Fire-Retardant Coatings on Acoustical Surfaces ... - ACS Publications

Fire-Retardant Coatings on Acoustical Surfaces and Test Methods for Their Evaluation ALICE C. WEIL, G E O R G E W . M O D , and A. W A T S O N C H A P M A N

Downloaded by UNIV OF ARIZONA on January 2, 2013 | http://pubs.acs.org Publication Date: January 1, 1954 | doi: 10.1021/ba-1954-0009.ch005

The Celotex Corp, Chicago, Ill.

Large quantities of fibrous materials are installed annually in this country in the acoustical treatment of the interiors of public and private buildings. Surface coating of such products offers a practical method of imparting improved flame resistance. A number of types of such coatings are discussed, as well as some of the test methods used to determine the degree of flame resistance. W i t h the increase i n knowledge i n the field of acoustics and the awareness of the need for the control of sound, various acoustical products have appeared for e m p l o y ment by the p u b l i c . This paper covers architectural acoustical materials only. T h e architectural acoustical products now on the market can be divided into two general classes, the inorganic and the organic type of product. The inorganic classification includes the m e t a l pan type, consisting of a perforated m e t a l pan with a sound-absorptive m i n e r a l wool pad; the perforated c e m e n t asbestos type, consiting of a perforated cement-asbestos sheet with a sound-absorptive m i n e r a l wool pad; acoustical plasters; and t i l e prepared from mixtures of inorganic or m i n e r a l i z e d fibers with or without asbestos and other fillers. In general, acoustical products i n this classification possess good fire and flame resistance, but are r e l a t i v e l y expensive and difficult to manufacture and apply. The organic classification includes acoustical t i l e board prepared from vegetable or wood fiber. These acoustical products are produced i n greater volume than the inorganic type, are easier to manufacture i n large quantities, are easier to apply, are cheaper, but are not as fire- or flame-resistant as the inorganic type, although they are not highly combustible. If the organic-type acoustical product could be rendered more fire- or flame-resistant, (and the potential is present), this would be a valuable service to the public and the building industry. Considérable work has been done to improve the flame resistance of organic fiber acoustical t i l e by both integral and surface treatments. Results by both methods have been very promising. However, surface treatments have been m u c h easier to apply, are less expensive, and do not require as much special equipment as does the integral treatment. T h e fire-retardant surface treatments have definitely increased the fire and flame resistance of the organic-type board, particularly by markedly retarding spread of flame. For complete insurance against fire, particularly behind those acoust i c a l treatments which are not fastened d i r e c t l y to the c e i l i n g , integral treatments are also required. 28 In FIRE RETARDANT PAINTS; Advances in Chemistry; American Chemical Society: Washington, DC, 1954.

WEIL, M O D , A N D C H A P M A N — C O A T I N G S O N A C O U S T I C A L SURFACES

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Types of Integral Treatments M a n y simple and c o m p l e x treatments have been devised through the years to i n crease the fire and flame resistance of vegetable and wood fiber acoustical title by impregnating the board with the treatment or forming the board i n the presence of the treatment. These treatments m a y be divided into three m a i n classifications - - treatment of the fiber with soluble salts, treatment of the fiber by processes wherein various waterinsoluble c h e m i c a l complexes are precipitated around the fiber or dispersed throughout the fiber mass, and treatment of the fiber by c h e m i c a l reaction between the c e l ulose and/or other fiber components by suitable reactants. The last two classifications are the most permanent of the treatments. Downloaded by UNIV OF ARIZONA on January 2, 2013 | http://pubs.acs.org Publication Date: January 1, 1954 | doi: 10.1021/ba-1954-0009.ch005

Treatments of fiber with soluble salts would i n c l u d e : A m m o n i u m salts, which liberate free a m m o n i a or s u b l i m e . Boric a c i d or borax, which liberates free moisture and tends to fuse around the fiber. Carbonates or bicarbonates, which liberate carbon dioxide and possibly moisture. Hydrated salts, which liberate moisture. Treatments with insoluble complexes would i n c l u d e : The m e t a l l i c oxide-chlorinated body type (7), which reduces f l a m m a b i l i t y by the rapid liberation of hydrogen c h l o r i d e . The precipitation of insoluble borates, oxides, carbonates, etc., upon the fiber, which reduces f l a m m a b i l i t y by the liberation of moisture, smothering cases, etc. The dispersion of water-insoluble phosphorylamides throughout the fiber, which is c l a i m e d to increase the fire resistance by liberating smothering gases and by the formation of a glasslike m a t e r i a l around the fiber (10). Treatments of fiber by c h e m i c a l reaction would i n c l u d e : The reaction of polybasic acids, such as phosphoric, with cellulose i n the presence of an organic base such as urea ( 5 , 8). The urea acts as a buffer i n the formation of the cellulose-phosphate reaction "products, reducing the weakening of the fiber. The flame resistance of this type of treatment is c l a i m e d to result From the inorganic or a c i d anhydride itself. The reaction of phosphoryl chloride with cellulose i n the presence of a nonaqueous solvent such as carbon tetrachloride or pyridine and subsequent reaction with

In general, a l l the above treatments affect the decomposition products, by heat, of the fibrous m a t e r i a l . After treatment, the solid carbonaceous residue from c o m bustion of fiber tends to increase and the quantity of tarry by-products to be reduced. Types of Surface Treatments M a n y chemicals and c h e m i c a l complexes have been evaluated i n various coating formulations, with detailed study of pigmentation. T h e quality of these formulations varies from poor to excellent, depending on materials employed. In general, these formulations c a n be divided into two classifications, aqueous, type and nonaqueous type, each exhibiting either nonintumescing or intumescing characteristics. By an intumescent-type coating is meant a coating that w i l l s w e l l , char, bubble, and produce a f i r m , charred ash when a flame is impinged upon i t , i m m e d i a t e l y shielding the fiber board from the flame. In FIRE RETARDANT PAINTS; Advances in Chemistry; American Chemical Society: Washington, DC, 1954.

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Under the aqueous-type classification, the nonintumescent types would i n c l u d e : Borax or borax-boric a c i d coatings containing a carbohydrate binder, with selected pigments. The borax or borax-boric a c i d combination w i l l liberate the usual m o i s ture when heated, with the binder and pigment furnishing some insulation. This type of coating has fair flame resistance. Coatings containing a m m o n i u m salts of polyhydric a c i d - - e.g., m o n o a m m o n i u m phosphate - - with pigments, sodium alginate, and a carbohydrate binder. The effectiveness of these coatings depends on the liberation of a flame-smothering gas and the insulating effect of pigments and binder. This type of coatings has fair flame resistance. A highly pigmented coating containing m i c a , asbestos, etc., with a carbohydrate binder. This type of coating depends on insulation effect only and possesses fair flame resistance at high coverages. Coatings c o m b i n i n g sodium silicate with asbestos and various pigments. This type of coating w i l l liberate moisture and produce insulation effect from the asbestos and pigment. It gives good i n i t i a l flame resistance, but the s i l i c a t e is changed gradually to sodium carbonate and s i l i c a by the atmosphere, w h i c h causes this type of coating to lose flame resistance and f i l m qualities with the passage of t i m e . Intumescent types of aqueous coatings have been produced containing an a m i n e aldehyde, the a m m o n i u m salt or salts of polyhydric a c i d , selected pigment, starch, and thickener.

When formulated properly, this type of coating possesses excellent

fire- and flame-resistant properties, but would be rated as a r e l a t i v e l y poor paint f i l m . A coating of this type is manufactured by the A I M C h e m i c a l C o . (6) under the name of A l b i - R and has had extensive acceptance. In the nonaqueous classification, nonintumescent types would i n c l u d e : Borax and borax-boric a c i d paint with appropriate pigments and linseed o i l (13). This type of coating has only fair fire and flame resistance. Antimony oxide, various pigments, and chlorinated paraffin or rubber, e t c . , blended to form a coating. This type of coating has only fair fire and flame resistance. Intumescent types of nonaqueous coatings have been produced containing a n a m i n e aldehyde resin, a m m o n i u m salt of polyhydric a c i d , and pigments, w i t h an appropriate binder. This type of coating possesses excellent fire and flame resistance and good paint properties. There are probably other types of intumescent paints, but their exact composition is not a v a i l a b l e . A l l the above formulations have been investigated and evaluated on perforated and unperforated C e l o t e x fiberboard. Results demonstrate that a satisfactorily formulated intumescent water- or oil-base paint is the best type of paint to apply to acoustical fiber board to secure optimum fire or flame resistance. These paints, by their i n t u mescent nature, tend to close the openings i n the acoustical fiber board and insulate the basic fiber under the coating. The nonintumescent-type coating does not produce as successful results, as the heat from the flame easily passes through the thin coating, permitting the basic fiber to char and burn more easily than w i t h the intumescent coating. Just because a paint itself w i l l not burn, it does not follow that it w i l l produce d e sirable fire or flame resistance on an acoustical fiber board. For unperforated board, intumescent paints s t i l l produce o p t i m u m fire and flame resistance. However, because the painted surface is continuous, the simpler less f l a m e resistant borax-boric a c i d pigmented paint produces satisfactory results.

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

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A successful factory-applied intumescent paint has been developed by the Celotex Corp. for application to acoustic board. In addition, a satisfactory package paint, D u e - T e x flame-retardant paint, is available for application over old fiberboard installations, wood, etc. This product bears an Underwriters* Laboratories l a b e l . Surface Finish Characteristics In addition to possessing the desired fire and flame resistance, the acoustical fiberboard paints and finishes must possess other requirements of an acceptable paint and finish. The paint or coating must be capable of satisfactory application by the desired method and it must have satisfactory shelf l i f e .


T h e paint finish after a p p l i c a t i o n must possess the following properties. It must maintain the desired fire and flame resistance with age — approximately 5 years. It must be attractive. It must have good color retention with age - - i t must maintain its original color or show only slight color change after approximately 3 years from the date of i n s t a l lation. It must maintain good f i l m qualities with age - - not crack, craze, chalk, blister, etc. For highest quality, the finish must be washable - - possess at least 2 0 0 - c y c l e washability (4). It must be mildew-resistant - - not permit the growth of Aspergillus oryzae, Asper gillus niger. and other c o m m o n organisms when exposed under the normal r e c o m mended range of atmospheric conditions. It must be capable of beine repainted - - with the c o m m o n interior, h i g h - q u a l i t y o i l - and v/ater-base paints and high-quality interior flame-resistant paints. It has been very difficult to produce intumescent coatings which possess excellent washability. The Celotex finishes mentioned possess a reasonable washability. A c t i v e work is now i n progress to obtain finishes with even better washability and at a lower cost. F i r e - and flame-resistant paints for acoustical fiberboard are now being satisfac torily applied by spray, brush, and r o l l . Flame-Resistance Tests M a n y tests have been devised to evaluate the fire and flame resistance of surfacetreated acoustical fiberboard. The most widely accepted test, recognized by both the building industry and the building code agencies, is the fire-resistance test specified i n federal specification (3). Other tests under consideration, but not universally adopted, are the tunnel test of the Underwriters* Laboratories, Inc. (11), and the F a c tory M u t u a l room burn out test (2). A s m a l l scale test that is being employed for plant control and quick finish evaluation is the Class F fire test (12). Basically, a l l the above tests evaluate the flaming tendency - - e.g., flame type, flame spread, flame duration, etc. Fire-Resistance Test (3). In this test method the preconditioned specimen, or spec imens, to be tested are mounted on an incombustible backing to form a 3 χ 3 foot test pannel. This panel is then mounted i n a horizontal position, with the specimen panel facing downward, on supporting 2 χ 2-1/8 i n c h steel angles framed to form a c l e a r opening of 30 χ 30 inches. The flame from a gas-air pressure burner, mounted 28-3/4


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inches below the surface of the panel at the center of the panel, is then directed against the specimen panel face following a specified time-temperature curve. These temperatures are measured with a specified thermocouple, mounted under the test panel. Observations are made p e r i o d i c a l l y during the test. Based on observations of the behavior of the test specimen and the length of exposure, the material is assigned one of four classifications. If the test is conducted for 40 minutes, following the C o l u m b i a curve (3), and no flame issues from the speci m e n itself, nor does glow extend beyond the area of the test flame, the material is rated as " i n c o m b u s t i b l e . ' * If, during the same exposure, any intermittent flaming issues from the specimen, but is l i m i t e d to the area covered by the test flame, and such flaming does not last longer than 2 minutes after the test flame is extinguished, the m a t e r i a l is classified as fire-retardant.** For the third classification, known as s l o w burning**, the exposure is 20 minutes following the standard time-temperature curve (3). No flame from the specimen m a y reach the angle frame at any point, and a l l flaming must cease w i t h i n 5 minutes after the test flame is discontinued. If a m a t e r i a l fails to meet these test requirements, it is rated a s c o m b u s t i b l e . * * For a l l classifications, there are restrictions as to the amount of m a t e r i a l which may f a l l from the test panel during the exposure period. 44


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A large number of testers of this type have been built and are being operated i n both private industrial and c o m m e r c i a l testing laboratories. Several points i n the test method need c l a r i f i c a t i o n . A t least two committees i n the A m e r i c a n Society for Testing M a t e r i a l s , and the Federal Specifications Board, are working on the probl e m of revising this test method. Under consideration are such items as a standard pre-conditioning requirement for the samples, the effect of using different gages of thermocouple wire, the effect of using fuels with different B.t.u. values, the interpretation o f s u s t a i n e d flame,** and the length of time during w h i c h the panel should be observed after the test flame is discontinued. Underwriters' Laboratories T u n n e l Test. In this test the samples are exposed to flame impingement i n a special fire test chamber which consists of a duct, rectangu44

lar i n cross section, with a width of 17 inches and a length of 25 feet. The duct has a removable top, against the lower face of w h i c h the test samples are attached. A t one end of the chamber the test burners are located, delivering flames v e r t i c a l l y u p ward against the samples. A t the other end of the chamber there is a vent pipe and the v e l o c i t y of a i r through the chamber is adjusted to 200 feet per minute. This tends to draw the test flame down the tunnel, and under the test condition the test flame extends about 4-1/2 feet beyond the burners. Adjustments are made so that a test sample of Grade A red oak w i l l become involved i n flame throughout its entire length i n 6 minutes. Following this, a test sample of cement-asbestos board is exposed to the same conditions, and the length of the test flame with this m a t e r i a l establishes the zero classification. Test samples are preconditioned i n a specified atmosphere before exposure, and the test flame exposure is continued for 10 minutes unless the sample is c o m p l e t e l y consumed before that t i m e . Observations of the spread of flame are made at 15second intervals during the test. If the flame spread reaches only part of the distance between the end of the test flame and the end of the sample, the percentage of the distance traveled establishes the classification. If the flame spread reaches the end of the tunnel, the percentage of the t i m e required against the t i m e for the red oak


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sample establishes the classification. Smoke density and temperature readings of the combustion products are also recorded. The A m e r i c a n Society for Testing Materials (1) has described this test. T h e U n derwriters' Laboratories, C h i c a g o , has test equipment as described above. The Forest Products Laboratory, Madison, W i s e , has built a smaller tunnel,approximately 1 foot wide and 8 feet long. As far as the writers know, this type of tester has not been i n stalled i n any private industrial or c o m m e r c i a l testing laboratories. This severely


restricts the rate of accumulation of test data by this method. In spite of this, c l a s sifications by this method are being incorporated i n various building codes. Factory M u t u a l Room Burn Out Test. This method involves the use of a special test room. The particular one referred to is located at Factory Mutual Laboratories, Norwood, Mass. It is 14 χ 20 feet i n area and 12 feet high, constructed of spruce studs and roof joists, with a floor of Douglas fir sheathing on spruce runners l a i d on a concrete floor underneath. The interior surfaces of walls and c e i l i n g are covered with 1/4 inch soft asbestos board. Thermocouples are located so as to record temper atures i n the corners and center of the room at both the c e i l i n g and breathing levels. Test samples are attached to the c e i l i n g , or walls, or both. A fuel pan is placed i n one corner of the room, and a specified quantity of wood brands and ethyl a l c o h o l is placed i n it and ignited. The test continues u n t i l the fire extinguishes itself. Photographs are taken at 1-minute intervals, as w e l l as before and after the test. This is rather bulky test setup, but it seems to be a realistic approach to the prob l e m of observing what happens to exposed materials when a fire starts somewhere i n the room. The extent of spread of flame beyond the test flame area is observed, and the thermocouple readings indicate the potential life hazard from breathing i n the atmosphere i n the test room. Perhaps the dimensions of the test room c o u l d be reduced and thus bring about the installation of this type of equipment at other laboratories. Class F Fire Test of C o m m e r c i a l Standards (12). The test specimen, precondi tioned at a temperature of 70* to 75* F. and a relative h u m i d i t y of 48 to 52%, is supported on the specified test rack at the specified 45* angle with the horizontal, with the board face downward, i n a draft-free l o c a t i o n . A flat-bottomed sheet iron cup of 5/8 i n c h internal diameter, 9/32 i n c h depth, and 1/32 inch thickness is placed on a support composed of m a t e r i a l of low thermal conductivity. It is supported so that the center of its base is 1 inch v e r t i c a l l y below a point on the lower surface of the test specimen, 3 inches from its lower horizontal edge, and midway between the i n c l i n e d edges. One cubic centimeter of absolute ethyl a l c o h o l is placed i n the cup from a suitable pipett or other means, and ignited with the test specimen i n place with a suitable p r a c t i c a l flame, which is removed as soon as the a l c o h o l is lighted. One minute after the .fuel has been exhausted, any flame and glow on the specimen are extinguished and reported and the area of char is measured. In accordance with the test specifications, the area of char is that portion w h i c h shows definite decomposition or shrinkage, and is black to dark brown i n color. However, the extent of the charred area is not always c l e a r l y distinguishable and this leads to variable reporting of the same charred area. The Class F fire test has been very useful i n m i l l control work, permitting quick evaluation of m i l l surface coatings. In FIRE RETARDANT PAINTS; Advances in Chemistry; American Chemical Society: Washington, DC, 1954.

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Conclusions


Considerable time and effort have been employed to improve the fire and flame resistance of the organic-type acoustical board, with both wood and vegetable fibers, employing both the integral and surface coating methods. Thus far, considerable prog ress has been made i n developing and introducing into production excellent flameretardant coating surface treatments, which have improved the fire and flame resist ance of the organic-type board. T h e most promising has been the intumescent type, i n both the aqueous and nonaqueous classifications. Some progress has been made with the integral treatments, but the economics, process difficulties, and deleterious effect of those treatments on the fibers have not been c o m p l e t e l y overcome. A d d i t i o n a l work is now i n progress to improve further the qualities of these fireretardant coatings, particularly i n finish washability and i n reducing the coating cost. Several promising coatings are now i n the laboratory stage. A d d i t i o n a l laboratory work is also i n progress with integral treatments. Several tests have been developed to evaluate fire-retardant coatings on acousti c a l fiberboard surfaces. These tests are being reviewed and modified where there is necessity for standardization of the test.

Literature Cited (1) A m . Soc. Testing Materials, Designation Ε 84-50T, "Tentative Method of Fire -HazardClassification of Building Materials." (2) Factory Mutual Laboratories, Lab. Rept. 11760 (1950). (3) Federal Standard Stock Catalog, Federal Specification SS-A-118a (Feb. 12, 1948). (4) Ibid., TT-P-81a (1943). (5) Groebe, F., U . S. Patent 2,089,697 (Aug. 10, 1937). (6) Jones, G . , Juda, W., and Soil, S., Ibid., 2,523,626 (Sept. 26, 1950). (7) Leatherman, M., Army Service Forces, Chemical Warfare Service, Memo. Rept. TDMR 936 (1944). (8) Little, R. W., "Flameproofing Textile Fabrics," A . C . S. Monograph 104, New York, Reinhold Publishing Corp., 1947. (9) Thomas and Kosolapoff, U . S. Patent 2,401,440 (June 4, 1946). (10) Truhlar, J., and Pantsios, Α. Α., Ibid., 2,582,181 (Jan. 8, 1952). (11) Underwriters' Laboratories, Inc., "Standard Test Method for Fire Hazard Classi fication of Building Materials," 1950. (12) U . S. Dept. Commerce, Commercial Standard CS42-49, "Structural Fiber Insu lating Board," 4th ed., 1949. (13) Van Kleeck, Arthur, Forest Products Laboratory, Rept. R1280, 3 (1948). Received April 1, 1943.


Fire-Retardant Coatings on Acoustical Surfaces ... - ACS Publications

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