A Study of the Variables Involved in

The Saturating of Roofing Felts

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UNITED STATES DEPARTMENT OF COMMERCE • Maurice H. Stans, Secretary

NATIONAL BUREAU OF STANDARDS • A. V. Astin, Director

A Study of the Variables Involved in the

Saturating of Roofing Felts

Sidney H. Greenfeld

Research Associate

Asphalt Roofing Manufacturers Association*

*( Formerly Asphalt Roofing Industry Bureau)

Building Research Division

Institute for Applied Technology

National Bureau of Standards

Washington, D.C. 20234

Building Science Series 19

Nat. Bur. Stand. (U.S.), Bldg. Sci. Ser. 19, 18 pages (June 1969)

CODEN: BSSNB

Issued June 1969

For sale by the Superintendent of Documents U.S. Government Printing Office Washington, D.C. 20402 - Price 30 cents
NATIONAL BUREAU OF STANDARDS

3£P 2 1 1970

TA ^ir

No. I'?

Contents

Page

1. Introduction 1

2. Materials 2

2.1. Felts-_- 2

2.2. Saturants 2

3. Apparatus 3

4. Procedures 4

5. Results and discussion 4

5.1. Contact times 4

5.2. Moisture and temperature 5

5.3. Spacers on press rolls 7

5.4. Pressure 9

5.5. Moisture absorption 11

5.6. Air permeability 15

6. Conclusions 15

7. References 16

8. Glossary 16

II
A Study of the Variables Involved in the Saturating of

Roofing Felts

Sidney H. Greenfeld

The degree of saturation of a #27 ^ felt with a typical roll saturant and a #55 felt with roll, mixed, and shingle saturants varied with saturation time and pressure, saturant temperature and viscosity, felt conditions, and press roll pressure and clearance. Optimum

temperature and viscosity ranges were determined for each asphalt-felt combination. Both

pressure and vacuum increased the completeness of saturation under optimum conditions, but frequently shortened the working temperature range in which optimum saturation could be produced. Rate and degree of moisture and liquid water absorption decreased with increasing

saturation. Air permeability decreased with increasing saturation. The consequences of some of these findings are discussed. Key words : Asphalts, felts, moisture, absorption, roofing, saturation.

1. Introduction

The function of a roofing felt is to supply a strong backing for a weather-resistant asphalt

coating. When used in the manufacture of pre- pared roofing, the felt permits the product to be

cut into appropriate designs, packaged, handled,

and applied without distortion. Wlien used in

built-up roofing, it serves to isolate the several

layers of waterproofing and provides the strength

necessary for large areas of roofing to cope with

the environmental stresses to which the roof

membrane is subjected.

In order for the felts to function properly over

a period of time, they must be protected both

externally and internally, for the felts themselves

are vulnerable to the weather.

The internal protection is provided by a light

bituminous saturant applied through a series of

dips, or sprays and dips, as described by Abraham [1] ^ and Krchma [2]. The external protection is provided by the coating applied to both

the weather side and back of the roofing. This

coating will not be discussed.

Complete saturation is very difficult to achieve

commercially, for modern roofing machines operate at 250 to 500 lineal feet ^ per minute and fre- c^uently allow times of less than 1 min for saturation to occur. During this time, the felt, usually at room temperature with 5 to 7 percent moisture,

must be heated to the saturant temperature, dried,

and saturated. The final stages of saturation

actually occur beyond the saturant baths, where

the liquid saturant on the felt surfaces is drawn

into the felt as the felt cools. The saturant in the vicinity of the felt is cooled

as the felt is heated and the moisture evaporated.

Thus, its increased viscosity at this lower temperature tends to slow the penetration of the saturant

into the felt. This cooling effect also makes it

1 Please see the glossary for definitions of unfamiliar terms or words used in this publication.

^ Figures in bracltets indicate the literature references on

page 16.

' One foot equals approximately 0.3 meter.

II

possible for the felt to carry more saturant with

it from the saturator. (A typical saturator running

at 400 ft per min would saturate 12 squares of

felt per minute. At 6 percent moisture content,

about 15,000 Btu* per minute would be required

to heat the felt and evaporate the moisture. This

quantity of heat, if supplied entirely by the satu- rant used in saturating those 12 squares of felt, would lower the saturant temperature about

135 °F (57 °C). In practice, there is agitation in

the saturator and heat is supplied by saturant

other than that which actually enters the felt; however, all of this heat must be furnished by

heating the saturant to temperatures in excess of

that desired.) Tlius, optimum conditions must be

found for particular felt-saturant systems.

While, in principle, it is desirable to protect

the felt by saturating it as completely as possible,

poor adhesion of coating to felt in shingles and

roll roofijig may result if a large excess of satu- rant is permitted to remain on the felt surface.

Incompatibility and coating slippage problems

(through thinning of the coating by the excess saturant ) are aggravated by this condition. In the

case of saturated felts, sticking in storage under

over-saturated conditions is possible. Thus, when

specifications are written, compromise saturations

are required.

In asphalt shingles 170 percent saturation (saturant weighing 1.70 times as much as dry felt) is the minimum permitted. For roll roofing this minimum is dropped to 160 percent, and for saturated

felt it is dropped further to 140 percent. These

figures ai-e the compromises made to accommodate

production, storage, and application requirements.

Theoretically, completely impregnated felt can hold more than 235 percent ^ of its weight in satu-

* One Btu equals approximately 1.05 X 10« joules. _ 5 Calculated on the assumption that the felt is cellulose with

a specific gravity of 1.53 [3], the ratio of space to cellulose in felt

is 2 35. If felt "is assume<l to be similar to cotton linters. true density values of 1.55-1.61 would have to be used [4] and a somewhat higher theoretical porosity obtained.

1
rant. Asphalt capacities of about 210 percent by

the vacuum method and 195 percent by the buret

method* may be more realistic values to try to attain commercially.

Contemporary commercial saturating techniques

produce felts meeting the specifications and ex- ceeding them only by small margins. Improved

techniques could lead to tighter specifications and

better internally protected felts. Based on these considerations, a study was un- dertaken to investigate the felt-saturating process and determine the effects of temperature, pressure, moisture, time, and saturant on the saturation of

organic felts.

2. Materials

2.1. Felts

Two grades of commercial felt were used. These

were taken from the normal production of a major

felt manufacturer and slit into 12-in ^ rolls for this

project. These felts had the characteristics reported

in table 1. Table 1. Felt characteristics "

Grade number 27 55 Dry weight, lb/480 ft^ 27 53

Caliper, mils (mm). 33 (0. 84) 64 (1. 63)

Tensile strength, machine

direction (Scott) lb/in« 31 40

Tensile strength, cross direc- tion (Scott)d, lb/in 15 •> 21 b Densometer, seconds/400 cm'_ 18 (16. 2)'' 18 (18.3)'' Asphalt capacity 183 (177)b 197 " (187)b

Moisture (as received),

percent _ . 4. 1 4. 1

" Manufacturer's data. Determined at NBS.

"= These numbers are based on a specific gravity of 1.035 for the saturant. When converted for a saturant of

specific gravity of unity, as used in this program, these

figures become 177 (#27 felt) and 190 (#55 felt). Scott Tester—speed 12 in/min.

"One pound = approx 0. 45 kg.

The furnish of the felt was not supplied; the

ratios of wood fibers, rags, and papers were continually being adjusted during production to keep

the felt properties uniform. The furnish contained

oak and pine fibers, along with No. 1 waste paper

and rags.

2.2. Saturants

Two saturants were obtained from a Kansas

refinery. These consisted of a soft, roll saturant and a hard, shingle saturant. These two were

blended to produce a third satvirant, tenned a "mixed" saturant. The properties of these three

materials are listed in table 2. The viscosity-temperature relations (determined with a Brookfield

Viscometer) are presented in figure 1. The selection

of ordinates has been found useful in characterizing the saturants since a straight-line relationship

is thus obtained. No theoretical significance can

be attached, for the fahrenheit scale of temperature is completely arbitrary in nature.

« Vacuum Method ASTM D 727 Buret Method ARIB No. 2.125 One inch = 2.54 cm.

Table 2. Properties of saturants

Saturant

Softening point, °F (°C)_

Penetration at 77 °F,

yio mm

Penetration at 32 °F, Mo mm

Specific gravity,

°F

Flash'point" Ic'd'c'.), °F (°C) Loss on heating, 5 hr at 325 °F, percent

Solubility in CCI4, per- cent

Roll

111 (44)

139

0. 9954

630 (332)

0

99. 4

Shingle

141 (61)

48

18

1. 0002

625 (329)

0

99. 4

Mixed

125 (52) j 81

23

f

625 (329) i 0 !

99. 4

10,000

1000

-T 100.0

1.0

n

1 1 1—I

1

VISCOSITY OF SATURANTS

VISCOSITY vs

1/ TEMPERATURE

SATURANT S P PEN. © 77 "F

ROLL

MIXED

SHINGLE

_L_L

III 125

141

l/io mm

139

8148

I / T, "F

Figure 1. Viscosity of saturants. The mixed saturant was obtained by blending the shingle and

roll saturants to produce a saturant with properties approximately mid-way between the two.

4
3. Apparatus

Three apparatuses were used in this study. For

all specimens saturated at atmospheric pressure,

the apparatus shown in figure 2 was used. For those

saturated under vacuum or pressure, the apparatuses in figures 3 and 4, respectively, were used.

The apparatus used for saturating at atmospheric pressure consisted of a stainless-steel sat- urant pan 7 in X 9 in X 2 in and press rolls. The

pan was heated on a thermostatically controlled

hot plate capable of temperatures up to 600 °F

(316 °C). Once the specimens were saturated, they

I were passed through the heated, manually operated

rolls shown to the left in figure 2. These rolls were

I provided with pressure adjustments to permit presI sures resulting from the weight of the roll and

lj higher. For most of the saturations, the weight of

the upper roll was the sole source of pressure. However, in one series of saturations, spacers consisting of multiple layers of 5-mil thick aluminum

d tape were used to permit controlled excesses of

jj saturant to be carried on the felt. A thermostatijj cally controlled air oven was used to maintain the

j saturated specimens at elevated temperatures

(250° or 350 °F) (121° or 177 °C) for a period of

I

I time to simulate the soaking-in period between

1

1 saturation and coating in commercial operation. A

jj similar oven, maintained at 225 °F (107 °C),

! was used to dry the felt prior to saturation (when

]: desired)

.

Figure 2. Saturator used for all atmospheric pressure

saturations.

Whereas 6- X 8-in felt specimens were saturated

at atmospheric pressure, under both vacuum and

elevated pressures, smaller specimens, 1- x 2.5-in, were used. The saturator (fig. 3) in the vacuum

studies Avas a 32- x 200-mm test tube heated in an aluminum block furnace. Vacuum was applied by

a water aspirator and measured with a mercury

manometer. The same furnace was used to heat a

brass pressure vessel for the above-atmospheric

pressure saturations, as shown in figure 4. Dry ni- trogen was used to produce the pressure.

Figure 3. Saturator used for saturations at pressures below atmospheric pressure.

Figure 4. Saturator used for saturations at pressures above atmospheric pressure.
4. Procedures

The procedures followed while saturating felts at ambient pressure, under vacuum and at aboveatmospheric pressure were different and, therefore,

will be described separately. Every day, while the

saturant was being heated, moisture determinations were made on two representative samples of

felt. It was found that both the #27 and #55

felts required at least 45 min in an oven at 225 °F

(107 °'C) to be dried to constant weight. Therefore,

the felts were heated in the oven for 1 hr and

weighed immediately, for even in a desiccator the

felts were found to absorb moisture. The average

of two moisture determinations was used in

calculating the percent saturation of the felts. When the saturant in the pan had reached the

desired temperature and the pressure rolls were at 240±10 °F (116±6 °C), a 6- X 8-in piece of felt was floated on the saturant for IV^ min, submerged

for 2 min. passed once through the rolls, hung in the "soakmg-in" oven at 250 °F (121 °C) for 5 min, and then weighed. This procedure was arbitrarily adopted because it required about II/2 ini^i for the saturant to penetrate through the floating

felt at 400 °F (204 °C) and it required about 2 min

of complete submergence for the bubbling of gases

and vapors from the felt to stop. Later in the work

it was found that, with the 2-min-submergence

time, saturation was independent of float time and,

therefore, the float time was eliminated. It was also

found that the "soaking-in" period for the commercial processes was more nearly 350 °F (177 °C)

than the 250 °F (121 °C) being used in these sat- urations. The higher temperature seemed to reduce

the number of felts rejected for "wetness" of their

surfaces, but had no effect on the quantity of sat- urant remaining in the acceptable felts. Thus the

saturation figures reported were not influenced

appreciably when this temperature change was

made.

In the vacuum series of saturations, the saturant was heated in the test tube as shown in figure 3. The felt was placed in the test tube above the sat- urant with the furnace inclined about 30°. The

tube was evacuated. The furnace was rotated to a

vertical position to permit the felt to submerge in the saturant. After the periods of time of submergence reported, the vacuum was broken, the specimen passed once through the rolls in the atmospheric-pressure apparatus, and soaked in the oven

for 5 min at 250 °F (121 °C) . Any excess saturant on the edges of these specimens was wiped off prior to final weighing, for this material was not part of the true saturation of the felt. When saturating under pressure, the 1- X 2.5-in specimen was dropped directly into the saturant when the latter was at the desired temperature. The

cover was fastened in place and the pressure raised

rapidly to the desired level. After the desired time

had elapsed, the pressure was released, the specimen passed through the heated rolls of the ap- paratus in figure 2, and hung in the oven for 5 min

at 350 °F (177 °C). Excess saturant was wiped

from the edges immediately prior to weighing.

In all instances, the reported value for each con- dition is the average of five specimens.

5. Results and Discussion

The saturating of organic felts is affected by

many variables. Those involved in the furnish and

production of the felt, or in the production of

saturants, will not be considered; those relating

to the saturating process, that is the conditions of

the felt and saturant at the time of contact and

their interactions during contact, will be discussed.

5.1. Contact Times

Large volumes of inert gases and vapors are

released from organic felts when contacted with

hot saturants. These expand and escape from the

felt as the saturant penetrates and saturates it. There is obviously a conflict between these processes during saturation. A number of methods

have been devised to cope with this problem. The

most common procedure has been wetting the felt from one side, either by spraying hot saturant on

it or by bringing the saturant into contact with

one side only, and permitting the gases and volatiles to escape from the other side. This approach was simulated by floating the felt on the asphalt saturant surface prior to complete immersion. In

figure 5 are the results of various times of floating

prior to complete submersion for 1 or 2 minutes

and various times of submersion with no float time

for both the #27 and #55 felts. For the #27 felt, which is only about 30 mils thick, the method of

processing had only a very limited effect on the

degree of saturation; the percent saturation was

essentially independent of the procedure. There is, however, a small, but consistent decrease in satura- tion with longer periods of exposure of the felts to the high temperature of the saturants. It is quite apparent that contact times between the

#27 felt and saturants of more than a quarterminute are adequate to produce saturations in excess of that required by current specifications

(140 percent minimum).

Saturation of the #55 felt, on the other hand, was sensitive to the means by which the felt was

saturated. When the felts were submerged with- . out previous floating, the saturation increased

progressively with time of submersion up to about

2 min ; however, beyond about li/^ min, saturation was essentially indeiaendent of submersion time.

When float time was followed by 2 min of submer-
sion, the shorter float times produced the highest

saturations. However, the results were essentially constant after 1 min of float time. Long submersion times were detrimental to the percent satura190

180

170

^ 160

=>< ISO

(Oh

z

UJO 140

IThi

0-

130 -

120

EFFECT OF IMMERSION

TIME ON SATURATION

SATURATION TEMPERATURE 400"'F 6-7% MOISTURE IN FELTS

No Float Variable Floot

Vorloble Submersion IMIn Sub 2 MIn Sub Fait Saturant • 0 27 Roll A 56 Shingle_L

0 I 2 TIME, MINUTES

i'lGURE 5. Effect of immersion time on saturation.

Because of its greater thickness, the #55 felt had saturating

characteristics different from the #27 felt.

tion. Based on these results, floating was eliminated

aiid 2 min of submersion became the standard

practice. This practice produced saturations of

about 170 percent for the #55 felt and 150 percent

for the #27 felt at 400 °F (204 °C) ; both would

meet current specifications.

5.2. Moisture and Temperature

The roofing manufacturer usually has little control over the moisture content of the dry felt, for it varies widely with the relative humidity of

the atmosphere in which the felt is stored. The

data presented in figure 6 show how rapidly the

felts absorb moisture from the atmosphere when

exposed to relative humidities in the range of

30 to 75 percent. At higher relative humidities,

the moisture content of the felts increases rapidly.

At room temperature and 78 percent relative

bumidity (saturated sodium hyposulfite solution),

the equilibrium moisture content of these felts was

about 12 percent ^ and in a saturated atmosphere

it was between 32 and 33 percent.

During the saturating process the moisture in

the felt must be eliminated. In the process of being

volatized, it absorbs large quantities of heat. As

this moisture escapes, it slows the penetration of

the saturant into the felt. However, moisture in

the felt serves two beneficial purposes. Felts with

moisture contents below about 3 percent are very

brittle. They frequently tear in the commercial

8 Moisture content is expressed on an "oven dry" basis rather than an "as received" basis.

O

Od

UJQ.a

UJm

cro

(/) CO<

UJ

CEz>

Icoo

MOISTURE ABSORPTION

DRY FELT

50% RH *27

#55

30 40 50

TIME, MINUTES

60

Figure 6. Moisture atsorption of dry felt. Dry felt, unprotected by saturant or coating, absorbs moisture very rapidly.

20 HR » 55 FELT % RH WT %

30 4.38 50 6.08 75 9.40

4» 27 FELT %RH % WT. 50 6.52

70 80

5
saturating process and require patching or re- threading of the machine. Thus, for continuous operation a minimum of 3 percent moisture is desirable. Moisture tends to kibricate the fibers or

fiber bundles to permit their movement over each

other and swells the fibers to permit the saturant

to penetrate more easily. However, when the moisture content is too high, the felts again become

weak and breaks occur. In order for relative humidity changes to affect

felts rapidly, there must be intimate contact between the atmosphere and the felts. Because felts are stored in large rolls, only their edges are af- fected by short-term changes in relative humidity.

(Some edge curling might be attributed to this

effect). The interior of the roUs of felt remains

essentially as they were when rolled, except after

long-term storage under extreme humidity

conditions.

The temperature of the saturant is more readily

controllable than is the moisture content of the

felts. Through heating the saturant and agitating

it in the saturators, fairly good temperature control can be attained. The data presented in figure 7

are of the variation in the saturant content of the

#27 felt with the viscosity of the saturant for three

conditions of the dry felt. There was little differ- ence between felt that was oven dry and cooled to room temperature in a desiccator and that which was saturated as it was removed from the drying

oven. However, the felt with 7 percent moisture

absorbed 3 to 7 percent more saturant in the normal saturating range. At the lowest temperatures

at which saturation was successful with these materials, the moisture content was relatively unimportant, for a heavy film of saturant remained on the surface of the felt and soaked in during the period in the oven. At the higher temperatures,

the saturant was very fluid and had a larger spe-

:

cific volume than at room temperature; the felt! could not carry enough saturant to meet specifica-

;

tions at temperatures above 400 °F (205 °C) with;

7 percent moisture or above 350-375 °F (177-190

°C) when initially dry.

For the #55 felt (fig. 8), some moisture wasi

necessary to permit sufficient saturation with the

shingle saturant to meet the ASTM specification

of 170 percent (ASTM D 225-65). Both dry felts, cold or warm, could not be; saturated beyond 165

percent. In addition, the saturant did not penetrate well at temperatures below 325 °F (163 °C)

(viscosity of about 180 cps) when dry felt was

used. With 7 percent moisture, good penetration was found down to 300 °F (149 °C). At the higher

temperatures, again, saturation was reduced rapidly with increasing temperature. In the range

above 400 °F (204 °C) the felt with 4 percent mois- ture saturated like the dry felt ; as the temperature was reduced below 400 °F (204 °C), at the point

tested, it behaved more like the felt with 7 percent!

moisture.

A few specimens of felt were exposed to high

humidities, and moisture contents of 12 and 32 per-

!

cent were achieved. At 12 percent moisture, the

220

200

<

UJo

a:

iLi a.

180

160

120,

EFFECT OF TEMPERATURE

AND MOISTURE ON SATURATION * 27 FELT ROLL SATURANT

O- 7% MOISTURE IN FELT

• - DRY AND WARM FELT

- DRY AND COOL FELT

300

350 'F 300 "F VISCOSITY, CPS

Figure 7. Effect of temperature and moisture on saturation—#27 felt mth roll saturant. A small amount of moisture in the felt seems to Improve the felt s saturating characteristics.
220

200

<

^ 180

H

<

liJ o

UJ

a.

160

140

120,

I

^

I \ EFFECT OF TEMPERATURE

AND MOISTURE ON SATURATION

tt 55 FELT

SHINGLE SATURANT

0-7 7o MOISTURE IN FELT

• -DRY AND WARM FELT -DRY AND COOL FELT A- 4% MOISTURE IN FELT

J L 200 300

I 300 "F

0

I

I 100 475"F 400"'F ZbO'F 325 °F VISCOSITY, CPS

FiGXJBE 8. Effect of temperature and moisture on saturation—#55 felt with shingle saturant.

saturation of the #27 felt was the same as with

7 percent of saturant. However, the #27 felt with

32 percent moisture absorbed 204 percent of saturant. This swelling of the felt structure by moisture

permitted improved saturation but was accompanied by a serious lowering of the tensile strength

of the moist felt and the production of a tremendous amount of foaming during the saturation

process.

5.3. Spacers on Press Rolls

One way of regulating the amount of free satu- rant carried on the sheet is to regulate the pressure

applied on the press rolls. All of the results al- ready discussed were obtained with the upper roll "floating." Attempts to increase the pressure re- sulted in decreased saturations. Attempts to decrease the pressure by elevating the bearings upon

which the upper rolls rotated produced a condition

that prevented the rolls from pulling the felt through themselves as they rotated ; there was not

sufficient "bite" to move the felt. A compromise

was sought in the use of spacers directly on the

upper roll, consisting of aluminum tape 5 mils

thick in multiple thicknesses. The edges of the felt were gripped between the bottom roll and the spacers on the top roll, leaving a free area over the felt to carry excess saturant. While this idea seemed

good theoretically, in practice the results were very

erratic. Wet areas frequently remained after the

soak-in period and the results could not be used.

All the results reported in figures 9, 10, and 11 are

based on only the specimens that were in a "sur- face-dry" condition when removed from the soaking-in oven. The low temperature cutoffs in these

figures represent the saturation temperatures below which "surface-wet specimens" only were

obtained.

From the results shown in figure 9, it is obvious

that the use of spacers did not improve the saturation with shingle saturant under any conditions.

The operating range was narrowed and only under the best conditions could satisfactory saturation be obtained with 30- or 50-mil spacers. When the mixed saturant was used, as seen in

figure 10, the saturation was improved at the

higher temperatures with both 30- and 50-mil

spacers. However, again the spacers raised the

lowest temperature at which surface-dry speci- mens could be produced.

Spacers thicker than 30 mils were not investigated with the #55 felt-roll saturant system.

However, when 30-mil spacers were used, viscosities at which satisfactory saturation could be

obtained were reduced further than with either

the mixed or shingle saturants. These data are shown in figure 11. The apparent anomaly of more

low softening point saturant remaining in the

felt at the lower viscosities may be explained on

the basis that this viscosity is attained at lower

temperatures, and a greater weight of asphalt

occupies the same volume. Another factor that

undoubtedly helped the saturation was that the

saturated felts were all exposed to a 350 °F

(177 °C) oven during the soak-in period. The

336-259 O—^9 2 7
220

200

180

160

140

120

EFFECT OF SPACERS

ON SATURATION

»55 FELT

SHINGLE SATURANT

O- NO SPACERS

• - 30-MIL SPACERS - 50-MIL SPACERS

J L

100 200

475 'F 400 "F aso'F 325 'F

300

I 300 "F VISCOSITY, CPS

Figure 9. Effect of spacers on saturation—#55 felt with shingle saturant. The use of spacers on the press rolls did not improve the level of saturation attainable with this system, but did shorten the working range in which satisfactory specimens could be made.

220

200

180

160

140-

120.

~1 I EFFECT OF SPACERS

ON SATURATION

»55 FELT

MIXED SATURANT

O - NO SPACERS

• - 30-MIL SPACERS

- 50-MIL SPACERS

_J_ 100 I Fioo

325 300

VISCOSITY, CPS

300

475 400 350

Figure 10. Effect of spacers on saturation—#55 felt with mixed saturant.

Spacers on the press rolls improved the saturation of the #35 felt with the mixed saturant at temperature around 400 °F. (204 °C).
220r

SATURATION WITH 30-MIL SPACERS * 55 FELT

<

(EU

I-<

UJo

UJ

Q.

ZOOISO

160

140

O - ROLL SATURANT

• - MIXED SATURANT

- SHINGLE SATURANT

I20i: 100 200 300

VISCOSITY, CPS

Figure 11. Saturation with 3-mil spacers—#55 felt. Under equlviscous conditions, tlie saturant at tlie lowest temperature results in the highest satu- ration over most of the working range.

softer saturant was the most fluid under these

conditions and excess saturant could soak in better

than the more viscous, hi^her-softening-point

materials. Thus, surface conditions that provided

"wet" saturated felts with the saturants normally

employed with #55 felt resulted in surface-dry

felts when the roll saturant was used. Undoubtedly, the "soaking-in" temperature could be modified in practice to accommodate the higher vis- cosity saturants.

5.4. Pressure

Another way of increasing the saturation of

felts is through increasing or decreasing the pres- sure in the saturator. The results of both pressure

variations are presented in figures 12 through 15. For the combination #55 felt-shingle saturants

in figure 12, a small increase in pressure produced

a significant increase in saturation. Progressively

higher pressures improved the saturation further

to 180 percent at 30 psig." The operating ranges

of temperature remained essentially the same at

all pressures; uniformly high saturations were

produced between 325 F (163 C) and 400 F

(204 C) at viscosities of 190 to 50 cps, respectively. Pressures higher than 30 psig were not

investigated.

Reduction of the pressure in the saturator below atmospheric pressure permitted further

increase in the saturation of the felts. At a vacuum

of 74 cm Hg (below atmospheric pressure) the

percent saturation was approximately 190, with a top figure of 195. The saturations under vacuum were extremely

slow; whereas those under pressure were accom210

200

140

130,

EFFECT OF PRESSURE ON SATURATION *55 FELT-SHINGLE SATURANT

74 CM VACUUM

^ 30 PSIG

' One pound force equals approximately 4.45 newtons.

BO go" 9

« w n lo »

VISCOSITY, CPS

Figure 12. Effect of pressure on saturation—

#55 felt laith shingle saturant.

Pressures both above and below atmospheric pressure resulted

in improved saturation levels.

9
plished rapidly. Periods of 30 mill were used for

the specimens saturated under vacuum because

bubbles continued to be released from the felt for

30 minutes. However, after the series was completed, it was found that times from 5 to 30 min

produced essentially the same results. Periods

below 5 min produced erratic results. The pressure

results were all accomplished with 1-min submergence, followed by a rapid decrease to atmospheric pressure while the specimen was submerged.

An interesting consideration involving the use of pressure is the appreciable increase in saturation with small increases in pressure. In practice,

pressure can be increased by merely making the

saturant tank deeper and running the sheet close to the bottom of the tank. Pressure is attained at the average rate of 0.44 psi per foot depth. Thus,

the results obtained in figure 12 at 2 psig could,

presumably, be accomplished with saturant just over 4 ft deep.

The beneficial effects produced by saturating

with shingle saturant under pressure were also

evident when the mixed saturant was used. As

seen in figure 13, a pressure of 2 psig was sufficient to take a combination of saturant, felt, and temperature that produced saturated felts failing to meet specifications under normal conditions and

produce results comfortably above 170 percent.

It is in this borderline type of situation that these

small modifications in procedure can be most

200

EFFECT OF PRESSURE ON SATURATION «55 FELT-MIXED SATURANT

IS PSIG

0 PSIG

200

VISCOSITY, CPS

Figure 13. Effect of pressure on saturation,—

#55 felt with mixed satwratit. For this system pressure increases beyond 15 psig did not

result in further improvement of the level of saturation.

beneficial. Further increases in pressure to 15 psig

produced additional improvement in saturation.;

However, beyond 15 psig, no further improvement ' was noted. As a matter of fact, 30 psig produced;

saturations essentially the same as 15 psig. i As might be expected, saturation with the most!

fluid saturant used, the roll saturant, was not; greatly influenced by pressure. The data in figure;

14 reveal that all elevated pressures produced 1 essentially the same degree of saturation between 1 325 °F (163 °C) and 400 °F (204 °C), as did: atmospheric-pressure saturation. However, the|

range over which the saturation of about 174 per-i cent was attained was extended about 50 °F

(28 °C) to 425 °F (218 °C) at above-atmospheric

;

pressures. Thus, even when roll saturant was used, j some improvement could be obtained by the use; of pressure. j

210

200

190

o

jZ 180 <

(EZ>§ '70

^ 160

ISO

140

130,

EFFECT OF PRESSURE ON SATURATION

^55 FELT-ROLL SATURANT

A 30 PSIG O IS PSIG • 0 PSIG 2 PSIG

li. 50 100 « Oio N lOCM

VISCOSITY, CPS

Figure 14. Effect of pressure on saturation—

#55 felt with roll saturant.

Saturation under pressure did not materially improve the level of saturation attainable with this system. Commercially no difficulty is encountered in saturating #27 felt. A very soft saturant is used

to keep the saturated felt pliable in cool weather

and compatible with mopping-grade asphalts.

The saturation is kept low, 140 percent minimum,

to prevent the adjacent layers in the rolls from adhering to each other. However, it is known that

greater saturations improve the protection of the

fibers. Therefore, the efi^ect of vacuum and pres- sure on the saturation of #27 felt with roll satu- rant was studied. The results are reported in figure 15.

10
220

200

-T I

\

I EFFECT OF PRESSURE

ON SATURATION

tt 27 FELT

ROLL SATURANT

O- ATMOSPHERIC PRESSURE - 10 CM Hg VACUUM

• - 74 CM Hg VACUUM - 2-5 PSI6 PRESSURE A- 40 CM Hg VACUUM A- 15 PSIG PRESSURE

V-30 PSIC PRESSURE

300

350 BOO-F

VISCOSITY, CPS

Figure 15. Effect of pressure on saturation.—#27 felt with roll saturant. Both pressure and vaccum increased the level of saturation attainable with this system.

Both elevated pressures and vacuums down to about one-half atmosphere greatly restricted the

temperature range in which surface-dry, saturated

felts could be obtained to 390 °F ( 199 °C) or higher. In this range, improved saturation was always

j obtained. When 74 cm Hg of vacuum was used,

I satisfactory and maximum saturation could be obItained over the complete temperature range from

300 °F (149 °C) to 400 °F (204 °C). The percent

! saturation began to decrease, however, as the sat- urant temperature was raised above 400 °F (204

; °C). The #27 felt, thus, could be saturated to 170

percent saturation and still be surface dry with the

use of vacuum. Elevated pressures could be used

to produce saturations up to 165 percent if the sat- urant temperature was closely controlled in the

higher temperature range.

5.5. Moisture Absorption

The purpose of saturating felts with asphalt is to protect the felts and make them more resistant to attack by the elements of weather. Dry felts are

particularly vulnerable to moisture in both liquid

and vapor form. The results in figure 6 show that

dry felts absorb up to 9 percent moisture when

exposed to relative humidities of 75 percent for less than a day. The equilibrium moisture will be higher if the storage temperature is lower and lower

if it is higher than 79 °F (26 °C). It has been

reported that large dimensional changes occur in

felts with moisture changes and progressively

larger shrinkages result [5].

To determine how well saturation protects felts, a series of exposures was made of #55 felt satu- rated with the mixed saturant in the range of 64

to 185 percent to relative humidities of 30, 50,

and 75 percent. It had been planned to contine

determinations at all three relative humidities for

500 hr, but the exposure conditions drifted out of

the control ranges after 200 hr at 30 percent rela- tive humidity and 150 hr at 75 percent relative

humidity. The figures in the inserts represent the

last set of readings under controlled conditions.

The specific data for the #55 felt saturated

with the mixed saturant are presented in figures

16, 17, and 18 for relative humidities of 30, 50, and

75 percent, respectively. Similarly, data for the

moisture absorption of the #27 felt saturated with

roll saturant and exposed at 73 °F (23 °C) and 50

percent relative humidity are in figure 19. At all relative humidities moisture absorption

proceeded rapidly at first and then at progressively lower rates until some constant moisture

content was attained. The rate of absorption, rate of attaining "equilibrium," and "equilibrium"

moisture content decreased as the saturation of

the felt was increased. The final moisture content decreased approximately linearly with the log of

the percent saturation. Similarly, for any particular saturation, the "equilibrium" moisture content

increased with the relative humidity to which the

felts were exposed.

11
n \ r MOISTURE ABSORPTION

TIME, HOURS

Figure 16. Moisture absorption—#55 felt with mixed saturant at 13 °F (23 °C) and 30 percent

relative humidity.

Both the rate of absorption and the amount of absorption decreased rapidly as the level of saturation of the felt was increased.

Figure 17. Moisture absorption—#55 felt with mixed saturant at 73 "F (23 "C) and 50 percent

relative humidity.
MOISTURE ABSORPTION

0 10 20 30 40 50 60 70 80

TIME, HOUR

FlGtTBE 19. Moisture absorptimi—#27 -felt with roll satiirant at 73 °F (23 °C) and 50 percent

relative humidity. The initial absorption of moisture is more rapid for the #27 felt than for the #55 felt with the same

saturation. However, the final moisture concentrations are essentlall.v the same.
Even a small degree of saturation, such as about

60 percent, reduced both the rate of moisture

absorption and final moisture content of the felts appreciably. Data from figures 6 and 16 show that

at 30 percent relative humidity the final moisture

content is reduced by 50 percent at this low saturation, and the time to attain it is increased appreciably. At specification saturations and higher, the

final moisture content is reduced by 75 percent and

the time to attain it increased. The beneficial

effects of greater saturation are more evident at higher relative humidities.

However, even the most highly saturated felts in this study absorbed moisture to some extent.

It is, therefore, necessary to front- and back-coat

roofing products to isolate and protect the felts from moist environments.

Wlien considering the #27 saturated felts, this

vulnerability to moisture absorption is very sig- nificant. They are normally saturated to above

140 percent and, thus, may absorb up to 2.5 pej cent moisture at 50 percent relative humidity ar I 73 °F (23 °C). Absorption can occur in storage on the roof, if the roof is not completed in oi, session. The exposure of an unsurfaced roof ovi' night, when the temperature drops and the rel | tive humidity increases, could lead to much high(

moisture absorption. As the roof is finished, tl hot asphalt application must vaporize this moi

ture. Asphalt cooling and some frothing an foaming often result. Moisture absorption, ; accomplished nonuniformly throughout a roll ( felt, can also lead to temporary or permanent diij tortious of the felt. 1 If conditions are made more severe, and th

felt is submerged in liquid water for periods il excess of 1 hr, the quantity of water absorbe

j increases rapidly. Felts meeting ASTM specifics'

tions will absorb about 10 percent water in a weel

The data in figure 20 are for the #55 saturate^

0 I 10 100 1000

TIME.HR

Figure 20. Water absorption—#55 felt with mixed saturant. The amount of water absorbed on immersion is greater for felts at any level of saturation than

that resulting from exposure to humid air. The final water content decreases as the level of saturation

Is increased.

14
! felts. Wlaile the #27 felts were not evaluated, it is anticipated that comparable resvdts would be

obtained in shorter periods of time. These data

further emphasize the necessity for protecting

saturated felts by impermeable surface coatings as rapidly as possible.

5.6. Air Permeability

Air permeability of saturated felts decreases

rapidly as the saturation is increased. With the

densometer normally used for dry felts the results become rather erratic and the times become long

for sa/turations higher than 125 percent. It is in- teresting to note that both the #27 and #55 felts

fell on the same curve in figure 21. (In order to obtain the data for this correlation, the entire felt from the actual areas through which the air per- meated was extracted with chlorothene to obtain

the saturations. Therefore, each point represents an individual determination. The local variations

in any piece of saturated felt were too large to permit the use of average values.)

For applications in which felt is used as a wind

barrier, but not as a vapor barrier, highly saturated, but uncoated, felts should be recommended.

If a vapor barrier is desirable, saturated and coated

felt should be used.

V)o

z

o

o

UI

to

iLl

O

CO

UJa

250

200

I 50

I 00

50

I

AIR

1 1 PERMEABILITY

o - Qn 27 FELT-ROLL SATURANT

tt 55 FELT- MIXED SATURANT

400 CC AIR _

-

1

1 O

o ~

o

?

1 1

1 0 50 100 150 200

PERCENT SATURATION

Figure 21. Air permeability. The air permeability of saturated felts decreases rapidly as the

level of saturation is increased.

6. Conclusions

Saturating organic felts under controlled conditions in the laboratory has demonstrated that

the efficiency of saturation varies with a large

number of parameters, including time of immersion, temperature and viscosity of the saturant, pressure on the press rolls, and pressure in the

saturator. However, even under the most favorable conditions, only 82 percent of the theoretically possible saturation was attained. This figure,

25 percent over the specification minimum, was

equal to the asphaJt capacity as determined by the

buret method ; thus, an efficiency of 100 percent of

the buret asphalt capacity was attained.

The technical conclusions obtained from this

study may be summarized as follows:

(1) At 400° F (205°C) with the saturants nor- mally used, it was immaterial whether the #27

felt was saturated from either one or both sides if more than 15 sec of submersion time was used. The

#55 felt required a minimum of 13/2 rnin of complete submersion to meet minimum specification

requirements.

(2) Felts containing about 4 percent moisture were saturated more easily and more completely

than dry felts. As the moisture content increased,

the level of saturation attainable also increased,

but beyond 7 percent moisture excessive foaming and cooling of the saturant were observed.

The moisture seemed to "open up" the felt.

(3) Under normal conditions felts saturated

best in the viscosity range of 50 to 150 Hz. At

higher viscosities the penetration was hindered;

at lower viscosities, the sheet could not "carry"

sufficient saturation to meet specifications.

(4) Spacers on the press rolls increased the

quantity of saturant carried on the sheet, but the

viscosity range in which surface-dry saturated

felts could be produced was greatly shortened. The

beneficial effects were more noticeable with the

softer saturants.

(5) Small increments of pressure in the sat- urator produced marked increases in saturation,

especially with the harder saturants. Higher pres- sures produced further improvements in saturation with the shingle saturant, but not with the

softer saturant.

(6) Vacuum saturation produced the highest

saturations.

(7) Kate of moisture and liquid water sorption

of saturated felt decreased with increasing saturation. A large fraction of the total sorption oc- curred in the first few hours of exposure.

(8) Air permeability decreased rapidly with

increasing saturation.

The author wishes to thank Messrs. J. C. Weeks

and T. R. Davis for their assistance in the experi15
mental work. The felts were supplied by Mr. J. J. Klimas, of the Building and Industrial Products

Division, GAF Corp. (Formerly Euberoid Co.).

The saturants were furnished by Mr. L. C.

Krchma, of the Mobil Oil Co. This work was spec I sored by the Asphalt Roofing Manufacturers M\ sociation (formerly the Asphalt Eoofing Industr

Bureau).

7. References

[1] Abraham, H., Asphalts and Allied Substances, Fifth

Edition, I, 743-747, D. Van Nostrand & Co., Inc., New York (1945).

[2] Krchma, L. C, Asphalts for Process Industries, Chapter in Bituminous Materials, II, 593, Interscience

Publishers, Inc. (1965).

[3] Casey, J. P., Pulp and Paper Chemistry and Technology I, 81, Interscience Publishers, Inc. (1960).

[4] Ott, E., H. M. Spurlin and M. W. Grifflin, Cellules and Cellulose Derivatives, 5, Part 1, Interscienci Publishers, Inc., New York (1955).

'

[5] Martin, K. G., Changes in Bituminous Roofing Felt' Associated with Changes in Moisture Content, Bh \ of Bldg. Res. Tech. Paper No. 8, C.S.I.R.O., Austra '

lia (1959).

8. Glossary

This glossary contains definitions of terms re- tricted to their use in this study. Many of these terms are more broadly defined for other uses. Asphalt—The residue from the distillation of some types of petroleum processed further to products with specific properties.

Asphalt capacity—The kerosene number multiplied by the ratio of the specific gravity of the

asphalt saturant to that of the kerosene used.

When no specific saturant is being considered,

1.035 is used as the specific gravity of the

saturant. Bmlt-up roofing—Roofing fabricated in place

from alternate layers of saturated felt and as- phalt.

Demometer—An air-permeability apparatus used

in the paper industry to measure the openness, or density, of paper and felts. Dry /eZ^—Unsaturated felt in an oven-dry condition. Felt—A paper-like material made by a felting

process, rather than a weaving process. While

felts may be made of asbestos, paper, wood, rags,

glass, etc., those in this study were made from

a mixture of paper, rags, and wood fibers. Felt number—The weight of 480 square feet of

dry felt, i.e., #27, #55.

Furnish—The composition of the felt in terms of

fiber types.

Kerosene number—The weight of kerosene tin felt can hold divided by the weight of the dr

felt, expressed as a percentage. The kerosenij

number varies with the procedure by which i | has been determined.

Mixed saturant—Saturant made by the blendinj

of the roll and shingle saturants. Moisture—Water vapor in the air and water con

tent of felts.

^ Percent saturation—The ratio of the weight of th( saturant to that of the dry felt, expressed as i percentage.

Prepared roopng—Roofing completely manufac

tured in a roofing mill, as distinguished fron

built-up roofing, which is fabricated in place

Roll saturant—Saturant normally used for mak ' ing roll roofing. ] Roof membrane—The built-up roof, exclusive o\

surfacing.

j Roofing felt—A felt used in the manufacture oJ asphalt roofing.

j Saturant—A relatively soft asphalt used tc impregnate felts. | Satusrated felt—Felt containing some asphalt

saturant, not necessarily as much as it can hold. Saturation—The impregnation of a felt with a saturant. Square—One hundred square feet of material.

Water or moiMure absorption—The penetration oi water (vapor or liquid) into the felt, including

both adsorption and absorption.

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