T^ureau of gtandarda

.••MAR- 2,

U. S. DEPARTMENT OF COMMERCE
The program of research on bviilding materials and structures mdertaken by the

National Bureau of Standards is planned with the assistance of the following advisorycommittee designated by the Subcommittee on Design and Construction of the Central

Housing Committee.

TECHNICAL RESEARCH GROUP

Waltee Junge, Federal Housing Administration, Chairman

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

A. G. Bear,

Veterans' Administration.

Pierre Blouke,

Home Owners' Loan Corporation.

C. W. Chamberlain,

Procurement Division.

Jos. M. DallaValle,

Public Health Service.

Hugh L. Dryden,

National Bureau of Standards.

G. E. Knox,

Bureau of Yards and Docks, Navy

Department.

Charles E. Mayette,

United States Housing Authority.

Vincent B. Phelan,

National Bureau of Standards.

E. A. Poynton,

Office of Indian Affairs.

John H. Schaefer,

Prociurement Division.

George W. Trayer,

United States Forest Service.

Elsmere J. Walters,

Quartermaster Corps, War Department.

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

H. C. Dickinson

W. E. Emley

G. E. F. LUNDELL

A. S. McAllister

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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BUILDING MATERIALS AND STRUCTURES REPORTS

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Office, Washington, D. C.
UNITED STATES DEPARTMENT OF COMMERCE • Harry L. Hopkins, Secretary

NATIONAL BUREAU OF STANDARDS Lyman J. Briggs, Director

BUILDING MATERIALS

and STRUCTURES

REPORT BMS14

Indentation and Recovery of

Low-Cost Floor Coverings

by

p. A. SIGLER and MYRTLE B. WOODWARD

ISSUED MARCH 7, 1939

The National Bureau of 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

BY THE SUPERINTENDENT OF DOCUMENTS,

OFFICE • WASHINGTON • 1 93 9

WASHINGTON, D. C. PRICE 10 CENTS
Foreword

In connection with the research program on building materials suitable for low-cost

house construction being conducted by the National Bureau of Standards, tests have

been made on various types of floor coverings in order to determine their relative per- formance with regard to indentation characteristics when in an atmosphere of 65-percent

relative humidity and at a temperature of 72° F. Tliis report presents in graphic form

the results of indentation and recovery determinations on such floor coverings as asphalt

tUe, pressed fiber board, linoleum, felt base, rubber, and wood. For the benefit of the

consumer, the results have been summarized in a chart showing the relative value of the

various floor coverings with respect to comfort in walking in comparison with the extent

to wliich they are permanently mdented under abuse.

This work constitutes one phase of the investigation being made of important

properties of floor coverings.

Lyman J. Briggs, Director.

II
Indentation and Recovery of Low-Cost Floor Coverings

by P. A. siGLER and myrtle b. woodward

CONTENTS

Page

Foreword ii

I. Introduction _' 1 II. Testing equipment 2

III. Test procedure 2

Pace IV. Description of floor coverings 3

V. Results 3 VI. Summary and conclusions 9

ABSTRACT

Indentation and recovery determinations for loads ranging from 25 pounds to 200 pounds on a flat-ended

pin Yi inch in diameter were made on 23 floor coverings

at a relative humidity of 65 percent and temperature

of 72° F. Indentation readings were taken for each

load at intervals of time up to 30 minutes and then

recovery readings at intervals of time up to 120 minutes.

Various types of floor coverings were tested, such as asphalt tile, pressed fiber board, linoleums, felt-base

floor coverings having various wearing surfaces, rubber,

and wood. A description of the apparatus and the

procedure used are given. The results are presented in graphic form to show the relative merits of the various

floor coverings with respect to initial and 30-minute

indentation under various loads and the recovery after removal of the load.

I. INTKODUCTION

The ability of a floor coverin<? to depress

readily under foot is a desirable property from

the standpoint of personal comfort in walking.

However, unless this property is coupled with

an ability to recover to approximately normal

shape upon removal of temporary loads, the

floor covering will soon present an ii'regular and

unsightly surface. The floor covering will gradually lose its comfort value and present a

surface difficult to clean. Because the load

applied in some locations is likely to be severe and prolonged, the ability of a floor covering to recover its shape after application of load is of

additional importance. The severity of the

loads applied by furniture can be reduced by

the use of ample-sized and properly maintained casters or shoes.

Although there are indentation requirements

in most of the Federal specifications for floor coverings,^ the methods employed in testing

the various types are quite varied with regard

to time, load, and indenting tool. Each specification deals with the quality of a particular

type of floor covering, not with the relative

qualities or outstanding features of the various

types. Comparable information on the several

types is of direct interest to the consumer in

selecting a floor covering to meet his particular

1 The following l<"ederal specifications tor floor coverings may be purcliased from the Superintendent of Documents, U. S. Government

I'rinting Office, Washington, U. C. at 5 cents each:

Title Symbol

Linoleum; battleship LLL-1^351 Linoleum; plain, inlaid and printed LLL-L-3(il

Tile; asphalt _.. SS-T-300

Floor-coverings; rubber sheet ZZ-F-46I

Matting; rubber ZZ-M-71

Tile; cork ..LLL-T^3t

Carpet; cork LLL-C-96

Carpets and rugs; axminster DDD-C-51

Carpets and rugs; velvet, plain DDD-C-61a

Carpets and rugs; wilton._ DDD-C-71a

liugs; American-Oriental (washed) DDD-R-751

123997°-39
need. In view of the lack of comparable test data and the importance of a consideration of

recovery or conversely residual identation along

with indentation under load, indentation and

recovery determinations were made on various

types of floor coverings wliich might be siutablc

for low-cost house construction.' ^ B}^ these

determinations an effort is made to show the

relative merits of the various floor coverings

with respect to initial and 30-minute mdentation under various loads and the recovery

after removal of the load, when in an atmosphere of 65-percent relative humidity and at a temperature of 72° F.

Figure 1.Indentation tester (at right) and thickness gage {at left).

II. TESTING EQUIPMENT

Figure 1 shows the indentation tester (at the

right) and thickness gage (at the left) used in

2 n. L. Dryden, Kesearch on Building Materials and Structures for Low-Cost Housing, NBS Eep. BMSl, (1938) . Price 10c.

3 Investigation of Low-Cost Floor Coverings, Letter Circular LCo02F. May be obtained free from the National Bureau of Standards, Washington. D. C.

these determinations. The indenting load (A)

is transferred from a baU-bearing support (B)

to the indenting plunger (CO by means of a screw and handwheel (D). Attached to the

indenting plunger, which rims through two

bearings, is a lever mechanism (E) which is used to counterbalance the weight of the

plunger. Also attached to the phmger is an

adjustable stop (F) which contacts the spindle

of a dial micrometer ((?) attached to the frame

of the machine. The dial micrometer is graduated in thousandths of an inch and registers

any movement of the phmger. The indenting

tool (H), consisting of a flat-ended cylindrical

steel rod % inch in diameter, is attached to the lower end of the indenting phmger. The

dial micrometer was adjusted to zero with the

indenting tool in contact with the base plate (/) at a pressure of 20 lb/in. ^, so that the dial

micrometer registered the thickness of a specimen (J) during indentation under load.

The tliicloiess gage used to measure the original tliicloiess of a specimen (J) as well as the

tliicliness during recovery is shown at the left in

figure 1. The dial gage (K) is graduated in

thousandths of an inch and is equipped with a

flat-ended foot (Z), % in. in diameter, which

exerts a pressure of 20 lb/in. ^ by means of a

ji-lh weight (AI) on the top of the spindle.

III. TEST PROCEDUKE

The specimens, consisting of 2-in. squares, were fu'st conditioned in an atmosphere of 65-

percent relative humidity and at a temperature

of 72° F for at least 48 hours. The thickness of

each specimen was measured at a marked location in the central portion with the thickness

gage. Precaution was taken to see that the bottom

edges of the specimens were beveled smooth

and that the specimens rested flat on the base

plate of the gage. Most of the specimens had some tendency to either buckle or curl. Finger

pressure was used to flatten the specimens. A

dead weight of 1 kg was found to be insufficient to assure a flat contact. The specimen was then placed under the

indenting tool and the load appUed. Time was
recorded from the instant the full load rested on the specimen; this could be readily determined from the movement of the hand on the

dial micrometer. The dial micrometer was

read at intervals for a total of 30 minutes.

The load was removed at the end of 30 minutes

and the thickness of the indented portion

measured with the thickness gage at intervals

up to a total of 120 minutes.

Indentation and recovery determinations were made on each floor covering for indenting

loads of 25, 50, 100, 150, and 200 lb, wliich

represent average pressures of 509, 1,018, 2,038,

3,058, and 4,075 lb/in. 2, respectively. Three

specimens of each floor covering were tested at each indenting load. The agreement between

the results obtained on individual specimens was good for most of the floor coverings.

IV. DESCRIPTION OF FLOOR

COVERINGS

Indentation and recovery determinations were made on 23 samples of floor coverings, in- cluding several asphalt tiles; pressed fiber

board; various linoleums such as battleship,

inlaid, jaspe, and priuted; felt-base floor coverings having various wearing surfaces, such as enamel, linoleum composition, asphalt mastic,

and other compositions ; rubber flooring in both

sheet and tile form; and several wood floors. The floor coverings are listed in table 1 with

brief descriptions. The sample numbers in

table 1 correspond with the figure numbers of

the graphs showing the results.

Table 1.Floor coverings tested

Table 1.Floor coverings tented—Continued

Sample number

Average

thick- ness 1

Floor covering Description

Inches

2 0. 127 Battleship linoleum Plain pattern, brown.

3 127 do Plain pattern, gray.

4 . 129 do Plain pattern, green.

. 129 Marbleized linoleum. _ Marbleized pattern, green, mottled.

6 .077 Inlaid linoleum _ . Molded pattern, gray, mottled.

7 .096 Jaspe linoleum .laspe pattern, brown, streaked.

8 . 076 Printed linoleum. Block pattern, brown. Wearing surface, enamel.

9 .081 Inlaid felt base... Straight-line pattern, cream,

mottled. Wearing surface. linoleum composition.

Sample number

Average

thick- ness '

Inches

0. 074

. 009

.090

. 077

. 080

. 128

. 135

. 12,5

.127

. 123

. 145

. 783

.796

Floor covering

Printed felt base

do. Mastic felt base

Ooinposilion fell base

do....

Asphalt tile

do

....do

Sheet rubber Rubber tile.

Pressed fiber board...

Strip yellow pine

Strii> Douglas fir .

Strip white oak

Short strip maple

Description '

Flowered pattern, brown. Wearing surface, enamel. Block patlern, lavender. Wearing surface, enamel.

Plain pattern, maroon. Wearing surface, asphalt mastic

composition.

.Jaspe pattern, brown, streaked. Wearing surface, nitrocellu- lose mastic composition. Mottled pattern, tan, mottled. Wearing surface, nitrocellu- lose mastic composition. Marbleized pattern, white, mottled. 1-minute indentation

-0. 007 in.

Plain pattern, black. 1-minute

indentation —0.012 in.s

Plain pattern, maroon. 1- minute indentation —0.012

in. 3 (so-called "economy tile") Marbleized pattern, brown,

mottled. Cloth backing. Marbleized iKittern, gray, mottled. N(i backing.

Plain pattern, brown. Density

67 Ib/cu ft.i Flat grain, hollow back. Density 44 Ib/cu ft.-i Edge grain, flat back. Density

36 Ib/cu !tJ Flat grain, flat back. Density

40 Ib/cu tt.i Flat grain, flat back, equal

length shorts. Density 47 Ib/cu ft.-i

' From original thickness measurements; '/s-iu. foot; 20 Ib/in.2 pressure

2 Color listed is the predominating color.

3 Method prescribed in Federal Specification SS-T-306, "Tile; Asphalt."

* At 65-percent relative humidity and 72° F.

V. RESULTS

The results of the indentation and recovery

determinations on the 23 floor coverings are shown graphically in figures 2 to 24, inclusive.

The solid-line curves at the left of each figure

show the indentation with respect to time

caused by the Yi-in. flat-ended indenting tool

for loads of 25, 50, 100, 150, and 200 lb. The

solid-line curves at the right show the residual

indentation with respect to time after removal

of the loads. The broken lines connect the

corresponding curves for each load.

The residual indentation at the end of 24

hours was also measured on most of the floor coverings. The results were not appreciably

different from those obtained at the end of 120

minutes.

[3]
.oos

.010

.015 OZO

.0 25

.040

.045

• OSO

.OSS

.060

.065

.0 70

.075

.OSO

.065

.090

.095

. 1 00

TIME - MINUTES

5 10 15 ZO 25 30 5 10 15 30 45 60 90 I20

1

< —

r-

'

/ ;

ji —i s < -es- '

' U

S ; ;; :—

se LB. [ill

1 1

iU-

>-—

) —I 1—

ISO LB

>

,

200 LB. ',

.00

.0 ! O

.0 1 5

.0 2C

.0 25

.030

.035

.040

.045

.050

.osr

.06C

.OSS

.070

.075

.06C

.085

.090

.035

1 00

TIME - MINUTES

JO 15 20 25 30 5 lO 15 30 45 60 90 120 —-f U4t—

L B.

J

50 LB.

(—

r =—

>—

'

' !'

100 LB.

: 1

ISO Lb.

', 1 —-I

1

too [lb.

I

Figure 2.

Brown baitleship linoleum. Figure 4.

Green battleship linoleum.

Figure 3.

Gray battleship linoleam. Figure 5.

Marbleized linoleum.

[4
TIME - MINUTE5

ro 15 JO 25 JO 5 lO IS 30 45 60 90 iZO

Xu

z

I .0 10 zO

(-< .020

I-S OSS Q

Z 030

.03S

.04O

Figure 7.-Jaspe linoleum.

TIME - MINUTE5

S lO IS 20 25 JO S 10 15 30 4S 60 90 I20

<

) <

S (

> c )

1 ^ 25 LB

^=—

SO LB.

' <

>—

3 ( lOO

) « LB.

1::

X

) 1 ISO 200

LB.

> f

r—

'

r « ' ( >

FiGTTRE 8.

Printed linolei Figure 10.Printed felt base.

[5]
TIME - M1NUTE5

.oos

.O I o

O I s

.02.0

.025 OJO

.0 25

.040

.045 OSO

.055

.060

.065

1—

)—

)

—

)

T: -< 1—

'—

'—

50 )

1 C

>—

1 ' ^

'*—

>-—

>

( ,100 LB."

r' ,c

1—

1—

)—

4-50 LB —< )

,(

1—

1—

—

goo >—

1

I )—

)

)—)—

TIME - MINUTES

IS ZO 30 S 10 15 30 45 60 90 IIP

Figure 11.

Printed felt base.

.03S

.040

.045 OSO

05s

.060

.065

.0 70

.07S oeo

085

OSO

OSS

1 00

Figure 13.

Composition felt base. TIME - MINUTES

10 15 20 IS ao S 10 15 30 45 60 90 120

>—

25 La.

!

< >

(

,

< 1—

P=—

1

1—

>^—

'—

+00 -tfir

'

(

)

t

A50 \ C

LB.

>

1—

i—

—

>

1—

1—

\N

200 >—=< LB. J—

>—

3—>

—

)—

5—

Figure 12.Mastic felt base. Figure 14.

Composition felt base.

[6]
TIME - MINUTES

lO 15 20 25 JO 5 10 15 30 45 60 90 I20 TIME - MINUTE5

Xu

z

— .005

I 2 -0 10 g

1- .0 I 5 <2 020

UJCI .025 2

.030

.035

FiGTTRE 15.

Asphalt tile.

TIME - MINUTE5

10 15 20 25 30 5 10 15 30 45 60 90 I20

1—

Use,

) £

1 1

, <

< rf i-—

1 < —

>!£° LB. ^==-< =—

>

LB.

)

Figure 16.

Asphalt tile.

TIME - MINUTE6

.COS

.010

.015

.ozo

.025

.030

.035

.040

.045

• 050

.05s

.060

.06S

.070

.07S

.O80

.085

.090

.OSS

. 1 00

.010

.015

.OZO

.025

.030

.03S

.040

.045 050

.055

.060

.06S

.070

.07S

.oao

.065

.090

.09S

.100

15 30 4S 60 90 120

Figure 18.

Sheet rubber.

TIME - MINUTE5

O S 10 IS 20 25 30 5 10 IS 30 45 6O 90 120

26 LB. A

i

> 1 /t

1—

'—

1 ( ISO

' —

LB.

) <

) C ( ;

> f

1 < > ( ) h ) 6

f~f

1-

, too

J

t \ ISO LB.

>—

' <

200 LB.

1 (

Figure 17.

Asphalt tile. Figure 19.

Rubber tile. [7]
TIME - MINUTES TIME - M1NUTE5

I O

P .015 ^ ozo

UJd .025 Z

r—

\—

1

i >—

T-C 38S—

) c fr—

)' i- -( 25

50

LB.-

UB.- 100 LB.-

Figure 20.

Pressed fiber board.

TIME

10 IS ZO 25 30 MINUTES

45 60 90 la

00 5

.0 I O

O 1 5 OZO

.025

.030

.035

.040

045 050

OSS

.oos

.Olo

.015

.020

.025

.030

.03S

-040

.045 OSO

Figure 21.Strip yellow piiie.

TIME - MINUTES

.5 lO IS 20 25 30 ^ ip [5 30 45 60 90 120

.OOS

1 Olo zO ols < .020 H2 .025 O

Z .030 035

.04O

2 .O I O o

(_ .O 1 5 <

2 .020

LUQ .02S

20

16

16

14

12

' lO

8

64

—i lOO LB.

> ^s t

'p—

) (e

J

1 ( P—

25 LB.- 50 LB I

< ISO LB.

1 < / c

)—

)

1

, 200 -LBr1— c

/

Figure 23.

Strip white oak.

TIME - MINUTES

5 1 T 5 2O 25 30 ^ MM Mp 9O 120

1 € y -c ''''(• M,—

)—

2oa

-c

' c I—

-< )' 25SO

LB,-

LB.-

Figure 24.—yS/!or< s^rip maple.

2

(

5

-e13 o

4

1/1 —

180 7 go

(§•20 22

.df l£

(,

ft

A7

' (

-23

--21 ^?4

Figure 22.

Strip Douglas fir.

O 2 4 6 6 lO 12 14 16 18 20 22 24

I Figure 25.

Summary of results.

C, initial indentation for load of 25 pounds, mUs. (An appro.fimate measure of the relative comfort value.) /, residual indentation 120 minutes after removal of load of 100 pounds, mils. (An approximate measure of the extent to which the surface is permanently indented under abuse.)
VI. SUMMARY AND CONCLUSIONS

Figure 25 represents a summary of the results,

wliich, with due consideration of price and other

properties, should aid tlie consumer in select- ing a floor covering. The numbers in the chart

correspond to the sample numbers in table 1. The quantity C, wliich is used as an approximate measiu-e of the relative comfort value, is the initial indentation (30 seconds after application of the load) for a load of 25 lb on the

indenting tool. This load gives an average

pressure of 509 lb/in.- on the covermg. The

quantity /, which is used as an approximate

measure of the extent to wliich the surface is permanently indented under abuse, is the

residual indentation 120 mmutes after the

removal of a load of 100 pounds which has been

applied for 30 minutes. Tliis load gives an

average pressure of 2,038 lb/in.'' These pressures may seem quite high, but it can readily be demonstrated that such pressures may be attained under particles of gravel on which a person is standing, under the edge

of a chair leg which is not squarely on the floor, or possibly under the edge of the heel when contact is first made with the floor in walking.

Corresponding charts for either lower or higher

loads can be prepared from the data shown in

figures 2 to 24. If the quantity / were taken

as the residual indentation 120 minutes after the removal of a load of 200 lb which has been

applied for 30 minutes, representing very severe

abuse, the relative performance of the several

coverings would be roughly the same except for

samples 5 and 9, wlu(di. gave large residual in- dentations following a load of 200 lb but did

not under a load of 100 lb. Pressures around

3,000 lb/in. ^ appear to be critical for many of

the floor coverings.

In the selection of a floor covering, the nature

of the exposure to which it will be subjected,

the desires of the occupant as to appearance

and comfort, and the price are of importance.

In general, so far as comfort and resistance to abuse are concerned, the coverings which are

nearest the upper left-hand corner of figure 25

are most desirable. If resistance to abuse alone

is considered, those farthest to the left are to be

preferred; whereas, if comfort alone is considered, those nearest the top are the best. It must not be concluded, however, that the group

of coverings to the right are not to be considered, because it is probable that the cost of this

group is the lowest.

It should be noted that this report deals only

with the particular samples tested and their

relative performance with regard to indentation

characteristics without consideration of other

properties, such as abrasive wear, effect of

moisture and temperature, effect of aging, adherence to subfioor, etc. Indentation and recovery determinations are

in progress on specimens of floor coverings

listed in table 1 after exposure to heat and light to determine the effect of accelerated aging on

indentation and recovery. Tests are also in

progress to determine the effect of elevated

temperature.

Washington, October 12, 1938.

[9]
1

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

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

of the United States Coast and Geodetic Survey. In addition, new scientific functions were assigned to the new Bureau. Originally imder the Treasury Department, the

Bureau was transferred in 1903 to the Department of Commerce and Labor (now the

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