FIRE RETARDANT PAINTS

High Heat- and Flame-Resistant Mastics J O H N C. ZOLA

Downloaded by UNIV OF ARIZONA on January 2, 2013 | http://pubs.acs.org Publication Date: January 1, 1954 | doi: 10.1021/ba-1954-0009.ch009

Ideal Chemical Products, Inc., Culver City, Calif.

Resinous mastics of low thermal conductivity and high temperature flame resistance may be used in contact with direct flame temperatures as high as 5 4 0 0 ° F. to prevent metal from losing structural strength. Formulations are influenced by the nature of the substrate, their function, and the degree of protection not only against fire but also the elements to which the coatings may be exposed. Supplementary materials such as fiber glass mats, woven glass fabrics, or expanded metal may be used.

U n c o n t r o l l e d fire is one of the most destructive forces which man must combat. In 1951, direct losses from fire reached an a l l - t i m e l e v e l of $730,000,000. Indirect losses i n business, taxes, and revenue would be at least three times this amount. Fire k i l l e d over 12,500 people and injured many thousands more. In time of war the losses are inestimable. In spire of these extraordinary losses to l i f e and property, very l i t t l e advancement has been made i n reducing fire through the application of fire-resistant coatings. In view of the fact that World War II was termed by some a war of fire, and the impending one would be even more so, a well-organized program for the study of fire-resistant coatings is l o g i c a l and imperative. The present available knowledge is meager and the intensity of pursuit very s m a l l i n relation to the potential market and its benefit to m a n . Fire Fire may be defined as a c h e m i c a l process c a l l e d o x i d i z a t i o n . When the o x i d i z a tion is so rapid that it is accompanied by a flame, it is c a l l combustion. T o start combustion, heat is required. T h e degree of temperature at which any substance w i l l c a t c h fire is c a l l e d the ignition point, w h i c h , of course, varies with the condition of the substance, the pressure of the air, and the movement of the air. A fire w i l l be self-supporting only when the temperature created by the combustion of the burning substance is as high as or higher than its ignition point. T h e heat of a fire depends upon the speed with which the chemicals combine with the o x i d i z i n g agent. There are two kinds of fire, with and without flame. T h e presence of a flame a l ways indicates that the heat has forced a flammable gas from the burning substance, and that this gas i n turn combines with oxygen i n the air. A substance is c a l l e d f l a m mable when it can be ignited i n the air under ordinary circumstances. The luminos82 In FIRE RETARDANT PAINTS; Advances in Chemistry; American Chemical Society: Washington, DC, 1954.

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ity of the flame is due to the presence of carbonaceous particles heated to incandescence, usually associated with incomplete combustion. A fire without flame is i l l u s trated by the glow of the paper of a burning cigarette. T h e oxygen combines d i r e c t l y with the carbon.


Terminology " F l a m e - r e t a r d a n t " conveys the meaning of slowing up of combustion, whereas "flame-resistant** means that some change i n physical state takes p l a c e , but no self-combustion or spread occurs once the igniting source is removed. This paper is concerned not only with preventing fire of combustible materials, but also preventing physical changes i n incombustible matter due to high temperatures resulting from the fire. Thus, at a temperature about 750* F. structural steel becomes progressively a weak m a t e r i a l . A t 950* F. ordinary steel has only 40% of its strength at 70* F. Buildings constructed of such steel can collapse from the heat of the fire. The word "heat-resistant** is used i n this relation. Heat-resistant, therefore, as used here refers to the thermal conductivity of the fire-protective m e d i u m , the mastic. The protective medium against fire discussed here is a water-insoluble mastic. Mastic is defined as a m a t e r i a l of heavy paste consistency which c a n be applied with a putty knife, trowel, brush, or heavy duty spray equipment to yield a coating from 1/32 i n c h to one i n c h or more. These mastics are of m i n e r a l composition, bound by an organic resinous m e d i u m , and dry to ultimate hardness by the v o l a t i l i z a t i o n of an organic solvent. They are further characterized by high i m p a c t strength, and assistance to abrasion, water, and many c h e m i c a l s . Theories u n d e r l y i n g H i g h Temperature F l a m e Resistance A number of theories may be considered to e x p l a i n the phenomena which occur to the fire-resistant coating during the course of the fire. The following theories are considered i n this paper: gas theory, thermal conductivity, "breathing** or gas perm e a b i l i t y , endothermic changes, and fusion. In a c t u a l p r a c t i c e , more than one of these theories is involved. A l l may occur i f the fire is of long duration, a c c o m p a nied by high temperatures. What are the temperatures attained by a fire? Protection Association^) :

According to the National Fire

The acceleration of combustion with increase i n temperature produces progressively higher temperatures, but then there are p r a c t i c a l l i m i t s to the temperatures produced in fires, due to a combination of several factors. As temperatures increase, neat is dissipated by radiation, which increases as the 4th power of absolute temperature, a greater proportion of the heat goes into heating up of the nitrogen i n the air and other inert materials i n the fire area, and there is a theoretical l i m i t to flame temperature. F l a m e temperature i n fire may range between 3000* and 5000* F. but the effective temperatures as measured by the melting points of metals and other heat effects have a p r a c t i c a l upper l i m i t of around 3000* F. and are usually lower. Gas Theory A fire c a n exist only when a l l of the three factors that cause a fire are present at the same time - - fuel, an o x i d i z i n g agent, and a temperature sufficiently high to m a i n t a i n combustion. The o x i d i z i n g agent with which this discussion is concerned

In FIRE RETARDANT PAINTS; Advances in Chemistry; American Chemical Society: Washington, DC, 1954.

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A D V A N C E S I N C H E M I S T R Y SERIES

is oxygen as supplied by the air. tinguish a fire.

Removal of any one of these three factors w i l l ex


The objective of this postulate is to dilute the oxygen i n the area of the fire with inert gases to such an extent that the ratio of this mixture with flammable gases e m anating from the combustible substrate (fuel) is below the l i m i t s of combustion. O x ygen may be diluted by the evolution of nonflammable gases which result from the decomposition of the ingredients of the fire-resistant mastic under fire conditions. Effective gases which c a n be generated from the fire-resistant mastic are hydrogen chloride, a m m o n i a , carbon dioxide, sulfur dioxide, and steam. The first two gases are generally obtainable i n effective quantities from the decomposition of resinous binders, for example, the chlorinated polymers and the amide resins. The last three gases are n o r m a l l y obtained from m i n e r a l fillers i n the mastic, thus the carbonates of c a l c i u m , magnesium, z i n c , and z i r c o n i u m are a source of carbon dioxide; the s u l fates of these metals y i e l d sulfur dioxide; while the water other than that resulting from combustion is derived from the water of c r y s t a l l i z a t i o n of such hydrated m i n erals as asbestos and v e r m i c u l i t e . The components for the fire-resistant mastic are selected on the basis of quantity of a v a i l a b l e gas, decomposition temperature, and ease of rate of gas release. A rapid gas evolution should take place at the tempera ture i n the v i c i n i t y at which the combustible materials y i e l d the greatest quantity of flammable gases. For c e l l u l o s i c products this is estimated to be at about 400* to 700* F.; therefore, the gases for d i l u t i o n should l o g i c a l l y c o m e from the organic binders. There are some facts to support a theory that effective quenching gases c a n be formed from the high temperature reaction products of the mastic, as, for e x a m p l e , hydrochloric a c i d and antimony oxide to form antimony oxychloride. The Depart ment of the A r m y , Office of Quartermaster General (1), reports that combination of antimony oxide and hydrochloric acid at flame temperatures is more efficient i n ex tinguishing a fire than either component alone. T h e r m a l C o n d u c t i v i t y Theory The objective of this theory is to insulate the combustible substrate (fuel) from attaining igniting temperature. The mastic becomes the thermal barrier for conduc t i v i t y of heat of fire. It can accomplish this i n two ways: through rapid conductivity of the heat away from the fire, as illustrated by the wire gauze over the Bunsen burner, through very slow thermal conductivity as exemplified by a fire-insulating brick. High heat conductivity works w e l l i f the area over w h i c h the fire is impinged is a s m a l l part of the t o t a l . The low heat-conductive mastic has proved more feasible on a fire over the total area. In order to accomplish low heat conductivity the mastic binder itself must be a poor conductor of heat and preferably nonflowing at high t e m peratures. The mineral components are selected on the basis of their low k value, the coefficient of thermal conductivity as derived from the following equation: Rate of flow, B.t.u. per hour = k(t ι - t2) X area i n square feet d where tj

is the high temperature and tg is the low temperature i n degrees Fahrenheit

and d is the thickness i n inches of the m a t e r i a l . T h e r m a l l y expanded minerals such as perlite and v e r m i c u l i t e , or naturally porous minerals such as diatomaceous earth In FIRE RETARDANT PAINTS; Advances in Chemistry; American Chemical Society: Washington, DC, 1954.

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ZOLA -- HIGH H E A T - A N D FLAME-RESISTANT MASTICS

and asbestos, may be employed as components of the mastic. Their efficiency is determined by their k constant, apparent bulk, specific gravity, and other properties which may be necessary to form a good mastic. Theory of Breathing or Gas Permeability


The objective of this postulate is to control the expulsion of the fuel gases, so that the ratio of fuel gas to oxygen is below the l i m i t s of combustion. This is accomplished by formulating fire-resistant mastics through which the fuel gases w i l l permeate or breathe. A "breathing** mastic can be attained by keeping the binder to the m i n i m u m . The porosity c a n be further increased during the course of the fire by the decomposition or phase changes. A breathing mastic is desirable to prevent blister formation or separation of coating from the protected surface. Endothermic Theory The objective of this theory i n relation to fire is to dissipate the heat of the fire and retard the combustible substrate (fuel) from reaching the ignition point. This concept presumes that the c a l o r i f i c input of the fire may be partly absorbed by the endothermic changes of the mineral substances employed in the formulation of the mastic. Thus, for example, such latent heat as the heat of fusion, heat of v a porization, heat of sublimation, and heat of transition (the heat required to change a unit mass of a given substance from one crystalline structure to another) a l l c a n absorb considerable energy which would otherwise be used to raise the combustible substrate to an ignition point. The efficiency of these fire-resistant minerals c a n also be a d judged by their specific heat values. Fusion Theory The objective of this postulate is to prevent the combustible substrate (fuel) from attaining the temperature of ignition. This would be accomplished by the gradual formation of a new inorganic thermal barrier of low heat conductivity to replace the original resinous mastic. The new thermal barrier would be on the order of a sintered or bloated structure, as exemplified by coke or pumice. The bloating effect c a n be attained through the use of minerals which tend to expand with heat, as, for example, unexpanded v e r m i c u l i t e . The sintering effect is attainable through the use of low fusion components, as, for example, glass fibers, " f r i t s * ' as used i n the c e r a m i c i n dustry, and other l o w - m e l t i n g - p o i n t chemicals which may also assist i n bloating. In a composition which is based on a u t i l i z a t i o n of many theories as w e l l as on obtaining a balance of properties, both sintering and bloating may be possible. Composition Materials of Fire-Resistant Mastics The binder of a mastic is an organic resin dissolved i n an organic solvent.

A de-

sirable resin is one w h i c h is fire-resistant and decomposes by evolution of gases which are preferably inert and nontoxic, and of m a x i m u m heat resistance.

Some c l a s s i f i c a -

tions of fire-resistant resins are: 1. V i n y l halogen polymers and copolymers 2. Halogenated natural rubber 3. Halogenated synthetic rubber In FIRE RETARDANT PAINTS; Advances in Chemistry; American Chemical Society: Washington, DC, 1954.


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4. 5. 6. 7. 8-

Halogenated naphthalene Halogenated diphenyls Halogenated hydrocarbons Polymerized cnloroprene (2-chloro-1,3-butadiene) A m i d e - a l d e h y d e resins

T h e plasticizers for these materials would be:


1. Esters of phosphoric a c i d 2. Halogenated m i n e r a l oils The efficiency of halogenated materials depends upon their v o l a t i l i t y at flame temperatures, halogen content, and the ease and rate of decomposition of the quench ing gas. Gas releases c a n be regulated to a degree through the use of stabilizers for the product. G e n e r a l l y the straight-chain hydrocarbon resins release the halogen a c i d more readily than the a r y l type. T h e c o m m e r c i a l l y a v a i l a b l e halogenated products are p r i n c i p a l l y of the chlorine f a m i l y and a few of the fluorine group. The f i l l e r composition of the mastic is generally a mixture of many materials, each one employed with a definite objective. The compositions of these materials vary with the source of supply; therefore, physical constants are d i f f i c u l t to compare. A l l materials are classified i n this paper w i t h respect to the properties i n attaining a fire-resistant coating based on the theories disclosed. Some of the minerals which are endothermic, c h i e f l y because of their water of crystallization or by decomposition and evolution of gases, are: A. Gas-evolvins material C a l c i u m carbonate (whiting or chalk) Magnesium carbonate Dolomite Z i n c carbonate Barium sulfate B. Water of c r y s t a l l i z a t i o n materials Asbestos Vermiculite China clay Some of the minerals w h i c h are of low thermal conductivity are illustrated by the following table. Density, Lb./Cu.Foot

Material Asbestos Fiber Long fiber Diatomaceous earth-powder M i n e r a l wool Glass wool Vermiculite a Κ = B.t.u.

23. 23.9 18.3 10.6 8.6 1.5 5-10

Mean Temp., *F. 122 50 86 103 75 70

K_? 0.798 0.499 0.30 0.27 0.27 0.48

Authority Groeber Randolph Bureau of Standards Bureau of Standards J.C.Peebles Heating and V e n t i lating Handbook

/hr./sq.ft.CF./ft.)

Illustrations of vitreoun types of materials for the fusion theory are: Glass tibers of various compositions Frits of various compositions Lead silicates Borate compounds In FIRE RETARDANT PAINTS; Advances in Chemistry; American Chemical Society: Washington, DC, 1954.

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Examples of useful flame-resistant pigments are: Antimony oxides Antimony sulfide Arsenic oxide Bismuth oxide Antimony oxide is c o m m o n l y used because of its c o m m e r c i a l a v a i l a b i l i t y and low cost.


Formulation of Fire-Retardant Mastic Coatings and A p p l i c a t i o n Methods Each fire hazard must be f u l l y analyzed, and then the fire-resistant mastic is formulated accordingly. Important points which must be considered are the fire c l a s s i fication, the nature of the substrate, the conditions surrounding the fire hazard, and other protective properties it must possess i n order that its fire-resistant properties w i l l not be destroyed by c h e m i c a l factors such as water or weathering, or by physical factors before or during the fire. In some instances, an extra demand is placed on the formulator, that the coating should not be removed by the pressure of the water used i n extinguishing the fire. When the desired properties are not attainable through the composition of the mastic alone, it becomes necessary to supplement the mastic with other fire-resistant m a terials and engineering knowledge. Supplementary materials which can be used i n conjunction with the mastic are (1) products of fiber glass such as fabric, mat, and fiberboard, (2) expanded metal wires of various kinds, and (3) stud welding of rods, split rods, etc. The fiberglass products may serve as supplementary thermal barriers or used as laminates to reinforce the mastic. The mastic can be anchored to the substrate by means of stud welding of rods, split rods, or expanded wire. This procedure assures the adherence of the coating during the course of the fire and against the i m pact of the pressure of the water used i n extinguishing the fire. Flame-Resistant Tests T h e nature of the flame tests is of the utmost importance i n the evaluation of the properties of the fire-resistant mastics. The proper tests are based on careful consideration of the type of combustile or incombustible substrate, the nature of the flame exposure to which these substrates may be subjected i n the course of the service, and other requirements which may be needed to meet the desired specifications. T h e combustible materials with w h i c h this paper is concerned are those used i n building construction, such as wood and other compressed c e l l u l o s i c derivative m a terials. The incombustible materials are metals which must be protected from reaching c r i t i c a l points when exposed to the heat of the fire. The c r i t i c a l points are the temperatures at which the metals soften and lose their structural strength under fire exposure. The National Board of Fire Underwriters defines the i g n i t i o n temperature of any solid material as the lowest temperature to w h i c h any part of it must be raised to cause the material to ignite (3). The ignition temperature of wood varies from 380* to 870* F. depending on the kind of wood and the size, shape and condition of the sample; the method, rate, and conditions of heating; the method of measuring the


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temperatures; and the condition of glow or flame considered as constituting i g n i t i o n . Tests by National Bureau of Standards show that ignition temperature of the same wood may vary from 440* F. when it is i n the form of thin shavings to 750* F. when it is i n a larger piece.


The Forest Products Laboratory illustrated the c h e m i c a l changes which wood under goes when it is subjected to temperatures below that necessary to produce quick i g n i tion. The test was conducted with wood blocks 1 1 / 4 x 1 1 / 4 χ 4 inches i n size, placed i n a quartz tube held v e r t i c a l l y . The source of heat was a heating element surround ing the tube. A free, natural draft occurred. Under these conditions, d i s t i l l a t i o n of the wood took place and the liberated vapors were ignited. The i g n i t i o n by flame was possible when the wood was held at 600* F. for about 2 minutes, at 500* F. for about 5 minutes, at 400* F. for 20 minutes, or at 340* F. for 40 minutes. The charring temperature of wood is lower than the ignition temperature. Forest Products Laboratory tests show that charring of the wood can take place at oven t e m peratures of 225* F. with long periods of heating, and field experience shows that wood i n long contact with low-pressure steam pipe becomes charred, and under f a vorable circumstances ignition may occur. There are many laboratory methods of evaluating the protection offered by f l a m e resistant coatings to combustible materials. A l l differ i n their techniques. F l a m e impingements on the test panel may be made while the test panel is resting i n the horizontal or v e r t i c a l position, or at an angle of 45*. The observations are noted for a given period, but differ for each test. Degradations of the combustible materials are also noted i n various ways: flame spread and rate of spread, fuel contributed, smoke produced, degree of charring i n terms of area or volume, and loss of weight. The Underwriters' Laboratories evaluate building materials of fire hazard nature i n their own devised equipment on a scale much larger than that followed i n the i n dustrial laboratories, and record the results by rate of flame spread, fuel contributed, and smoke produced. The evaluations are recorded n u m e r i c a l l y i n relation to the data recorded during the burning of select red oak under standardized conditions as producing the 100-point on a classification scale, while the data recorded during s i m i l a r exposure of an incombustible material (asbestos-cement board) produced the 0-point. Some c o m m o n l y practiced laboratory methods developed for determining the flame-resistance of combustible materials are: Federal Specification S S - A - 1 1 8 a , Schlyter test or its modifications, and British Standard Specification 476a or its m o d ifications. The Federal Specification S S - A - 1 1 8 a , which is designed for slow-burning c o m bustibles i n the horizontal position, measures the flame spread w i t h i n a 20 or 40 minute period under a prescribed flame temperature curve. A m i l d Schlyter test measures the flame when the test panel is i n the v e r t i c a l position, whereas a m o d i f i c a t i o n of the fire test of British Standard Specification 476a measures char area on an i n c l i n e d test panel. Reasonably good correlation trends between results of these three test methods were found by the Forest Products Laboratory (2). A good flame-resistant coating w i l l effectively check flame spread by a l l three tests. A coating w h i c h w i l l perform effectively with one material w i l l not necessarily be satisfactory for another. While reasonably good correlation trends between the re sults of the three test methods were found, the accumulated data indicated the dif ficulty of predicting i n f a l l i b l y , on the basis of performance i n one test method, what the performance would be i n another test method. In FIRE RETARDANT PAINTS; Advances in Chemistry; American Chemical Society: Washington, DC, 1954.


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HIGH HEAT- AND FLAME-RESISTANT

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The heat-insulating properties of the mastic applied over metals is measured i n the laboratory by impinging a fire on the mastic side and measuring the heat transfer to the opposite side by thermocouple readings. T o qualify i n the b u i l d i n g construction field it is desirable to conform to A m e r i c a n Standard A2.1-1942, w h i c h Underwriters* Laboratories use to grant approval of fire-resistant coatings. This test prescribes a standard exposing fire of controlled extent and severity, and the performance is defined as the period of resistance to standard exposure elapsing before the first c r i t i c a l point i n behavior is observed. The performance is expressed as " 2-hour,* * ••1-hour,** etc. The most effective and convincing tests are those w h i c h are made to reproduce the true conditions to which the materials of fire hazard nature may be exposed. Thus, the railroads evaluate a fire-resistant coating for the protection of their c r e osote-impregnated wood trestles by reproducing a fire on a section of a r e p l i c a trestle built to scale and treated w i t h the fire-resistant coating. In a l l evaluation i t is necessary to remember that the results of any test are i n f l u enced by the thickness of the coating, the period allowed for complete drying of these coatings, and the method of a p p l i c a t i o n . Because of the difference i n the ignition points of various combustibles or the y i e l d points of metals, every satisfactory test must be qualified as to application method and full description of substrate given. Some Properties of Fire-Resistant Mastics Some of the unique properties which c a n be attained by fire-resistant mastics are exemplified by a c o m m e r c i a l formula of a composition w h i c h cannot be disclosed. The high temperature flame-resistance and low heat transfer are illustrated through the use of T h e r m i t , a mixture of powdered a l u m i n u m and iron oxide, w h i c h on i g n i tion develops a heat of 5400* F. i n 60 seconds. The test panel consists of a slab of steel 3/8 inch thick and 18 inches square, over which a coating of 1/2 i n c h of f l a m e resistant mastic has been imposed. On this panel a sand mold 3 inches i n diameter is formed, and paper cup containing 1/4 pound of T h e r m i t is placed w i t h i n the ring of sand, and then i t is surrounded with 1/2 pound of magnesium shavings. A gasoline torch is used to ignite this mass of fuel. T h e intense heat and flame last about 3 minutes. I m m e d i a t e l y after the exhaustion of the T h e r m i t , a hand placed on the m e t a l opposite where the reaction occurred does not feel an appreciable change i n temperature. The same T h e r m i t test on 1/8-inch steel burns a hole 2 inches i n d i ameter within 20 seconds. As a result of the T h e r m i t test, the mastic shows a black, sintered crust approximately 3 inches i n diameter and about 1/8 i n c h deep. The heat transfer through the same composition mastic by flame temperature of 2000* F. directed against it is illustrated by three test panels of steel 3/16 i n c h thick and 12 inches square. One panel was soated with 9/16 inch of mastic, and the second bad steel wire lath welded on a five points and then covered with 1/2 inch of mastic; the third panel was left bare. The source of fire for the tests was a large gas burner with forced air feed. Temperatures of the heat source and heat transfer on the u n i n sulated side were made with the thermocouple. results of the fire test were as follows. Temperatures on Bare Side of Steel, * F . Test 5 min. 15 m i n . 25 m i n . 40 m i n . Panel T

No mastic 9/16 i n c h mastic Wire lath and 1/2 i n c h mastic

850 176 176

h

e

386 496

522 658


604

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A t the conclusion of the test, the unanchored mastic exhibited the loss of appre c i a b l e i n i t i a l adhesion to the m e t a l . The lath-anchored panel was subjected to the fire only 25 minutes because the extreme heat fused the jets of the burner, necessi tating cessation of the test. After c o o l i n g , the mastic layer from this panel could not be removed even with application of considerable f a c e . Whenever excellent bond age under fire is desirable, anchorage of the mastic is desirable. Another illustration of the low heat transfer of the mastic at moderate temperatures was demonstrated i n connection with a test for spraying the underside of vehicles used for carrying explosives. A steel panel 1/16 i n c h i n thickness was coated on one side with 3/8 i n c h of mastic. The panel was suspended h o r i z o n t a l l y with the insulation side down. A pine box wood block, 3/8 χ 3/4 χ 11/2 inches, was placed i n the c e n ter of the panel. The block rested on the 3/8 χ 11/2 i n c h side. A Fischer burner was placed under the block. It was set to develop a temperature of 800* F. It required 8 minutes before any sign of charring showed on the wood and 30 minutes before a p proximately 1/8 i n c h charring occurred. Under s i m i l a r circumstances a block of this wood placed over the bare steel showed charring i n 10 seconds and burst into flame i n 65 seconds. S i m i l a r l y , a 1/4-inch m i l l b o a r d and 1/16 inch sheet i n place of the mas tic would delay the charring of the wood for 9 minutes and produce 1/32 i n c h of c h a r ring of the wood i n 30 minutes. T h e r m a l conductivity, k, of the mastic under illustration was determined to be 1.03 at 10* F. mean temperature as measured by apparatus designed by the N a t i o n a l Bureau of Standards, k equalsthermal conductivity i n terms of B.t.u. per hour, per hour, per degree Fahrenheit temperature difference, for a specimen 1 foot square and 1 i n c h thick. This value of k compares with the following values obtained from the " H e a t i n g , V e n t i l a t i n g and A i r - C o n d i t i o n i n g G u i d e " : Light-weight concrete Sand and gravel concrete M i n e r a l wool insulation Expanded v e r m i c u l i t e insulation Expanded v e r m i c u l i t e concrete

2.50 12.00 0.27 0.48 0.86 - 1.10

The i m p a c t resistance of the mastic applied on 16-gage steel, 4 x 6 inches, as a layer of less than 1/8 i n c h was determined by dropping weights from various heights. A 100-gram brass weight dropped on a panel placed at a 45* angle at varying heights up to 10 feet results only i n dents i n the mastic, but no r e m o v a l . A 5-kg. weight dropped from a height of 2 feet onto the center of a panel placed at a 45* angle, bent the panel to an angle of 22* and removed enough mastic to expose 1/32 sq. i n c h of bare m e t a l . The force exerted by a 5-kg. weight f a l l i n g 2 feet is approximately equivalent to that of a 1-lb. rock traveling at 35 miles per hour. The Taber abrader test for abrasion resistance of the mastic shows that the mastic has an abrasion resistance of rubber t i l e and unprinted l i n o l e u m . The salt-fog corrosion resistance of the mastic appears excellent. Incipient c o r rosion of a mastic-coated steel panel of 1/16 i n c h thickness appears only after 1 mont. This compares to complete failure of red lead primer i n 4 to 5 days. A p p l i c a t i o n of Fire-Resistant Mastic The resinous mastics have opened, through the m e d i u m of thickness of a p p l i c a t i o n In FIRE RETARDANT PAINTS; Advances in Chemistry; American Chemical Society: Washington, DC, 1954.

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and accordingly a wider scope i n formulation, new usages which have not been possible to attain by thin coatings. T h e resinous mastics also overcome the shortcomings of the inorganic matrixes: chiefly, the lack of adequate and retained adhesion, insufficient f l e x i b i l i t y under various temperatures, absorption of flammable oils, water, and corrosive agents, and the lack o f sufficient expansion with thermal changes of the substrate.


T h e resinous mastics have also shown their superior characteristics against various finishes i n shock resistance under extremely rapid changes i n temperature, such as -60* to 4123* F. In the building f i e l d , as fire-resistant coating for wood, fiberboard, and metals, they have numerous applications. Unusual usage of the fire-resistant mastics is their a p p l i c a t i o n against brush fires on railway trestles constructed of wood which had been impregnated with as m u c h as 3 gallons of creosote-petroleum oils per cubic foot. Another new a p p l i c a t i o n of the mastic is on the underside of motor vehicles used for transportation o f explosives and other dangerous flammables. Experiences of the past few years indicate that motor vehicles equipped with dual tires are l i k e l y to be involved i n serious fire should one of the dual tires become deflated. In this case, the mastic must not o n l y exhibit fire-resistance and low thermal conductivity, but must have good i m p a c t and good abrasion resistance as w e l l as weatherability. The inherent properties o f the fire-resistant mastic m a y be exploited for many other applications. O n the basis of low thermal conductivity, the mastic forms a suitable coating o n m e t a l sheet buildings which prevents condensation, reduces noise coefficient, and retards radiated heat. Another property w h i c h is sometimes i m p o r tant is that the mastic does not support m i l d e w . For this and other reasons, the mastic has been applied on the interior o f concrete storage granaries to prevent the grain from m i l d e w i n g i n the area adjacent to the concrete walls. Literature Cited (1) Church, J. M., U . S. Dept. Commerce, Research Development Report, Textile Series 38, 277-9 (1952). (2) Forest Products Laboratory, Madison, Wis., "Evaluation of Flame-Spread Resistance of Fiber Insulation Board," Rept. D 1756 (April 1, 1950). pp. 9-12. (3) National Board of Fire Underwriters, Bull. 2 (October 1952). (4) National Fire Protection Association, Boston, Mass., "Handbook of Fire Protection." Received April 1, 1953.


FIRE RETARDANT PAINTS

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