2 15^ BMS44 Surface Treatment of Steel Prior to Painting.. 10^ BMS47 Structural Properties of Prefabricated Wood-Frame Constructions for Walls, Partitions, and Floors Sponsored by American Houses, Inc 20^ BMS48 Structural Properties of "Precision-Built" Frame Wall and Partition Constructions Sponsored by the Homasote Co 15^ BMS49 Metallic Roofing for Low-Cost House Construction 20^ BMS50 Stability of Fiber Building Boards as Determined by Accelerated Aging 10^ BMS51 Structural Properties of "Tilecrete Type A" Floor Construction Sponsored by the

Tilecrete Co lOfS BMS52 Effect of Ceiling Insulation Upon Summer Comfort 15^ BMS53 Structural Properties of a Masonry Wall Construction of "Munlock Dry Wall Brick"

Sponsored by the Munlock Engineering Co 10^ BMS54 Effect of Soot on the Rating of an Oil-Fired Heating Boiler 10^ BMS55 Effects of Wetting and Drying on the Permeability of Masonry Walls 10^ BMS58 Strength of Soft-Soldered Joints in Copper Tubing 10^ BMS59 Properties of Adhesives for Floor Coverings 15p

BMS60 Strength, Absorption, and Resistance to Laboratory Freezing and Thawing of Build- ing Bricks Produced in the United States 30^ BMS61 Structural Properties of Two Nonreinforced Monolithic Concrete Wall Constructions. 10^ BMS62 Structural Properties of a Precast Joist Concrete Floor Construction Sponsored by

the Portland Cement Association 15^ BMS63 Moisture Condensation in Building Walls- 15^ BMS64 Solar Heating of Various Surfaces lOji BMS65 Methods of Estimating Loads in Plumbing Systems 15^ BMS66 Plumbing Manual 35ji BMS67 Structural Properties of "Mu-Steel" Prefabricated Sheet-Steel Constructions for Walls,

Partitions, Floors, and Roofs, Sponsored by Herman A. Mugler 15^ BMS68 Performance Test for Floor Coverings for Use in Low-Cost Housing: Part 3 20fi BMS69 Stability of Fiber Sheathing Boards as Determined by Accelerated Aging lOjS BMS70 Asphalt-Prepared Roll Roofings and Shingles 20<S BMS71 Fire Tests of Wood- and Metal-Framed Partitions 20^ BMS72 Structural Properties of "Precision-Built, Jr." Prefabricated Wood-Frame Wall Construction Sponsored by the Homasote Co 10^ BMS73 Indentation Characteristics of Floor Coverings 10^ BMS74 Structural and Heat-Transfer Properties of "U. S. S. Panelbilt" Prefabricated SheetSteel Constructions for Walls, Partitions, and Roofs Sponsored by the Tennessee

Coal, Iron & Railroad Co 20^ BMS75 Survey of Roofing Materials in the North Central States 15^ BMS76 Effect of Outdoor Exposure on the Water Permeability of Masonry Walls 15f5 BMS77 Properties and Performance of Fiber Tile Boards 10^ BMS78 Structural, Heat-Transfer, and Water-Permeability Properties of Five Earth-Wall

Constructions 25^

BMS79 Water-Distributing Systems for Buildings 20^

BMS80 Performance Test of Floor Coverings for Use in Low-Cost Housing: Part 4 ISjj BMS81 Field Inspectors' Check List for Building Constructions (cloth cover, 5x7^ inches). 30^

[List continued on cover page iv]
BUILDING MATERIALS AND STRUCTURES REPORTS

[Continued from cover page iii] BMS82 Water Permeability of Walls Built of Masonry Units _ 25^ BMS83 Strength of Sleeve Joints in Copper Tubing Made With Various Lead-Base Solders.. 16^ BMS84 Survey of Roofing Materials in the South Central States.. I 15^ BMS85 Dimensional Changes of Floor Coverings With Changes in Relative Humidity and

Temperature 10^ BMS86 Structural, Heat-Transfer, and Water-Permeability Properties of "Speedbrik" Wall

Construction Sponsored by the General Shale Products Corp 16^ BMS87 A Method for Developmg Specifications for Building Construction—Report of Subcommittee on Specifications of the Central Housing Committee on Research,

Design, and Construction 20^ BMS89 Structural Properties of "Precision-BuUt, Jr." (Second Construction) Prefabricated Wood-Frame Wall Construction Sponsored by the Homasote Co 16^ BMS90 Structural Properties of "PHC" Prefabricated Wood-Frame Constructions for Walls,

Floors, and Roofs Sponsored by the PHC Housing Corporation 15^ BMS92 Fire-Resistance Classifications of Building Constructions 30^ BMS93 Accumulation of Moisture in Walls of Frame Construction During Winter Exposure.. lOji BMS94 Water Permeability and Weathering Resistance of Stucco-Faced, Gunite-Faced, and

"Knap Concrete-Unit" Walls 15^ BMS95 Tests of Cement-Water Paints and Other Waterproofings for Unit-Masonry Walls 25^ BMS96 Properties of a Porous Concrete of Cement and Uniform-Sized Gravel 10^ BMS97 Experimental Dry-Wall Construction With Fiber Insulating Board 10^ BMS98 Physical Properties of Terrazzo Aggregates 15^ BMS99 Structural and Heat-Transfer Properties of "Multiple Box-Girder Plywood Panels" for Walls, Floors, and Roofs 15^ BMSlOO Relative Slipperiness of Floor and Deck Surfaces 10^ BMSlOl Strength and Resistance to Corrosion of Ties for Cavity Walls 10^ BMS102 Painting Steel 10^ BMS103 Measurements of Heat Losses From Slab Floors 15^ BMS104 Structural Properties of Prefabricated Plywood Lightweight Constructions for Walls,

Partitions, Floors, and Roofs Sponsored by the Douglas Fir Plywood Association. 30^ BMS105 Paint Manual with particular reference to Federal Specifications $1. 25

BMS106 Laboratory Observations of Condensation in Wall Specimens . 10^ BMS108 Temperature Distribution in a Test Bungalow With Various Heating Devices 10^ BMS109 Strength of Houses: AppUcation of Engineering Principles to Structural Design $1. 60 BMSllO Paints for Exterior Masonry Walls 15^ BMSlll Performance of a Coal-Fired Boiler Converted to Oil 15^ BMS112 Properties of Some Lightweight-Aggregate Concretes With and Without an Air- entraining Admixture 10^ BMS113 Fire Resistance of Structural Clay Tile Partitions. 15i BMS114 Temperature in a Test Bungalow With Some Radiant and Jacketed Space Heaters. _ 25^ BMS115 A Study of a Baseboard Convector Heating System in a Test Bungalow 15)6 BMS116 Preparation and Revision of Building Codes 15^ BMS117 Fire Resistance of Walls of Lightweight Aggregate Concrete Masonry Units 20j5 BMS118 Stack Venting of Plumbing Fixtures... 15^ BMS119 Wet Venting of Plumbing Fixtures 20ji BMS120 Fire Resistance of Walls of Gravel-Aggregate Concrete Masonry Units 15ji BMS121 Investigation of Failures of White-Coat Plasters 25i

BMS122 Physical Properties of Some Samples of Asbestos-Cement Siding 15jS BMS123 Fire Tests of Wood-Framed Walls and Partitions With Asbestos-Cement Facings 15^ BMS124 Fire Tests of Steel Colunms Protected With Siliceous Aggregate Concrete 15i BMS125 Stone Exposure Test Wall 30^ BMS126 Self-Siphonage of Fixture Traps 20^ BMS127 Effect of Aging on the Soundness of Regularly Hydrated Dolomitic Lime Putties BMS128 Atmospheric Exposure Tests of Nailed Sheet-Metal Building Materials