IMBSIR 77-1256

Properties of 21 Year Old

Coal-Tar Pitch Roofing

Membranes: A Comparison

with the NBS Preliminary

Performance Criteria

Robert G. Mathey

Walter J. Rossiter, Jr.

Center for Building Technology

Institute for Applied Technology

National Bureau of Standards

Washington, D.C. 20234

June 1977

* *

U. S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS

NBSIR 77-1256

PROPERTIES OF 21 YEAR OLD

COAL-TAR PITCH ROOFING

MEMBRANES: A COMPARISON

WITH THE NBS PRELIMINARY

PERFORMANCE CRITERIA

Robert G. Mathey

Walter J. Rossiter, Jr.

Center for Building Technology

Institute for Applied Technology

National Bureau of Standards

Washington, D.C. 20234

June 1977

U.S. DEPARTMENT OF COMMERCE. Juanita M. Kreps. Secretary

Dr. Sidney Harman, Under Secretary

Jordan J. Baruch. Assistant Secretary for Science and Technology

NATIONAL BUREAU OF STANDARDS. Ernest Ambler. Acting Director

TABLE OF CONTENTS

Page

Abstract 1

1. INTRODUCTION 2

2. LABORATORY EVALUATIONS 3

3. VISUAL EXAMINATION OF MEMBRANE AND INSULATION SAMPLES 5

4. LABORATORY TESTS 5

5. COMPARISON OF MEMBRANE PROPERTIES WITH THE PRELIMINARY

PERFORMANCE CRITERIA 7

6 . ACKNOWLEDGMENT 8

7 . REFERENCES 9

iii
'
Properties of 21 Year Old Coal-Tar Pitch Roofing Membranes:

A Comparison with the NBS Preliminary Performance Criteria

Robert G. Mathey

Walter J. Rossiter, Jr.

Abstract

The properties of coal-tar pitch roofing membranes

approximately 21 years old were compared to the properties of new membranes and the suggested level of performance for such

membranes reported previously by the National Bureau of

Standards (NBS) . Samples of old membranes were taken from

eight buildings having roof areas that ranged from 0.5 to 1.5

2 million square feet (0.05 to 0.14 km ). The buildings were

located at three sites in or near the state of Kentucky. The

roof membranes on these buildings had been subjected to

different maintenance procedures.

Laboratory tests conducted on 47 membrane samples

included tensile strength, load-strain determination and

coefficient of thermal expansion. The thermal shock factor was calculated for each sample. Laboratory observations were

made to determine between-ply bitumen thickness, weight per

unit area, ply adhesion, pliability and condition of the

membrane.

The tensile strengths of the old membranes determined at

0°F (-18°C) in their longitudinal and transverse directions

and values of the coefficient of thermal expansion measured

over the temperature range of 0 to -30°F (-18 to -34°C) were

comparable to those values reported earlier by NBS. The

moduli of elongation were considerably higher for the old

membranes than for the new ones which resulted in lower

1
values of thermal shock factor. The lower values of extensibility (higher moduli of elongation) of the old membranes

were attributed to their brittleness caused by aging.

Differences in roof maintenance procedures appeared to have

caused significant differences in the properties of membranes

from the three different sites.

Key Words: Bituminous roof membranes; built-up roof membranes;

coal-tar pitch; performance criteria; physical and engineering

properties; test methods.

1. INTRODUCTION

A study was conducted to determine the properties of 21 year old

coal-tar pitch membranes and to compare their properties to those reported

for similar new membranes in NBS Building Science Series 55, "Preliminary

Performance Criteria for Bituminous Membrane Roofing" [1]*. Samples of

old roofing membranes for laboratory tests and observations were taken

from eight buildings located at three sites in or near the state of

Kentucky. The roof areas ranged from 0.5 to 1.5 million square feet

2 (0.05 to 0.14 km ). The buildings at the three sites were constructed

about the same time with similar types of construction and were exposed

to comparable interior and exterior climatic conditions. The inside

temperature in the buildings at roof level was approximately 120°F

(49°C). All of the roofs had slope sufficient for adequate drainage,

with a few exceptions. All roofing samples taken for test were from

well-drained areas. The roof construction consisted of heavy gage steel

decks with small flutes, fiberglass insulation measuring between 1/2 and

3/4 in (13 and 19 mm) thick, coal-tar built-up membranes and gravel

surfacing. Two-ply bituminous built-up vapor barriers covered the steel

decks. Two types of built-up membranes were used on the buildings. At

one site, designated as A, the membranes generally contained a base

* Numbers in brackets indicate references listed in Section 6.

2
sheet and three plies of coal-tar saturated organic felts. At the two

other sites, designated as B and C, the membranes contained four plies

of coal-tar saturated organic felts. The felts had been laid in shingle

fashion except at site A where the first ply, generally a base sheet, was applied and then three plies laid in shingle fashion.

The maintenance of the roofs varied at the three sites. The roofs

at site A were in very good condition. They had been well maintained

and were recoated and graveled twelve years after fabrication. During

the resurfacing process the bitumen and gravel were removed to the top

ply by means of water jets. After the membrane surfaces had dried, hot

coal-tar pitch was applied and the roof surfaced with gravel. The

gravel was well distributed and the flood coat provided a good protection

to the roofing membrane. Pipe vents three inches (76 mm) in diameter

and spaced about fifty feet (15 m) apart were installed prior to re- surfacing.

The roofing at site B was in good condition which was attributed in

part to periodic and adequate maintenance. These roofs had not been

recoated as was the case for roofs at site A, however, the flood coat was intact and was in general protecting the membrane.

The general condition of the roofing membranes at site C ranged

from fair to poor. There were many areas of exposed felts and many

blisters and ridges in the membranes. These roofs had not been maintained

as well as those at site B.

2. LABORATORY EVALUATIONS

Forty-seven roofing membrane samples, 14 x 40 in (0.4 x 1.0 m)

,

were cut from the roofs at the three sites. These samples had their

long dimension perpendicular to the direction in which the plies of felt

were applied. A strip 4 x 40 in (0.1 x 1.0 m) was cut from each of the

47 samples to determine by visual examination the number of plies, ply

3
adhesion, bitumen interply thickness and the general condition of the

membrane samples. Specimens for determining the tensile strength and

the weight per unit area were prepared from the remaining portion of

each membrane sample. The tensile test specimens conformed to those

described in ASTM Standard D 2523 [2]. Two specimens in both the longitudinal and transverse direction of the felt orientation were tested in

tension at 0°F (-18°C) . As part of the tension test, the strain was measured and the moduli of elongation were determined by the method

described in ASTM Standard D 2523 [2]. The coefficient of linear thermal

expansion was determined using the tensile test specimens (prior to the

tensile tests) for the temperature range of 0 to -30°F (-18 to -34°C)

,

according to the procedure described in the proposed ASTM method of test

for determining the coefficient of linear thermal expansion of roofing

membranes [3],

The weight per unit area of the membrane samples was determined by

weighing 6 x 12 in (150 x 300 mm) specimens. The gravel surfacing was

removed prior to weighing, but some of the flood coat and some bitumen

which bonded the membrane to the insulation were present in most specimens.

Samples of insulation, 6 x 6 in (150 x 150 mm) , were taken to

determine qualitatively if the insulation was wet at the same location

on the roofs where the membrane samples were cut.

It is important to note that the roof membrane samples were taken

from areas of the roofing that were not subjected to ponding and appeared

to be in good condition. Subsequent laboratory inspections revealed

that the top plies of some membrane samples exhibited some deterioration.

This deterioration had been obscured during the field inspection by the

gravel surfacings and flood coats on the membranes. In the selection of

the membrane samples for laboratory test, problem areas of roofing are not desirable because testing of obviously deteriorated membrane samples

would yield little practical information. In this study the deterioration

of the top plies was not considered extensive enough to render the test

specimens unusable.

4
3. VISUAL EXAMINATION OF MEMBRANE AND INSULATION SAMPLES

Roofing membrane strips, 4 x 40 in (0.1 x 1.0 m) , cut from the

membrane samples were cooled to -40°F (-40°C) and delaminated. Individual plies were examined and their condition, between-ply adhesion,

pliability and number of plies per sample were recorded. Information

from the visual examinations of the membrane strips is presented in

tables 1, 2 and 3.

Visual examinations of the 47 fiberglass insulation samples showed

that only one sample, C9, was wet. All the other samples of insulation

were apparently dry. These insulation samples appeared to be firm

except for 12 of which 7 were soft, 3 were delaminated and 2 were disintegrated. Reasons for these conditions were not investigated.

4. LABORATORY TESTS

An average value of the approximate weight of the between-ply

2 2 bitumen per 100 ft (9m) of roof area for each of the membrane samples

is given in tables 1, 2 and 3. These weights were calculated from the

bitumen thicknesses between each of the plies measured at two locations

on each tensile test specimen using a machinist's microscope. The

procedure for measuring between-ply bitumen thickness has been described

by Rossiter and Mathey [4], The measurements of between-ply bitumen

thicknesses for the old coal-tar membranes were converted to bitumen

2 weight using the relationship that 0.01 inch equals 6 lb/100 ft (0.1 mm

2 equals approximately 0.1 kg/nO .

Most of the membrane samples were four ply, although one was three

ply, seven had five plies and one had six plies. It is possible to cut

tensile test specimens which have more plies than indicated from delamination of the 40 in (1.0 m) long membrane samples. This is because

tensile test specimens may be cut where laps in the felts occur.

5
The weights of the roofing membranes per 100 ft (9 m ) of roof area are given in tables 4, 5 and 6. The values are in general somewhat

less than would be expected for a four-ply membrane of this type. A

four-ply coal-tar pitch membrane consisting of type 15 felts and no

2 2 flood coat would weigh about 135 lb/100 ft (6.6 kg/m ). This weight is

2 2

based on 60 lb/100 ft (2.9 kg/m ) for four plies of coal-tar saturated

2 2 organic felt and 75 lb/100 ft (3.7 kg/m ) for three layers of betweenply coal-tar pitch. The calculated weights of the between-ply coal-tar

pitch given in tables 4, 5 and 6 are considerably lower than the normally

2 2

expected 25 lb/100 ft (1.2 kg/m ). Since the weights of the membrane

samples were only somewhat less than the expected weights of properly

applied membranes, it is therefore assumed that some of the between-ply

coal-tar pitch was absorbed by the felts. This would account for the

relatively high weights of the membranes in comparison to the low weights

of the between-ply bitumen.

The tensile strengths, moduli of elongation, coefficients of

thermal expansion and thermal shock factors for the 47 membrane samples

are listed in tables 4, 5 and 6 and plotted in figures 1, 2, 3 and 4.

The tensile strengths, moduli of elongation and coefficients of thermal

expansion were determined by procedures outlined previously in Section 2.

Four tests of each of the 47 membrane samples were conducted to

determine these properties; two tests in the "machine" or longitudinal

direction of the felt and two tests in the "cross machine" or transverse

direction of the felt.

The thermal shock factor (TSF) for each specimen was calculated

from the following equation:

TSF _ Tensile Strength

(Coefficient of Expansion) x (Modulus of Elongation)

6
The ranges and average values of tensile strength, modulus of

elongation, coefficient of thermal expansion and thermal shock factor

are listed in table 7 and shown in figures 1, 2, 3 and 4. These values

are presented for both the "machine" and "cross machine" orientations of

the felts for membrane samples from each of the three sites. No attempt

was made to analyze statistically the data given in tables 4, 5 and 6.

The average values are presented as a convenience to the reader.

5 . COMPARISON OF MEMBRANE PROPERTIES WITH THE PRELIMINARY PERFORMANCE

CRITERIA

Values of tensile strength, modulus of elongation, coefficient of

thermal expansion and thermal shock factor can be compared with values

of laboratory prepared four-ply coal-tar membranes reported by Mathey

and Cullen [1] in their paper dealing with preliminary performance

criteria for bituminous membrane roofing. Their data for four-ply coaltar saturated organic felt membranes are presented in table 8 and noted

on figures 1, 2, 3 and 4 along with the corresponding suggested preliminary performance criteria for bituminous roofing membranes.

It can be seen from figure 1 that the average values of tensile

strength of the old membranes tested in this study were less than values

reported by Mathey and Cullen [1], Figure 3 indicates that the average

values of the coefficient of thermal expansion of the old membrane

specimens were in general agreement with those determined from new

specimens

.

The strength of the membranes appeared to reflect the quality of

maintenance that they had received. Membranes at site A were better

maintained than those at sites B and C. Membranes at site B were maintained better and were in better condition than those at site C. It can be seen from figure 1 that membranes from site A had the highest average

strength and those from site C had the lowest. This comparison of

membrane strengths assume that their initial properties were similar.

7
The values of load-strain modulus (modulus of elongation) for the

old membranes were in most cases considerably higher than values reported

for new membranes as readily seen in figure 2. As the membranes age

they tend to become brittle, their ability to elongate under tensile

stress is reduced.

The values of thermal shock factor varied considerably for the old

membranes but were, in general, low compared to those for the new membranes

as shown in figure 4. These low values are attributed to the old membranes'

inability to extend as much under tensile load which accounts for the

higher values of the load-strain modulus.

With one exception, the average values of the tensile strength and

coefficient of thermal expansion for the old membranes at all three

sites agreed with or met the suggested preliminary performance criteria

for bituminous membrane roofing [1], The average tensile strength at

site C was about 12 percent lower than the suggested value. The average

values of the thermal shock factor ranged from 32 to 40 percent of the

suggested performance criterion [1],

The types of laboratory tests and visual observations described in

this paper can be used as the basis for the evaluation of the condition

of old built-up roofing membranes. The data presented herein give an

insight into some of the properties of bituminous roofing membranes and

changes in these properties which may occur with aging. The data also

reflect the effect of different maintenance procedures on the properties

of built-up roofing membranes. Even though the membranes were over twenty years old, some of their properties were similar to those reported

for new coal-tar membrane roofing.

6 . ACKNOWLEDGMENT

The authors acknowledge the important contribution of Mr. Jessie C.

Hairston who performed the extensive laboratory tests.

8
7. REFERENCES

1. Mathey, Robert G. and Cullen, William C., Preliminary Performance

Criteria for Bituminous Membrane Roofing, National Bureau of

Standards, Building Science Series 55, November 1974.

2. Recommended Practice for Testing Load-Strain Properites of Roof

Membranes, ASTM Designation D 2523-70, Part 15, ASTM Annual Book of

Standards, 1976.

3. Proposed Test for Coefficient of Linear Thermal Expansion of

Roofing and Waterproofing Membranes, Part 15, ASTM Annual Book of

Standards, 1974.

4. Rossiter, Walter J. Jr. and Mathey, Robert G., The Viscosities

of Roofing Asphalts at Application Temperatures, National Bureau

of Standards, Building Science Series 92, December 1976.

9
Table 1. Properties of Membranes Determined by Visual Inspection (Site A)

Sample Appearance^/ Pliability^/

Number of

Plies

Ply

Adhesion

Between Ply , Bitumen Weight-^

lb/100 ft z kg/mz

A1 Excellent Brittle 4 Good 8 0.4

A2 Excellent Brittle 3 + iV Good 8 0.4

A3 Excellent Brittle 4 + 1 Fair 8 0.4

A4 Very good Brittle 4 Good 7 0.3

A5 Very good Brittle 4 Good 5 0.2

A6 Excellent Brittle 4 Good 8 0.4

A7 Excellent Flexible 3 + 1 Good 33 1.6

A8 Excellent Very brittle 3 + 1 Good 8 0.4

A9 Very good Brittle 3 + 2 Good 9 0.4

A10 Excellent Brittle 3 + 1 Good 10 0.5

All Excellent Very brittle 3 + 1 Good 7 0.3

A12 Excellent Brittle 3 + 1 Good 8 0.4

A13 Excellent Brittle 3 + 1 Good 24 1.2

A14 Excellent Brittle 3 + 1 Fair 5 0.2

_V Visual examination prior to delamination.

JV Visual and manual examination at room temperature, 70°F (21°C)

.

_V Average value determined from measurements using a machinist's

microscope.

V Indicates phase application with 3 plies applied in shingle fashion

over one ply.

10
Table 2. Properties of Membranes Determined by Visual Inspection (Site B)

Sample Appearanc e—

Pliability^

Number of

Plies

Ply

Adhesion

Between Ply

Bitumen Weight!/

lb/100 ft z kg/m 2

Bl Fair Brittle 4 + i±! Good 9 0.4

B2 Good Brittle 4 + 1 Good 11 0.5

B3 Good Brittle 4 Good 6 0.3

B4 Fair Brittle 5 Good 7 0.3

B5 Fair Brittle 3 Good 6 0.3

B6 Fair Brittle 4 Good 5 0.2

B7 Fair Brittle 3 + 1 Good 14 0.7

B8 Good Brittle 5 Good 6 0.3

B9 Fair Brittle 4 Good 7 0.3

BIO Excellent Brittle 4 Good 8 0.4

Bll Poor Brittle 4 Good 6 0.3

B12 Good Brittle 5 Fair 6 0.3

B13 Good Brittle 4 Good 5 0.2

B14 Good Brittle 4 Fair 6 0.3

B15 Fair Brittle 4 Good 7 0.3

B16 Fair Brittle 4 Good 7 0.3

B17 Good Brittle 4 Good 6 0.3

B18 Good Brittle 4 Good 5 0.2

B19 Good Brittle 5 Good 14 0.7

B20 Excellent Brittle 4 Good 6 0.3

_// Visual examination prior to delamination.

_£/ Visual and manual examination at room temperature, 70°F (21°C).

2/ Average value determined from measurements using a machinist's

microscope.

2/ Indicates phase application with 4 plies applied in shingle fashion

over 2 plies which were applied shingle fashion.

11
Table 3. Properties of Membranes Determined by Visual Inspection (Site C)

Sample Appearance^ Pliability^/

Number of

Plies

Ply

Adhesion

Between Ply . Bitumen Weight-^-

lb/100 ft* kg/m*

Cl Fair Brittle 4 Good 7 0.3

C2 Fair Very brittle 4 Fair 5 0.2

C3 Fair Very brittle 4 Good 6 0.3

C4 Good Very brittle 4 Good 8 0.4

C5 Good Very brittle 4 Good 6 0.3

C6 Fair Very brittle 4 Good 6 0.3

C7 Good Very brittle 4 Fair 6 0.3

C8 Very poor Very brittle 4 Fair 6 0.3

C9 Very poor Very brittle 4 Good 5 0.2

CIO Fair Very brittle 4 Good 5 0.2

Cll Very poor Very brittle 4 Good 6 0.3

C12 Poor Very brittle 4 Good 7 0.3

C13 Poor Very brittle 4 Good 6 0.3

}_/ Visual examination prior to delamination.

£/ Visual and manual examination at room temperature, 70°F (21°C).

V Average value determined from measurements using a machinist's

microscope.

12
Table

4.

Mechanical

and

Physical

Properties

of

Membranes

(Site

4)-

13
Table

4.

Mechanical

and

Physical

Properties

of

Membranes

(Site

A)^-

(cont.

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<u>

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14
Table

5.

Mechanical

and

Physical

Properties

of

Membranes

(Site

B)

15
Table

5.

Mechanical

and

Physical

Properties

of

Membranes

(Site

B)-^

(cont.

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16
Table

6.

Mechanical

and

Physical

Properties

of

Membranes

(Site

C)

17
Table

6.

Mechanical

and

Physical

Properties

of

Membranes

(Site

C)-^

vcont.)

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Q)C

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18
Table

7.

Ranges

and

Average

Values

of

the

Membrane

Properties

for

the

Three

Sites

CJ> o<-m

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t—i I

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values

and

they

cannot

be

calculated

from

other

values

given

in

this

table.
Table

8.

Average

Property

Values

of

Four-Ply

Coal-Tar

Membranes

and

Suggested

Preliminary

Performance

Criteria

for

Bituminous

Membrane

Roofing,

as

Reported

by

Mathey

and

Cullen

mm

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22

Figure

3.

Coefficients

of

thermal

expansion

Figure

4.

Thermal

shock

factors

for

the

for

the

membrane

specimens

at

membrane

specimens

at

the

three

sites.

three

sites.
NBS-1 14A (REV. 7-73)

U.S. DEPT. OF COMM. BIBLIOGRAPHIC DATA

SHEET

1. PUBLICATION OR REPORT NO.

NBSIR 77-1256

2. Gov’t Accession

No.

3. Recipient’s Accession No.

4. TITLE AND SUBTITLE

Properties of 21 Year Old Coal-Tar Pitch Roofing Membranes:

A Comparison with the NBS Preliminary Performance Criteria

5. Publication Date June 1977

6. Performing Organization Code

7. AUTHOR(S)

Robert G. Mathey and Walter J. Rossiter, Jr,

8. Performing Organ. Report No.

9. PERFORMING ORGANIZATION NAME AND ADDRESS

NATIONAL BUREAU OF STANDARDS

DEPARTMENT OF COMMERCE

WASHINGTON, D.C. 20234

10. Project/Task/Work Unit No.

11. Contract /Grant No.

12. Sponsoring Organization Name and Complete Address (Street, City, State, ZIP)

Same as 9 above.

13. Type of Report & Period Covered

14. Sponsoring Agency Code

15. SUPPLEMENTARY NOTES

16. ABSTRACT (A 200-word or less factual summary of most significant information. If document includes a significant

bibliography or literature survey, mention it here.) The properties of coal-tar pitdh roof membranes approximately 21 years old were

compared to the properties reported for such membranes in NBS Building Science Series

55, "Preliminary Performance Criteria for Bituminous Membrane Roofing." Samples of the

old membranes were taken from eight buildings having roof areas that range from 0.5 to

1.5 million square feet (4.6 to 15 km^). The buildings were located at three sites

in or near the state of Kentucky. The roof membranes on these buildings had been

subjected to different maintenance procedures.

Laboratory tests conducted on 47 membrane samples included tensile strength, modulus

of elongation and coefficient of expansion. The thermal shock factor was calculated

for each sample. Laboratory observations were made of the membrane samples to determine

between-ply bitumen thickness, weight per unit area, ply adhesion, pliability and

condition of the membrane.

The tensile strengths of the membranes determined at 0°F (-18°C) in their longitudinal

and transverse directions were comparable to values reported in NBS Building Science

Series 55. Values of the coefficient of expansion measured over the temperature range

of 0 to -30°F (-18 to -34°C) were also comparable to thos reported in NBS Building

Science Series 55. The modulus of elongation was considerably higher for the old

membrane samples which resulted in lower values of thermal shock factor. The lower

values of extensibility of the old membranes were attributed to their brittleness causec b? aging. !he ?ype aid

yf?equency of roof maintenance procedures was considered to have

hid I dffinUe effect on the properties of these old roof membranes.

17. KEY WORDS (six to twelve entries; alphabetical order; capitalize o/lTy'SSfc first letter of the first key word unless a proper name; separated by semicolons

)

Bituminous roof membranes; built-up roof membranes; coal-tar pitch; performance

criteria; physical and engineering properties; test methods.

18. AVAILABILITY ^Unlimited 19. SECURITY C 1 ASS 21. NO. OF PAGES

( I'M IS REPORT)

25

1 For Official Distribution. Do Not Release to NT1S

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