NATIONAL BUREAU OF STANDARDS REPORT

9426

SATURATING ORGANIC FELTS

by

Sidney H. Greenfeld

Research Associate

Asphalt Roofing Industry Bureau

Sponsored by

Asphalt Roofing Industry Bureau

U. S. DEPARTMENT OF COMMERCE

NATIONAL OUREAU OF STANDARDS
THE NATIONAL BUREAU OF STANDARDS

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NATIONAL BUREAU OF STANDARDS REPORT

NBS PROJECT NBS REPORT

421.04-20-4212247 9426

SATURATING ORGANIC FELTS

by

Sidney H. Greenfeld

Research Associate

Asphalt Roofing Industry Bureau

Sponsored by

Asphalt Roofing Industry Bureau

NATIONAL BUREAU OF STA

for use within the Government. B and review. For this reason, the whole or in part, is not authoriz Bureau of Standards, Washington

the Report has been specifically p

IMPORTANT NOTICE

Approved for public release by the

Director of the National Institute of

Standards and Technology (NIST) on October 9, 2015

accounting documents intended

ibjected to additional evaluation

isting of this Report, either in Office of the Director, National

le Government agency for which

lies for its own use.

U. S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS

SATURATING ORGANIC FELTS

ABSTRACT

A study of the saturation of a #27 felt with a typical roll

saturant and a #55 felt with roll, mixed and shingle saturants revealed

that the degree of saturation 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 system. Both pressure and vacuum increased

the degree of saturation under optimum conditions, but frequently

shortened the working temperature range under which optimum saturation

could be produced. Rate and degree of moisture and liquid water sorption

decreased with increasing saturation. Air permeability decreased with

increasing saturation. The consequences of some of these findings are

discussed

.

i

SATURATING ORGANIC FELTS

Sidney H. Greenfeld

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

prepared roofing, the felt permits the product to be cut into

appropriate designs, packaged, handled and applied without distortion.

When 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 they are

subjected. In order for the felts to function properly, they must be

protected both externally and internally, for the felts themselves are

vulnerable to the weather.

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.

The internal protection is provided by a light bituminous saturant

applied through a series of dips, or sprays and dips, as described by

s / Abraham (1) — and Krchma (2). Complete saturation is very difficult

to achieve commercially, for modern roofing machines operate at 250 to

500 feet per minute and frequently allow times of less than one minute

for saturation to occur. During this time, the felt, usually at room

temperature with five to seven percent free moisture, must be heated to

a/ The numbers in parentheses refer to the references at the end of

this report.

1

saturant temperature, desiccated and saturated. The final stages of

saturation actually occur beyond the saturant baths, where the excess

saturant on the felt surfaces is drawn into the felt as it 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 possible for the

felt to carry more saturant with it from the saturator. Thus, 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, problems of adhesion of coating to

felt in shingles and roll roofing may result if a large excess of saturant is permitted to remain on the felt surface. Compatibility and coating slippage problems (through thinning of the coating) are aggrevated

by this excess saturant. In the case of saturated felts, sticking in

storage under over-saturated conditions is possible. Thus, when specifications are written, compromise saturations are required.

b/ A typical saturator running at 400 ft per min would saturate 12

squares of felt per min. At six percent moisture content, about

15,000 Btu per min would be required to heat the felt and evaporate

the moisture. This quantity of heat, if supplied entirely by the

saturant used in saturating those 12 squares of felt, would lower the

saturant temperature about 135°F. 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 the optimum.

2

In shingles, 170 percent saturation; that is, saturant weighing

1.70 times as much as the 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 are the compromises

made to accommodate production, storage and application requirements.

c/ Theoretically, completely impregnated felt can hold about 235 percentof its weight in saturant. Asphalt saturating numbers-^-/ at about 210

percent by the vacuum method and 195 percent by the burette method may

be more realistic values to try to attain commercially.

Contemporary commercial saturating techniques produce felts meeting

the specifications and exceeding them only by small margins. Improved

techniques could lead to tighter specifications and better internally

protected felts.

Based on these considerations, a study was undertaken to investigate

the felt-saturating process and determine the effects of temperature,

pressure, moisture, time and saturant on the saturating of organic felts.

c/ On the assumption that the felt is crystalline cellulose with a

specific gravity of 1.53 (3), the ratio of space to cellulose in

felt is 2.35. If felt is assumed 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.

The asphalt saturating number is the kerosene number multiplied by

the ratio of the specific gravity of the asphalt saturant to that

of the kerosene.

3

2. MATERIALS

(a) Felts

Two grades of commercial felt were supplied by the Ruberoid

Company. These were taken from the normal production at their

Gloucester City, New Jersey, mill and slit into 12-inch rolls for this

project. These felts had the characteristics reported in Table I.

TABLE I

Felt Characteristics

Grade Number 27 55

Dry Weight, lb/480 ft^ 27 53

Caliper, mils 33 64

Tensile Strengths Machine

Direction (Scott), Ib/in. 31 40

Tensile Strength, Cross

Direction (Scott) , lb/in. 15* 21*

Densometer, seconds/400 cc 18 (16.2*) 18 (18.3*)

Asphalt Saturating Number 183** (177*) 197** (187*)

Moisture (as received), % 4.1 4.1

* 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).

4

The felt furnish was not supplied; the ratios of wood fibers, rags

and paper are continually being adjusted during production to keep the

felt properties uniform. Oak and pine fibers were used along with No. 1

waste paper and rags.

(b) Saturants

Two saturants were provided by the Mobil Oil Company from their

Kansas refinery. These consisted of a soft, roll saturant and a hard,

shingle saturant. These two were blended to produce a third saturant,

termed a "mixed" saturant. The properties of these three materials are

listed in Table II.

TABLE II

Properties of Saturants

Saturant Roll Shingle Mixed

Softening Point, °F 111 141 125

Penetration at 77°F, 1/10 mm 139 48 81

Penetration at 32°F, 1/10 mm - 18 23

Specific Gravity, 77/77°F 0.9954 1.0002 -

Flash Point (c.o.c.) , °F 630 625 625

Loss on Heating 0 0 0

Solubility in CCl^, % 99.4 99.4 99.4

The viscosity-temperature relations are presented in Figure 1.

5
: ; " • .s • •
VISCOSITY,

CPS

I / T, °F

200°F

3. APPARATUS

Three apparati 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 apparati in Figures 3 and

4, respectively, were used.

The apparatus used for saturating at atmospheric pressure consisted

of a stainless-steel saturant pan 7" x 9" x 2" (18 x 23 x 5 cm) and

press rolls. The pan was heated on a thermostated hot plate capable of

temperatures up to 600°F (316°C) . Once the specimens were saturated,

they were passed through the heated, manually operated rolls shown to

the left in Figure 2. These rolls were provided with pressure

adjustments to permit pressures resulting from the weight of the roll

and 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-ml thick aluminum tape were

used to permit controlled excesses of saturant to be carried on the

felt. A thermostated air oven was used to maintain the saturated

specimens at elevated temperatures (250°or 350°F) (121° or 177°C) for

a period of time to simulate the soaking-in period between saturation

and coating in commercial operation. A similar oven, maintained at

225°F (107°C) was used to dry the felt prior to saturation (when

desired)

.

6
-

, -
Figure 2

Figure

F

igure

Whereas 6- x 8-inch (15 x 20 cm) felt specimens were normally

saturated, under both vacuum and elevated pressures 1- x 2.5-inch

(2.5 x 6.4 cm) specimens were used. The saturator (Figure 3) in the

vacuum studies was 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 super-atmospheric pressure saturations, as shown in

Figure 4. Dry nitrogen was used to produce the pressure.

4. PROCEDURES

The procedures followed while saturating felts at ambient pressure ,

under vacuum and at super -atmospheric 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 minutes in an oven at 225°F (106°C) to be

dried to constant weight. Therefore, the felts were heated in the oven

for one hour and weighed immediately, for even in a desiccator the felts

were found to sorb moisture. The average of the two moisture

determinations was used in calculating the percent saturation of the

felts

.

7

When the saturant in the pan was at the desired temperature and the

pressure rolls were at 240 ±10°F (116° ±6°C), a 6- x 8-inch (15 x 20 cm)

piece of felt was floated on the saturant for one and a half minutes,

submerged for two minutes, passed once through the rolls, hung in the

"soaking-in" oven at 250°F (121°C) for five minutes, and then weighed.

This procedure was arbitrarily adopted because it required about one and

a half miixutes for the saturant to strike through the floating felt at

400°F (204°G) and it required about two minutes 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 two -minute -submergence time,

saturation was independent of float time and, therefore, tha float time

was eliminated. At about the same time, the Research Committee reported

that the "soaking-in" period occurred commercially at temperatures more

nearly 350°F (177°C) than the 250°F (121°C) being used. This higher

temperature seemed to reduce the number of felts rejected for "wetness"

on their surfaces, but had no effect on the quantity of saturant

remaining in the acceptable felts. Thus, the figures reported were

not influenced appreciably by these changes.

8
' •' ••• ; -
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 saturant 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 five minutes 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 sufficient to raise the saturations reported for these

small specimens.

When saturating under pressure, the 1- x 2.5-inch (2.5 x 6.4 cm)

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 apparatus in Figure 2, and hung in the oven for five

minutes at 350°F (177°C). Excess saturant was wiped from the edges

immediately prior to weighing.

9

5. RESULTS AND DISCUSSION

The saturating of organic felts is affected by many variables, some

of which are within the scope of this program and some not. Those

Involved in the furnish and production of the felt, or in the production

of saturants, will not be considered; some of those relating to the

saturant and the actual contact between the felt and the saturant will

be discussed.

(a) Contact Time

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 tries to saturate 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 contacting the saturant on 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

one or two 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 saturation with longer periods of exposure of the felts to

10
.

os.
MAI 8

wun

8

WO

8

the high temperature of the saturants. It is quite apparent that contact

times between the #27 felts and saturants of more than a half-minute are

adequate to produce saturations in excess of those required by current

specifications (140 percent minimum)

.

Saturation of the #55 felts, on the other hand, was sensitive to the

means by which the felt was saturated. When the felts were submerged

without previous floating, the saturation increased progressively with

time of submersion up to about two minutes j however, beyond about one

and a half minutes, saturation was essentially independent of submersion

time. When float time was followed by two minutes of submersion, the

shorter float times produced the highest saturations. However, the results were essentially constant after one minute of float time. Long

submersion times were detrimental to the percent saturation. Based on

these results, floating was eliminated and two minutes 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; both would meet current specifications.

(b) 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 sorb 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 humidity

11
>. ' mi .
MOISTURE

ABSORPTION

DRY

FELT

FIGURE

6

(1M) lN30d3d ‘Q3adOS8V 3dfUSIOW

TIME,

MINUTES

(saturated sodium hyposulfite solution), the equilibrium moisture cone/ tent of these felts is about 12 percent - and in a saturated atmosphere

it is 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 it escapes, it slows the penetration of the

saturant into the felt. However, moisture in the felt serves two

beneficial purposes. Felt with moisture contents below about three

percent are very brittle. They frequently tear in the saturating

process and require patching of the felt or rethreading of the machine.

Thus, for continuous operation a minimum of three percent moisture is

necessary. Moisture also lubricates the fibers or fiber bundles to

permit their movement over each other and swells the fibers to permit

the saturant to penetrate them 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 affected

by short-term changes in relative humidity. (Some edge curling might

be attributed to this effect). The interior of the rolls of felt remain

essentially as they were when rolled, except after long-term storage

under extreme humidity conditions.

e/ Moisture content is expressed on an "oven dry" basis rather than an

"as received" basis.

12

The moisture content of the felt is not very readily controllable;

the temperature of the saturant is. 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 difference 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 seven percent moisture absorbed three to seven

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 in an "expanded" state; the felt could not carry enough saturant to meet specifications at temperatures above 400°F (205°C) with

seven percent moisture or above 350° - 375°F (175° - 190°C) when dry.

For the #55 felt, (Figure 8) some moisture was necessary to permit

sufficient saturation with the shingle saturant to meet the ASTM

specification of 170 percent (ASTM D 225-65). Neither dry felt, cold

or warm, could be saturated beyond 165 percent. In addition, the

o saturant did not penetrate well at temperatures below 325°F (163 C)

(about 180 cps), when dry felt was used. With seven percent moisture,

13
'
o

NOIlVUniVS lN3DH3d

VISCOSITY,

CPS

EFFECT

OF

TEMPERATURE

AND

MOISTURE

ON

SATURATION

#

55

FELT

200

-

SHINGLE

SATURANT

FIGURE

8

o o

o —

o

to to

o

©

OJ

so

CM

SO

O

o

®o

iO

ro

LloOO

sr

»to

J 1 1 o

o o o o

m <0 * cj

NOIlVdfllVS lN30H3d

VISCOSITY,

CPS

good penetration was found down to 300°F (150°C). At the higher

temperatures, again, saturation was reduced rapidly with increasing

temperature. In the range above 400°F (205°C) the felt with four

percent moisture saturated like the dry felt; as the temperature was

reduced below 400°F (205°C) , it behaved more like the felt with seven

percent moisture.

A few specimens of felt were exposed to high humidities and

saturated when they had moisture contents of 12 and 32 percent. At 12

percent moisture content, the saturation of the #27 felt was the same as

with 7 percent moisture. However, the #27 felts with 32 percent moisture

absorbed 204 percent of saturant. This opening of the felt structure

by moisture to permit improved saturation is accompanied by a serious

lowering of the tensile strength of the moist felt and the introduction

of a tremendous amount of foaming during the saturation process.

(c) Spacers on Press Rolls

One way of regulating the amount of free saturant carried on

the sheet is to regulate the pressure applied on the press rolls. All

of the results already discussed were obtained with the upper roll

"floating". Attempts to increase the pressure resulted 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 five mils thick in multiple thicknesses. The edges

14

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 remained after the soak-in period quite

frequently 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 "surface-dry” condition when removed from the soaking-in oven.

The low temperature cutoffs in these figures represent the saturation

temperatures below which only surface-wet specimens 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 specimens 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

15

Nouvanivs ±N3oa3d

VISCOSITY,

CPS

Nouvanivs iN3oa3d

IOO |

I

200

300

350

325

300

VISCOSITY,

CFS

220

O

CM ” “ NOiXV&fUVS 1H30U36

VISCOSITY,

CPS
' v -
temperatures and the specific volume of the saturant is lower under these

conditions (the density of the saturant is greater at a given viscosity

as the softening point of the saturant is decreased) . Another factor

that undoubtedly helped the saturation was that the saturated felts

were all exposed to a 350°F oven for the soak-in period. The softer

saturant was the most fluid under these conditions and excess saturant

could soak in better than the more viscous, higher-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 viscosity saturants.

(d) Pressure

Possible ways of increasing the saturation of felts include

the use of pressure or vacuum. The results of both of these techniques

are presented in Figures 12 to 15.

For the system #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 185

percent at 30 psig. The operating ranges of temperature remained

essentially the same at all pressures; uniformly high saturations were

produced between 325°F (190°G) and 400°F (205°C) at viscosities of 190

to 50 cps, respectively. Pressures higher than 30 psig were not

investigated

16

VISCOSITY, CPS

300*F

PERCENT

SATURATION

210

200 -

190 h180 hS70 -

ISO -

S 50 I—

|AQ -

130j0

EFFECT OF PRESSURE ON SATURATION

*55 FELT MIXED SATURANT

FIGURE 13

VISCOSITY, CPS

PERCENT

SATURATION

280

200 -

1

0

—

i 8 0 —

170-

I s 0 *

1 50 —

14 © i—

I^Oq

EFFECT OF PRESSURE ON SATURATION

* 55 FELT ROLL SATURANT

FIGURE 54

A 30 PSIG

O 15 PSIG

® 0 PSIG

(ft. U» Ifc, u. U. 50 y. h.

® • ® © • • » OtfS © » © «o © «o CM * to to to VISCOSITY, CPS

300*F

o

N CM

Nouvanivs xuiouid

VISCOSITY,

CPS

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, the percent saturation was approximately 190, with

top figures of 195.

The saturations under vacuum were extremely slow; whereas

those under pressure were accomplished rapidly. Periods of 30 minutes

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 five to thirty

minutes produced essentially the same results. Periods below five

minutes produced erratic results. The pressure results were all

accomplished with one-minute 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 rate of 0.43 - 0.45 psi per foot of

depth. Thus, the results obtained in Figure 12 at 2 psig could,

presumably, be accomplished with saturant just over four feet deep.

17
BI
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, 2 psig were sufficient to take a combination

of saturant, felt and temperature that produced saturated felts failing

to meet specifications and produce results comfortably above 170 percent.

It is in this borderline type of situation that these small modifications

in procedure can be most 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.

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

essentially the same degree of saturation between 325° (190°C) and

400°F (205°C) as did atmospheric pressure saturation. However, the

range over which the saturation of about 174 percent was attained was

extended about 50°F to 425°F at super-atmospheric pressures. Thus,

even when roll saturant was used, some improvement could be obtained

by the use of pressure.

Commercially no difficulty is encountered in saturating the

#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.

18

Therefore, the effect of vacuum and pressure on the saturation of #27

felt with roll saturant was studied. The results are reported in

Figure 15.

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 (200°C) or higher. In this

range, improved saturations were always obtained. When 74 cm Hg of

vacuum was used, satisfactory and maximum saturation could be obtained

over the complete temperature range from 300°F (150°C) to 400°F (205°C)

The percent saturation began to decrease, however, as the saturant

temperature was raised above 40Q°F (205°C). The #27 felt, thus, could

be saturated with 170 percent saturant and still be surface dry by the

use of vacuum. Elevated pressures could be used to produce saturations

up to 165 percent if the saturant temperature was closely controlled in

the higher temperature range.

(e) Moisture Absorption

The purpose of saturating felts with asphalt is to protect

them and make them more resistant to attack by the elements of the

weather. Dry felts are particularly vulnerable to moisture in both

liquid and vapor form. The results in Figure 6 show that dry felts

sorb up to 9 percent moisture when exposed to relative humidities of

75 percent for less than a day. This equilibrium moisture will be

higher if the storage temperature is lower and lower if it is higher

than 79°F. It has been reported that large dimensional changes occur

in felts with moisture changes and progressively larger shrinkages

result (5)

19
'

.. {
To determine how well saturation protects felts, a series of

exposures was made of #55 felt saturated 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 continue determinations at all three

relative humidities for 500 hours, but the exposure conditions drifted

out of the control ranges after 200 hours at 30 percent relative

humidity and 150 hours 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 felts 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 felts saturated with roll saturant and

exposed at 73 °F 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.

20

TIME,

HOURS

MOISTURE

ABSORPTION

#55

FELT-MIXED

SATURANT

73

®F

50

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RH

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TIME,

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MOISTURE

ABSORPTION

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27

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It is significant to note that 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 much more. At the higher humidities,

the improvements are more pronounced.

On the negative side of the picture, however, is the inescapable

fact that even the most highly saturated felts in this study sorbed

moisture to a degree. Front and back coating shingles thus offer the

isolation fully saturated felts need from moist atmospheres.

When considering the #27 saturated felts, this vulnerability to

moisture sorption is very significant. They are normally saturated to

above 140 percent and, thus, may sorb up to 2.5 percent moisture at

50 percent relative humidity and 73°F. This sorption can occur in

storage or on the roof if the roof is not completed in one session.

The exposure of an unsurfaced roof over night, when the temperature

drops and the relative humidity increases, could lead to much higher

moisture sorption. As the roof is finished, the hot asphalt application

must vaporize this moisture. Asphalt cooling and some frothing and

foaming result. This moisture sorption if accomplished non-uniformly

throughout a roll of felt could lead to temporary or permanent distortions of the felt.

21
*
If conditions are made more severe, and the felt is submerged

in liquid water for periods in excess of one hour, the quantity of water

sorbed increases rapidly. Felts meeting ASTM specifications will sorb

about 10 percent water in a week. The data in Figure 20 are for the

#55 saturated felts. While the #27 felts were not evaluated, it is

anticipated that comparable results would be attained in shorter periods

of time. These data further emphasize the necessity for protecting

saturated felts by impermeable surface coatings as rapidly as possible,

(f) 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

saturations higher than 125 percent. It is interesting 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 actual areas through which

the air permeated were extracted to obtain the saturations. 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.

22

(JLM) J.N30d3d ‘NOlidaOSaV M31VM

TIME,

HR

DENSOMETER

TIME,

SECONDS

PERCENT SATURATION

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

(or 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

asphalt saturating number as determined by the burette method; thus, an

efficiency of 100 percent of the burette asphalt saturating number was

attained.

The technical conclusions obtained from this study may be

summarized as follows:

(1) At 400°F (205°C) with the saturants normally used, it was

immaterial whether the #27 felt was saturated from either one or both

sides if more than 15 seconds of submersion time was used. The #55

felt required a minimum of one and a half minutes of complete submersion

to meet minimum specification requirements.

(2) Felts were saturated to a greater extent and more easily if

they contained a small quantity of moisture. Moisture seemed to "open

up" the felt. Large moisture contents permitted still greater

saturation, but produced foaming and cooled the saturant excessively.

23

(3) Felts saturated under normal conditions best in the viscosity

range of 50 to 150 cps. At higher viscosities the penetration was

hindered; at lower viscosities, the sheet could not "carry" sufficient

saturant 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 saturator produced

marked increases in saturation, especially with the harder saturants.

Higher pressures produced further improvements in saturation with the

shingle saturant, but not with the softer saturant.

(6) Vacuum saturation produced the highest saturations.

(7) Rate of moisture and liquid water sorption of saturated felt

decreased with increasing saturation. A large fraction of the total

sorption occurred in the first few hours of exposure.

(8) Air permeability decreased rapidly with increasing saturation.

24
...

- - v. _

! -
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. Grafflin, Cellulose and Cellulose

Derivatives, 5^, Part 1, Interscience Publishers, Inc., New York

(1955)

(5) Martin, K. G., Changes in Bituminous Roofing Felts Associated with

Changes in Moisture Content, Div. of Bldg. Res. Tech. Paper No. 8,

C.S.I.R.O., Australia (1959).

25
"t •; • .
8 . ACKNOWLEDGMENT

The author wishes to thank Messrs. J. C. Weeks and T. R. Davis for

their assistance in the experimental work.

26


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