Unusual deterioration of bituminous roofing materials under high humidity

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Unusual deterioration of bituminous roofing materials under high

humidity

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C A N A D A

I I

I -L Ser I

I

B92 c. 2

UNUSUAL

DETERIORATION

OF

BITUMINOUS ROOFING

MATERIALS U N D E R HIGH HUMIDITY

7 ; :q.-?c

. " & > - -

(3)

UNUSUAL

DETERIORATION OF

BITUMINOUS ROOFING

MATERIAhS UNDER HIGH HUMIDITY

Samples of several bituminous roofing materials s e l e c t e d f o r

examination as part of a roofing research program w e r e left exposed t o

controlled high humidity conditions for approximately one yeas. A

difference in relative humidity w a s maintained acr'oss the samples, one

s i d e being held at nearly 100 per cent. When the samples w e r e removed

from the permeability t e s t cups, and it became possible to examine both

s i d e s of the specimens, it was noticed that unusual deterioration of the bituminous coating on the s i d e with the higher humidity had occurred.

N o

explanation can be given for these results, but as they may be of considerable relevance to a better understanding of roofing performance,

they a r e now described in same detail,

EXPOSURE

Seven different types of roofing materials (described in Table

I)

w e r e prepared for water vapaur transmission t e s t s in accordance w i t h

ASTM Specification

E96

-637,

P r a c edur e B. The permeability of the

roofing materials is determined by measuring the amount of water vapour

that passes through a sample w h e n the conditions are maintained at 100

per cent RH at 73°F on one s i d e and 50 per cent

RH

at 7 3 ° F - o n the other.

As

shown in Figure I , the specimen under t e s t is sealed in

a

metal cup

into which 50 gm of d i s t i l l e d w a t e r is introduced. Care i s taken to en-

sure that the specimen never comes in direct contact with the w a t e r : a

minimum 3/8-in. gap i s maintained between the water surface and the

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perrneance determined from the rate of weight loss caused by the water

vapoux passing through the sample. Four samples from each material

w e r e t e s t e d and the results averaged. The initial average membrane

thickness, exposure time, and water vapour permeance of the t e s t m a - terials a r e reported in Table

IZ.

No

visual examination of t h e underface

of the membranes was possible at this time, as the t e s t specimens w e r e

left intact for further exposure,

On

completion of the permeability t e s t , the samples w e r e left exposed o u t s i d e the cup to new controlled conditions of 9 0 per cent RKI

and 100" F, where they r ernained undisturbed f o r an 1'1 -month period,

At the end of this second p e r i o d of exposure, it was noted that

the w a x seals on 14 of the original 28 t e s t cells had f a i l e d . These w e r e

discarded and are not given further consideration in this note. T h e r e

-

mainder of t h e membranes were carefully separated from the cup w h e n

it w a s noted that unusual deterioration of the under -surface had occurred.

The weight of each wet sample was immediately determined, After a

3 -day period at room temperature, during which t i m e photagraphs and

d e t a i l e d visual observations w e r e taken, the samples w e r e inserted in a desiccator under vacuum and d r i e d t o constant weight. Table LII gives

the final percentage rnoistur e content by weight.

Figures 3 t o

9

show one of the exposed underfaces

of

each material

a l o n g s i d e an unexposed portion. A visual examination of these exposed

surfaces w a s also c a r r i e d out with the aid of 12-power stereo magnifi- cation. T o a v o i d ambiguity, the u s e of the terms "concave, convex,

upper surface and under face1' is illustrated in Figure 2. These obs er

-

vations w e r e as follows.

Sample

No. VB

-1 -65 { F i g u r e 3)

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average diameter of 1/16 in. These craters apparently resulted from

the bursting of small bitumen blisters. Very little bitumen remained

over the reinforcing material at the bottom of these areas. Several

mushroom-like colnrnns of bitumen extended from the underface of t h e

sample to the bottom of

the

cup. The sample had deformed to concavity

and had

a

spongy appearance; it exuded considerable water when pressed gently w i t h a probe.

(Figure 4)

This underface w a s covered entirely with blister craters, aver-

aging from 1/16 in. to 1/8 in. in diameter, These craters were f i l l e d

w i t h water which supported a v e r y thin brittle film, slightly brown in

colour. Mounds of bitumen were scattered over the exposed surface.

The sample w a s slightly convex and quite resilient.

No.

VI3 -4-65 (Figure 5 )

As in the previous samples, blister craters covered the under

-

face of this sample and their diameters ranged in s i z e f r o m approxi- mately 1/32 in. ta a maximum of 1/8 in. The depth 02 these craters w a s such that very little of the bituminous coating remained over the

reinforcing material at the bottom

of

these areas. This sample had be

-

corn e concave and a large amount of the bituminous coating had flowed

to the centre of the specimen.

No.

VB

-5

-45

(Figure

6 )

T h e most notable effect of exposure on this sample w a s the

creation of small water - f i l l e d blisters which covered the entire under

-

face. A considerable number of craters, such as d e s c r i b e d for sample

No. VB-4-65, w e r e also scattered over the exposed surface. The m a -

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No. VB-6-65

(Figure 71

This specimen suffered none of the previously mentioned effects

other than becoming convex in shape. It did change colour from black to

a

medium shade of brown.

No.

VB

-7 - 6 5 [Figure 8 )

The underface of this sample w a s covered with small blister craters with an average diameter

of

1/16 in. The specimen had also

become convex.

No,

VB-12-65

(Figure

9)

This under face was covered with very small blister craters

and had become slightly convex in shape.

SUMMARY

Results

of

the w a t e r vapour transmission t e s t s indicate that

t w o of the seven experimental roofing materials h a d permeance values

of 0. 14 and 0. 31, while the remainder w e r e considered impermeable

(Table 11).

Two samples,

VB

-4-65 and

VB

-6-65, showed a high percentage moisture content by weight on removal f r o m an atmosphere of 9 0 per

cent RH

and

100°F. T h e s e w e r e also two of the thinnest sam.ples em-

ployed. 'LE3 -4-65, the one -ply asphalt -mopped jute -r einforced h a f t paper sample, (asphalt softening point of 140"

F)

showed m a r k e d de

-

terioration, while

VB

-6 -65, a base -sheet, manufactured without an asphalt surface mopping, showed no apparent degradation other than colour change when subjected to the same exposure.

Sample

V 3

-I-65, a two-ply felt mopped with a low softening

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material, the thickest of those subjected to test,

had a

relatively high

percentage moisture content after exposure.

Roofing sample

No.

V B - 2 - 6 5 used as the bituminous material

a coal-tar pitch with a softening point in the range of 140 to 155" F.

This specimen, the heaviest in weight, had an average thickness of

- 1 6 3 in. and, on completion of t e s t , showed a similar substantial in-

crease in moisture content to sample

VB-1-65.

Its characteristics

w e r e also quite similar to sample VB-1-45.

The two asphalt -coated base sheets [ V B - 7 - 6 5 and

VB-12-65),

which w e r e given relatively light coatings of asphalt with softening

points of 140°F, accumulated relatively little m o i s t u r e and can be con- s i d e r e d impermeable. While some deterioration w a s present in the

form of very small blisters, it

is

considered to be

of

a minor nature.

CONCLUSION

These effects were quite unexpected and had

not

previously

been observed under laboratory conditions. N a explanation of the

cause can be offered at this time.

The pos sibility that expas ur e conditions in practic e, particularly

in flat roofs, may approximate those used here makes them of con-

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TABLE

I

Description of Roofing IMaterials

V B -1 - 6 5 Two -ply, 15 -1b perforated asphalt f e l t , m o p p e d

w i t h I. 40 "

F

softening paint asphalt ( 3 moppings

of 20 Pb p e r sq. ft). Figure 3

VB

- 2 - 6 5 Two-ply, 15-lb tarred f e l t , mopped with pitch

( 3 moppings of 2 5 lb per 100 sq, f t ) . Figure 4

V B -4-65 _{One-ply, j u t e - r e i n f o r c e d kraft paper,}mopped

both s i d e s with asphalt ( 2 rnoppings of 2 0 Ib

each p e r 100 sq. f t ) .

VB

-5

-65

One-ply, 3 3 - l b base sheet, mopped both s i d e s

with asphalt ( 2 moppings of 20 lb each p e r 1 0 0

sq. f t ) .

VB

-6

-65 One -ply, 45 -lb base sheet without surface

m opping.

Figure 5

Figure 6

F i g u r e 7 VB -7 - 6 5 O n e - p l y , 45 -1b. base s h e e t mopped both s i d e s

w i t h asphalt ( 2 rnoppings of 20 Ib each per 100

sq. i t ) . F i g u r e 8

VE

-1 2 - 6 5 One-ply, 33 - I b s e l f - s e a l base sheet, 1 coat

1 4 0 " F softening point asphalt on tap s i d e of

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T A B L E fI

R e s u l t s of Water Vapour Transmission Tests with

Exposure to 50 percent RH and 7 3 " F

Initial

aver age ~ t / u n i t area Exposure t i m e

thickness, in 1bs/100 in hr 50 p e r cent RH

Sample No. in. sq. ft 73" F Permeance Remarks

VB -1 -65

.

172 81. 4 YB - 2-65 . I 6 3 91. 8 V B - 4 - 6 5 . Q 8 9 39. 3 VB -5-65 , 1 3 1 65.0 VB -6-65

.

070 3 9 . 0 VB-T -65

.

126 6 6 . 7 VB -1 2 -65 .088 45, 4 Nil Impermeable Nil h p erm e a b k .Q14 N i l Impermeable -031 M i l Impermeable Nil h p e r m eable

The p e r m e a n c e is calculated as:

(10)

T A B L E III

Percentage Moisture Content After dry in^

Percentage moisture

Satr~plc No. content by weight

Wn. 2 No. 5 VB - 2 - 6 5 No. 1 No. 2 V B - 4 -65 No. 1 No. 2 V B -5 -65 No. 1 No. 2 VB -6 -65 No. I

(11)

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