irERE.

NBS TECHNICAL NOTE 778

Guidelines for Selection of

and Use of Foam Polyurethane

Roofing Systems

U.S.

TMENT

I

OF

MERCE

National

J— of

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153

72
NATIONAL BUREAU OF STANDARDS

The National Bureau of Standards1 was established by an act of Congress March 3, 1901. The Bureau's overall goal is to strengthen and advance the Nation's science and

technology and facilitate their effective application for public benefit. To this end, the Bureau conducts research and provides: (1) a basis for the Nation's physical measure- ment system, (2) scientific and technological services for industry and government, (3) a technical basis for equity in trade, and (4) technical services to promote public safety. The Bureau consists of the Institute for Basic Standards, the Institute for Materials Research, the Institute for Applied Technology, the Center for Computer Sciences and

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4 Part of the Center for Building Technology.
Guidelines for Selection of and Use of

Foam Polyurethane Roofing Systems

William C. Cullen and

Walter J. Rossiter, Jr.

Center for Building Technology

Institute for Applied Technology

National Bureau of Standards

Washington, D.C. 20234

Prepared for Naval Facilities Engineering Command, U.S. Navy

Directorate of Civil Engineering, U.S. Air Force

Office of Chief of Engineers, U.S. Army

NBS Technical Notes are designed to supplement the Bureau's regular publications program. They provide a means for making available scientific data that are of

transient or limited interest. Technical Notes may be

listed or referred to in the open literature.

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U.S. DEPARTMENT OF COMMERCE, Frederick B. Dent, Secretary

NATIONAL BUREAU OF STANDARDS, Richard W. Roberts, Director

Issued May 1973
National Bureau of Standards Technical Note 778

Nat. Bur. Stand. (U.S.), Tech. Note 778, 46 pages (May 1973) CODEN: NBTNAE

For sale by the Superintendent of Documents, U.S. Government Printing Office, Washington, D.C. 20402 (Order by SD Catalog No. 03.46:778).

Price $0.75 domestic postpaid or $0.50G.P.O. Bookstore
Contents

Page

1. Introduction 1 2. Purpose of the Report 2 3. Conduct of Study 2 4. Rigid or Structural Polyurethane Foams and Their

Properties 4

4.1 Introduction 4

4.2 The Chemistry of Polyurethane Foams 4

4.3 Components of Foams 5 4.3.1 Isocyanates 5 4.3.2 Hydroxy1 Components 6

4.3.3 Blowing Agents 6

4.3.4 Catalysts 7 4.3.5 Surfactants » 7 4.3.6 Fillers 7 4.3.7 Additives . 8

4.4 Properties of Rigid or Structural Foams 8

4.4.1 Compressive Strength 8

4.4.2 Impact Resistance 11

4.4.3 Dimensional Stability 11

4.4.4 Thermal Stability 12

4.4.5 Photolytic Stability 13

4.4.6 Water and Water Vapor Transmission 13

4.4.7 Insulation 14

4.4.8 Flammability 15

4.4.9 Weathering 18

4.4.10 Adhesion 18

5. Performance Parameters . 18

5.1 Substrates and Surface Preparation 18

5.2 Slope 20

5.3 Application Techniques 20

5.4 Utilization of Vapor Flow Retarders 22

5.5 Flashings and Expansion Joints 23

6. Weather Protection of Foamed Urethane in Roofing

Applications 23

6.1 Properties 23

6.2 Materials 24

6.3 Application 25

7. Discussion and Comments 25

7.1 Durability 26

7.2 Fire Safety 26

7.3 Problem Areas 28

7.3.1 Performance of Protective Coating 28

7.3.2 Cracking 28

7.3.3 Adhesion and Blisters 29

7.3.4 Bird Damage 29
Contents - continued

Page

8. Guidelines for Selection and Use of Urethane Foam

in Roofing Applications 29

8.1 New Roofing Applications 30

8.2 Reroofing Applications 31

9. Performance Specifications for Polyure thane Foam

Roofing Systems 32

9.1 Suggested Performance Specification for Guidance in

Selecting a Foam Urethane Protective Coating

Roofing System 33

9.1.1 Fire Safety 33

9.1.2 Wind Resistance 34

9.1.3 Water Resistance 34

9.1.4 Stress Resistance 35

9.1.5 Resistance to Impact and Foot Traffic 36

9.1.6 Dimensional Stability 36

9.1.7 Durability of the Protective Coating 37

10. Acknowledgment 37

11. References 39

li
Guidelines for Selection of and Use of

Foam Polyurethane Roofing Systems

William C. Cullen

Walter J. Rossiter, Jr.

The use of spray-in-place polyurethane foam for roofing

application in the United States is increasing at a rapid

rate. Little unbiased information is available to guide the user in the specification, selection, application, and

performance of this innovative roofing system. This report

describes the current state-of-the-art of rigid polyurethane

technology as applied to roofing systems. The performance

parameters as observed during the field survey are discussed

in terms of protective coatings, fire safety, durability and

problem areas. Guidelines to assist the supplier and user alike in the use and selection of polyurethane foam roofing

systems are given. Finally, a performance specification for

spray-in-place polyurethane foam roofing system is suggested.

Key words: Durability; fire safety; performance guidelines;

protective coatings; rigid polyurethane; roofing.

1. Introduction

During the decade of the 1960 's, spray polyurethane foam attained

prominance as a roofing material in the United States. Basically, the

roofing system consists of a sprayed-in-place polyurethane foam insulation combined with a protective cover. In some cases it has been

recommended and specified for use over decks which, for one reason or another, cannot accommodate a conventional bituminous built-up roof. In

other cases it has been recommended and specified for use in lieu of con- ventional membrane roofings and in still others it has been used as a repair covering over various and sundry roofing systems including builtup, metal and others. In brief, it is indeed unfortunate that the foamedin-place urethane materials have been proposed, mostly by the uninformed,

as a panecea for the many roofing problems which have plagued the

industry for many decades. The number of contractors who have entered

and departed the foam urethane roofing business during the past 10 years

provides adequate testimony that foam urethane does not offer the

universal solution to all roofing problems. On the other hand, when

properly specified and applied, urethane has solved severe and costly

roof problems which could not be easily solved by more conventional means,

The user, including the construction agencies of the. U.S. Government, is

faced with a dilemma when a decision is necessary whether or not to

select a urethane foam roofing system over the more conventional system

for a particular use. Nevertheless, a decision must be made. In doing

so the advantages and limitations of competitive systems must be considered in terms of utility, performance, durability and cost. In selecting

his choice, the decision maker must recognize the possible trade-offs

which will have to be made. Further, he must be willing to accept the
consequences of the trade-offs. To assist in the decision process,

valid data should be gathered and analyzed to obtain factual information.

This can be expressed:

DATA + ANALYSIS > INFORMATION

The information then must be combined with sound engineering judgment

to make the decision:

INFORMATION + JUDGMENT > DECISION

Several sources have been used to gather information including a survey of the current literature, personal contacts with suppliers and

applicators of urethane foams and their protective coatings, and on-site

observations of the performance, utility and durability of both new and

aged foam urethane roof applications. We believe that it is the best

information available at this point- in- 1 itne . To be useful, the information must be used in combination with sound engineering judgment to:

1. Determine whether or not foam urethane provides the solution.

If the answer is positive,

2. Select the proper system to meet the requirements of the

specific job.

In this report we have suggested guidelines and a performance

specification for spray-in-place polyurethane used for roofing to assist

the decision maker.

2. Purpose of the Report

Heretofore little unbiased information has been available regarding

the choice, application, performance, advantages and limitations of the

foamed- in- place urethane roofing systems to assist personnel charged with

design, construction and maintenance responsibilities. Therefore, at the

request of the Naval Facilities Engineering Command, U. S. Navy; the

Directorate of Civil Engineering, U. S. Air Force; and the Office of Chief

of Engineers, U. S. Army, a project was conducted to survey the state-ofthe-art of polyurethane roofing technology. The purpose of this paper is

to provide guidelines for the selection and use of foamed- in- place polyurethanes for roofing applications. A further purpose is to suggest a performance specification concerning the urethane foam system and its

protective coating system.

3. Conduct of Study

Initially, in formulating the project plan, it was decided not to

perform laboratory research due to the magnitude of the problem and

funding limitations. We believed that the better approach was to

utilize in-use experience as the primary source of information. In this

connection field inspections of almost a hundred roofs have been made in
many areas of the United States. The roofs which were observed varied

in size from a few squares!.' to more than three acres2^ in area. Several

varieties of substrates used for the urethane systems, including

weathered built-up roofing, were observed. The roofs surfaced with

urethane ranged from flat to vertical. The urethane was exposed to

climates varying from the relatively mild climates of California to those

experiencing large temperature extremes such as Northern Alaska. The

performance of protective coverings of many different types and characteristics were observed. These observations were used in developing the

performance guidelines.

Several leading roofing contractors, including spray foam applicators, were contacted, interviewed and, in some cases, visited to obtain

their views, experiences, and opinions on the use, application and

performance of urethane roofing systems. These included successful and

unsuccessful foam applicators and roofing contractors who have not been

in the business directly but had definite opinions as expert "outside"

observers. These contacts provided us with opportunities to hear and

observe the "good and bad", the advantages and limitations, and the

strengths and weaknesses of the foamed urethane systems in roof

applications

The opinions of owners and users were also solicited. The private

as well as the public sector became involved and the opinion givers

ranged from housewives to plant engineers who were responsible for

urethane roofing systems of several acres in area. These opinions were

also used in developing the performance guidelines.

Scientists experienced in the chemistry of polymers and in the

chemistry and use of protective coatings were queried regarding chemical

structure, reactions, chemical and physical properties, weathering and

aging characteristics, compatibility, engineering properties and the like

Further, the experience of personnel of the National Bureau of

Standards familiar with the properties of materials and performance of

all types of roofing systems over many years was called upon to condense

the multifarious data obtained from the many and various sources into

useful information to assist the decision maker.

Finally, a comprehensive survey of literature concerning polyurethane foams was completed to complement the information developed

from in-service data sources.

—' One square of roofing is equal to 100 square feet.

%.' One acre is equal to 43,560 square feet.
4. Rigid or Structural Polyurethane Foams and Their Properties

4.1 Introduction

Polyurethane foams (often referred to as urethane foams) can be

obtained in a broad variety of physical characteristics ranging from

resilient and flexible to non-resilient and rigid. The formation of one

type versus another is governed by the chemistry involved in their production. For the purpose of this report, we will be concerned only with

the rigid polyurethane foams. However, even in this limited topic, there

exists a very large variety of rigid foams and variations in formulating

the foams which can result in changes in properties. Moreover, changing

the proportions of reactants (without changing the reactants themselves)

can also affect the resultant foam and its properties. Thus, it is difficult to generalize about the properties of rigid foams. Reactants can

be chosen to give the desired product [ 1] — . Therefore, what is presented

here is a synopsis of the properties of rigid polyurethane foams. Each

property has been covered in considerably more detail in the literature.

Rigid polyurethane foams are often referred to as structural polyurethane foams. However, the term structural is used only to differentiate these foams from the flexible polyurethane foams. It does not

mean that a rigid foam in a building has load-bearing capacity. On the

contrary, a rigid or structural polyurethane foam should not be used in

a building as a load-bearing member.

4.2 The Chemistry of Polyurethane Foams

The chemistry of polyurethane has been reviewed [2-4]. However,

since the properties of polyurethane foams are so diversified and

dependent upon the chemistry involved, some brief comments reviewing the

chemistry would seem appropriate. This will be of value when discussion

properties from a chemical viewpoint.

The most generally employed reaction for the formation of a urethane

is that between a hydroxyl compound (alcohol) and an isocyanate (Eouation

I).

R-OH + 0=C=N-R R-OOCNHR (Eq. I)

alcohol isocyanate ^ urethane

Other reactions are known for the formation of urethanes but these are seldom used in the production of rigid polyurethane foams. Modification

of the reactants in the previous equation to di- or polyfunctional

alcohols and di- or polyisocyanates results in the formation of a polyurethane (Equation II).

HO-R-OH + 0=C=N-R-N=C=0 v 0-R-OOCNH-R-NHCO (Eq. II)

3/ Figures in brackets refer to literature reference at the end of the

paper.

4
Equation II shows both the hydroxyl and isocyanate compounds as difunctional . This reaction produces linear polyurethanes. If the

functionality of either is increased to three or more, then a crosslinked or chainbranched polyure thane is produced. The rigidity of a polyurethane foam is greatly dependent upon the degree of cros slinking

As the number of crosslinks increases, the foam becomes more rigid [ 5] .

Besides the hydroxyl and isocyanate reactants, other components

used in the production of polyurethane foams are blowing agents,

catalysts, surfactants, fillers, and additives such as flame retardants

and antioxidants [6].

4.3 Components of Foams

4.3.1 Isocyanates

For foams in general, these compounds may be either aliphatic or aromatic. However, rigid foams use aromatic di- or poly- isocyanates

[7]- These isocyanates are toxic. The most common of these are tolylene

diisocyanate (TDI) (IA + IB), 4,4' - diphenylmethane disocyanate (MDI)

(II) and the "crude" TDI and MDI.

CH CH

NCO OCN >C NCO

IB

2, 4-tolylene diisocyanate 2, 6-tolylene diisocyanate

OCN —( (^J)

V- ch

2 —

\\y /

NC0

4, 4-diphenylmethane diisocyanate

II

TDI is generally a mixture of two isomers, the 2,4 - (IA) and the

2,6 - (IB) isomers. TDI is a colorless liquid with a relatively high

vapor pressure, a lachrymator, and respiratory irritant [3], and care

should be used in spraying. MDI is a solid with a low vapor pressure.

Consequently, it is not as bad an irritant. However, in handling, care

should again be taken that it is not spilled on the skin. When used in

conjunction with a solvent in spray applications caution should be

exercised so that the fine spray is not inhaled.

The "crude" isocyanates have lower reactivities and lower vapor

pressures. The lower reactivities mean that less heat is built up during

the foaming process; the lower vapor pressures reduce the health hazard.

"Crude" TDI is an undistilled grade of TDI. "Crude" MDI is prepared by

the phosgenation of aniline-formaldehyde condensates and can be
represented by the following structure:

This material is also referred to as polymethylene polyphenylisocyanate,

and its functionality usually varies from two to three [3].

Other isocyanates are available for use in polyurethane production

but these are not generally used.

4.3.2 Hydroxy 1 Components

The first hydroxyl components (polyols) used in the production of

polyurethanes were hydroxyl- terminated polyesters. These commercial

compounds were mainly formed by the reaction of adipic or phthalic acids

with diols or triols. For rigid polyurethane foam production, polyesters

have been largely replaced by hydroxy 1-terminated polyethers [8] . These

polyethers are prepared by the base catalyzed addition of an alkylene

oxide to a poly functional alcohol. The alcohols may be diols, triols,

tetrols, hexitols, or octols [3]. In rigid foams, the polyethers

usually have a functionality of 4 or greater. Refined castor oil or deviatives have also been used for the production of rigid foams. It

has been stated that the presence of castor oil in a polyurethane imparts

water resistance and weathering resistance to it [3].

The properties of the foam are dependent upon the polyol chosen for

its production [9]. Selection of the polyol is the major means of con- trolling the properties of the foam [10]. The reason is that there are

a large variety of polyols available for rigid foam production, while

only a few polyisocyanates are used.

4.3.3 Blowing Agents

The blowing or foaming agents are the gases trapped in the solid

polyurethane polymer, producing the cellular character of the foam.

There are two major methods of foaming polyurethanes. In the first

method, a gas is produced in situ during the polymerization process. The

major reaction in polyurethane technology is that between an isocyanate

and water (Equation III) . The resulting carbamic acid is

r-N=C=0 + H

2 -> RNHCOOH

carbamic acid

unstable

-> RNH + C0 o (Eq. Ill)

2

gas

unstable and it eliminates carbon dioxide, which becomes the foaming

agent. In cases where the foam is to be used as insulation this
technique is rarely used. Also, this type of foaming tends to be expensive since excess isocyanate must be used to react with the water.

The second technique for foaming involves the incorporation of a volatile liquid in the formulation for polymer production. During the

polymerization process which is highly exothermic, the heat of reaction

is sufficient to vaporize the liquid and the resultant gas is entrapped

in the polymeric solid producing the cellular structure. The most

commonly used blowing agent for this type of foaming is monofluorotrichloromethane, CC1„F, (Refrigerant 11), although others might be used

depending upon the application. For example, in spraying in a hotter

climate, a higher boiling blowing agent such as C CLF might be used

instead of CC1 F.

4.3.4 Catalysts

Catalysts are used to control the rate of reaction between the hydroxyl and isocyanate components. Also, the catalyst governs chain

propagation, chain extension, and crosslinking [3]. Moreover, it is

important in the "cure" of the foam. An incompletely cured foam will

not achieve its maximum strength properties.

The two types of catalysts employed in foam production are tertiary

amines and organotin compounds [6]. The choice of either is dependent

upon the system being foamed and the properties desired in the resultant

foam. In some cases, a combination of both may be used for synergistic

effects among catalysts can be observed. For example, both types might

be used in a spray application where a fast "cure" is desired [6].

Although the previously discussed components, isocyanate, hydroxy 1,

and blowing agent, have more influence on the properties of a foam, the

catalyst can also influence the properties. One effect that should not

be overlooked is that the catalyst in the foam can have an effect on the

long term service properties of the foam. It is possible that a foam

with good initial properties may not have good long term properties since

the catalyst may enhance the rate of deterioration of the foam. For

example, it has been stated that tin diethyl dicaprilate foams degrade

to a greater extent than foams produced with other catalysts [11].

4.3.5 Surfactants

These compounds, usually silicon or silicon- polyether copolymers,

are used to regulate cell size and cell wall rigidity in the foam [1].

4.3.6 Fillers

These are lightweight, bulky, inorganic materials added to extend

the foam, either to lower its cost or to alter a physical property [12].

When using a filler, its compatibility with the polymer should be established. Also, if used to lower costs, it should be determined that an actual weight-to-cost reduction is achieved.
4.3.7 Additives

These are included to alter a property of the foam. Included here

are flame retardants, antioxidants, and pigments. The effect of such

additives on the properties of the foam should be determined.

4.4 Properties of Rigid or Structural Foams

Polyurethane foams possess many properties that make them attractive

in the construction industry. Among these are the high strength-toweight ratio, good thermal stability as compared to other organic polymers, low thermal conductivity and excellent adhesion to metals [6,13].

Like other polymers, the properties of polyurethanes are dependent upon

molecular weight, degree of cross linking, effective intermolecular

forces, stiffness of chain segments and crystallinity [3]. The preceding

section describing the raw materials for foam production has been included

here since the service properties of the foam can not be separated from

the raw materials [l] . This section will now describe some of those

properties that are important in roofing applications. The discussion

will deal with each property independent of the other properties,

although in many instances there is necessarily overlap between properties

There are some general statements that may be made concerning polyurethane foams. Structural polyurethane foams obtain their rigidity

from a high degree of cross linking. Also rigid polyurethane foams con- tain a mostly closed-cell structure (as compared with the flexible polyurethane foams which are mostly open-celled). Rigid foams, as commonly

used in construction, normally possess densities from 1 to 3 pounds per

cubic foot (pcf) [ 13] . However, roof spray density ranges from 1.8 to

4 pcf.

Frisch has stated that the properties of rigid polyurethane foams

are dependent upon three factors [10]:

1) the chemical structure of the foam components and of the

resulting polyurethane polymer,

2) the mode of preparation and the mechanical factors in

the foam manufacture, and

3) the density and cell geometry of the foam.

4.4.1 Compressive Strength

The compressive strength of rigid polyurethane foams is dependent

upon the density of the foam and the shape of the gas cells in the foam

[ 14] . Of the two density is the property which most governs the strength

of the foam. As the density increases, the strength of the foam increases

[ 15] . Deverell prepared a number of rigid foams with densities ranging

from 2 to 75 pcf [16]. He concluded that at room temperature there

existed a parabolic relationship between compressive strength and density.

These results have been observed by others (Figure I and Table 1) [1,14].

8
Hilado states that in most applications of rigid polyurethane foams, the

foam density ranges from 1.5 to 2.5 pcf [14]. If the density of the foam

is below 1.5 pcf, then the foam does not possess adequate mechanical

strength. If more strength is needed, then a higher density foam should

be used. However, even though the lower density rigid foams have con- siderable strength, a foam with a density even as high as 20 pcf should

not be used as a structural member [17].

« 200

>

M J 100

CO 4J

<D 00 u c

a. <u e n

O 4J

— . , i 1 1 1 —

1 i L 2 3 4 5 6 7 8

Density, pcf

Figure I Compressive strength vs. density of rigid

foam (according to Hilado [14]).

Density, pcf Compressive Strength, psi

3

6

9

12

40-50

120-160

240-280

400-440

Table I Compressive strength vs. density of rigid

foams (according to Gordon [1]).

The effect of temperature on the compressive strength of rigid foams

has been studied [16,18]. As the temperature is increased above ambient,

the compressive strength decreases until the foams become soft and flexible. This temperature is approximately 130-150°C (266-302°F) and is

slightly dependent upon the blowing agent [17]. Above 150°C (302°F)

most rigid polyurethane foams have no load bearing capacity but they can still possibly support their own weight. Figure II shows one example of

the decrease of compressive strength with increasing temperature for a particular rigid foam. This figure shows that the decrease in strength

is non- linear with increasing temperature. But, this is not always the

case since a linear decrease for another foam has been reported [17]. As

the temperature is decreased below room temperature, there is a slight

increase in compressive strength [17].
>

•H

CO

CO

0)U

a

e •H o CO o a

s n

CO x: o •U

pE4 (DO Cl c a)

CD S-i CD 4-1 s ^

42

r " r i

1

>vd=3.0

36 \

^d=2.5 \

30 ~^^"\\

24 " d=2.0 \\

18 ^^x\

12 d=l.5 v\

6

25 50

tii.

75 100 125 150

T, °C

Figure II Compressive Strength vs. Temperature for Various

Densities (according to Harding and Hilado [18])

The effect of chemical structure on compressive strength has been

studied [9,18]. It was concluded that for commercial applications the

most practical method for changing the foam strength is to change the

density and the cell structure [18]. The compressive strength is increased most effectively by using polyols of low equivalent weight, but

this method is not always commercially practical [18].

Besides changing the chemical reactants to effect structural changes,

one may also alter the stoichiometric ratio of the reacting isocyanate

and polyol. This ratio, times 100, is called the isocyanate index

([NC0] /[OH] x 100). Results of changes in isocyanate index have been

reported by Frisch [10]. In regards to compressive strength, it in- creases as the isocyanate ratio increases from 0.9 to 1.1. At the

higher isocyanate ratio, however, the foams become more brittle.

The compressive strength of rigid polyurethane foams may be affected

by water and water vapor. However, this only occurs when water has penetrated into the interior of the foam [16]. In other words, the water

must penetrate the closed cells. The open cells at the exterior of the

foam may hold a large quantity of water but the foam properties will not

generally be affected. In one case, exposure of a foam for 1000 hours

at 100% relative humidity and 20°C had a negligible effect on the strength

properties of the foam. However, data describing longer exposures of

10
foams to water were not found. For a roofing system which should last a minimum of 20 years, the effects of slow hydrolysis of the foam should be

considered

Besides density, the second major factor governing the compressive

strength of foams is the shape of the cells holding the blowing agent.

As previously mentioned, rigid polyurethane foams contain mostly closed

cells. During the foaming process, these cells tend to elongate in the

direction of the foam rise. This cell elongation gives an anisotropicity

to the foam. The compressive strength of the foam is greatest in the

direction of foam rise and minimum perpendicular to the foam rise [9,17].

For our area of interest, this has significance in the fact that a foam

sprayed on a roof may not have uniform strength across the roof (even on

a flat roof) . This results because the direction of the flow of the

rising foam may be either lateral or vertical in different spots. Thus,

the possible variation in compressive strength in different areas depending upon the direction of foam rise.

4.4.2 Impact Resistance

This property of the foam is important since it prevents damage to

the roof from falling objects. Such objects might include hail, tools,

tree limbs, and the like. The review of the literature revealed little

information in this area. In particular, nothing was found concerning

hail damage to roofs. There was one recent report describing the impact

resistance of uncoated rigid urethane foams [14]. The major conclusion

is that the density is the main factor in controlling impact properties.

As the density of the foam is increased, the impact resistance of the

foam increases.

4.4.3 Dimensional Stability

Like all plastics, rigid polyurethane foams have a high linear co- efficient of thermal expansion. These coefficients are higher than those

of metals, for example 5-8 x 10

_5

/°C (22-44 x 10 /°F) for polyurethane

vs. 2.3 x 10" 5 /°C (13 x 10_6 /°F) for aluminum [17]. However, the problem

of dimensional stability of the polyurethane foam is caused primarily by

changes in gas pressure within the cells and not by changes in the dimension of the solid plastic [9, 15-17]. As the temperature of the foam is

raised, the gas pressure increases and the foam has a tendency to expand.

Likewise, as the temperature is decreased, the gas pressure decreases

and the foam has a tendency to contract. The better the foam can resist

such gas pressure changes, the more dimensionally stable it is. The

ability of the foam to resist these changes is governed by the foam density, the cell structure, and the polymer composition [15]. As the

density is increased, the foam strength is increased allowing the foam

to resist the increased pressure. Nearly round or uniform cells give

better resistance to pressure changes. Foams that resist water vapor

penetration are also more dimensionally stable since water infusion

into the cells results in increased pressure. Water vapor transmission

can be minimized by the choice of polymer since some polymers have less

11
tendency to transmit water vapor than others. In general, hot and humid

conditions are the worst climates for foams.

4.4.4 Thermal Stability

Polyurethane foams, as organic materials, are susceptible to thermal

degradation. The chemistry involved in such decomposition has been

studied and it is known that there are three major reaction pathways for

decomposition [20]. This chemistry is important for it is through the

use of such knowledge that the polymer chemist may modify the polymer to

increase stability. Tilley and coworkers have reviewed the factors that

govern the stability of the foam. These are the number of crosslinks,

interchain forces, rigidity of the molecules, molecular fit, and molecular

weight. Among these the number of crosslinks is most important, the

higher the crosslink density, the more thermally stable the polymer [5].

Increased crosslinking also increases the softening temperature [21].

Increased crosslinking is accomplished by increasing the functionality

of either the component isocyanates and polyols, or by lowering the

equivalent weight of these [5]. A more detailed discussion of the

chemistry of thermal decomposition and stabilization does not seem appropriate here. Instead, some general observations about polyurethane

foam thermal stability as obtained from the literature will be mentioned.

Methods such as heat aging, differential thermal analysis (DTA) and

thermogravimetric analysis (TGA) have been used to study the thermal

stability of foams. Although it would seem likely that foams may be

synthesized that would not withstand temperatures encountered on a roof,

all papers that discussed thermal stability and that were encountered in

this study described foams that are capable of withstanding temperatures

much higher than those on roofs. Smith reported the results of TGA and

DTA on three different rigid polyurethane foams [22]. Even with the

least stable foam, TGA showed no weight loss until 150°C (302°F) and on

the same foam DTA also showed no major changes until 150°C (302°F) . In a similar experiment Reegen and Frisch reported no weight loss until 260°C

(500°F) as determined by TGA. This point corresponded to an exotherm on

DTA. In this case, DTA showed a slight endothermic change at 110-115°C

(230-239°F) which corresponded to the softening point of the foam.

In regards to heat aging and long term temperature stability, the

type of information that was desired could not be found. Nothing appeared

to be available describing the behavior of a polyurethane foam that had

been heat aged at temperatures less than 100°C (212°F) . Most experiments

were designed to heat age at higher temperatures where changes might be

expected. In one experiment, a number of foams were heated at 100°C but

in an oxygen atmosphere [21].

In general, it can be stated that increased stability is imparted to

polyurethane foams by:

1) increasing the crosslink density [5,21,23] and

12
2) using polyisocyanates of high aromaticity (i.e., MDI, PAPI)

[5,21,24].

Certain flame retardants are known to decrease thermal stability [24].

4.4.5 Photolytic Stability

In a paper written in 1966, Tarakanov and co-workers remarked that

"The problem of change of polyurethane properties under the influence of

ultraviolet radiation is given little attention in the literature...."

[25]. We have made the same observation in our search of the literature.

Data describing the behavior of polyurethane foams to ultraviolet light

or sunlight was very scant.

The Tarakanov study was undertaken to elucidate the mechanism of

photolytic destruction of polyurethanes . In one experiment, it was determined that a polyurethane formed from MDI was photolytically more

stable than that from TDI. The same polyol was used in both foams.

However, the formulations used were not of the type that would be

encountered in rigid polyurethane foams.

Reegen and Frisch, in another experiment, exposed three different

films, differing only in isocyanate reactant , to Fade-Ometer testing

[21]. Their results showed that a TDI based polyurethane was more stable

than a PAPI based polyurethane. This result is reversed from that of

Tarakanov. These two reports show a good example of how formulation

determines the properties of foams.

In general, polyurethanes based on aromatic isocyanates yellow after

exposure to sunlight [3]. For outdoor applications such as roofing,

foams must be protected from the weather by either covering with another

material or painting [26].

4.4.6 Water and Water Vapor Transmission

The closed-cell structure of rigid polyurethane foams renders them

resistant to water penetration [17]. This property is an asset in roofing usage since even if the protective coating on the foam is broken,

water still will not soak through the roof [27].

However, water vapor transmission, which should not be confused with

water transmission, is possible through polyurethane foams [17,26]. It was previously pointed out that water vapor penetration into the foam can have an adverse effect on the strength and dimensional stability of the

foam. Likewise, the insulation value of the foam can be considerably

lowered. Since rigid foams are commonly applied for insulation, water

vapor penetration should be minimized.

In order to minimize water vapor transmission, it has been suggested

that in structures with high interior humidities, a vapor barrier be

erected on the warm side of the insulated object [28]. In many applica13
tions in certain climates, the warm side of the insulation may be the

low vapor pressure side. In such cases, a vapor barrier might then be

necessary on the outside in the form of the protective coating. In any

situation, if moisture does enter the foam, it should be allowed to get

back out

Hilado and Harding have reported on the relationship between water

vapor permeability and chemical-physical structure in rigid polyurethane

foam [20]. Water vapor permeability is lowered by higher functionality

and aromaticity, and by lower equivalent weight and fewer polar elements

in the polyol. Density and cell structure are also important. Permeability increases as density decreases and as cell size increases.

Chemically to insure low water vapor permeability, the aromaticity

should be kept as high as possible. Hilado and Harding also state that

crosslink density higher than that required for rigidity is not a criterion for low water vapor penetration. Frisch states that cross- link density has a distinct effect [10]. As the crosslink density

increases, the water vapor permeability decreases.

4.4.7 Insulation

The low thermal conductivity (K-value or K- factor) of polyurethane

foam is one of its most important properties. In fact a good insulating

foam will have a K-value that is considerably lower than other insulations. However, the initial K-value does change with time, and it

varies depending upon the aging conditions [30].

The mechanism of heat transfer through foams has been described by

Levy [28] . It involves conduction, convection, and radiation. Radiation theory says that the large number of cells in foams minimizes

radiation heat transfer. Cell size controls convection transfer, as the cells decrease in size, convection decreases. In foams with cells

0.2 in*- (5.1 mm) or less in diameter, convection is essentially non- existent. Therefore, in closed-cell foams, heat transfer is mainly due

to conduction through the foam materials.

In line with the theory of heat transfer, Varland has listed the

factors which influence the initial and aged K-values of the foam F 30

31]. These are: 1) the blowing agent used; 2) the open cell content

of the foam; 3) the dimensions of the foam; 4) the temperature during

aging; 5) orientation and size of the cells; and 6) the presence of

natural or applied skins. Low thermal conductivity is one property of

foam which is not directly related to density [32].

The most important of these factors is the blowing agent that is

used. High molecular weight gases have lower thermal conductivities

than low molecular weight gases [28]. Thus, the initial K-values of

monof luorotrichloromethane blown foams are 0.10 to 0.15, while the

initial K-values of carbon dioxide blown foams are about 0.22 to 0.24

[10]. Moreover, the K-values of carbon dioxide foams increase more than

those from monof luorotrichloromethane as the foams. age. Table III shows

14
this effect. The increase in K-value is due to air permeating the foam

and/or the other gases diffusing out [30,31]. Thus, for best insulation

a foam blown with monof luorotrichloromethane should be used. It has

been stated that with this gas, loss of insulation will only be significant if the foam is used at high temperatures (100°C), in thin sections

(1 in.), and without a protective barrier [33].

Aging in Days K- Value K-Value

at 60°C (140°F) CO Blown CC1 F Blown

0.186 0.112

7 0.222 0.128

14 0.233 0.136

21 0.237 0.140

28 0.238 0.144

50 0.239 0.149

100 0.24 0.155

150 0.24 0.156

200 0.24 0.157

250 0.24 0.157

Table III The change in K- values of foam with time

(according to Frisch [10]).

As previously mentioned water vapor penetration has an adverse

effect on the insulating properties of rigid polyurethane foams. Used

as insulation, the foam has a warm side and a cold side. Warm air

normally contains more water than cold air and as the heat tends to migrate to the cold, water vapor is accompanied with it [29]. At the cold

surface, the water can condense and liquid water has a thermal conductivity that is 10-40 times greater than that of the foam [29]. If the temperature is low enough, an ice barrier may even form which lowers the

insulation value of the foam even further. Ice has a thermal conductivity about 100 times that of the foam [28]. Furthermore, such an ice

barrier prevents the passage of water vapor and therefore, the ice barrier enlarges. To minimize such problems, a water vapor barrier should

be used on the warm side.

4.4.8 Flammability

As organic materials rigid polyurethane foams are combustible. The

15
degree of flammability is controlled by both physical and chemical flame

retardant techniques. The important characteristics of flammability of

cellular plastics have been described [34,35]. There are:

1) Ease of Ignition - The ease by which the plastic or its

pyrolysls products can be ignited under given conditions of

oxygen and temperature

2) Flame Spread - The rate of spread of the flame once the fire

begins under the conditions of burning. ASTM Standard E 176

defines this parameter as flaming combustion along a surface.

3) Fuel Contribution - Heat produced by the combustion of a given

weight or volume of foam.

4) Smoke Density - Degree of light or sight obscuration produced

by the smoke of the burning foam under the given conditions

of combustion.

5) Products of Pyro lysis and Combustion - From foams, these are usually solid, carbonaceous char or residue, volatile gases,

and entrained solid particles (smoke) . Toxicity of combustion

gases is included here.

Flammability tests are designed to evaluate these characteristics.

A list of the most widely used and accepted flammability tests employed

with polyurethane foams has been compiled by Hilado [36]. He states

that in general there are two types of fires which these tests seek to

simulate. The first is the small accidental fire with limited amounts

of heat; the second is the large-scale fire with massive amounts of heat.

He further states that tests for rigid foams tend to be large-scale

since rigid foams, as used in construction, are used in large quantities,

e.g., on a roof. Also, these tests for rigid polyurethane foams tend to

be identical or related to tests for other construction materials. A

single material may perform differently in different tests. For example,

a plastic may be rated self-extinguishing in one test but yet it might

burn vigorously in another [37]. This is quite significant. It means

that foams should not be used that have not been completely evaluated for

flammability. Using a foam because a particular fire test gives the foam

a good rating could lead to a disaster. The fire rating could be com- pletely meaningless under the service conditions. In the field, the foam

might readily burn. Some tests are designed for standardization and com- parison, and they do not necessarily represent field conditions. That

is, the tests give relative ratings for burning but do not show the behavior of the material in an actual fire. This does not mean that flammability tests should not be used, but that tests used should be specific

for the application and the conditions of application of the foam.

Of the various tests that have been employed for foams, the most common small-scale test is the ASTM D 1692 (Flammability of Plastic

Sheeting) . Another small-scale test is the ASTM E 162 (Radiant panel

test). A large-scale test frequently conducted is the ASTM E 84 (tunnel

test). The U. S. Bureau of Mines flame penetration test measures the

16
foams ability to act as a flame barrier. For roofing purposes, ASTM

Method E 108 (Fire Test for Roof Coverings) is often used to evaluate

the total system.

Besides being used to show how foams will behave in fire conditions,

some flammability tests are also conducted to show how variations in foam

formulation can alter the flame retardancy of a foam [27]. Flame retardancy is imparted to the foam by incorporating into the formulation com- pounds which contain halogen, either bromine or chlorine, phosphorus, or nitrogen [38]. These may be used either alone or in combination. Also,

additives are used which have no or little flame retardancy in themselves

but act synergistically with other compounds. The most well known

example of this phenomenon is the use of antimony oxide with a chlorine

containing compound

There are two methods of incorporating these flame retardants into

the foam. The first combines the retardant with the polymer molecule

through chemical bonding; the second mixes or disperses the retardant

in the foam only as an additive. The second method has drawbacks not

associated with the first. The primary concern is that the retardant may

not be permanent. If the additive is not compatible with the polyurethane

polymer, it will diffuse from the polymer. Also, the additive may cause plasticization of the foam [38]. This leads to a reduction of the

strength and dimensional stability of the foam and, consequently, may

accelerate degradation of the foam.

Flame retardancy of the foam may also be governed by the chemistry

of the polymer. For rigid polyurethane foams produced from polyether

polyols, maximum flame retardancy is obtained from the following:

1) high functionality of the polyether; 2) high hydroxyl number polyether; 3) polyether with cyclic groups; 4) polycyclic isocyanate; and

5) poly functional isocyanate [39].

Another method for imparting flame retardancy to the foam is to cover the foam with a non-flammable or flame retardant covering such as an intumescent coating. A major difficulty here is that if the coating

is damaged or destroyed, then the foam loses its protection from fire.

In one study involving flame retardant rigid polyurethane foams, it was concluded that such foams would not ignite when exposed to small

flame sources [40]. They would burn rapidly when exposed to large sources

of heat and flame. However, if flames did not strike the foam and air were excluded, the foam would not burn. This situation is encountered in

sandwich panel construction where, for example, the panel is constructed

with steel skins with a urethane core. A member of the NBS fire section

concurred with the findings on sandwich panels [41]. However, in the

same conversation it was mentioned that polyurethane foam slabs have

cracks between them and the fire begins under the slabs. The cracks give

a chimney type effect providing the fire with a means of burning into the

foam.

17
Although foams are available that possess a high resistance to

ignition and flame penetration, and a low rate of flame spread, these

materials release a lot of smoke when burned [42]. Smoke is a problem

since it obscures the vision of occupants of a building who are attempting to leave or the vision of firefighters attempting to put the fire out

Even if the smoke does not obscure vision it is an eye irritant and

many of the gases are toxic. In a roof-top fire where the fire is only

on the exterior of the building, the problem of smoke generation is not

as great as where the fire is in the interior of the building. A problem could arise if environmental conditions caused the smoke to be

carried into the building.

4.4.9 Weathering

This is one area of polyurethane foam technology in which data is

completely lacking in the literature. It is a recognized fact that polyurethane foam sprayed on a roof must be protected from ultraviolet

radiation by covering or coating. However, articles describing this

could not be found. Also, no information was available comparing the

outdoor behavior of foams covered with various materials.

4.4.10 Adhesion

It has been previously stated that rigid polyurethane foams have

excellent adhesion to metals and other surfaces. To achieve good

adhesion, the surface on which the polyurethane foam is applied must be

clean, free from rust and corrosion, and dry. Field experience indicates

that moisture may reduce the strength of the adhesive bond of urethane

to the substrate.

5 . Performance Parameters

There are several parameters which will affect the performance of

a foam polyurethane roofing system. They include, among others which

will be discussed later in this report:

° Substrates and Surface Preparation

"Slope

°Application Techniques

"Utilization of Vapor Flow Retarders

"Utilization of Expansion Joints.

5.1 Substrates and Surface Preparation

Sprayed urethane foams have been applied to several types of substrates in roofing applications. It has been estimated by one large

applicator that probably 40% of urethane applications involve repairing

or resurfacing existing bituminous built-up roofs. Other resurfacing

applications involved the protection of weathered metal decks such as

18
corrugated aluminum or steel.

In new work, urethane foam has been used over concrete, wood, and

shredded wood fiber decks. As in the case of reroofing procedures, an overlayment over metal decks may be required before application of the

urethane foam.

Structural concrete probably provides the better substrate for the

urethane foam, followed closely by a firm plywood deck. However, before

applying foam to a new concrete deck, the concrete must be dry! In

short, the more stable the substrate and the fewer the joints between

units of the substrate, the better will be the performance of the

urethane. This statement applies equally to all types of roofing.

Although urethane s are noted for their good adhesive properties to

clean, dry surfaces of many types, they may not adhere to oily, waxy, or extremely dirty or dusty surfaces. Therefore, it is generally suggested

that surfaces of questionable characteristics be cleaned and primed before the application of the urethane foam. Asphalt primer conforming to

Federal Specification SS-A-701 or ASTM Specification D-41 applied at a spreading rate of 33 to 50 square feet per gallon has been found to be

satisfactory. The primer must be thoroughly dry before application of

the urethane. Asphalt emulsions and hot applied asphalt have also been

successfully used for this purpose.

Urethane foams are frequently applied in two layers. Therefore, the

foam itself often becomes the substrate and the deterioration products

(urethane foam surfaces degrade rather rapidly when exposed to ultraviolet radiation) may interfere with the proper adhesion of succeeding

applications of foam. Inadequate adhesion between foam layers has re- sulted in bonding problems at the interface of the layers which can show

up as severe blistering.

Previously, it was mentioned that probably 40% of the sprayed ure- thane foam for roofing applications is used over existing roofs. We

believe that the reason is purely economical since it has been estimated

that it is 35 to 40% cheaper to clean and prepare the old surface and

apply urethane than it is to tear off and discard the old roof and apply

a new one in kind

In reroofing applications a prime requisite is that the old roof be

in such a condition to receive the urethane system. In most cases special preparation of the old roof substrate is essential. The surfacing of slag or gravel, if present, should be spudded off. Defects as blisters, buckles, wrinkles, or splits should be repaired in accordance

with accepted roofing practices. If wet insulation is part of the old

roofing system, vents should be installed every 10-15 squares to relieve

any potentially damaging vapor pressures due to moisture entrapped in the

insulation. The surface should be cleaned of dust and dirt and, as in

the case of new decks, the surface primed with asphalt primer at a spreading rate of 33 to 50 square feet per gallon. When the primer has

19
dried, the urethane should be applied about one inch in thickness except

in cases where gravel or slag particles are still present the thickness

should be about 11/2 inches to compensate for thickness of any remaining gravel or slag.

In any substrate, be it old or new, areas where potential stresses

can be transferred to the urethane foam such as cracks, joints, or splits should be provided with bond breakers so as to distribute stresses over larger areas of the urethane to avoid the cracking problem.

An acceptable criterion for adhesion of urethane to any substrate

including itself is that it should be firmly adhered, a minimum of 95%

of the surface area.

5.2 Slope

Roof decks with no slope (frequently and erroneously referred to as "dead level") are not acceptable substrates for any roofing system. The

same criterion is even more valid for the sprayed urethane foam roofs.

Generally, a minimum 1/4 inch fall per foot run is suggested, but frequently ignored, for most bituminous roofing membranes. In the case of

urethane foams, due to surface irregularities and application practices

an absolute minimum of 1/4 inch per foot slope-to-drain appears to be

desirable. Since water is among the greater enemies of urethane foam,

it is desirable to get water away from the foam as quickly as possible.

Frequently, varying thicknesses of foam have been specified to provide a positive slope to drain. In one case, foam as deep as 12 inches was proposed. This does not provide an economical solution to the slope

problem. In fact, experience has shown that such a practice is detrimental. When a slope is required for urethane foam, it is the better

practice to make provisions to slope the substrate to which it is to be

applied.

5.3 Application Techniques

The successful application of a spray foam application depends on

a number of factors including:

the base chemical components (see Section 4)

° spray equipment

surface preparation

weather conditions, i.e. temperature, moisture, and wind

° skill of applicator

The skill of the spray man gained through experience is the most essential factor. Poor application techniques negate all other factors which

might otherwise be adequate. The choice of base chemicals and spray

equipment is generally left up to the contractor and, hopefully, is based

20
on his experience with good application and performance characteristics

and not on economics alone.

The surface preparation has been discussed in detail in Section 5.1.

However, it might be well to reiterate here that foam will not bond to

wet, oily, waxy or extremely dusty surfaces. A minimum of 95% adhesion

of the foam to the substrate is a primary requirement. Any less is not

acceptable.

Proper storage of the raw materials used in foam production is

important. First, they must be kept sealed until used. The raw materials

must be kept dry and the temperature should be controlled. A number of

manufacturers suggest storage temperatures in the range of 50 to 85 °F

(10 to 29°C) as suitable.

As with all other roofing systems, the weather plays an important

role in the application of foam urethane. In fact, since the foaming

event on the roof depends on a chemical reaction the rate of which is

temperature dependent, the importance of application and surface temperatures is obvious. It is the consensus of manufacturers and applicators

alike that the temperature of the surface to be sprayed should be at

least 40°F (4°C) . Obviously, the temperature restrictions severely

limit the application season in several parts of the United States. In

most northern states urethane generally can be applied only from April

to October. There is an inherent risk at other times of the winter

season. The warmer climates present no such restrictions as far as temperature is concerned.

Moisture, in the form of rain or condensation, is another factor

which determines the success or failure in a foam urethane roof. As previously pointed out, urethane will not adhere to a damp or wet surface.

Therefore, it is a rule of thumb in the trade that the application of

spray foam shall not commence during the inclement weather or when precipitation is imminent. This rule should not be waived under any circumstances. On clear, cool mornings, condensation is often present on the

roof surface. This surface should be treated as a wet surface and

allowed to dry before spraying is initiated.

In the foam application, wind becomes even a more important variable than it does in the application of other types of roofing. The

surface texture of sprayed urethane is heavily dependent on wind

velocity and the performance of a protective coating depends on surface

texture. Wind velocities in excess of 15 mph make the spraying of

urethane foam impracticable. Since urethane adheres rather tenaciously

to most surfaces, caution should be taken to protect those areas not

intended to receive foam. Provisions should also be made to protect

areas and objects (automobiles and the like) from overspray.

In the spraying operation certain signs should be apparent to indicate the quality of the foaming operation. The two main ingredients of

the plastic foam are sprayed simultaneously, usually in 1:1 ratio. Generally, if the ratio becomes out of balance, an immediate color change

21
occurs which alerts the spray applicators. Adjustments should be

immediately made to obtain proper mixture.

The surface of the foam should be sufficiently smooth to receive the

final protecting coating. "Popcorn" or "tree bark" like or rougher sur- faces result from one or a combination of events as improper spraying

techniques, improper mixing, or by application during windy periods.

This type of surface is not acceptable.

Thickness of the urethane foam is important to its performance from

a fire durability and performance aspect. The optimum thickness is one

inch. The minimum thickness should be no less than one inch and the

maximum no more than two and one quarter inches. When used as reroofing

over a previously surfaced (gravel or slag) built-up roof, it is mandatory that all gravel or slag be first removed. A thickness of one and one half inches is suggested to compensate for the thickness of any individual gravel or slag particles which may remain after the spudding

operation.

5.4 Utilization of Vapor Flow Retarders

A vapor flow retarder, often erroneously referred to as vapor barrier, has, in modern times, become an important element of the roofing

system. So much so that a vapor retarder is frequently specified and

applied when it is not required at all. In fact in some instances, the

inclusion of the so-called vapor barrier is often detrimental to the performance of the roof. In the case of foam urethane roofing system as with other roofs, the question arises as to whether or not a vapor

retarder is required. A general answer cannot be given. The ambient

environment, the design and material aspects of the roofing system in

question, and the interior environment of the building are factors

which will influence the decision.

A further complication is that urethane foam cannot tolerate water

for any prolonged length of time without being adversely affected.

Therefore, the prudent designer should give special consideration in the

selection of a vapor flbw retarder. Certainly, it is the better practice

to use vapor retarders in cases where the diffusion of moisture into the

urethane is probable. For example, in roofing systems placed over high

temperature-high humidity areas (swimming pools, laundries, bakeries, and

the like) located in cold climates, the use of vapor retarders are mandatory. Frequently, the use of a continuous film of asphalt primer recom- mended for adhesive purposes will provide a suitable vapor retarder over concrete decks. The venting of insulation of old built-up roofs, as mentioned previously, assists in relieving vapor pressures generated at

this origin. In cases over high temperature-high humidity areas, the

application of an asphalt saturated and coated base sheet (ASTM Specification D 2626) with sealed side and end laps coated with hot asphalt

will provide a sufficient vapor retarder for all practical purposes.

22
5.5 Flashings and Expansion Joints

Most urethane foams have a relatively high coefficient of linear

thermal expansion. Although the measured and reported values fall in

the 30 to 40 x 10"" per °F or even much greater ranges, we have not been

able to verify these values. They are at least 2 to 3 times the coefficients given for aluminum metal (13 x 10" 6 per °F) which is considered

quite high in the building trade. Therefore, provisions should be made

to compensate for the thermal movements expected in on-the-roof applications by the use of expansion or control joints. A good guideline for

placement of expansion or control joints is that one should be used for

every 90 to 100 squares of roof area. The guideline should be modified

for irregular shaped roofs. Further, they should always be placed at

reentrant corners to form square or rectangular roof areas.

In order to guard against future defects of urethane foam at vent

pipe, vertical surfaces, fascia, gutters, and the like, fabric stripping

reinforcement should be provided at these junctions. In addition cant

strips to provide a 45° angle must be used under the urethane at all

vertical surfaces which project above the plane of the roof.

6. Weather Protection of Foamed Urethane in Roofing Applications

Urethane foams possess certain inherent weaknesses which makes it

mandatory to protect the foam from the weather with a coating or covering

system. Since water is an enemy of the urethane foam, the foam must be

kept dry. Further, polyurethane foam appears to photooxidize very

rapidly when exposed to radiation in the ultraviolet region of the

spectrum. This is characterized by the development of a yellowish or brownish color at the surface of the urethane usually within a matter of

hours of exposure. Therefore, a protective coating is required. Urethane foam used for roofing purposes is generally of a low density.

Therefore, it is susceptible to damage from abrasion, scuffing, and

impact. Protection against abrasion, scuffing and impact is another

reason why a protective coating is required. In summary, the purposes

served by the protective coating are threefold and are listed in

priority order:

1. Shield it from ultraviolet radiation.

2. Keep the foam dry.

3. Protect from abrasion and impact.

6.1 Properties

In order to fulfill its intended function, a protective system must

first be compatible with the foam urethane. Next, it must possess and

retain upon exposure for some period of time, certain requirements as:

1. Adhesiveness to urethane in order to remain in place under

conditions of exposure, e.g. wind, temperature, humidity,

and the like.

23
2. Impact resistance from hail, falling objects, and the like.

3. Adequate susceptibility to temperature change, e.g. good

flexibility at low temperature, no flow at high temperature.

4. Abrasion resistance to foot traffic, water and sand erosion,

and the like

5. Water resistance both in liquid and vapor states.

6. Weather resistance, e.g. sun, rain, dew, wind, and the like.

7. Maintainability, i.e. ease of repair if damaged and ability

of weathered surface to accept and retain additional coating

when recoating becomes necessary.

8. Durability, i.e. the ability of the coating or system to

remain within acceptable performance levels over some period

oft ime

9. Strength and elasticity, i.e. strong enough and elastic

enough to accommodate normal movements in the substrate

without rupture

Certain other characteristics which technically cannot be classed

as performance characteristics are also important and are worthy of

mention:

1. Appearance

2. Coverage

3. Tack- free time

4. Cost

6.2 Materials

Several coatings and other protective systems have been used to protect foam urethane roofing materials. Field experience varies from one

to a few years and costs vary from as low as 10 cents per square foot up

to about $1 per square foot for the coating system alone.

We have listed a number of materials and systems which have been

used as protective coatings for foamed urethane. This listing is not

necessarily complete but represents information developed from survey of

literature as well as from field investigations. The opinions of the

informed urethane producers, applicators and users vary considerably as to what constitutes an acceptable coating. There is certainly no con- sensus in the industry, although there has been considerable promotion

of specific coatings for this use since the market is potentially large

and apparently profitable. The materials whcih have been used as protective systems include:

24
1. Asphalt, clay-type emulsion and asphalt aluminum paint

2. Asphalt roof coating

3. Aluminum roof coating

4. Hot-applied asphalt with gravel surfacing

5. Asphalt emulsion or asphalt roof coating surfaced with

mineral granules

6. Latex paint with polyester coating

7. Several so-called elastomeric coatings based on polymeric

resins as:

Butyl

Neoprene

Chlorosulfonated polyethylene

Vinyl chloride and copolymers

Acrylic

Vinyl acrylic

Polyurethane

Epoxy

Silicone

6.3 Application

It is extremely important from both a cost and performance viewpoint

to understand application procedures. First, it must be established what

application method, i.e. pour, brush, spray (air or airless), is to be

used. Next, the number of coats required to obtain the specified thickness should be known. Is a primer required and, if so, is it of a different color than the specified top coat? The myriad of foams, spray

equipment, surfacing materials which face the specifier make the decisions and judgments very difficult ones at best.

7. Discussion and Comments

The subject of the adequacy of the in-service performance of foamed

urethane for roofing is a difficult one because of the many complex

factors involved. First, the innovation of foamed urethane roofs has

brought many factions unfamiliar with roofing materials, practices and

performance into the roofing industry. As a result, the very basic

rules of roofing technology have been often violated, hopefully through

ignorance, with rather disastrous and costly results. Next, the

customer's roof deck has often become a research facility to test the

hypothesis of the manufacturer, contractor and owner alike concerning

materials, equipment and application procedures. The scientific and

engineering method of an ordered, intelligent approach through research

and development techniques have virtually been ignored in the haste to

share in the profits of protecting the billions of square feet of roof area in the United States. This is evident in many of the areas of the

country and has been condoned by the private and public sector alike.

25
On the other hand, the intelligent use of foam urethane has

resulted in the solution of very difficult roofing problems when

solutions were not available from the more conventional sources. It

becomes clear that urethane in roofing application has both merit and

disadvantages. The advantages must be carefully weighed, the performance

and economic trade-offs considered, and the choice made. It is worth

repeating the word of caution that foam polyurethane is not a panacea

for all roofing problems as many would like to believe.

It may be well to discuss some primary properties which affect performance and attempt to place them in perspective.

7.1 Durability

Durability as used here is the time -dimension of performance. In

other words, the acceptable performance properties of the foam urethane

system must remain below and above prescribed maxima and minima limits

for some period of time under its conditions of exposure. Therefore,

durability considers the many properties of urethane which determine its

performance as a roofing system.

In brief, the long term durability of urethane foam roofing systems

is still unknown. Four or five years of in-service experience, some good and some not so good, is hardly a criterion for urethane foam

roofing when a useful life in excess of 20 years is expected from the more conventional bituminous, built-up roof.

Field experience indicates that the urethane foam exhibits poor

durability when exposed to ultraviolet radiation. Therefore, it must be

protected. This poses another question - What is the durability of the

protecting coating system?

At the state-of-the-art there is no way of predicting, with any

amount of certainty, the long term, i.e. 20 years or more, performance

of foamed urethane. The best that can be provided is a raw extrapolation of past experience into the future. The guidelines and suggested

performance specification at the conclusion of this report are the best

information available at this time which can be used in lieu of a valid

extrapolation.

7.2 Fire Safety

From time immemorial the fire resistance of roofing material as a part of the roof system has been of primary concern to building code

officials, fire prevention personnel and, of course, the roofing industry

itself. The roofing industry through the services of Underwriters'

Laboratories Incorporated has developed voluntary standards for roof

covering materials which are generally accepted throughout the United

States as a measure of fire resistance. The fire tests for roof coverings are conducted in accordance with Underwriters Standard UL 790 which

is similar to ASTM Designation E-108, Fire Tests for Roof Coverings.

26
According to these methods three different tests must be conducted to

determine the fire retardant characteristics of roof coverings as follows:

(1) Intermittent Fire Exposure

(2) Spread of Flame Tests

(3) Burning Brand Tests

Depending on materials performance in the series of test

systems are given a classification as follows:—

s, the roofing

Class A - Effective against severe fire exposure. Under such ex- posures roof coverings are not readily flammable and do

not carry or communicate fire. They afford a fairly

high degree of fire protection to the roof deck and do

not slip from position. They do not possess a flying

brand hazard and do not require frequent repairs to

maintain their fire resistant characteristics.

Class B - Effective against moderate fire exposure. They are not

readily flammable and do not carry or communicate fire.

They afford a moderate degree of fire protection to roof

deck. They do not slip from position, and do not possess

a flying brand hazard. However, they may require infrequent repairs to maintain their fire resisting properties.

Class C - Effective against light fire exposure. They are not

readily flammable and do not readily carry or communicate

fire. They afford some degree of protection to the roof

deck and do not slip from position. They do not possess

a flying brand hazard but may require occasional repairs

or renewals to maintain their fire resisting properties.

We contend that the foam urethane roofing system (deck, foam and

coating) should provide at least the same degree of fire resistance as

is expected of the conventional roofing systems. The system should be

tested exactly as it is to be applied in the field as to the type of

deck (combustible or noncombustible) , the vapor barrier, the fire

barrier, the type and thickness of foam and the type and thickness of

the protective coating system. In most cases, Class B ratings should be

specified. However, a Class C rating may be specified when the roof is

readily accessible for fire fighting. A listing by Underwriters Laboratories Inc. indicates that the products have been found to be in compli- ance with the Laboratories' requirements. It is interesting to note that

the urethane systems of at least three manufacturers are listed in the

Underwriters Laboratories, Inc. Building Materials Directory, January

1972.

4/ Building Materials List, Underwriters Laboratories, Inc

January 1971, p. 667.

27
For roofing purposes the f lammability data from other tests such as ASTM E-84 or ASTM D-1692 can be and are often misleading. In fact, we believe that a SE (Self Extinguishing) rating or a flame spread of 25 , as is often quoted in the industry, is meaningless as far as fire safety

in roofing applications is concerned and should be ignored . The total

system, i.e. the deck, the foam and the coating, must be considered.

7.3 Problem Areas

7.3.1 Performance of Protective Coating

One of the more common problems of the foamed urethane system which

we have observed is the poor performance of the protective coating.

Blistering, flaking, cracking, eroding, pinholing and sometimes complete

loss of coatings have been observed. The most common failure is erosion

or weathering off of the coating which exposes the urethane to the

destructive forces of solar radiation and water. This deficiency frequently appears at "bird baths" where water collects and stands. We

have observed that the aluminum pigmented coatings have been particularly susceptible to this type of failure. There are several factors which

contribute to the failures. They include: (1) lack of compatibility

between urethane surface and the protective coatings; (2) failure to

provide sufficient slope to drain which permits water to collect and

stand; (3) application procedures not in accordance with acceptable

practices; and (4) poor weatherability of the coating material.

The obvious solutions to eliminate or ameliorate these problems are:

(1) to require a total urethane system, that is one that consists of

foam and coating system supplied by a single manufacturer, applied to

his specifications and the total system guaranteed by the single supplier;

(2) to provide sufficient slope (greater than 1/4 in/ft) to allow quick

and complete drainage; and (3) the single supplier to provide clear and

proven application instructions to competent applicators under ample

construction inspection.

7.3.2 Cracking

A frustrating and rather common type of deficiency we have observed

has been cracking of the urethane foam and protective coating. The

cracks often penetrate to the substrate and cause water problems. We

have identified several conditions under which cracking occurs. The

most common cracking failures were observed at reentrant corners where

control joints were not provided. As a matter of fact, this problem is

also associated with membrane roofing. We also observed cracking in the

urethane system over joints between units of the substrate. Movement

which occurs at these joints is translated to the urethane foam. The

foam, being inelastic and weak in tension, fractures. Random type

cracks which occur in foam urethane are thought to be associated with

thermal movements which take place in urethane due to its rather large

thermal expansion coefficient. Polyurethane may reach as high as 350°F on solidifying and their normal cooling produces significant thermal

stress which may contribute to cracking.

28
Once the sources of the deficiencies are identified and understood,

it becomes elementary to prevent them. For example, as a matter of

practice, control joints should be placed at reentrant corners to provide square or rectangular roof areas. Further, slip sheets provided

over joints or other substrate areas which may exhibit differential

movement between units of the substrate will distribute stresses over

larger areas of the urethane foam, thus tending to reduce tension breaks.

7.3.3 Adhesion and Blisters

Urethane foam adheres rather tenaciously to most surfaces with some exceptions. The exceptions are wet, dusty, dirty, oily, greasy, and

waxy surfaces. Adhesion failures generally are evident as blisters or in rare cases as wind blow-offs. We have observed adhesion failures re- sulting in very large blisters, often several feet in diameter. The

adhesion failures sometime occur at the urethane-urethane interface

which again stresses the importance of an acceptable surface for urethane

application oven as the second application over urethane.

The prevention of this type of failure becomes obvious Surfaces

to be sprayed with foam urethane should be clean and dry. Experience

has shown the urethane adheres well to an asphalt surface. Therefore, a thin coating of an asphalt primer, hot asphalt or asphalt emulsion, over questionable surfaces will usually provide a good base for the application of foam urethane.

7.3.4 Bird Damage

We have received several complaints and have observed several ure- thane applications which were subject to bird damage. Possibly the birds

are seeking worms and insects in the foam which has the appearance of

rotten wood. We hasten to add here that the damage we have observed has

been superficial for the most part and more of a curiosity than a real

problem area. The damage is readily repaired.

8. Guidelines for Selection and Use of Urethane Foam

in Roofing Applications

Due to the lack of data on polyurethane roofing systems and to differences in climates where these roofing systems may be applied, it is

not possible to provide a general set of guidelines to the designer to

guide him in whether or not to select a urethane foam roofing system.

In fact, it is extremely difficult to provide guidance about the selection of a roofing system or roof repair system without knowing the

specifics involved in the particular roof under question. However, we

can provide information based on the properties and performance experience of urethane and can describe properties which affect performance

and attempt to place this knowledge in perspective as far as the perfor- mance of the roof is concerned. The designer, specifier or owner, as the case may be, can use this information in conjunction with the eco- nomics of his alternate choices and make a decision whether or not the

29
use of foamed urethane is justified. While we have not made a study of

the economics of various roofing systems, we would certainly suggest

that this aspect should play an important role in the decision. Life

cost must be considered and should take priority over the first cost.

This is especially true with the presently high cost of protective coatings and their questionable life span. The high life cost is readily

apparent when a polyurethane roof must be recoated every 3-5 years at a cost of 50 cents to one dollar per square foot.

8.1 New Roofing Applications

First, let us discuss the application of urethane foam systems in

new roofing work. Some guidelines are:

(1) In cases where the conventional surfaced built-up membrane

roofing can be specified, it should have a higher priority than the foam

polyurethane system.

(2) In cases where there is no slope , i.e. less than 1/4 inch per

foot run, the selection of urethane foam system should not be considered.

(3) In cases where industrial type roofings are concerned the fire

resistance rating must meet the Class B requirement of Underwriters 1 Laboratories as listed by the Laboratories. SE (Self Extinguishing)

classification or a flame spread of 25 or less when tested in accordance

with ASTM procedures E-1692 or E-84 respectively should not be accepted

as evidence that the system is acceptable or that it meets the UL Class

B rating. In cases when the roof is readily accessible for fire fighting

the UL C classification may be accepted. The remarks concerning SE and

flame spread of 25 apply equally to residential roof construction.

(4) It is suggested that the complete system, i.e. the foam and the

protective coating, be recommended, specified and guaranteed by a single

foam supplier. Protective coating should be applied at the specified dry

film thickness.

(5) The thickness of the urethane foam should be at least 1 inch

and no more than 2 1/4 inches. Foam of varying thicknesses should not

be used to provide slope to drain. However, low areas can be successfully leveled by the application of greater thickness of foam within

reason. A good guideline is that it should not exceed 3 inches in depth.

(6) Fabric reinforcement of the polyurethane foam must be provided

at all flashings including vents and stacks, gutters, edge flashing,

skylight or expansion joints and vertical surfaces. Cant strips should

be provided at junction of vertical and horizontal surfaces.

(7) Control joints shall be provided at reentrant corners and other

areas where stresses may occur in substrate which can be translated to

the urethane.

30
(8) Cast in-place concrete provides the excellent deck for the

applications of urethane in new work. However, urethane has been

successfully applied to corrugated metal and plywood decks.

(9) Urethane foam should not be applied directly to the conventional, fluted metal deck. A minimum 1/8 inch plywood or equivalent board

securely fastened to the metal deck with mechanical fasteners will provide a satisfactory surface for urethane application.

(10) Urethane will not adhere to a waxy, oily or wet surface. Cleaning and priming the surface with an asphalt primer (Federal Specification

SS-A-701 or ASTM Specification D-41) or an asphalt emulsion (Mil. Spec.

MIL-R-3472) and allowing it to dry provides an acceptable receiving surface for the polyurethane and is recommended.

(11) When applied over high humidity areas as swimming pools, laundries and the like, an asphalt saturated and coated base sheet, either

nailed or adhered with hot asphalt depending on the deck, and coated with

hot asphalt should be provided as the substrate for urethane foam.

(12) Slip sheets or bond breakers should be provided at joints in the

substrate where stresses can occur which may be transferred to the ure- thane foam causing cracking.

(13) Application temperatures should be above 40°F (4°C) and below

120°F (49°C) at all times. In many situations these limits will be quite

restrictive and may be extended providing measures are taken to compensate for application at lower or higher temperatures.

(14) The finished surface of urethane (before protective coating is

applied) shall be free of lumps, and ridges and smooth enough to receive

the coating. An orange peel effect is acceptable, however, a "popcorn"

or "tree bark" type surface should be rejected.

(15) Applicators shall be required to follow instructions in the

"Guide for the Safe Handling and Use of Urethane Foam Systems" as published by the Urethane Systems Manufacturers Committee, Cellular

Plastics Division, Society of the Plastics Industry.

8.2 Reroofing Applications

The best estimate is that, at the present time, about 407o of the

urethane foam used in roofing applications is for reroofing work. Probably the main reason for this use is because it is reportedly 357o to

407o cheaper to apply urethane over an old bituminous built-up roof than

it is to remove and discard the old roof and replace it in kind. The

question arises whether or not this is the more economical solution when

one considers the cost per year. This question must remain unanswered

until we have more information regarding the long-term durability of

urethane foam systems

31
A primary criterion concerning the choice of polyurethane vs. con- ventional systems in reroofing applications is whether or not funds are available. If they are available we believe that, at the present stateof-the-art, the better choice is conventional roofing. Our experience

indicates that this is the more economical choice on a cost per year

basis in spite of the reported 35% to 407o lower initial cost for polyurethane. We predict that this will continue until the life span to cost

ratio of protective coating systems becomes considerably higher than it

is at present. In certain situations a decision to use polyurethane will

be made based on limited funding or on uncertainties concerning the future

of the building in question. It is for use in these situations that we suggest the use of the following guidelines. We believe they will help

insure the better chance of adequate performance from the polyurethane

system.

(1) The slag or gravel surfacing, if present, must be removed. Do

not attempt to foam over gravel or slag.

(2) The deficiencies of the old roof, such as blisters, buckles,

wrinkles or cracks, must be repaired in accordance with good roofing

practice before the application of the urethane.

(3) If insulation is a part of the existing roofing system, it

must be vented with stack vents, preferably at the high points of the

roof. One vent for not less than each 10 squares should be sufficient

unless the insulation is wet. If the judgment is made that reroofing is

still feasible then more vents will be required.

(4) Dust and dirt must be removed and the surface primed with an asphalt primer (SS-A-701 or ASTM D 41) at a spreading rate of 33 to 50

sq. ft. /gallon or other suitable material. If the surface of the old

roof is inherently damp, an asphalt emulsion (Military Specification

MIL-R-3472) should be applied at a spreading rate of 33 to 50 sq. ft./

gallon as primer.

(5) Any gravel or slag on the old roof must be removed as completely

as possible. The thickness of the urethane foam should be a minimum of

1 1/2 inches to compensate for any gravel or slag that remains.

(6) The guidelines set forth in new work (see 8.1) should also apply

for reroofing work in addition to the guidelines stated herein.

9. Performance Specifications for Polyurethane

Foam Roofing Systems

The complexity of the rigid urethane foams and their protective coating systems, the lack of technical data, and subsequent information about

performance, durability, and long-term weatherability of foam urethane

roofing systems are major constraints in developing adequate material

specifications for urethane foams and protective coatings respectively.

In the course of this study, we have attempted to set limiting values for

32
specific properties in order to define acceptable service. However, we have been unsuccessful in these attempts since we have discovered large

and uncomfortable gaps in the correlation of material property given by

material suppliers and performance in service. We believe, at the current

state-of-the-art, that these gaps are so large as to preclude the development of meaningful material specifications. The question now arises as

to what steps can be taken to assist the designer, specifier, applicator,

and owner in selecting a system which will insure acceptable performance.

We believe that the performance approach offers a valid means to

this end. What it does is sets up what are believed to be acceptable

performance levels for the complete foam urethane and protective coating

system. We have attempted, as an innovative procedure, to develop a performance format to describe the complete system. We emphasize that the

levels we have selected are based on the best information we have available. Therefore, they should be considered preliminary in nature and are subject to change as new data become available. We contend, however,

that even at this embryonic stage, the document will be useful to guide

the supplier and consumer alike, once the decision has been made to

specify a urethane roofing system. Further, such a document will serve

as a basis for a more comprehensive and perhaps a more valid performance

standard for foam urethane roofing systems.

The performance format, as used here, consists of a stated requirement which is qualitative in nature. It is a statement of how we want

the system to perform under specific exposure conditions. A criterion or criteria follow which express quantitatively the limiting value or values

for performance in a specified test. Next in order to evaluate the

criterion which is selected, a test method is identified. Finally, a commentary is added, where appropriate, to place in perspective the

relation of the test procedure and the criteria to performance of the

roofing system in service.

9.1 Suggested Performance Specification for Guidance in Selecting

a Foam Urethane Protective Coating Roofing System

9.1.1 Fire Safety

°Requirement The roofing system (deck, foam urethane , and protective coating) shall present no fire hazard either

to the occupants or contents of the building nor to

adjacent structures. The roofing shall not be

susceptible to ignition from sparks or firebrands.

°Criterion The roof system shall have an Underwriters'

Laboratories Class B rating.

°Test Underwriters' Laboratories Standard UL 790, ASTM

E 108-58 (1970) Fire Tests of Roof Coverings.

33
"Commentary For roofing purposes, flammability data from tests

such as ASTM E 84 or ASTM D 1692 shall not be used

for acceptance in lieu of the ASTM E 108 Test. A

Class C rating may be substituted for the Class B

rating where deemed appropriate.

9.1.2 Wind Resistance

"Requirement The urethane foam roofing system shall withstand

anticipated wind loads without damage to the system.

"Criterion The urethane foam shall attain a minimum of 95%

adhesion to the substrate.

"Test Field experience and engineering judgment.

"Commentary The above criterion is believed to be adequate for

most locations. However, in high wind areas more

rigid criteria may be required.

Underwriters' Laboratories procedure

(Ul Bulletin of Research No. 52, 1962) may be

accepted as evidence of wind resistance according

to their classification of (30), (60), or (90).

Other tests as Factory Mutual and Owens -Corning

Fiberglas Corporation methods may also be suitable

for determining wind resistance.

9.1.3 Water Resistance

'Requirement

'Criteria

The foamed urethane shall evidence no signs of

deterioration or loss in value of essential performance properties, e.g. thermal conductivity,

strength and the like, when exposed to water.

a. The urethane foam shall have a closed cell

content of not less than 90%.

b. The water absorption of urethane foam shall not

be greater than 0.02 lb/ft 2

.

c. The water vapor permeability of the urethane

foam shall not exceed 3.0 perm-inches.

d. When the urethane roof system is used in cold

storage applications or in high temperature -high

humidity locations (tropical) the water vapor

permeance of the protective coating system shall

not exceed 0.5 perms.

34
o

'Tests a. ASTM D 2856-70 Open Cell Content of Rigid

Cellular Plastics by Air Pycnometer.

b. ASTM D 2842-69 Water Absorption of Rigid

Cellular Plastics.

c. ASTM C 355-64 desiccant method Water Vapor

Transmission of Thick Materials.

d. ASTM E 96-66 Procedure A Water Vapor Transmission of Materials in Sheet Form.

Commentary Moisture is a prime enemy of urethane foam. It can enter the foam from interior sources (vapor

flow and condensation) or from the exterior (rain,

dew, snow) . When the urethane system is used over high humid'.ty areas, especially in cold climates,

it is prudent to incorporate a vapor flow retarder

on the high vapor pressure side.

9.1.4 Stress Resistance

"Requirement The urethane foam shall possess sufficient strength

to resist or withstand the normal stresses imposed

from both internal and external sources.

"Criteria a. The tensile breaking strength shall not be

less than 25 p . s . i. when measured perpendicular

to the direction of rise.

b. The shear strength of the foam shall not be

less than 25 p.s .

. when measured parallel to the

direction of rise.

°Test a. ASTM D 1623-64 Tensile Properties of Rigid

Cellular Plastics.

b. ASTM C-273-61 (1970) Shear Test in Flatwise

Plane of Flat Sandwich Constructions or Sandwich

Cores.

°Commentary Field experience has shown urethane foams are sus- ceptible to fracture for both internally and

externally produced stresses. The above stated

values are absolute minimums based on products

available at this point in time.

Urethane foam products exhibit anisotropic behavior

due to the shape of cell formation during the foaming operation. The values given above are for the

direction which is most appropriate for roofing

application.

35
9.1.5 Resistance to Impact and Foot Traffic

"Requirement

'Criteria

'Test

'Commentary

The urethane foam and its protective coating shall

resist impact from foot traffic and falling objects

a. The density of the urethane foam shall not be

less than 2 lb/ft 3

.

b. The compressive strength of the urethane foam

shall not be less than 30 p.s.i. when measured

parallel to the direction of rise.

c. The protective coating over the urethane foam

shall withstand the impact of an 1 1/4 inch ice

sphere traveling at a velocity of 82 ft/sec without rupture or fracture of the protective coating.

a. ASTM D 1622-63 (1970) Apparent Density of

Rigid Cellular Plastics.

b. ASTM D 1621-64 Compressive Strength of Rigid

Cellular Plastics.

c. NBS Hail Resistance Test [43].

The criteria of core density and compressive

strength are related to impact and foot traffic re- sistance. Common roofing systems such as asphalt

shingles and built-up membranes meet the criterion

for falling ice spheres and have performed satisfactorily under field conditions involving hail.

We believe similar criteria are reasonable for

urethane foam systems.

9.1.6 Dimensional Stability

'Requirement

'Criteria

The urethane foam roofing system shall not exhibit

movements under service conditions of moisture and

temperature changes so large as to inhibit the performance of the total system.

a. The coefficient of linear thermal expansion of

the urethane foam shall not exceed 40 x 10 per °F,

b. The volume change of the urethane foam shall

not exceed the following values when exposed to

the following conditions:

-40°F at ambient R.H. - ±3% for 1 week

140°F at ambient R.H. for 1 week - +5%

158°F at 100% R.H. for 1 week - +12%

36
°Test a. NBS Test Procedure for Built-Up Membranes

[44] Temperature range 30°F to -30°F.

b. ASTM D 2126-66 Resistance of Rigid Cellular

Plastics to Simulated Service Conditions.

"Commentary The value stated for the expansion coefficient may

be too low. There are preliminary indications that

polyurethanes for roofing applications may have con- siderably higher coefficients at the temperatures

stated. Deficiencies observed in urethane roofing

systems during the field survey have been attributed

to lack of moisture and thermal stability. The

above limits are based on a survey of literature

and should be regarded as maximum. Lower values

will decrease chances of adequate performance in

service

9.1.7 Durability of Protective Coating

°Requirement The protection system for the urethane foam shall

withstand the environment of its exposure with re- gard to: (a) movements in the substrate (urethane

foam), (b) moisture and temperature, (c) solar

radiation, (d) atmospheric contaminants.

"Criterion The protective coating shall not crack, blister,

peel, pit, or erode to expose the urethane for a period of not less than five years. Further,

during the same period there shall be no evidence

of loss of adhesion between the protective coatings and urethane substrate.

"Test Field observation and laboratory tests. Engineering and scientific judgment.

°Commentary Performance data for many types of coatings used

for the protection of urethane foam are incomplete.

Experience based on performance in service should

be used whenever possible. The durability of protective coatings is intimately connected with the

performance of the total roofing system.

10. Acknowledgment

The authors express their sincere appreciation to William Darnell,

James Long and Walter McCartha of the Tri-Service Committee for their

advice and encouragement during the program. The assistance and arrangements provided by Harry Lee, Western Division of the U. S. Naval

Facilities Engineering Command and Norman Ammermann, Christiansen Foam

Corporation, Milwaukee, Wisconsin during the field survey are appreciated

and worthy of special mention.

37
The project was carried out under the Tri-Service Program at the

National Bureau of Standards sponsored by the Naval Facilities Engineering Command, U. S. Navy; the Directorate of Civil Engineering, U. S. Air Force; and the Office of Chief of Engineers, U. S. Army.

38
11. References

1. Gordon, Joseph, "Watch Polyurethanes Bid for Big Time. II.

Properties, Reaction, Additives, Control, Applications",

Hydrocarbon Process . Petrol . Refined , 42 , 123-34 (1963).

2. Saunders, J. L. and Frisch, K. C, "Polyurethanes, Chemistry and

Technology", Part 1, Chemistry, High Polymers Vol. XVI, Interscience

Publishers, New York, 1962.

3. Frisch, Kurt C. in "Polyurethane Technology", Bruins, Paul F., Ed.,

Interscience Publishers, New York, 1969, Chapter 1.

4. Hyman, Donald J., "Polyurethanes", Rev . Macromol . Chem . , 1,

191-237 (1966).

5. Tilley, James N. , Nadau, Herbert G., Reymore, Harold E., Waszeciak,

Paul H., and Sayigh, Adman A. R., "Thermal Degradative Behavior of

Selected Urethane Foams Related to Variations of Constituents. I. Thermal Stability and Test Methods", J. Cell . Plast., 4, 22-36 (1968)

6. Frisch, K. C. and Robertson, E. J., "Advances in Technology and Uses

of Rigid Urethane Foams", Mod. Plastics , 40, 165-6, 168, 170, 172,

174, 212, 216 (1962).

7. Benning, Calvin J., "Plastic Foams: The Physics and Chemistry of

Product Performance and Process Technology", Vol. II, Wiley-Interscience, New York, 1969, p. 68.

8. Gordon, Joseph, "Watch Polyurethanes Go Big Time. I. Chemistry, Raw

Materials, Diisocyanates , Polyethers, Polyesters", Hydrocarbon

Process . Petrol . Refiner , 41, 191-9 (1962).

9. Hermansen, Ralph D., "Molded Rigid Urethane Foams: Dimensional and

Physical Characteristics", J. Cell . Plast ., 4, 459-73 (1968).

i — —

10. Frisch, Kurt C, "Relation of Chemical Structure and Properties of

Rigid Urethane Foams", J. Cell . Plast ., I, 321-30 (1965).

11. Tarakanov, 0. G., Orlov, V. A., and Belyakov, V. K. , "Thermal

Degradation and Thermal Oxidative Degradation of Polyurethanes",

J. Polym . Sci., Part C 1966 (Pub. 1968), No. 23 (Pt. 1), 117-25.

12. "Cellular Plastics", Proc . Conf., Natick, Mass., April 13-15, 1966,

Pub. 1462, Natl Acad. Sci., Natl Res. Council, Wash. D.C., 1967,

pp 33-36, pp 66, 67.

13. Orefice, James D. and Pigott, Kenneth A., "Urethane Foam", Mod . Plastics Encycl. Vol. 48, No. 10A, 1971-1972, pp 152-154.

39
14. Hilado, Carlos J., "Getting the Most from Rigid Polyurethane Foams",

Chem . Eng., 74, 190, 192, 194, 196 (1967).

15. Hull, G. K., "Formulating Principles of Rigid Polyurethan Foam

Systems", Rubber Plastics Age , 47, 773-774 (1966).

16. Deverell, D., "Applications of Some Novel Plastics Systems",

Brit . Plast., 39, 707-13 (1966).

17. Doherty, D. J., Hurd, R., and Lester, G. R. , "Physical Properties of

Rigid Polyurethane Foams", Chem . Ind. (London), 1962, 1340-56.

18. Harding, R. H. , and Hilado, C. J., "Relations among Strength,

Temperature, and Chemical -Physical Structures in Rigid Urethan

Foams", J. Appl . Polymer Sci. , 8, 2445-60 (1964).

19. Harris, R. F., "Impact Testing of Rigid Urethane Foam", J. Cell . Plast ., 6, 221-5 (1970).

20. Tilley, J. N. , Nadeau, H. G., Reymore, H. E . , Waszeciak, P. H., and

Sayigh, A. A. R. , "Thermal Degradative Behavior of Selection Urethane

Foams Related to Variations of Constituents. II. Chemical Reactions

in Urethane Decomposition", J. Cell . Plast . , 4, 56-66 (1968).

21. Reegen, S. L. and Frisch, K. C, "The Effect of Chemical Structure

on Thermal, Hydrolytic, and Solvent Resistance of Polyurethane

Films", J. Polym. Sci., Part C , No. 16 (Pt . 5), 2733-49 (1967).

22. Smith, Clifford C, "Thermal Characteristics of Some Rigid Urethan

Foams", J. Appl . Polymer Sci. , 9, 3851-61 (1965).

23. Saunders, J. H. , "Relations between Polymer Structure and Properties

in Urethans", Rubber Chem . and Technol ., 33, 1259-92 (1960).

24. Backus, J. L., Darr, W. C., Gemeinhardt, P. G., and Saunders, J. H.

"Thermal Decomposition of Rigid Urethan Foams", J. Cell . Plast . , 1_, 178-86 (1965).

25. Tarakanov, 0. G., Nevskii, L. V. , and Belyakov, V. K. , "Photodegradation and Photooxidative Degradation of Polyurethanes"

J. Polym . Sci., Part C , 1966 (pub. 1968), No. 23, (Pt. 1), 193-9.

26. Mitchell, R.G.B., "Cellular Plastics in the Building Industry",

SPE Journal , p. 21, March 1966.

27. Buist, J. M. and Wilson, J. W., "The Use of Urethanes in Building

Applications. II.", Rubber J., 149 , 16-17, 20, 22-3, 25, 27 (1967).

28. Levy, Marshall M. , "Moisture Vapor Transmission and Its Effect on Thermal Efficiency of Foam Plastics", J. Cell . Plast . , 2, 37-45

(1966).

40
29. Hilado, C. J., and Harding, R. H. , "Relations between Water Vapor

Permeability and Chemical -Physical Structure in Rigid Urethane

Foams", J. Appl . Polymer Sci ., 7, 1775-90 (1963).

30. Varland, Robert H., "Long-term k-Factor Aging of Rigid Urethan Foam

Insulation", ASHRAE J. , 8, 84-7, 89 (1966).

31. Varland, Robert H. , "Rigid Polyurethane Foams: Effect of Age on Heat

Transfer", SPE Journal , p. 34, November (1966).

32. Eldib, I. A., "How to Make Polyurethanes" , Hydrocarbon Process . Petrol

Refiner , 42, 121-7 (1963).

33. Ball, George W. , Hurd, R. , and Walker, Maxwell G., "Thermal Conductivity of Rigid Urethane Foams", J. Cell . Plast . , 6, 66-78 (1970).

34. Hilado, Carlos J., Burgess, Jr., Paul E., and Proops, William R.,

"Bromine, Chlorine, and Phosphorus Compounds as Flame Retardants

in Rigid Urethane Foam", J. Cell . Plast . , 4, 67-78 (1968).

35. Hilado, Carlos J., "Flammability Characteristics of Cellular

Plastics", Ind. Eng . Chem . , Prod . Res . Develop . , 6, 154-66 (1967).

36. Hilado, Carlos J., "Flame -Re tardant Urethane Foams", J. Cell . Plast .

4, 339-44 (1968).

37. Anon., "Coping with Flammability", Mod. Plastics , 48, 79-80 (1971).

38. Robitschek, Paul, "Flammability Characteristics of Cellular

Plastics", J. Cell . Plast . , 1, 395-9 (1965).

39. Dickert, E.A. and Toone, G.C., "Chemistry and Flame Retardancy of

Rigid Urethan Foams", Mod. Plastics , 42, 197-9, 201, 204, 264, 267

(1965).

40. Doherty, D.J. and Wilson, W.J., "Protection of Rigid Urethane Foam

from Fire Damage", Bull . Inst . Int . Froid, Annexe, 5, 185-200 (1969).

41. Benjamin, Irwin A., personal communication

42. Martin, K.G., "Degradation of Rigid Cellular Plastics Under Fire

Conditions in Buildings", Rev. Pure Appl . Chem. , 21, 121-43 (1971).

43. Greenfeld, Sidney A., "Hail Resistance of Roofing Products", National

Bureau of Standards (U. S.), Building Science Series 23, 11 pages

(August 1969)

44. NBS Test Method for determining the coefficient of linear thermal

expansion of built-up membranes (work in progress).

feU. S. GOVERNMENT PRINTING OFFICE :] 973-. 511 -326/258

41
FORM NBS-114A (1-71) U.S. DEPT. OF COMM. BIBLIOGRAPHIC DATA

SHEET

1. PUBLICATION OR REPORT NO. NBS TN-7782. Gov't Accession

No.

3. Recipient's Accession No.

4. TITLE AND SUBTITLE

Guidelines for Selection of and Use of Foam Polyurethane

Roofing Systems

5. Publication Date May 1973

6. Performing Organization Code

7. AUTHOR(S)

William C. Cullen, Walter J. Rossiter, Jr,

8. Performing Organization

9. PERFORMING ORGANIZATION NAME AND ADDRESS 10. Project/Task/Work Unit No. NATIONAL BUREAU OF STANDARDS

DEPARTMENT OF COMMERCE

WASHINGTON, D.C. 20234

11. Contract/Grant No.

12. Sponsoring Organization Name and Address Naval Facilities Engineering Command, Department of the Navy,

Washington, D.C. 20390; Directorate of Civil Engineering,

U.S. Air Force, Washington, D.C. 20330; Office of Chief of

Engineers, U.S. Army, Washington, D.C. 20314

13. Type of Report & Period Covered Final 1972

14. Sponsoring Agency Code

15. SUPPLEMENTARY NOTES

16. ABSTRACT (A 200-word or less factual summary of most significant information. If document includes a significant bibliography or literature survey, mention it here.) The use of spray-in-place polyurethane foam for roofing application in the United

States is increasing at a rapid rate. Little unbiased information is available

to guide the user in the specification, selection, application, and performance

of this innovative roofing system. This report describes the current state-ofthe-art of rigid polyurethane technology as applied to roofing systems. The

performance parameters as observed during the field survey are discussed in terms

of protective coatings, fire safety, durability and problem areas. Guidelines to assist the supplier and user alike in the use and selection of polyurethane foam

roofing systems are given. Finally, a performance specification for spray-in-place

polyurethane foam roofing system is suggested.

17. KEY WORDS (Alphabetical order, separated by semicolons) „ , ., . ... ,. _ Durability; fire safety; performance

guidelines; protective coatings; rigid polyurethane; roofing.

18. AVAILABILITY STATEMENT

[3 UNLIMITED.

I I FOR OFFICIAL DISTRIBUTION. DO NOT RELEASE

TO NTIS.

19. SECURITY CLASS

(THIS REPORT)

UNCLASSIFIED

20. SECURITY CLASS

(THIS PAGE)

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21. NO. OF PAGES

46

22. Price

$.75 Domestic postpaid S.50G.P.O. Bookstore

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