The program of research on building materials and structures, carried on by the

National Bureau of Standards, was undertaken with the assistance of the Central

Housing Committee, an informal organization of governmental agencies concerned

with housing construction and finance, which is cooperating in the investigations through a committee of principal technicians.

CENTKAL HOUSING COMMITTEE

ON RESEARCH, DESIGN, AND CONSTRUCTION

A. C. Shire, Chairman.

United States Housing Authority.

Howard P. Vermilya, Vice Chairman.

Federal Housing Administration.

Sterling R. March, Secretary.

Pierre Blotjke,

Federal Home Loan Bank Board.

Hugh L. Drtden,

National Bureau of Standards.

Louis A. Simon,

Public Buildings Administration.

Luther M. Leisenring,

Construction Division (War).

Edward A. Poynton,

Ofl&ce of Indian Affairs.

John S. Donovan,

Farm Security Administration.

George W. Trayer,

Forest Service (F. P. Laboratory).

Joseph M. DallaValle,

Public Health Service.

George E. Knox,

Yards and Docks (Navy).

William R. Talbott,

Veterans' Administration.

Wallace Ashby

Bureau of Agricultural Chemistry and Engineering

NATIONAL BUREAU OF STANDARDS

STAFF COMMITTEE ON ADMINISTRATION AND COORDINATION

Hugh L. Dryden, Chairman.

Mechanics and Sound

Phaon H. Bates, Gustav E. F. Lundell,

Clay and Silicate Products. Chemistry.

Hobart C. Dickinson, Addams S. McAllister,

Heat and Power. Codes and Specifications.

Warren E. Emley, Henry S. Rawdon,

Organic and Fibrous Materials. Metallurgy.

The Forest Products Laboratory of the Forest Service is cooperating with both

committees on investigations of wood constructions.

[For list of BMS publications and directions for purchasing, see cover page III.]
UNITED STATES DEPARTMENT OF COMMERCE • Jesse H. Jones, Secretary

NATIONAL BUREAU OF STANDARDS • Lyman J. Briggs, Director

BUILDING MATERIALS

and STRUCTURES

REPORT BMS69

Stability of Fiber Sheathing Boards as Determined

by Accelerated Aging

by

DANIEL A. JESSUP, CHARLES G. WEBER,

and SAMUEL g. weissberg

ISSUED JANUARY 22, 1 941

The National Bureau ol Standards is a fact-finding organization;

it does not "approve" any particular material or method of construction. The technical findings in this series of reports are to be construed accordingly.

UNITED

FOR SALE

STATES GOVERNMENT PRINTING OFFICE - WASHINGTON •

BY THE SUPERINTENDENT OF DOCUMENTS, WASHINGTON, D. C. • PRICE lO

I 94 I

C E N T S
Foreword

Fiber sheathing comprises fiberboards of a comparatively new

type, and it gives considerable promise as a material for house construction. Samples of the boards were tested in connection with

the research on building materials and structures for low-cost housing.

Particular attention was given to tests of the lasting qualities of the

boards, and this report contains data on their resistance to accel- erated aging. The changes in the properties of the materials are used

as a basis for judgment of stability.

Lyman J. Briggs, Director.
Stability of Fiber Sheathing Boards as Determined by Accelerated

Aging

Bv DANIEL A. JESSUP, CHARLES G. WEBER, an^i SAMUEL G. WEISSBERG

CONTENTS

Foreword L Introduction IL Description of samples

III. Properties and testing

1. Thermal insulation

2. Flexural properties

3. Nail-holding strengths

Page Fage

II III. Properties and testing—Continued.

1 4. Water permeability 3

1 5. Air permeability 3

1 6. Outdoor weathering 3 2 7. Resistance to rot-producing fungi 4 2 IV. Summary and Conclusions 4

ABSTRACT

Fiber sheathing boards were aged by exposure to

wetting, freezing, drying, and to outdoor weathering.

Judgment of stability was based on changes produced

in the properties of the boards. The properties tested were weight, thickness, expansivity, thermal conductivity, fiexural properties, nail-holding strength, and

permeability to air and water. Data were obtained on

the resistance of the boards to rot-producing fungi. In general, the retention of the essential properties

under the aging treatments was excellent. Practically no loss of insulating value was noted, and the strength

and water resistance of most of the samples after aging were satisiactory. The boards were not readily subject

to mold growth even at excessivelj' high humidities.

I. INTRODUCTION

The properties and stability of the K-inch

type of fiber building boards have been previously determined, the data being contained in

previous publications.^ ^ This article presents the results of tests on

relatively rigid insulating boards of approximately the same thickness as the lumber usually

employed for sheathing, 25/32 inch. These

boards are treated with asphalt to improve

then- resistance to the infiltration of air and

water. They are designed to contribute to the

rigidity of a structure, to serve as barriers

against the infiltration of water and air, and to provide thermal insulation.

Resistance to rot-producing fungi under con1 NBS Building Materials and Structures Report BMS1.3 (1939). lOfi.

' NBS Building Materials and Structures Report BMS50 (1940). 10|4.

trolled conditions was observed, and the

resistance of the different boards to deteriorative influences was judged by the effects of

accelerated aging and outdoor weathering

exposures.

Experience at the Bureau with record

papers,^ roofing materials,® sheathing

papers,^ and fiber building boards ^ has demonstrated the usefulness of accelerated aging for predicting the relative stability of fibrous

materials.

II. DESCRIPTION OF SAMPLES

The boards tested in this investigation were

secured from cooperating manufacturers. No

attempt was made to obtain all the commercial

brands available, but those tested were considei-ed to be representative of commercial

products. Ten different manufacturers submitted samples for test. Three boards were

laminated and consisted of two plies of equal

thickness. The others were homogeneous

boards, one of which had kraft paper cemented

to both face and back with asphalt.

III. PROPERTIES AND TESTING

The sheathing of a structure is, in the course

of normal events, exposed to a wide range of

3 BS J. Research 7, 466 (1931) RP352.

< BS J. Research 11, 727 (1933) RP620.

« J. Research NBS ?3, 405 (1939) RP1241.

« J. Research NBS 18, 669 (1937) RP1002.

' NBS Building Materials and Structures Report BMS35 (1939). lOf.

s NBS Building Materials and Structures Report BMS50 (1940). IOC.

[1]
Table 1.

Properties of fiber sheathing boards and effects of accelerated aging

from and Flexural properties b Water

I

Linear

expansion

(for

increase

50%

to

90%

RH)

before Brealring load Deflection at rupture Nail- holding

permeability (time of Air permeability

(rate of Sow

through board)

Laboratory designation nduftivity

iter

aging

» Across

long

direc- tion

Across

short

direc- tion

Across

long

direction

Across

short

direction

strength

(lateral) penetration through

board)

j

Thickness !

Density

Thermal

co a

Initial After

aging j

Initial j

After

aging j

Initial

|

After

aging j

Initial After

aging j

j

Initial

[

After

aging

Initial 1

After

aging

Initial After

aging

Btulhr cm^lsec cm'Isec

1

in. 0.74

Ib/ft^ 17. 8 %

0.32 fPC Flin.) 0.37

lb13

lb10/611

lb10

in. 0.31

in.

0. 30

in.

0. 28

in.

0. 30

lb98

lb 90

ftr96hr

70 65 326

2 .74 15. 8 . 31 .36 13 12 12 12 .75 .90 .71 .81 105 99 24 20 867 943

3 .83 20.0 .10 .39 48 43 45 37 .48 .55 .45 . 55 171 147 72 45 125 150

4 ° .81 17.0 .30 .38 38 33 28 26 .69 .69 .63 .72 103 80 168 200 0.001 0. 006

5 .78 18.2 .39 .39 27 22 25 22 .33 .37 .39 . 52 109 96 48 20 141 480 6— .74 19.3 .27 .40 45 38 40 32 .28 .32 .32 .39 135 118 48 48 583 305

7 .80 17.2 .20 .36 52 42 45 40 .48 .43 .51 .44 145 120 45 24 315 363

.77 23.3 .27 .40 33 14 30 14 .29 .30 .58

.29 .30 .68159 72 72 24 0.001 «2100 9d .82 19. 5 .32 .37 43 18 46 20 .36 .44 144 96 500 240 0.001 e 10 10 d . 74 21. 5 .34 .40 27 18 20 11 .43 .58 .54 .46 156 138 48 24 1.29 ' 108

« The thermal conductivity was not in any instance affected by aging. For specimens 3 inches wide on supports 12 inches apart, loaded at center,

f Kraft paper cemented to each surface with asphalt.

d Two-ply laminated boards. The plies separated under accelerated-aging treatment.

= Determined on the individual plies of the specimens that had separated during aging.

conditions of temperature and moisture. Accelerated aging was employed to obtain data on

the resistance of the fiber sheathing boards to such variations. They were subjected to these

influences with the conditions made more

drastic in order to speed up their action, and

the extreme conditions in much more rapid succession than normally occurs. The treatment

consisted in the following cycle: Heating 3 hours at 65° C in dry air; immersing in water

at room temperature for 3 hours; and freezing

the wet boards at —12° C for 18 hours. This

cyclic treatment was continued for a total of 600 hours, 25 cycles.

Although the fiber sheathing boards are not

designed for use as exterior finish, they are often considered for such use, particularly on temporary or semitemporary structures. The

Bureau receives numerous inquiries regarding

the performance of the boards as outside finish. Hence, a number of weathering tests were made.

The tests consisted in outdoor exposures, the

eft'ects of which were accelerated by sproying

with water at regular intervals. The edges of the specimens were sealed against moisture with

a coating of spar varnish containing powdered

aluminum. Two specimens of each board

selected were exposed. In each instance, the

exposed surface of one specimen was painted

with a linseed-oil-white-lead paint, and the

exposed surface of the other specimen was left unpainted.

Data on the properties of the boards before

and after accelerated aging are shown in table 1

.

Inasmuch as the methods of test are the same as those used in testing the /^-inch building boards,

and described in detail in previous publications,^ '° they are described but briefly here.

1. Thermal Insulation

Insulating value is determined by measuring

the rate at which heat is transferred through a board, and is expressed as the number of heat

units (Btu), passing through a square foot

of board, 1 inch thick, per hour, with a temperature dift'erence of 1° F. Thermal conductivity was determined by the guarded hot-plate

method previously described.^'

The values reported in this article were

obtained by H. W. Woolley and J. G. Eeid, Jr., in the Heat Transfer Section of the Bureau.

Accelerated aging of the fiber sheathing

boards did not result in measurable losses of their insulating values.

9 NBS Building Materials and Structures Report BMS4 (1938). lOf'.

i« NBS Building Materials and Structures Report BMS13 (1939). llifi.

11 NBS Building Materials and Structures Report BMS 13 (1939). 10^.

[2]
2. Flexurat. Properties

The fiber sheathing must supply considerable

stiffening and structural strength or the struc- ture must be otherwise braced. Hence, res- onably high strength is important, and good

retention of that strength with aging is essential. Flexural strength was determined by the

method used for insulating boards and previously described. 1- It consists in loading at midspan a specimen 3 inches wide, supported

by two parallel rods 12 inches apart, until the

specimen breaks. With two exceptions, namely

boards 1 and 2, the initial strength was considered high; the average for the two directions

ranged from 23 pounds to 48 pounds. Boards

1 and 2 had much lower strengths. Losses of flexural strength during aging were

not large except for boaids 8, 9, and 10. These

were laminated boards and the plies separated

under the accelerated aging treatment, owing

to softening of the adhesive during the heating.

This would possibly not occur under natural

aging, as the maximum temperatures employed

here are not encountered.

3. Nail-Holding Strength

The nail-holding strength of fiber sheathing is an essential property. The benefits of high

physical strength and rigidity will be lost if the nailing fails, and strength tests at the Forest Products Laboratoiy of large panels have

shown that many of the failures occurred at the point of nailing. Nail-holding strength was

determined by measuring the force recjuired to move a 6-penny common nail to the edge of

the board from a position inch from the edge.

Accelerated aging caused some di-op in the

nail-holding strengths of all of the boards.

However, the losses do not apjjear to be indicative of serious deterioration except for the

laminated boards 8 and 9. In these instances,

the loss was caused by separation of the plies.

4. Water Permeability

It is generally recommended that where the

fiber sheatliing boards are used, sheathing paper

is unnecessary except to cover the joints.

" See footnote 11.

's G. E. Heck, Rigidity and Strength of Framed Walls Sheathed with

Fiberboard. U. S. Dept. Agr. Forest Products Laboratory.

Hence, the boards must be capable of functioning as a primary moisture barrier to prevent

infiltration of water. The rate of penetration

of water through the boards was determined

by the dry-indicator method. An indicator

consisting of a mixture of eosin dye, powdered

sugar, and starch is sprinkled on one surface of

the specimen; a glass cover is sealed over the

indicator to prevent evaporation of the tran- suded moisture; and the edges of the specimen

are sealed with wax to prevent water from

reaching the indicator except by penetration

through the board. The specimen thus pre- pared is floated on water, and the time of transudation of water in an amount sufficient to develop color in the indicator is a measure

of the permeability.

With respect to water permeabihty, the

boards were, in general, superior to most ordinary sheathing papers. i"* The water resistance

dropped somewhat under the treatment, but

the losses were considered not serious, since all of the boards retained good resistance to the

passage of water after aging.

5. Air Permeahility

Leakage of air through the walls is a factor

affecting heating, cooling, and the general

comfort of a building. To function satisfactorily, fiber sheathing must prevent infiltration of air under conditions of wind pressure, because

the boards are designed for use without the

protection of sheathing paper. The fiber sheathing boards a.ppear to be excellent in this respect. The initial permeabilities were low

for most of the boards and were not increased

appreciably during aging.

6. Outdoor Weathering

Table 2 contains data on the comparative

results of tests after accelerated aging and after 15 months' exposure to outdoor weathering.

The results of the outdoor exposures appear to be rouglily comparable to those of accelerated

aging. Outdoor aging did not cause boards

8 and 9 to spht, and their flexural strength and

nail-holding strength did not decrease as much

as with accelerated aging. The boards which

had been painted on the exposed surface were

little affected by the exposure.

n NBS Building Materials and Structures Report BMSS.'i (1939). lOji.

[3]
Table 2.

Comparison of effects of accelerated aging and outdoor loeathering

Water permeability

(time of penetration) Air permeability (rate of flow through board) Flexural strength Nail-holding strength

Laboratorv

designatinn

Initial

After

accele" After outdoor

Initial

After

accele- After outdoor

exposure

Initial

After

acceleAfter outdoor

exposure

Initial

After After outdoor

exposure

rated agingexposure rated agingrated aging Unpainted Painted

rated aging Unpainted Painted

cm^lsec cm^/sec cm'Isec

4 hr168

hr200hr

30

m^(g/c7n'')

0. 001 0.006 3.6

lb38lb 33lb 24

lb 32lb103

lb 80

lb 90

lb 94

3 72 45 45 125 150 196 48 45 44 55 171 147 163 192

7 45 23 15 315 363 386 52 42 35 55 145 120 164 192 8 72 24 15 0. 001 2,100 414 33 14 1836

25 159 7296124 144 9_ 500 240 120 0. 001 10 2.9 43 18 38 144 131 128

7. Resistance to Rot-Peoducing Fungi

There has been much interest in the susceptibility of the fiberboards to rotting. Tests were made on the sheathing boards in connection

with similar work on fiber insulating boaids to determine their susceptibility to attack by rot- producing fungi. The selection of fungi was

based on a recommendation of the Division of Forest Pathology, United States Department of

Agriculture, and the cultures were prepared in the Forest Pathology Laboratory.

Specimens of the sheathing boards were inoculated on the edges and on the protected surface

with cultures of rot-producing fungi and stored over water at approximately 95-percent relative

humidity and room temperature. The speci- mens supported fungus growth at the edges, but

generally, where the coating produced a rela- tively impervious surface, there was no visible

fungus growth. It was found that growth

proceeded most favorably at humidities above

85 percent, and that the fiberboards supported

fungus growth to about the same extent as did

the woods commonly used in house construction.

IV. SUMAIARY AND CONCLUSIONS

The stabihty of fiber sheathing, a relatively new product in the field of house construction, was determined by measuring the resistance of

fiber sheathing boards to accelerated aging and

to attack by rot-producing fungi.

The boards had, in general, excellent stability

under the aging treatments. Losses of flexural strength were, with few exceptions, not serious,

and the nail-holding strength was equally

satisfactory.

The materials were excellent with respect to resistance to the passage of water and air and

maintained those properties well under aging.

They appear to be sufficiently impervious to serve as primary barriers against the infiltration of both water and air when used in a wall

without sheathing paper, provided that all joints are covered with waterproofed paper or otherwise sealed. The fiberboards are apparently no more

susceptible to damage from the growth of rot- producing fungi than are the woods commonly

used in house construction.

Washington, October 10, 1940.

o

[4]
BUILDING MATERIALS AND STRUCTURES REPORTS

On request, the Superintendent of Documents, U. S. Government Printing Office, Washington,

D. C, will place your name on a special mailing list to receive notices of new reports in this

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If 100 copies or more of any paper are ordered at one time, a discount of 25 percent is allowed. Send all orders and remittances to the Superintendent of Documents, U. S. Government Printing

Office, Washington, D. C.

The following publications in this series are available by purchase from the Superintendent of Documents at the prices indicated:

BMSl Research on Building Materials and Structures for Use in Low-Cost Housing lOfi BMS2 Methods of Deternaining the Structural Properties of Low-Cost House Constructions 10^ BMS3 Suitability of Fiber Insulating Lath as a Plaster Base 10^ BMS4 Accelerated Aging of Fiber Building Boards 10^ BMS5 Structural Properties of Six Masonry Wall Constructions 15fi BMS6 Survey of Roofing Materials in the Southeastern States 15^ BMS7 Water Permeability of Masonry Walls 100 BMS8 Methods of Investigation of Surface Treatment for Corrosion Protection of Steel 10^ BMS9 Structural Properties of the Insulated Steel Construction Company's "Frameless-Steel"

Constructions for Walls, Partitions, Floors, and Roofs 10(4 BMSIO Structural Properties of One of the "Keystone Beam Steel Floor" Constructions Sponsored by the H. H. Robertson Co lO^S BMSll Structural Properties of the Curren Fabrihome Corporation's "Fabrihome" Constructions for Walls and Partitions 100 BMS12 Structural Properties of "Steelox" Constructions for Walls, Partitions, Floors, and Roofs

Sponsored by Steel Buildings, Inc 150 BMS13 Properties of Some Fiber Building Boards of Current Manufacture 100 BMS14 Indentation and Recovery of Low-Cost Floor Coverings 100 BMSl5 Structural Properties of "Wheeling Long-Span Steel Floor" Construction Sponsored by

Wheeling Corrugating Co 100 BMS16 Structural Properties of a "Tilecrete" Floor Construction Sponsored by Tilecrete Floors, Inc 100 BMS17 Sound Insulation of Wall and Floor Constructions 100 BMS18 Structural Properties of "Pre-Fab" Constructions for Walls, Partitions, and Floors Sponsored by the Harnischfeger Corporation 100 BMS19 Preparation and Revision of Building Codes 150 BMS20 Structural Properties of "Twachtman" Constructions for Walls and Floors Sponsored by

Connecticut Pre-Cast Buildings Corporation 100 BMS21 Structural Properties of a Concrete-Block Cavity-Wall Construction Sponsored by the National Concrete Masonry Association 100 BMS22 Structural Properties of "Dun-Ti-Stone" Wall Construction Sponsored by the W. E. Dunn Manufacturing Co 100 BMS23 Structural Properties of a Brick Cavity-Wall Construction Sponsored by the Brick

Manufacturers Association of New York, Inc 100 BMS24 Structural Properties of a Reinforced-Brick Wall Construction and a Brick-Tile CavityWall Construction Sponsored by the Structural Clay Products Institute 100 BMS25 Structural Properties of Conventional Wood-Frame Constructions for Walls, Partitions,

Floors, and Roofs 150 BMS26 Structural Properties of "Nelson Pre-Cast Concrete Foundation" Wall Construction

Sponsored by the Nelson Cement Stone Co., Inc 100 BMS27 Structural Properties of "Bender Steel Home" Wall Construction Sponsored by The

Bender Body Co 100 BMS28 Backflow Prevention in Over-Rim Water Supplies 100 BMS29 Survey of Roofing Materials in the Northeastern States 100 BMS30 Structural Properties of a Wood-Frame Wall Construction Sponsored by the Douglas

Fir Plywood Association 100 BMS31 Structural Properties of "Insulite" Wall and "Insulite" Partition Constructions Sponsored by The Insulite Co 150 BMS32 Structural Properties of Two Brick-Concrete-Block Wall Constructions and a Concrete- Block Wall Construction Sponsored by the National Concrete Masonry Association. 100

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

(Continued from cover page III] BMS33 Plastic Calking Materials lOfi BMS34 Performance Test of Floor Coverings for Use in Low-Cost Housing: Part 1 10)4 BMS35 Stability of Sheathing Papers as Determined by Accelerated Aging 10^ BMS36 Structural Properties of Wood-Frame Wall, Partition, Floor, and Roof Constructions

with "Red Stripe" Lath Sponsored by The Weston Paper and Manufacturing Co.- 10(4 BMS37 Structural Properties of "Palisade Homes" Constructions for WaUs, Partitions, and

Floors, Sponsored by Palisade Homes 10(S BMS38 Structural Properties of Two "Dunstone" Wall Constructions, Sponsored by the W. E. Dunn Manufacturing Co 100 BMS39 Structural Properties of a Wall Construction of "Pfeifer Units," Sponsored by the Wisconsin Units Co 10(S BMS40 Structural Properties of a Wall Construction of "Knap Concrete Wall Units," Sponsored

by Knap America, Inc 10(i BMS41 Effect of Heating and Cooling on the Permeability of Masonry WaUs 100 BMS42 Structural Properties of Wood-Frame Wall and Partition Constructions With "Celotex"

Insulating Boards, Sponsored by The Celotex Corporation 100 BMS43 Performance Test of Floor Coverings for Use in Low-Cost Housing: Part 2 100 BMS44 Surface Treatment of Steel Prior to Painting 100 BMS45 Air Infiltration Through Windows 100 BMS46 Structural Properties of "Scot-Bilt" Prefabricated Sheet-Steel Constructions for Walls,

Floors, and Roofs, Sponsored by The Globe-Wernicke Co 100 BMS47 Structural Properties of Prefabricated Wood-Frame Constructions for Walls, Partitions,

and Floors Sponsored by American Houses, Inc 100 BMS48 Structural Properties of "Precision-Built" Frame WaU and Partition Constructions,

Sponsored by the Homasote Co 100 BMS49 Metallic Roofing for Low-Cost House Construction 100 BMS50 Stability of Fiber Building Boards as Determined by Accelerated Aging 100 BMS51 Structural Properties of "Tilecrete Type A" Floor Construction, Sponsored by the Tile- crete Corporation 100 BMS52 Effect of Ceiling Insulation on Summer Comfort 100 BMS53 Structural Properties of a Masonry Wall Construction of "Munlock Dry Wall Brick,"

Sponsored by the Munlock Engineering Co 100 BMS54 Effect of Soot on the Rating of an Oil-Fired Heating Boiler 100 BMS55 Effects of Wetting and Drying on the Permeability of Masonry WaUs 100 BMS56 A Survey of Humidities in Residences 100. BMS57 Roofing in the United States : Results of a Questionnaire 100 BMS58 Strength of Soft-Soldered Joints in Copper Tubing 100 BMS59 Properties of Adhesives for Floor Coverings 100 BMS60 Strength, Absorption, and Resistance to Laboratory Freezing and Thawing of Building

Bricks Produced in the United States 150 BMS61 Structural Properties of Two Nonreinforced Monolithic Concrete Wall Constructions 100 BMS62 Structural Properties of a Precast Joist Concrete Floor Construction, Sponsored by the Portland Cement Association 100 BMS63 Moisture Condensation in Building WaUs 100 BMS64 Solar Heating of Various Surfaces 100 BMS65 Methods of Estimating Loads in Plumbing Systems 100 BMS66 Plumbing Manual 200 BMS69 Stability of Fiber Sheathing Boards as Determined by Accelerated Aging. 100