Document K62E9vmDo1dYN1jzZGqg0qNMX

FILE NAME: CertainTeed (CERT) DATE: 1950 Oct 17 DOC#: CERT065 DOCUMENT DESCRIPTION: US Patent Patented Oct. 17, 1950 2,526,066 UNITED STATES PATENT OFFICE 2,526,066 PLASTIC COMPOSITION MATERIALS AND PRODUCTS MADE THEREFROM Michele Croce, Evanston, HL, assignor to D dtaihTeed Products Corporation, Chicago, 111., a cor poration of Maryland ' Continuation of application Serial No. 510,365, November 15, 1943. This application August 7,1946, Serial No. 688,843. In Canada Septem ber 8,1944 2 5 Claims. (Cl 196-- 110) 1 This invention relates to plastic composition Fig. 1 is a vertical cross-sectional view through mixtures and products, and it hae-for Its object a piece of wallboard embodying my invention; the provision of a new and improved form of ma and terial by which highly advantageous results shall Fig. 2 is a vertical cross-sectional view through, be attained in connection with building materials g a portion of a wall plastered at one face with embodying the Invention. The Invention relates my improved plaster. particularly to the provision of an improved form This application is being filed as a continuation of plastic composition by the use of which greatly of my earlier application Serial No. 510,365, filed improved protection against fire shall be ob on November 15, 1943, which earlier application tained. 10 became abandoned on September 30, 1947. When a layer of plaster such as the core of an In Fig. 1 of the drawing, a wallboard 5, one- ordinary gypsum wallboard forming the facing half Inch thick is shown, comprising a set and portion of a building wall is attacked by a de dried body portion 6 formed of my improved structive fire, the heat in due time Causes the composition as hereinafter described, such com plaster to contract In volume so as to produce i5 position having calcined gypsum as its principal cracks in the plaster, with a tendency for the ingredient, with paper liners T and 8 bonded to plaster to break up and fall off the wall. My in opposite faces of the body portion. vention has for one of Its objects to provide an In Fig, 2 ,1 have shown -my improved plaster in improved form of composition material for form dried condition on a wall comprising studdings S, ing the plaster for use in the core of a wallboard, 20 with metal lath IDsecured thereon so as to carry in one embodiment, or for application by any a plaster facing portion 11 formed of my im approved plastering method for the formation of proved composition and applied in any suitable a wall, In an alternative embodiment, so that by manner and dried in position on the lath. This the use of such improved form of composition plaster facing II as Illustrated is formed with material a layer of dried plaster formed there- 25 comparatively little or no sand and expands only from shall be afforded greatly increased resist slightly if at all under the influence of heat ex ance to the tendency for cracks to open up in cept for the expansion of the vermiculite content the layer when it is subjected to heat. To this by exfoliation. end, It is one of the objects of the invention to In the preferred embodiment of my invention, provide an improved composition of materials for as embodied either in the wallboard panel of Fig. a plaster either for the formation of a wallboard 1 or the stationary panel of Fig. 2, the composi or for the production of a plastered wall, com tion which with water makes up the body portion prising a non-combustible ingredient such as 6 of the wallboard B as shown in Fig. 1 and the comminuted raw vermiciilite in unexpanded form plaster facing 11 of the wall as shown in Fig. 2, thoroughly distributed through a layer of dried gg comprises about 2% by weight of fibrous mate plaster made from the composition and adapted rial, from about 2y2% to 7 Vi% of minus 28 mesh under the influence of heat when the layer of commercial grading raw or unexpanded vermicu plaster Is attacked by a fire to expand so as to lite such as that obtained from the Libby, Mon compensate for the contraction of the gypsum or tana, mine of the Universal Zonollte Company, other ingredients of the dried plaster and thus 40 and the balance largely- calcined gypsum. The protect the layer of plaster against distortion and usual small amounts of additives, such as starch, maintain it intact to act as a barrier for prevent fine sawdust, accelerator, foam, etc., may he in ing progress of th fire. cluded. It is another object of my invention to provide, I have found th at highly useful results are at in a composition for making plaster of this type, tained by the use of the following proportions of means adapted to hold adjacent portions of the the dry ingredients as specified. dried plaster together so as to minimize the dis rupting effect produced by the contraction of one Table No. I particle or the expansion of an adjacent particle under the Influence of heat. For this purpose, I No. 1 No. 2 No. 3 No. 4 have employed non-combustible fibrous material distributed throughout the composition, and I Calcined Gypsum; com- Per cent Per cent Per cent Per dent mercial grade________ 95 93 90.5 94.5 have found th a t a fairly small amount of such Glass wool____________ 1 1 1 None non-combustible fibrous material is effective for Asbestos fibres.._______ . 1 Minus 28 mesh tmex- 1 1 2 attaining the desired results. paneled vermiculite___ 3 5 ' '7.5 3,0 It .is another object of my invention to improve compositions and products of this type in sundry details hereinafter pointed out. The two pre Substantial amounts of wallboard of one-half ferred embodiments of the invention are shown Inch nominal thickness have been made up with In the accompanying drawing, in which: Bo body portions comprising respectively the ingredi- Castleman.CERT001397 Oct. 17, 1950 m. croce PLASTIC COMPOSITION MATERIALS AND PRODUCTS HADE THEREFROM Original Filed Nov. 15. 1943 2,526,066 _ Z t7 t/e-n ' o r*;~ TH iC'/deies 6 ro c e \ './ f tf c m e t/ . Castleman.CERT001398 2,526,066 3 4 ents of the four mixtures set forth in this Table 500 P. is well in excess of any temperature to No. X, mixed with water in the usual manner, which any of the ingredients of a wallboard are formed between the usual paper liners bonded normally raised diming the formation and the thereto, and dried, the usual amount of starch drying of the board, it will be appreciated that adhesive to obtain bond of paper to core and a 15 the vermiculite content ox such board will nor small volume of soap foam or lather to reduce mally be maintained in its unexpanded condi weight being incorporated in the wet plaster mix tion up to the time when the board is attacked ture. Xhave found that such board can be made by a destructive fire. Studies made by authori up readily on a conventional board machine tative sources have shown th at fires of normal equipped with suitable material-feeding means 10 severity develop temperatures of 1000 P. in about and can be dried in the ordinary kilns without five minutes. The heat developed in a building danger that expansion of the vermiculite will be fire attacking a wall embodying my improve effected by the drying operation, the comminuted ments, therefore, is normally sufficient for bring raw vermiculite going through the board machine ing about substantial expansion of the raw ver- and the drier without any complications, the 15 miculite contained in the wallboard or other lay same as sawdust or other fillers in use heretofore. er of plaster forming the facing of the wall, such A series of fire tests have been carried out at the expansion of the vermiculite taking place in the Underwriters Laboratories, Chicago, Illinois, on layer of plaster a t the same time when the con 2 " x 4" wood stud load-bearing partitions faced traction of the gypsum is being effected and be- with these half-inch boards produced by the use 20 fore the heat has been built up to the point where of my improved mixtures, said fire tests being the complete destruction of the layer of plaster conducted according to Standard Methods of Mre takes place. The destruction of the layer of Tests of Building Construction and Materials, plaster is thus delayed substantially, the resist A. S. T. M. designation C19-41. The fire tests of ance to the progress of the fire being thus sub- my improved boards in comparison with similar 25 stantially increased. tests of ordinary high-grade half-inch boards not I have found satisfactory results in the use of embodying my improvements, show for the im high-grade vermiculite such as that found in the proved boards substantially improved results, Ubby, Montana, deposit, and prefer to employ demonstrating that 2" x 4" wood stud load-bear such mineral, but I do not desire to limit the ing partitions faced with the boards employing 30 invention thereto, except as it may be specifically the mixtures as shown in the table and including claimed, since there are other minerals of the the raw, unexpanded vermiculite as specified in vermiculite group which can be used to advan the table are entitled to fire endurance ratings tage, such as jefferisite, kerrite and philadel- of from 45 to 51 minutes, as compared with a fire phite. It will be understood that any of these endurance rating of from 35 to 40 minutes for 35 minerals may be used effectively in a board, pro 2" x 4" wood stud load-bearing partitions faced vided such mineral, when used within proper with ordinary high-grade half-inch board in limits as to the amount employed, and when which no expansible mineral of the vermiculite ground to the proper fineness for mixture with group is present. This is, of course, of utmost the other ingredients, is found to expand suffi- importance commercially for enabling the manu 4u ciently in a fire to offset to a large extent at facturer to meet the requirements for fire resist least the contraction of the gypsum or other ance walls. body material of the board. In the above-mentioned fire tests of my im The amount of the expansible mineral to be proved boards, the contraction of the gypsum employed is preferably controlled by reference to content brought about by the influence of the 45 its capacity to expand. As will be readily under heat applied to the faces of the partitions was stood by those skilled in the use of the vermicu accompanied by an expansion of the raw ver lite group of minerals, there is a substantial vari miculite by exfoliation which compensated for ation in the expansiveness of vermiculite from and offset the contraction of the gypsum. In different mines and even a substantial variation these fire tests, the expansion of the vermiculite 50 in the expansiveness of different batches of the and the contraction of the gypsum in the board mineral taken from different parts of the same took place at so nearly the same time that there mine, m the use of this type of. material, ac was little or no tendency for the board to crack cordingly, in the manufacture of plaster or wall or open up due to shrinkage. At the same time, board or in any case where the capacity to ex- any tendency for displacement or disarrange 55 pand by exfoliation when heated is important, a ment of the particles of the body material of the more or less continuous check should be made as boards by reason of the contraction and expan to the effectiveness of the mineral for expanding, sion of the different ingredients was opposed by the amount of the mineral used being changed the mechanical bonding or matting effect of the preferably from time to time for maintaining the particles of non-combustible fibrous material 60 desired total amount of expansion. Generally distributed throughout the mixture. The result speaking, when it has been determined that a was that the board, with the fibre and un particular lot of vermiculite is adapted to expand expanded vermiculite distributed thoroughly only one half or one third as much as a different through the gypsum, was prevented from dis lot, it wifi, be found necessary to use twice as rupting' and disintegrating and was enabled to 66 much or three times as much of the less expan hold its form intact without serious cracks or sible mineral for obtaining the same results with breaks for a considerably longer period than can respect to expansion. be expected in similar fire tests of boards from As showing the variation in the volume expan which the unexpanded vermiculite and the fibre sion of different samples of vermiculite from the have been omitted. 70 same mine, three specimens of Libby, Montana, When raw or unexpanded vermiculite is in vermiculite, all ground so as to pass through a corporated into a wallboard or into a layer of 35 mesh screen and to be retained on a 48 mesh plaster on a wall, it does not begin to expand by screen, showed different percentages of expan exfoliation until the temperature reaches a point sion under similar conditions. For one specimen in excess of 500 p. Since the temperature of 75 the percentage of volume expansion by exfolia, Castleman.CERT001399 5 2, 526,066 s tion when heated was 320%, for a second speci tially th period preceding the complete break men 391%, and for the third specimen 367%, down of the board structure. After the vermicu which is typical of the differences to be expected. lite has expanded, it is a good heat insulating As showing the variation in the expansion of material and increases the resistance of the board specimens of vermiculite from different mines, 5 to the passage of heat in proportion to the three specimens of Libby, Montana, vermiculite amount added. I have found th at where an showed an average expansion of about 359%, as excess of the vermiculite is employed beyond that above specified, while three specimens of En necessary for offsetting the contraction of the campment, Wyoming, vermiculite under similar gypsum or other body material of the board, the conditions as to fineness of grind and other fac 10 thickness of the board core or piaster layer is tors of treatment, showed an average expansion increased somewhat by reason of the expansion of about 161%. A similar sample from a South of the vermiculite under the influence of the Carolina mine expanded 298%. heat of the fire, serving thus to afford increased With respect to the fineness of the grind, or insulation against the passage of the heat particle size, of the vermiculite type of mineral 15 through the board or plaster. If this excess of used, I have found th at the percent expansion vermiculite is fairly small, the increased insula when heated decreases as the average particle tion effect may be had without any radical in size is decreased. This is demonstrated in Table crease in the tendency of the board or plaster to No. n which shows the variation in expansion go to pieces as the heat of the fire builds up. under high heat of several screen sizes of raw 20 Seven fire tests have been made on 2" x 4" Libby, Montana, vermiculite, based on three sam wood stud partitions raced with my improved %" ples of each classification of the mineral. gypsum board of six different formulations con Table No. II taining raw vermiculite and non-combustible fibre in comparison with a partition faced with 25 regular %' ' gypsum board. In all such fire tests, P er C ent Expansion the partitions using the improved gypsum board P article Size Including the vermiculite and the fibre gave No. 1 No. 2 No. 3 greater fire protection than the partition using the ordinary gypsum board. To show the effect Passing through 35 m esh and retained on 48 m e s h . _________________ ,----------------- 367 391 320 30 of various amounts of raw vermiculite in these Passing through 48 m esh an d retained on core materials, gypsum boards of nominal half 60 m e s h .. ________ _ _ ------------ 202 362 P a s sin g th ro u g h GOm e sh a n d re ta in e d on 250 inch thickness of various formulations were pro 10D m e sh ---------------------------------------------- 250 294 250 duced and samples cut from such boards were P a ssin g th ro u g h ICO m e sh a n d in c lu d in g . fines__________ _______________ __ 181 193 163 heated In a furnace to 1400" F. for a period of 30 35 minutes in each instance to thoroughly calcine In the development of the data above set forth, the gypsum and to expand the vermiculite. The thickness of the core was measured before and 3 c. c. of the vermiculite were in each instance after heating and the change in thickness due measured in a graduated glass centrifugal cyl to the heating of the boards was determined inder of 15 c. c. capacity, and then transferred 40 with results as shown in Table III, allowance be to a porcelain crucible of about 17% c. c. capacity. ing made for the thickness of the paper in the The crucible and contents were then placed in measurements before heating. The percentages the full heat of a Meker C type gas burner using of fibre and raw vermiculite shown in the table the medium orifice and heated for one minute, are the percentages by weight of the total weight after which the contents were stirred for 15 seconds by means of a small steel rod while the 45 of dry ingredients used in making the slurry from which the board core was formed. The heating was continued. The heat was then ap vermiculite used was all of the same quality. plied for an additional 3% minutes, after which the vermiculite was cooled and then returned to Table No. Ill the graduated centrifugal cylinder. In each case the volume of material was read after tapping 00 Change in Thickness the bottom of the cylinder on a laboratory bench Mineral R aw V erm iculite three times by dropping the cylinder from a No. Fibre Inches Percent height of one inch for settling the particles. By the use of my invention for the production Per of wallboard, a gypsum board of normal appear 50 ttn t ance and having substantially the same physical 1_........... 2 ______ 2 3 \i% ofmm.ua 28 m esh. m inus 0.008.. m in u s 1.3. 2 5% of m in u s 28 mesh__ p lu s 0 .0 1 5 __ p lu s 3.34. properties as other high-grade products of the 3 . ........... 2 7Yi% of m in u s 28 m esh p lu s 0.0 8 8 . -- p lu s 19.1. same type, and having the mineral of the vermic 4 ............ 5 _____ 2 5% of m in u s 35 m e s h .. m in u s 0 .0 0 3 . m in u s C. 67. 2 7% of m inus 35 m esh- plus 0.059 p lu s IS. 1. ulite group and the small amount of fibre mixed e______ 2 10% of m in u s 35 m esh. plus 0 .0 7 1 ... plus 17.4. thoroughly throughout the body material, may be 00 7 N orte m inus 0 030. m inus 6.7. made on the usual board machine provided with the necessary material feeding equipment. The Expansion of the board core or plaster layer expansible mineral is not expensive, and the op when exposed to fire is actually beneficial as eration of grinding the mineral and otherwise regards fire resistance, provided the amount of preparing it for use is not difficult. The mineral 00 expansion is not so great as to cause bulging of so employed In its raw, unexpanded condition co the board or plaster layer to such degree that it operates with the remaining ingredients of the cracks and opens up or falls off in sections. If body material for giving the board the desired it remains in place to serve as a barrier to the normal characteristics. When, however, the passage of heat and flame, the increased ther board is subjected to the heat of a destructive fire, 70 mal insulating value resulting from the increased the mineral expands in situ for offsetting the thickness of the expanded board core or piaster contraction of the other body material ingredi layer offers additional resistance to temperature ents and thus substantially preserves the form, rise on the side opposite the fire. the size, and the shape of the board with a mini The increased thermal Insulating value result mum of distortion so as to lengthen gubstan- ing from the increased thickness was demonstrate Castleman.CERT001400 8,628,066 7 8 ed by additional tests. A series of 6" x 6" sam In actual practice, I have found th at a grade ples take from the same boards 7,1, 2 and 3 listed of asbestos designated as 5-R is suitable and eco in Table H I were placed In a horizontal posi nomical for the purpose. This asbestos fibre is tion at a definite height above a Meker C type of medium length and is economical in cost. Re gas burner and exposed to the action of the 5 sults of a typical screen test of this fibre, using flame under carefully controlled conditions of a 50 gram sample and 8 inch diameter nested gas pressure. The time required for the paper screens shaken on a Ro-tap machine for 15 min on the top (unexposed) side of each sample to utes were as follows: char was recorded. The thickness of the core before and after heating was also measured and 10 Table No. VI the change in thickness was recorded. Results Per cent are shown in Table IV. Retained on 8 mesh------------------------------n.7 Through 8 mesh and retained on 28 mesh_53.3 Table Na. TV Through 28 mesh and retained on 48 m esh.. 13.2 15 Through 48 mesh_____________________ 21.8 T im e re- Board No. Change in Thickness auired to char paper on to p side 7 ___ ______________ 1 *>. a 20 Inches M inutes ____ ______ m in u s 0 .020- 13 m inus 0.006. 16H. p lu s 0 . 0 3 4 . . . 10. p lu s 0. (J72__ p lu s 30. I have had very satisfactory results by the use of Libby, Montana, vermiculite from the mine of 25 the Universal Zonolite Company, using such vermiculite comminuted to either minus 28 mesh commercial grading or minus 35 mesh commer cial grading and employing from 3y2% to 10% 30 of such vermiculite based on the weight of the mixture. I have also had very satisfactory results by the use of 2% of fibre, either 2% of asbestos fibre or \% fibre. of asbestos fibre and 1% of glass wool I have found the asbestos fibre more sat 35 isfactory with respect to controlling and feeding the fibre into the mixture. Results of typical screen tests of the commi nuted nated raw vermiculite as used by me and desig as "minus 28 mesh commercial grading" 40 and "minus 35 mesh commercial grading" are shown as follows :I Table No. V 45 ' M inus 28 m esh M inus 35 m esh R e ta in e d o n 28 m e sh s c r e e n ____ _____ T h ro u g h 2B m e sh a n d re ta in e d o n 3 5 m e sh screen __ _________________ _ . _ Through 33 mesh and retained on 80 mesh T hrough 60 m esh and retained on 100 mesh T h ro u g h 1 00 m e sh s c r e e n ......................... ........ P er cent 0.4 11.8 58.2 20.4 9.2 100.0 P e r ceni 0 0 50 0.7 46.0 30.3 23. 55 mo I have also found th at the amount of fibre re quired depends to a considerable extent upon the length and thickness of the individual fibres and 00 upon their ability to withstand mechanical mix ing and handling without excessive reduction in length. With very long, tough fibres, I have found th a t 1% is sufficient in most cases, while with shorter fibres as much as 5% to 10% may 05 be required. One of the principal functions of the fibre is to prevent spalling of the plaster as the raw vermiculite particles expand when the plaster is exposed to fire. Without any fibre present the plaster spalls and disintegrates as 70 calcination progresses and expansion of the raw vermiculite particles occurs under the Influence of heat. Sufficient fibre should be used to pre vent such spalling and to bind the calcined board Core or other plaster layer together. 75 100.0 Longer fibred asbestos is more effective on an equal weight basis, but the cost per pound is also higher. TWF bulk glass wool manufactured by the Owens Coming Flberglas Corporation is a sat isfactory grade of glass wool for the purpose. Rock wool may be used but it is more difficult to disperse in the mixture and is not as effective as the glass wool on an equal weight basis. In making the various gypsum boards, con taining unexpanded vermiculite and fibre as shown in Table No. in, about 1 % bonding starch was used in the core mixture. In making the boards, 100 parts of dry ingredients were mixed with about 90 parts of water to make a moldable slurry to which a sufficient quantity of soap foam or lather was added to produce dry board of onehalf inch thickness weighing from 2 to 2.3 lbs. per square foot. The slurry was molded between cover sheets and when the core had set the board was dried in the usual manner in a conventional wall-board drier. In connection with the form of my improved panel as shown in Mg, 1; the cover sheets of paper function in the same way as they do in connection with the ordinary wallboard, serving to protect the plaster body and to give the prod uct strength during the formation of the board on the board machine and to give the board the desired strength and stiffness in position on a wall. Such cover sheets are not relied upon, how ever, for affording any protection against fire, since the cover sheet at the face of the board at which the fire attacks is very soon burned away so as to give the fire direct access to the face of the body material of the panel. After the cover sheet is burned away, the plaster slab alone is relied upon to maintain its form without cracks and without warping such as might permit the fire to force its way through the wall. It will be understood that it is highly impor tant that when my improved plaster panel is at tacked by a fire at one face only of the panel, such face of the panel shall be protected effec tively against either contracting or expanding. If the attacked face of the board of Fig. 1 con tracts greatly as compared with the opposite face of the board, the board will be caused to warp so as to present a concaved face toward the fire. If the attacked face should expand substantially as compared with the opposite face, the board would warp In the opposite direction so as to present a convex face toward the fire. In the event of such warping in either direction, a very strong pressure is applied on the side margins of the board edgewise of the board serving to force such margin portions loose from the se curing means by which they are held on their Castleman.CERT001401 2,526,066 9 10 stpprts, serving -thus to open up the joints be would, when the gypsum board is subjected to tween adjacent sections of the board and thus heat, approach closesly to the amount of ex to destroy very quietly the effectiveness of the pansion which would be obtained with the lesser board for stopping the advance of the fire. By amounts of high-grade raw vermiculite as speci th use of my improved plaster board, in which 6 fied. \ ' the tendency for tHe'fHie'oTThe board to con When my improved plaster is to be applied by tract by reason of the presence of the set gypsum ordinary wall plastering methods, the propor is balanced and counteracted by the tendency tions of the vermiculite and fibre may be about for the face of the board to expand by reason the same as are specified above in connection of the presence of the vermiculite, substantia! 10 with wallboard, or the amount of the vermiculite protection is afforded against the opening up of and fibre may be substantially increased so as to cracks in the face of the wall and also against obtain an increased insulating effect. The use Warping of the board such as might break the of the increased amount of vermiculite and fibre joints between adjacent panels. The period of is possible in the plastered wall by reason of the time, thus, during which this stiff self-sustained 15 fact that the lath in such wall provides more board is effective for protecting against the ad secure structural support for the plaster. vance of a fire is very substantially increased. The mineral of the vermiculite group and the The use of my invention in connection with a fibre may be mixed with the gypsum or other plaster wall as shown in Pig. 2 is of substantially body material either at the time of manufacture the same importance as in connection with a 20 of the plaster or at- any other time prior to the wallboard. When a fire attacks the face of a application of the cementitious mixture to the wall such as is shown in Pig. 2, in which there wall. Such plaster on the wall may'-be-covered are no paper liners employed, any substantial by a white coat of any suitable type as well amount of warping of the plaster panel would known in the art, or it may be covered by a have a marked tendency to open up cracks be 25 special white coat having mineral of the ver tween portions of the wall face, so as to permit miculite group incorporated therewith, and with the fire to advance through such cracks, or so preferably a small amount of non-combustible as to cause fragments of the face material to be fibre as indicated above. come dislodged as the initial step in a speedy The subject m atter of applicant's earlier ap breakdown of the wall as a whole. 30 plication, Serial No. 510,365, was covered by an When a fire attacks a wall having a face made application in Canada, Serial No. 51B,157, filed principally of gypsum without any vermiculite September 8, 1944. dispersed therethrough so as to cause the face of I claim: the board toward the fire to contract, or, alter 1. A plastic composition comprising commi natively, made principally of gypsum with too 35 nuted calcined gypsum adapted to set when great a proportion of vermiculite dispersed mixed with water, high-grade comminuted ver- therethrough so as to cause the face of the board mieulite of about minus 28 mesh commercial toward the fire to expand substantially as com grading adapted to expand by exfoliation upon pared with the opposite face of the board, in the application of heat thereto and used in an either case the face of the wall is broken up 40 amount in the range between 3M>% and 7%% of into separated pieces so as to destroy the effec the weight of the mixture, and non-combustible tiveness of the wall for stopping the advance of fibrous material dispersed through the mixture a fire long before the separate pieces have been and constituting by weight in the range between greatly weakened in strength or stiffness, the 1% and 10% of the composition, the gypsum con failure being due to the breaking up of the wall 45 tent in said mixture constituting a quantity suf as a whole rather than to the destruction or ficient with said mineral and said fibrous ma weakening of the separate pieces of the panel. terial to substantially complete the 100% content My improved gypsum wallboard is comparable of the mixture. in'evirsTunpoffanTrespect with offier high-grade 2. A plastic composition mixture comprising gypsum wallboards on the market. In the fire 00 comminuted calcined gypsum adapted to set tests conducted at Underwriters Laboratories, when mixed with water, a mineral of the ver Chicago, Illinois, according to Standard Methods miculite group in comminuted form capable of of Fire Tests of Building Construction and Ma being expanded by exfoliation by the applica terials, A. S. T. M. designation C19-41, on wood tion of heat thereto, and non-combustible fibrous studded, load bearing partitions faced on each fui material dispersed through the mixture and con side with one thickness of such board, the par stituting by weight in the range between 1% and titions received a fire resistance rating of at least 10% of the composition, the degree of comminu 45 minutes in each instance. A minimum fire tion of the mineral of the vermiculite group and resistance rating of 45 minutes is required in the grade and amount of such mineral used being F. H. A. regulations for certain types of partitions fi'i such that when the cast made from such mixture in rental housing projects. Wood studded par is heated to a high temperature the expansible titions faced on each side with one layer of regu mineral in the cast shall have about the same lar Vz" gypsum board have failed to meet this total amount of expansion as would 3%% to requirement. It is evident, therefore, that % " 7%% of high-grade vermiculite of minus 28 gypsum board having a core made according to or, mesh commercial grading, the gypsum content my invention serves a definite need and has a in said mixture constituting a quantity sufficient definite advantage over conventional Vz" board. with said mineral and said fibrous material to When using a lower grade of vermiculite, or substantially complete the 100% content of the some other mineral of the vermiculite group not mixture. adapted to have so great expansion as high-grade 70 3. A stiff self-sustaining panel adapted for use 1 vermiculite, I would expect to use an increased as the outer structural layer of a wall structure amount of such lower grade mineral, or would and in the form of a body member comprising increase the particle size of such low grade min about 93% of set calcined gypsum as the major eral, so as to insure that the amount of the ex ingredient, about 2% by weight of asbestos fi pansion of the mineral of the vermiculite group 75 bres; and about 5% by weight of high-grade j Castleman.CERT001402 2,526,066 11 12 comminuted vermiculite in its unexpanded form from 1 to 10% by weight of non-combustible and of a particle size of about minus 28 mesh fibres dispersed through the body, and about 5% commercial grading, said fibres and said com to 10% of high-grade comminuted vermiculite in minuted mineral being dispersed through the body. 6 its unexpanded form and of about minus 35 4. A stiff self-sustaining panel adapted for use mesh commercial grading dispersed through the body, the gypsum content in said mixture con as the outer structural layer of a wall structure stituting a quantity sufficient with said vermic and in the form of a body member comprising set ulite and said fibres to substantially complete calcined gypsum as the major ingredient, from the 100% content of the mixture. 1% to 10% by weight of non-combustible fibres 10 MICHELE CEOCE. dispersed through the body, and about 3%% to 7Yz% of high-grade comminuted vermiculite in its unexpanded form and of about minus 28 mesh commercial grading dispersed through the body, the gypsum content in said mixture con- 15 stituting a quantity sufficient with said vermic ulite and said fibres to substantially complete the 100% content of the mixture. 5. A stiff self-sustaining panel adapted for use as the outer structural layer of a wall structure 20 and in the form of a body member comprising set calcined gypsum as the major ingredient, REFERENCES CITED The following references are of record in the file of this patent: UNITED STATES PATENTS Number 1,702,965 1,890,674 2,009,146 2,060,295 2,090,480 Name Date H aggerty--------------- Feb. 19, 1929 Delaney-----------------Dec. 13, 1932 New---------------------- July 23, 1935 Finefrock et a l . ___ Nov. 10, 1936 Hawley------------------Aug. 17,1837 Castleman.CERT001403