ireau of Standards

NATIONAL

BUREAU OF STANDARDS
The program of research on building materials and structures undertaken by the

National Bureau of Standards is planned with the assistance of the following advisory

committee designated by the Subcommittee on Design and Construction of the Central

Housing Committee.

TECHNICAL RESEARCH GROUP

Walter Junge, Federal Housing Administration, Chairman

A. C. Shire, United States Housing Authority, Vice Chairman

A. G. Bear, Charles E. Mayette,

Veterans' Administration. United States Housing Authority.

Pierre Blouke, Vincent B. Phelan,

Home Owners' Loan Corporation. National Bureau of Standards.

C. W. Chamberlain, E. A. Poynton,

Procurement Division. Oflfice of Indian Affairs. Jos. M. DallaValle, John H. Schaefer,

Public Health Service. Procurement Division.

Hugh L. Dryden, George W. Trayer,

National Bureau of Standards. United States Forest Service.

G. E. Knox, Elsmere J. Walters,

Bureau of Yards and Docks, Navy Quartermaster Corps, War DepartDepartment. ment.

Sterling R. March, Secretary

The program is administered and coordinated by the following staff committee of

the Bureau:

Hugh L. Dryden, Chairman

P. H. Bates W. E. Emley A. S. McAllister

H. C. Dickinson G. E. F. Lundell H. S. Rawdon

The Forest Products Laboratory of the United States Department of Agriculture

is cooperating with the National Bureau of Standards in studies of wood constructions.

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UNITED STATES

NATIONAL

]) E P A R T M E N T O I' C O M MERGE • ] larry ] I lopkins, Secretary

BUREAU OF STAN])ARDS • Lyman J. Briggs, Director

BUILDING MATERIALS

end STRUCTURES

REPORT BMS13

Properties of Some Fiber Building Boards

of Current Manufacture

by CHARLES G. WEBER a/icl SAMUEL G. WEISSBERG

ISSUED FEBRUARY 23, 1 939

The National Bureau of Standards is a tact-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.

j

I UNITED STATES GOVERNMENT PRINTING OFFICE • WASHINGTON • I9.>9

I I" OR S.VLE li V THE SUPERINTENDENT Of DOCUMENTS, WASHINGTON, U. (J. • TRICE XU C i: N T S
Foreword

Fiber Building Boards are becoming increasingly popular as a building

material, especially in the field of low-cost house construction.

The National Bureau of Standards receives numerous requests for infornuition concernuig the suitability of this class of material for various purposes and,

in order to meet this need, the Bureau has been conducting investigations on

the physical properties of some typical fiber building boards of current manufacture. This report covers the results of these investigations.

An earlier report in this series, BMS4, describes tests made to determine

the relative deterioration of such boards under accelerated aging.

Lyman J. Briggs, Director.

II
Properties of Some Fiber lUiilding Hoards

of Current Manufacture

hy Charles G. Webkk iuid Samuel (i. We issue rg

C O N T E N T S

Page

Foreword ii

I. Introduction 1 II. Description of boards tested 1 III. Properties and testing 2

1. Thiclvness and density 3

2. Insulating properties 3

3. Flexural properties 3

III. Properties and testing- -Continued.

4. Water absorption

Permeability to water and air Linear expansion with change in humidity

Nail-holding strength

5.

6.

I'age

3

4

7. IV. Summarv

ABSTRACT

This article describes the fiber building boards that

are under study in connection with a research on materials for low-cost house construction. Test data are given showing the properties of the different boards,

and the test methods are described. Tests were made

for thickness, density, thermal conductivity, flexural properties, water absorption, water permeability, air permeability, linear expansion, and nail-holding

strength.

I. INTKODUCTION

The research on building materials and structures for use in low-cost housing, now in progress ^ at the National Bureau of Standards, in- cludes a study of fiber building boards. This

study deals primarily with the accelerated

aging ^ of these materials to find how they may

be expected to retain their properties under the

conditions to which tliey will be exposed in use. In order to obtain data on the effects of accel- erated aging, it was necessary, of course, to test the original properties of the boards. The test

(lata on these properties are known to be of

immediate interest to users of the current commercial boards, and for that reason are given

liere in advance of the data being obtained on

the aging qualities of the boards.

The manufacture of the fiber boards, and the raw materials used in them have been described

in a previous publication.^ Tlie properties of a number of wall boards and insulating boards were also described in articles*^ containing the

results of previous studies. No important developments have occurred relative to the fibrous raw materials used or the general methods of

manufacture since those articles appeared.

The boards are made of partially refined vegetable fibers obtained principally from crop plant

wastes or waste wood. These materials are reduced to fibers by mechanical means or by

exploding them with steam, usually after softening them with chemicals or by steaming them.

The boards are fabricated from the pulps on

modified paper-making machines. Improvements in the finished products have been rapid,

however, and new types of boards have recently come on the market, notable among which is insulation sheathing. The data contained in

this article were obtained on samples of current

commercial products furnished by the manufacturers aa representative of the boards now on

the market.

IT. DESCRIPTION OF BOARDS TESTED

While fiber boards are designed for a great

number of special uses, only those designed for

applications that appear to have a place in

low-cost houses are included in this investigation. Those tested to date may be divided

into three classes according to the uses for which

1 Building Materials and Structures (1938) NBS Rep. BMSl.

10 cents, see cover page II.)

2 Building Materials and Structures (1938) NBS Rep. BMS4.

10 cents.)

(Price

(Price

3 Ind. Eng. Chem. 27, 896-898 (1935).

< Misc. Pub. BS (1931) M132.

5 Paper Trade J. 89, 61-68 (1929).

124068°—39 1]
they were primarily intended. All were of the

homogeneous type, that is, not laminated, made

to have comparatively low density to obtain the

maximvmi heat insulating value. These boards owe their heat insulating properties primarily

to innumerable, small air cells, and the thermal

conductivity usually increases with the density

at a fairly uniform rate.'' The first two classes, the more or less standard K-inch insulating boards used within walls,

and the K-inch insulation wall boards used for interior finish, respectively, differ only in that

those of the latter class either have one side

painted or have one surface smoothed and sized

for decorative treatment. The insulation

sheathing is a new class of material. It includes

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

employed for sheathing, ^^32 inch.

The boards in class / are designed for use as heat insulation in walls, roofs, attic floors, and

basement ceilings, and are sometimes used as lath or under stone or brick veneer. Boards in class // would serve in those applications practicallv as well as those of class / and have the

added feature of being designed for use as wall

boards, for finish cover on interior walls and

ceilings. The insulation sheathing boards in

class /// are for use as sheatiling, and as insulat- 1 ing roof boards. They are of approximately

the same density as the boards in the other two j classes, are nearly twice as thick, and have

asphalt treatments for protection against infil- tration of water and air. The samples included boards made of fibers ; from at least five quite dift'erent raw materials;

wood, bagasse (extracted sugar cane), cornstalks, licorice roots, and waste papers. However, the general properties of the finished products were essentially the same. All of them

can be classed as insulating structural boards.

III. PROPERTIES AND TESTING

The properties of the boards as determined

by the present laboratory methods are shown

in table 1 . The methods of testing were, insofar as possible, the methods that have been more

or less standardized.''

' BS J. Research 5, 973 (1930) EP243.

' The assistance of M. S. Van Dusenand H. W. WoolU'y of the Bureau's

heat transfer section in obtaining data on thermal conductivity is jrrate- fullv aclcnowledsed. Table 1.

Properties of fiber building boards

Board Thickness Density

Tliermal conductivity

riexural properties " Water

absorj)-

tion, by

volume

(2-hr immersion)

Water per- meability

(time of penetration through

the board)

Air permeability

(rate of flow through the board)

Linear ex- pansion (for increase from 50- to 95-percent

relative humidity)

Nail- holding

strength

(lateral)

Breaking

load

Deflection at rupture

Across

long di- rection

Across

short di- rection

Across

long di- rection

.\cross short di- rection

CLASS I. —H-INCH INSULATING BOARDS WITHOUT SPECIAL FINISH

Stu/br fr- cTn^/m^ sec

ii. Ibim °Flin. lb tb in. in. Percent hr g/cm'^ Percent /) A 0. 49 1*1.9 0.35 14. 3 11.3 0. 72 0. 76 5. 7 25 454 0. !5 74 B .50 16. 2 .34 16. 5 13.0 .60 . 72 12. 5 6 1,0,84 .20 72 / .52 16. 9 .36 25. 4 18.0 .54 . 64 5. 5 30 505 . 15 95 J. .53 16. G .34 20. 6 15.6 .52 . 68 7. 9 21 498 .20 87 L .49 19. 5 .37 12. 7 12. 4 .30 .31 6. 0 26 3, 780 . 10 64 M . 51 1.5. 7 .37 17. 2 11. 3 . .V2 fi. 3 5 383 . 10 67 N .47 16. 5 . 33 9. 7 10. 5 . 50 .'4S 5.4 22 1,215 . 10 57 0 .55 17.0 ..33 12. 2 11.4 .55 . 50 6.8 25 2.665 .20 87 R .48 18. 2 .36 1,5.3 14. 5 .98 1. 05 5.3 5 479 .40 83 K .51 16. 5 .37 10. 5 12. 1 . 54 ..57 4. 2 5 700 .30 64

A-^ - . 53 21.8 .40 20. 5 20. 7 1. 27 1.32 .3.4 6 760 .40 112

CLASS II. —H-INCH INTERIOU-FINISH INSULATING BOARDS c 0. 47 21.0 0. 39 14. 4 14. 0 0.61 0.89 5. 1 26 676 0. 35 7t D .48 16. 9 .36 15. 1 11. 4 .83 .89 9.0 18 207 .30 79 JI .49 25. 6 .43 33. 3 32.7 .85 .72 4. 1 47 30 .20 143 P .46 20. 7 .35 12. 0 12.

.77 .97 9.3 21 704 .40 91 RK.- .49 18. 3 .36 16. 4 14.

.98 1. 10 5. 6 5 339 .40 87

CLASS in. INSULATION E HEATH7NG E 0. S3 20. 0 0. 39 48. 0 45. 0 0. 48 0. 45 (M 125 0. 10 171

C-' .81 17. 0 ..38 37.8 28.2 .72 .69 (") 1S3 0. o:i .30 103

Test .5 Kiade un;ler standard atmospheric conditions of 6.5-pereent relative humidity and 7.)° F. i> Test not applicable to this class of boards. [2]
' 1. Thickness and Density

I The density of board is the weight per unit

of volume; hence, it is computed from dimensional measurements and weight determina-

- tions on test specimens. Thiclvness and den1 sity values were obtained on specimens 12 by 12

j inches. The specimens were weighed on a

balance reading to 0.1 g, and the thickness was

; measured with a vernier caliper graduated to

: 0.1 mm.

2. Insulating Properties

' The insulating value of a board depends upon

I its thermal conductivity or the rate at which

! heat is transferred through the board. The

boards having lowest thermal conductivity have

the best insulating value. The conductivity is expressed as the number of heat units (Btu)

j that would be transferred through a square foot

j of the board in 1 hour with a temperature drop

I of 1° F per inch of thickness. It was deter1 mined on specimens 8 by 8 inches, which were

j prepared by drying them to constant weight at

1 160° F before the testing, and the tests were made on the dry specimens at a mean temperature of 90° F. The guarded hot-plate method was used.

Details of this test together with the construction of the necessary apparatus are described

in the Federal specification® for insulating

I board. An electrically heated copper plate is sandwiched between two 8- by 8-inch test

; specimens the other surfaces of which are in

contact with water-cooled copper plates which

are kept at constant temperature. The power

required to keep the heated plate at constant

I temperature is measured, and the thermal conI ductivity is calculated from the expression

I Pd/JT, where P is the power applied per unit

area of slab (watts per square foot); d is the

I average thickness of specimen (inches) ; T is

' the temperature difference (° F) ; and J is the

electrical equivalent of heat (1,054 j/Btu).

A guard-ring arrangement is included to make certain that the flow of heat is perpendicular to the faces of the slabs and uniformly

. distributed over the area of the slabs. In

I placing the specimens in the apparatus, one on

« Fed. Spec. LLL-F-321a.

each side of the central heating plate, enough

pressure is applied to insure good contact between the specimens and the copper plates, but

not enough to cause an appreciable diminution

in the thickness of the specimens.

.3. Flexural Properties

With the exception of the sheatliing boards,

the boards are not usually installed where they

are required to add structural strength to a

building. A reasonable flexural strength is important, however, to allow handling and

installation without undue breakage. The

deflection at rupture is a rough measure of the

stiffness. Little or no deflection would indi- cate that the board was too brittle for economical application, and excessively high deflection

might indicate lack of sufficient stiffness to hold its shape in panels.

The flexural strength tests were made in

accordance with the standard method described

in the Federal specification® for insulating

board, and also in a previous Bureau publication.® The test is made by applying a load

at midspan of a specimen 3 inches wide, laid across two parallel supports 12 inches apart.

The load required to break the specimen, or rupturing load, and the amount that the board

bends up to the brealdng point, or deflection at rupture, are recorded. The load may be applied

conveniently by means of a tensile testing

machine with suitable fixtures. As the sheatliing boards are designed for use

as siding they must provide bracing strength to the structure. Hence, high strength and stiff- ness are to be desired in this class of boards.

4. Water Absorption

Water absorption is an important consideration factor because it indicates the extent to which the fibers will become wet when water

reaches them. Wetting is accompanied by

swelling of the fibers and warping or buckling

due to the resulting expansion. Also, the wetting results in loss of stiffness and insulating

value. The water absorption was determined

by the standard method described in the Federal specification ® for insulating boards. Speci9 Misc. Pub. BS (1931) M132.

[3]
mens 1 2 by 1 2 inches are weighed and immersed

in water for 2 hours, removed and allowed to drain 10 minutes, and reweighed. The increase

in weight is the water absorbed. The result is converted to volume of water absorbed and is expressed as a percentage of the original

volume of the specimen.

5. Permeability to Water and Air

As a structural component of the walls of a

house, a board should offer relatively high

resistance to the passage of both water and air. The fiber boards are not, with the exception of

the sheathing boards, commonly used where

they must function as a primary moisture

barrier. However, the rate of water penetration is often important in these boards as it may

affect the resistance of the finished walls to the

infiltration of water. Air permeability is important, of course, because the infiltration of

air causes transfer of heat in addition to that

transmitted by thermal conduction.

The time of water penetration was determined by the dry indicator method.^" " An

eosin dye in mixture with powdered sugar and

starch is sprinkled on one side of the test specimen and the specimen is floated on water with

that side up until color is developed in the dye

by water permeating the board. The dye is covered with glass during the test to prevent

contact with atmospheric moisture, and the

edges of the specimen are sealed with wax to prevent the water from entering there. The

principle of the dry indicator test, which was

developed by F. T. Carson of the Bureau, has

been applied satisfactorily in the testing of

papers and fibrous sheet products in general.

The results are expressed in time of penetration in hours. This time should be as long as practicable.

PermiCability to air was determined with the

Carson precision permeability tester for sheet

materials. The test is described in detail in a

publication by Carson.'^ The volume of air that will flow through the board per unit of area for a given pressure gradient is measured

by means of a capillary flow meter. The presi» Paper Trade J. 98, No. 21 (May 1934). " TAPPI Std. T433m, Tech. Assn. Pulp & Paper Ind., 122 East

42d Street, New York, N. Y.

12 BS J. Research 12, 567 (19341 RPRSi.

sure gradient is kept constant during the test by means of a sensitive pressure regulator, and

errors due to edge leakage are avoided by bypassing the leakage air around the measuring

apparatus.

The permeability to air should be as low as practicable.

6. Linear Expansion with Change of

Humidity

Low linear expansion with changes of humidity is an important attribute of a fiber board,

particularly if it is to be used for interior finish. Low expansion means a minimum of waving,

buckling, and opening of seams when wall

panels are subjected to extremes of relative

humidity as they often are. The linear expansion tests were made in

accordance with the method described in the

Federal specification.'^ Test specimens measuring 3 by 12 inches are conditioned first at 50-percent relative humidity, then at 95-percent, and the change in length determined by

measuring the displacement of reference marks

placed approximately 10 inches apart.

7. Nail-Holding Strength

Nail-holding strength is of interest in considering the properties of the wall-finish boards

and ordinary insulating boards, as it indicates

the probable danger of their becoming loosened

after installation. For the sheathing boards

high nail-holding strength is essential if they

are to impart the required rigidity and strength

to the building. For measuring nail-holding

strength, a modification of a method suggested

by a manufacturer'* was used. It is not a test for the resistance to pulling of the nails, but is a method of finding the force required to move

a 6-penny common nail laterally to the edge of

the board. The nail is driven in a 3-inch strip

of the board, centered % inch from one end and

driven through far enough to project about

equally from both sides of the board. The

opposite end of the strip is clamped in one jaw

of a tensile tester, and a metal stirrup is hooked

over both ends of the nail and clamped in the

other jaw of the tester. Operation of the tester

" Fed. Spec. LLL-F-321a.

'* This method was proposed by M. S. Wunderlich, of the Insulite Co.

[4]
niuvos the nail to the edge and records the

force required to do so.

IV. SUMMARY

A good insulating board shoidd luive high

insulating value, as indicated by a low rate of thermal conductivity, sufficient strength for economic liandhng, and low permeability to air and water. The average heat-transmission

value was 0.35 for the K-inch insulating boards

and 0.38 for the K-inch interior-finish insulating

boards, the average densities being 17.1 and

20.5 pounds, respectively. These data indicate

that the surface treatment of the wall-finish

boards raises the density slightly and that the

insulatmg value is decreased accordingly. The

boards show a wide range of values for per- meability to air and water. A thermal conductivity of 0.33 to 0.36 is the

minimum that was obtained in K-inch boards

that met the strength requirements contained

iu tiie i^'ederal spccilicalioii I'ui' lihci- iusiilii ling

board. Apparently, a lower value can be

obtained only with densities below 16 pounds

per cubic foot, and such boards are not likely

to meet the present requirements for strength

and absorption of water. The strength properties show a, considerable

range of values for fiexural strengtli and nailholding strength.

The insulation sheathing boards had high

strength because of their greater thickness, and

the low permeability to water and air was significant, particularly for board C\

That the source of the vegetable fiber used

had a relatively unimportant effect on the

essential properties of the boards may be

observed from the rather uniformly good correlation between the density and other properties,

especially thermal conductivity, for all boards.

Washington, November 11, 1938.

[5]

The National Bureau oj Standards was established by act of Congress, approved

March 3, 1901, continuing the duties of the old Office of Standard Weights and Measures

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