: NI E-l tl U I INI CCATIN4 Revised November 1943 II n ■>. LI [ No. R128C UNITED STATES DEPARTMENT OF AGRICULTURE FOREST SERVICE FOREST PRODUCTS LABORATORY Madison, Wisconsin In Cooperation with the University of Wisconsin FIBB-K5TAKDIITG CCATIl'&S By ARTHUR VA1 T KL3ECK, Chemist The present emergency has stimulated considerable interest in fire- protective treatments for wood, 'food has replaced steel for construction purposes in many new structures, and there has been some anxiety concerning potential fire danger not only from normal sources "but also from incendiar- ism. There is likewise more than usual interest in fire protection for wood structures already "built. Protection of '-rood against fire can be provided by two types of treat- ments, impregnation with fire-retarding chemicals and surface coverings of fire-retarding coatings. Impregnated wood has been in use to a limited extent for many years and during recent months, large quantities have been used in the construction of military installations. It is an established commodity. Fire-retarding coatings have not received much recognition, partly because of extravagant claims made by manufacturers of preparations possess- ing very little fire-retarding effectiveness and partly because of a lack of standards for minimum requirements. The Forest Products Laboratory has been interested for some time in the possibilities of fire-retarding coatings to check the spread of small fires and has made many fire tests of the effec- tiveness of such materials. This mimeograph outlines what can be expected in the way of protection from known fire-retarding coating formulations and contains information on the properties of such preparations. Toocl exposed to fire temperatures will char, regardless of whether it is coated or not. The best that can be expected of a paint-type coating is to stop or retard the spread of flame along the surface. The degree to which flame spread is checked is dependent on the type of coating and its thickness and on the fire conditions present, such as design of the painted structure, size of the fire, duration of exposure, presence of draft, and temperature cf the air. After fires develop to large size and burn rapidly or for consid- erable periods, they may overcome the resistance of fire-retarding coatings; but small fires can often be kept small or even caused to die out by suitable coatings. Various tests have been devised to measure the effectiveness of fire- retarding coatings in checking flame spread under varying conditions of severity, but the work done has been insufficient to determine how effective such coatings are in actual use. The Laboratory has used the fire-tube test for much of its fire-testing work. In this test, a specimen measuring Uo inches by 3/U inch by 3/g inch is suspended vertically within a sheet-iron cylinder 3 inches in ^.iameter, and a bunsen burner with an 11-inch flame is placed beneath the specimen. The percentage loss in weight of the specimen Mimeo, No. R1280 -1- ( Revised November I9U3) and the temperature at the top of the fire tube are recorded at intervals of 30 seconds. At the end of h minutes the burner is removed, but -ercent losses in weight and temperatures are recorded until burning ceases. In this test, untreated or uncoated wooc 1 loses about 50 percent of its weight after a 3- m i n-u te exposure to the flame and 70 percent or more of its weight is gone when blazing and glowing cease. In evaluating the degree of pro- tection afforded by coatings, a loss of weight of less than 30 percent after an exposure of 3 minutes is considered to indicate protection against mild fires, whereas a final loss of weight of less than 25 percent is con- sidered to indicate protection against fires of considerably greater severity. Another method of test being used is a modification of one developed by Ragnar Schlyter of the Swedish Government Testing Institute; In this method two test panels, 12 inches by J>1 inches by 3/3 inch, 1 are stood in a vertical position, parallel to each other and 2 inches apart j with the bottom of one panel k inches above that of the other. A wing-top Bunsen burner flame is placed between the two panels and readings are taken of the progress of the flame spread with time. With unprotected \\rood, the flame will spread over the surfaces and destroy the specimens, but with effective fire-retarding coatings on the exposed surfaces the flame ceases to spread as soon as the gas burner is removed. More recently a flame with more intense ignition properties has been used in the Schlyter-type test, and a limited number of tests on a larger scale have been made using incendiary bombs. The Forest Products Laboratory has used the foregoing methods to study the performance of a large number of formulations in its efforts to find good fire retardants and to determine their ability to provide good protection with a reasonable number of coats. In addition to fire-retarding effectiveness, other properties must be taken into consideration. Among these are reasonable permanence of both fire-retarding effectiveness and adherence of coating to the wood, resistance to comparatively high relative humidity, and, to some extent, ^the appearance of the coating. Resistance to weather is also desirable but/usually absent. On the basis of the examination of numerous coatings, the Laboratory has drawn the following conclusions regarding certain types of preparations tested. Borax-linseed Oil Fire-retardant Faints Linseed-oil-base paints of good fire-retarding effectiveness can be made by replacing an appreciable portion of the pigment with finely ground borax. The percentage of borax required varies with the kind of pigment. The following table gives four examples of single pigment formulations, heavy coats of which were found to provide sufficient protection to keep the final Mimeo. Ho. R12S0 -2- loss in weight in the fire-tube test under 25 percent; 3 or ^ thick coats or approximately 1 gallon per 125 square feet are required. Coatings of ordinary thickness undoubtedly would provide protection against comparatively weak fires, "but for highest resistance thick .coatings must tie used. This type of paint is good for interior, use from the stand- points of appearance, moderate moisture resistance, and permanence. It will not retain its effectiveness, however, after repeated exposure to rain and for that reason it is not suitable for outdoor use. . Borax-linseed oil f ire-retardant paint formulas Pigment : Formula I (1) Formula (2) Formula: Formula (3) : M Percent by weight White leadr-. ..'.. , Titanium-calcium Lithopone Zinc oxide , Borax Raw linseed oil , Turpentine Japan drier Ul.O 32.0' 22. g 3.6 .6 3C0 35cO 30. g 1 .6 2U,0 39.5 32.3 3.6 .6 21.0 50.0 2U.g 3.6 .6 —Basic carbonate' white lead. Water Solutions of Fire-retarding Chemicals Sodium silicate Sodium silicate is an excellent fire retardant when freshly applied. Very good protection is furnished for a limited time -by three coats of the commercial viscous syrup (water glass) diluted with a minimum .quantity of water necessary to give a liquid of suitable brushing consistency., The addition of a small quantity of liquid soap or other wetting agent improves the wetting properties of the silicate solution. Moderate protection is fur- nished by two coats. Sodium silicate is available in a number of grades based on the soda- silica ratio. The grades with a high silica ratio are preferred for fire- retarding coatings. The serious weakness of sodium silicate coatings is their instability. A series of tests on fire-tube specimens coated with various silicate formu- lations and exposed, to different relative humidity conditions revealed the following: Exposure to a relative humidity of 65 percent at SO F. caused a Mimeo. ITo. R12g0 -3- serious decrease in effectiveness after only one month and a relative humidity of 90 percent at 20° P. caused the high silica-ratio coatings to check, crack, and peel* Under similar conditions, low silica-ratio compositions became soft and sometimes dripped. In dry situations, the effectiveness continued over a much longer period, being retained under favorable conditions for more than a. year; but it is seldom that use con- ditions are such that high humidities are always avoided. The fire protection given by sodium silicate is largely due to its property of intumescence; that is, the coating when exposed to heat shells to a frothy mass that hardens ano 1 thus insulates the wood against heat. The property of intumescence is absent in silicate coatings that have beer, exposed to high relative humidities; this seems to account for the decrease in effectiveness of silicate coatings after such exposures. The explanation given for the decrease in effectiveness with time, especially under high moisture conditions, is that the carbon dioxide of the air in the presence of moisture reacts with the sodium silicate to convert it to sodium car- bonate and silica, neither of which intumesce on exposure to heat. The inclusion of pigments in the silicate formulations improves the appearance and brushing properties of the preparations. The British! recommend such a pigmented sodium silicate preparation for the protection of wood in attics against incendiarjr-bomb fires. The British formula is: Sodium silicate solution - 112 lbs. (Specific gravity 1,^+1 to 1.U2 Silica-soda (5) ratio 3.2 to 3.U) Kaolin - 150 lbs. Water _ 100 lbs. Three to k coats of this preparation are required to give good protection. One gallon will cover approximately 100 square feet (k coats). Ammonium phosphate and ot her fire-retarding chemicals Strong solutions (25 percent or higher) of such good fire-retarding chemicals as monoammor.ium phosphate, diamioovji 'im phosphate, a mixture of ammonium sulfate and mo no ammonium phosphate, and a high- solubility mixture of borax and boric acid ire-retarding properties when applied to wood. These solutions, however, are not syrup/ as is wate: glass, and the quantity of dry chemical that can bo appli r coat is so that an unpractical number of coat- in necessary to build a? the coating weight sufficiently to give protection comparable to 'chat obtained with j to k coats of borax- linseed oil paint or 2 to j coats of sodium silicate. Hev rbhcless, 3 coats of saturated solutions of good fire-retarding chemicals do have definite, although moderate, fire-retarding effectiveness. —British Standards Air Raid Precaution Series 35, February I9U0. Mimeo. ITo. R1280 _h_ Alginate Preparations A new type of f iro-retarding coating developed at the Forest Products Laboratory consists of finely ground f ire-retardant chemical dissolved and susT)ended in an aqueous sodium or ammonium alginate gel. Tests have shown this type of preparation to -oossess excellent effective- ness. The alginates, manufactured from an extractive of kelp, are good thickening agents. One- to 2-percent aqueous solutions are very viscous On a "basis of percentage "by weight, concentrations of amnonium alginate gels are more viscous than sodium alginate gels, a 1.6-percent ammonium alginate gel having approximately the same viscosity as a 2-per- c< it sodium alginate gel. The cost of the ammonium compound is, however, proportionately higher. Uo chemical reaction occurs "between these alginates and ammonium f iru-retardant salts. Borax causes the gel to set, but boric acid and mixtures of boric acid and borax arc compa.tibl-- with the gel. The best formulations thus far prepared, considered from all angles, contain mono- ammonium phosphate, but fairly satisfactory preparations can be made from a mixture of borax and boric acid. The use of the alginate makes it possi- ble to incorporate in the preparation a auantity of f ire-retardant con- siderably in excess of that reouired to saturate the solution. The undis- solved portion is held in suspension. Pigments may also be introduced into such preparations. Three methods have been used for making these preparations. These methods, using typical ammonium phosphate formulas, arc described as follows; Method I Parts by weight Mo no ammonium phosphate 50 (6) Iwo percent sodium alginate gel 50 1. Prer^are the alginate gel by adding 2 parts by weight of sodium alginate to 98 parts of hot water. Stir until a uniform gel is obtained. 2. Grind in a pebble mil] eaual parts by weight of monoammenium phosphate and alginate gel. A grinding period of 12 to 2k hours is sufficient. Method II Parts by weight iionammonium phosphate 50 Titanium dioxide 5 (7) Two percent sodium a ' e gel ^5 Mimeo. Ho. R12S0 -5- 1. Frepare alginate gel. 2. Grind mo no ammonium phosphate and titanium dioxide together in a pebble mill until the material is reduced to approximately 200 mesh. 3. Mix in a blade mixer 55 parts by weight of the phosphate -titanium dioxide- powder and U5 parts by weight of the alginate gel until a uniform prepa- ration is obtained. The purpose of the titanium dioxide is to facilitate grinding and prevent lumping of the ammonium phosphate in storage and to give the coat- ing better hiding power. Inclusion of the titanium dioxide also improves the brushing properties of the paint and produces a coating somewhat finer grained than a pure ammonium phosphate coating. Method III Farts by weight Mo no ammonium phosphate 88.5 China clay 10.0 (8) Dry sodium alginate 1.5 1. Grind sodium alginate to 325 mesh. 2. Grind the prescribed quantities of monoammonium phosphate, china clay, and pondered sodium alginate until the particle size of the ammonium phosphate is approximately 200 mesh. This procedure will produce a powder similar to calcimine or dry casein paint. To prepare it for use, a^d U to 5 parts by weight of water to 6 parts by weight of the powder ?nd. stir until the powder is mixed thoroughly with the water. Allow to stand for at least an hour and stir again until a smooth mixture is obtained. bhods I and II can be used to prepare such borate formulations as the following: Farts by weight Formula (9) Formula (l.O) 3orax (Fa^O-. 10H 2 0) 32.5 Boric acid 32.5 37.5 Two percent alginate gel _^5 62.5 The procedure of Method III can be used satisfactorily to prepare dry-mix powders consisting of boric acid arm 1 dry sodium alginate. Dry- mix powders containing borax and boric acid can be prepared, however, only Mimco. No. R1280 -6- "by using a partially dehydrated "borax. The grade of borax most commonly sold, containing ^7 percent of water of crystallization, is not satis- factory for preparations of this typo because a reaction occurs between it and boric acid in which sufficient water is liberated to cause the mixture to become damp and to pack. If the borax is dehydrated sufficiently, satisfactory dry mixes can be prepared. Examples of dry-mix borate prepa- rations are: tarts by weight Formula (11) Formula (12) 92 6o 38 Boric acid Borax (820 lTagB^Oy) Pry sodium alginate 2 2 The properties of preparations with a monoammonium phosphate base may be summarized as follows: The paints have good brushing properties, producing smooth coats. The solids remain in suspension during application and, although they settle after standing for some time, can be returned to suspension very readily by stirring. The preparations are stable fo:r an indefinite period so far as is known. Solutions of monoammonium phesphats are corrosive to many metals. If the paints are packaged in unocated metal containers or are to be applied by spray-gun, the addition oi* bhe corrosion inhibitor, 3odium dichromate, is desirable. Two to 3 percent of the ammonium phosphate content is sufficient. The body of the preparations is such that sufficient dry fire retardant can be applied in 2 or 3 coats to gi'e sufficient pro- tection to keep the final loss in weight, as measured by the fire-tube, under 25 percent. Eea,vy coats of these preparations stopped the spread of fire in the severe Sehlyter test and in tests involving the high tempera- tures developed by different t^pes of incendiary bombs. The coverage per gallon is approximately JZ square feet for 3 coats. The coating'.) oh drying are flat white, resembling casein paints or calcimine. Their adherence to wood is good, ilelative humidities up to 91 percent feet upon monoammonium phosphate, but at humidities higher than Lhis , the phosphate takes on water. Under oidiiiar^ conditions, the fire-retarding eix'ecciveness should be retained indefinitely. The borate coatings do not have so good fire-retarding effective- ness as the phosphate coatings on an equal weight basis so that it is necessary to use them in slightly heavier coats to obtain the same effec- tiveness. The borate coatings, especially those with a high percentage of boric acid, withstand high relative humidities better than do the ammonium pho s phat e c a t i i . Aii indication of the ability of the alginate type of coatings to with- stand atmospheric rxposures at Madison, Wisconsin is shown by the following: Mimeo. No. R1280 -7- Panels coated with mo no ammonium phosphate-alginate and with borate- alginate preparations were placed in an open shed in which they were protected against rain , hut were exposed to outside temperature and relative humidity conditions. After an exposure of one year, the coatings are intact and show no evidence of deterioration. The formulations given are illustrative of moderately heavy-bodied preparations. If still heavier-bodied paints suitable for trowelling or coarse spray are desired, they can be prepared by increasing the percentage of solids. If thinner mixtures are desired, they can be made by decreas- ing the percentage of solids or using a less viscous alginate gel. Like- wine, if colored paints are desired, they can be made by substituting suit- able pigments for the china clay. Methyl Cellulose Preparations Methyl cellulose is a thickening agent that can be used to prepare saints with properties similar to those described under alginate prepara- tions. It is suitable for use with borax, boric acid, and mixtures of borax and boric acid, but it cannot be used with ammonium phosphate, as it is coagulated by this salt in the high concentrations used in fire-retard- ing preparations. The material is furnished in several viscosity grades. In the experimental formulations tested, the grades capable of producing viscous solutions with a minimum quantity of material have been used. Typical formulations together with the method of preparation are as follows: Parts by weight Formula (13) Formula (lU) Formula (15) Borax (tta^O-.lOHgO) 50 — 30 Boric acid — 50 30 2$ methyl cellulose 50 50 ho (1500 c.p,) gel 1. Prepare the methyl cellulose gel as follows 5 Mix 2 parts (by weight) of the methyl cellulose thoroughly with 50 parts of water at boiling temperature, and allow it to soak for 20 to 30 minutes. Add Hg parts of cold water and stir until smooth. 2. Grind in a pebble mill the required quantity of boron compound and of methyl cellulose gel until the mixture is of fine-grained consistency. The properties of these preparations and of the dry coatings are similar to those of the borate-alginate preparations. Three coats provide sufficient protection to stop the spread of flame in the severe Schlyter test. Mimeo. No. R12S0 -g- TT hitewash TThitewash is generally regarded as having fire-retarding properties. Significant effectiveness cannot, however, "be obtained with a one-coat a't lication. The following t^o whitewash formulations that were tested gave moderate protection when three coats ^-ere applied: National Fire Protection Handbook (8th edition) formula - page k2h. Mix together 10 parts slaked lime, 1 part of Portland cement, and sufficient salt water to give a mixture (l6) of rather stiff consistency. (Bulletin No. 30^- D, Formula 9> - National Lime Association) Casein - 5 Its, Borax - 3 lbs. (17) Lime paste - 8 gals. (Approximately 8 gallons of stiff lime paste are produced by slaking 25 pounds of quicklime with 10 gallons of water, or by soak- ing 50 pounds of hydrated lime in 6 gallons of wat er . ) Directions as given by the association: "Soak the casein in H. gallons of hot water until thoroughly softened (about 2 hours). Dissolve the borax in 2 gallons of water and add this solution to the casein. T Then both are cold, slowly add the borax- casein solution to the lime paste, stirring con- stantly and vigorously. Thin to desired consis- tency. Do not prepare a larger quantity of this formula than can be used in a day, as it may deteriorate. " Tests made at the Laboratory show that neither the adherence nor the fire-retarding effectiveness of whitewash (formula 17) is seriously affected by exposure of several months to a. relative humidity of 90 per- cent at 80° P. Casein Paints Casein paints possess moderate fire-retarding effectiveness if at least three coats are applied. The effectiveness is increased if borax is introduced into the formula. The degree of fire protection provided by three coats of whitewash or casein paint is by no means comparable with that provided by three coats of borax-linseed oil paint, sodium silicate, or the phosphate-alginate preparations, 24imeo. No. R1280 -9- Magnesium Oxychloride and Magnesium Oxysulfate Coatings Preparations of this type made "by mixing magnesium oxide (magnesite) with a solution of either magnesium chloride or magnesium sulfate provide good protection when applied in heavy coats (100 grams of dry coating per square foot). The only formulations tested were proprietary. The test of those tested adhered reasonably well to wood, hut some showed a strong tendency to flake off, especially xvhen applied in heavy coats. Synthetic-resin formulations Preparations of urea-formaldehyde resins containing ammonium phos- phate provide very good protection. This type of resin intumesces when exposed to heat, and the frothy mass chars to form a protective coating of combustion resistant carbon. The formulations tested that contain mono- ammonium phosphate tend toward brittleness and serious checking which, in some cases, caused the coating to chip or scale from the wood. Those con- taining di ammonium phosphate possessed poor moisture resistance. Moder- ately high relative humidities at room temperature caused them to become tacky. While this type of coating is still in the experimental stage, the initial work done holds sufficient promise to indicate that additional research may remove objectionable properties. Paints Containing Water- insoluble Pire Retardants A major weakness of the f ire-retardant coatings discussed in this paper is their inability to retain their effectiveness after exposure to water, due to the removal of the water-soluble fire retardant. So far as is known, no water-insoluble compound has been found equal in effectiveness to such water-soluble compounds as ammonium phosphate, borax and sodium silicate. Zinc borate, a water- insoluble chemical, is mildly fire retardant and some paints containing it, when applied in heavy coats, provide suffi- cient protection to check flame spread under the conditions of the mild Schlyter test. Because of the absence of water-solubles, such preparations may be expected to retain their effectiveness after exposure to water. A formulation of this type is Percent by weight (IS) Zinc borate 30.0 Basic carbonate white lead 3^3 Raw linseed oil 31.6 Turpentine 3-5 Drier .6 Mimeo. No. £1280 -10- UNIVERSITY OF FLORIDA III III lllll llll II II llll III III lllll II! Illl II 3 1262 08927 '3287 Lcose-texture Compositions Certain compositions applied "by spray gun in a thickness of 1/2 to 1 inch are in use for heat insulation purposes. These coatings con- such materials as mineral wool, asbestos, or shreclded cellulosic materials treated with fire-retarding chemicals, with only sufficient binder to hold the mass loosely together. Such coatings have good fire- retarding properties and are useful where a combination heat-insulating, fire-retarding preparation is desired. Coatings of such compositions thinner than those necessary for heat insulation purposes possess suffi- cient fire retardance to he useful for fire protection only. The soft, spongy nature of these coatings limit their use for fire protection to such applications as ceilings and attics, or other places where resistance to wear is not required. The adherence of certain types of this material to laboratory-size specimens of wood was not good, especially under fire conditions, hut how serious this defect would he on large installations under fire conditions is not known. Mimeo. No. K12S0 -11-