US2383609A - Hardenable plastic compositions - Google Patents

Description

Patented Aug. 28, 1945 HARDENABLE PLASTIC COMPOSITIONS Murray .ll. MacDonald, Katonah, and Christopher S. Schwendler, Woodside, N. Y., and Frederick C. Schwendler, Dayton, Ohio, assignors'to National Casket Com Island City, N Y.

pany Incorporated, Long No Drawing. Application May 8, 1941, Serial No. 392,518

18 Claims.

Our invention relates to hardenable plastic compositions, and more particularly to improved magnesia base plastics.

This application is in part a continuation of our application Serial No. 77,592, filed May 2, 1936.

Our improved compositions are particularly suitable for use in the formation of articles of relatively large surface area and of relatively small cross sectional area. i

The present invention includes the process of preparing improved hardenable magnesia base plastic adapted for a variety of purposes such as the making of slabs, caskets, sarcophagi, vaults, boxes, and other containers, monuments, statuary and other ornamental pieces and objects subject to weather and soil conditions, as well as articles intended for other uses.

The present invention also includes the provision of various plastics having the same basic characteristics but which may be used respectively for surfacing, together with a plasticising fluid, all capable of conjoint use for the purpose of finally producing objects of monolithic character, although certain of the hereinafter described plastics are capable of commercial use separately from the other described plastics.

Our invention further consists in the preparation of improved hardenable magnesia base plastics of such nature that the exposed surfaces of articles made therefrom can be treated or dec'orated and finished by usual surface finishing methods such as water-proofing, painting, lacquering, oiling, and waxing.

A further object of our invention is to produce a magnesia base plastic material capable of being cast or otherwise molded, without heat or pressure, the material setting uniformly without warping or cracking, with small change in final volume, and with shrinkage of such uniformity that sections cast therefrom are substantially alike in size and can be readily assembled together and interchanged at will. In addition, the material will adhere to surfaces of similar material and to other surfaces such as wood, fabrics, and metals.

The invention further consists in the provision of a basic material capable of hardening to an article which will also be light in weight, of high mechanical strength, of porous character, shockproof, resistant to weather and soil erosion, resistantto various acids and alkalis, and resistant to moisture and water.

As a full exposition of the objects of our invenbody or filler, and assembly,

tion would unduly lengthen this specification, the

other and further objects of our invention will be understood from the following specification.

By way of example, this specification will be .written from the standpoint of burial caskets which heretofore have been made commercially either of wood or metal, the latter being either stamped, cast or electro-deposited.

Prior to this invention attempts have been made to use moldable plastic compositions in the production of caskets, but these have not proven commercially feasible for a variety of. reasons. The most common of hardenable plastics is cement, concrete and the like. These compositions are objectionable for the uses contemplated by this application because of excessive weight, poor surface, incapability of being molded in thin sections, readily afiected by water, soil and weather conditions, brittleness, and other objections. Among the further objections may be mentioned that concrete, cement and the like, cannot be practically satisfactorily decorated or painted, and finished.

Attempts have also been made to use other plastic compositions for the molding of objects referred to above but in all such attempts known to us the resultant product has been too brittle for handling in commerce, or the surface has not been adaptable for decorative finishing, or

materials, such as paint, varnish, lacquers, etc.

Furthermore, such material is not chemically inert. Being a carbonate, it is attacked and decomposed by all ,acids, such as soil and weather acids, releasing gaseous carbon dioxide during the reaction. This gas is generated within the material and in escaping will crack the material.

In the production of burial caskets, for example, according to this invention there may be used material made from one formula as a surfacing composition, and a material made according to another formula as a backing or filler material, and, if desired, material made according to a third formula may be used as an assembly cement for precast sections: and in all of these formulae a specially prepared plasticising fluid is used.

Examples of compositions having the foreoing and the hereinafter described characteristics and which have been found to be satisfactory will now be described in suihcient numher to illustrate the principles involved.

First, a body or backing material, which is light in weight and free from warping-cracking, 10

etc., yet strong and shock-proof may be produced according to any of the following formulae, when it is desired to have all the ingredients mineral in character and the filler materials inert:

- 2 s',sss,soc

formulae given, in this specification may be made according to the formula:

Parts by weight Magnesium chloride 37.4 Magnesium sulphate... 8.2 Water 54.4

Ingredients Ex. 1 Ex. 2 Ex. 3 Ex. 4 Ex. 5 Ex. 6 Ex. 7 Ex. 8 Ex. 9 Ex. 10

Parts by Parts by Paris by Parts by Parts by Parts by Parts by Paris by Paris by Parts by weight weight weight weight weight weight weight weight weight weight Magnesiie 40. 0 40. 0 40. 0 40. 55. 55. 55. 0 37. 8 3S. 4 40. 0 Bilex.-. 5. 0 5. 0 5. 0 l. 7 2. 2 27. 0 Asbestos short films) 40. 0 45.0 21. 0 48 0 3. 0 7.0 .8. 0 12.0 Asbestos ong iibre) 15.0 18.0 16 0 Diatomseeous earth 8 Pumi 6 Asphalt 8o ution In the foregoing as well as in the other formulae hereinafter set forth the magnesite is ground to a fine particle size, such as all through a 325 meshscreen, and the other ingredients, when used, are of various sizes, i. e.. substantially all the pumice will pass through about a 16 mesh screen, the silex is about the same particle size as the magnesite, and the short asbestos fibre has a maximum length of about one-eighth of an inch, while the long asbestos fibre has a maximum length of about one-quarter of an inch. The asphalt emulsion is approximately 75 percent concentration.

Certain substitutions may be made in whole or in part in the ingredients listed above without altering the major characteristics of the fin-- ished article. For example, talc or fine ashes to have smoother, and hard, finely textured, easily decorated outer surfaces. The following examples are given of suitable compositions for such purposes, again preserving the all mineral character of the composition:

Ingredients Ex. 1 Ex. 2 Ex. 3 Ex. 4 Ex. 5 Ex. 6 Ex. 7 Ex. 8

Parts by Parts by Parts by Paris by Parts by Parts by Paris by weight weight weight weight weight weight weight Magnesite 45. 0 45. 0 45. 0 45. 0 40. 0 45. 7 40. 0 Silex 30. 30. ll 30. 0 30. 0 Asbestos 10.0 10. 0' l0. 0 8. 0 Talc 19.0 l0. 0 l2. 0 Diatomsceous cart 5.0 Bentonite 15.0 5. 0 5. 0 5. 0 Solution 00 0 100.0 96. 0 96. 0 96. 0 80. 0 100. O

may be substituted for the silex; and a slag known by the trade-name Pottsco may be used in place of the pumice. Infusorial earth, kieselguhr, celite and diatomaceous earth are interchangeable. Also, a small percentage of asphalt emulsion may be added to any of the above formulae whenit is not specified, if desired. -We have used throughout a calcined magnesite sold under the trade or brand name Bald Eagle by West Coast Chemical Company. If magnesite of other grade is substituted due allowances will need to be made in the formulae herein given. For example, more or less silex may be used depending upon the amount of silica, etc., present; more or less magnesium sulphate may be needed to neutralize the lime impurity; and the amount of plasticizer used may vary from the proportions indicated herein.

The plasticising fluid used throughout the The compositions just recited will be referred to as the surface material, but it is to be understood that we have found that complete articles may be produced which are made solely from this so-called surface mix.

The talc will preferably all pass a 325 mesh screen, and the bentonite will desirably be of somewhat smaller particle size such as to pass through a 400 mesh screen. If desired, a small percentage of a coloring matter such as iron oxide or carbon black may be added to these latter formulae, in which case the amount of silex used may be reduced slightly and not over a corresponding amount to that of the added coloring material.

The finished product made according to any of the latter formulae is denser than those made according to the formulae first given above so that the surface is very smooth, and hard. While the weight of the latter is greater than the former,

materials, as will be described, only a thin coating of the surface material will be needed.

For certain purposes it has been found desirdseaeoe 3 greater space rin the finished product in spite of the fact that by weight the silex appears more.

Inpreparing all the above mixes,'the dry in gradients are very thoroughly mixed together able and possible to obtain a hardenable plastic s either mechanically or by hand. Thereafter the composition producing articles having all the required quantity oi the dry mix is placed in a above major characteristics, such astreedom from mechanical mixer and the. m m' t amount of wa pin uniformity in size. inhe ent st e t rilasticisin material is added, the whole being resistance to weather and acid conditions, etc. stirred until complete distribution of th mu without using all mineral ingredients In such 10 has been obtained throughout the batch. cases organic materials have been substituted for In t case of the backing or n mix the some of the mineral fillers, and this hasresulted terial at the end 01 the mixing is of the conin a f n d Pr th s lishter in weight. sistency of dough, while in the case of the sur more resilietrlilt to shocks and stresses, and cheaper l5 1fsace mix the material at the end of the mixing tomanufac re. thinner, more of the consistency of batter. Examples oi such compositions which have been The backing or filler material in its dough-11k found to be satisfactory and which may be used form can be cast,- molded, extruded, or worked in place of the aforesaid body or backing material with forming tools. The surfacing material may are asfollows: be poured, prayed or applied by brush.

Ingredients Em ELZ n a End Ex.5 am

by fornby Pomby f4 40. at .0 E080 s z m 012 1010 11I0 10.0 10.0 13.6 Woodflour as 0.0 4.1 a0 a0 3.0 Aggsstos (5110 7.0 6.1 Atsilboes tos (long so so 1'6 iiiiiifiiiitffiit: at 8 at Talc 9.0 10.0 10.0 Solution 78.5 78.5 10.4 100.0 100.0 1110.0

Similarly with the so-called surface material, In the foregoing tables various, proportions, if i i fffli if? ill i fr'i'i fi ifin th i l i ft??? on ,an ye w e ar,smoo an o rve g epncpesuse o inapropcharacteristicsof articles made from the all mlnerly balanced composition having the advantages eral surfacing material, are as follows: and characteristics outlined in this specification.

Ingredients Ex. 1 Ex. 2 Ex. 3 Ex. 4 I Ex. 6 its. 6 Ex. 7 I Ex. 8 Ex. 9

a Part Part P rt 'P n 0 322313 22th? wait watt Mt "its" 3335" ti-3t 25th? Mame s2 s: 32-3 wfifi'fiBhR-IIIIIIIIII 31s 318 4.2 4.2 318 318 310 310 2'2 sbostos. 9. g: g g. g g. g amalgam earth- 3: 0 g: 0 5tiin.'i:::::::::::::: sac de m sac "66.6' 96:8

Again, these compositions produce articles or surfaces that are more resilient than that using Other formulae can be devised in the same or aillngeinelgalniatirials, as wellasbeing cheaper and v, substantiialLv sinlfilar pilfiportions and within the lgh r we g ranges g ven, w on w produce articles having $23 313?;1fn??$f;?;$3322; 3,}; $32313, g gg f g gg as may come mpo ant acmesh, the talc is such 1:30 P 1 5: i s i g iggig centuate or reduce some particular characteristic mesh screen, and tg t a 400 3 mesh- 60 or characteristlcs. However, the proportions oi l i e v egz tflfle fi re which w: have found to be gi i a in 2 the amount of any ngre en canno e va ed more than two i? tiifiiffi ii oifefifliitiif Percent without Seriously affecting the physics in 1815i; 6 arliglsmmmsi(18m ctrength to the an: clhemicil izlggelties of the resultant product. h a s mpor an a. a proper balance be main-' 05 Eggs pflide g gi a stronger fibre than as taineoL'such as that between the magnesium oxide Contrary to the conditions in the all mineral and the magnesium chloride, and that between terials above while it appears in some of the the calcium Oxide and the magnesium lfate: figmulae j gthat the nomcenular sflex and, as further explained hereinafter, to obtain a dominates the filler materials as expressed m m sufficient distribution and absorption of the fluid percent by weight, this is not the case when conin around th p res of the cellular filler maidering the volume occupiedv by the ingredients. terials, and to maintain the viscosity of the final in the finished product. Because of the very low ixes u h that he calcium sulphate will not setspeciflc'glavity and large bulk of the cellular 75 tie in the mass during the setting periods.

fillers, those fillers predominate andoccupy the One method that may be used in pr du ina articles using the foregoing materials is as follows:

The surface of a suitable mold is covered with one or more thin layers of the surfacing material, ai'ter which a layer of the backing or filler material, of desired thickness for the article, is applied over the surfacing material. The backing material may be applied immediately after the surface material has been applied, but we prefer that a time interval intervene between the respective applications of the two materials so as to allow for the preliminary setting ofthe surface material. If desired, the whole plastic mass can be rolled or smoothed to an even thickness, or the laminations may be extruded as layers of desired thickness. In our experience to date we have successfully used both open top and gated molds, without the'use of heat and pressure.

The moldand its contents are then set aside for the initial drying and setting periods, which require respectively two hours to four hours and eight to ten hours. times are merely relative and depend somewhat upon the temperature and humidity of thesurrounding air at the time of drying and setting. At the end of this time the article can be removed from the mold, and it is then set aside for a period of aging of from ten to fourteen days to thirty days, after which the article is ready for use as is, or after surface decoration, as desired. It is also to be understood that this aging is relative and also depends upon temperature and humidity of the surrounding air during the aging period.- We have found that objects formed of the mixes outlined above, or a combination thereof, can be dried in the air without the use of forms or other means to prevent warping during the drying, setting, and aging times. The articles or parts are merely dried in open racks, in a room of the factory; or a drying chamber may be set up with regulated conditions as to humidity and temperature.

We have found that at the end of this time the surface material'and the body or filler material have become a hard mass with the strata firmly bonded or combined together into one unitary structure of monolithic character. The original interfaces of the two strata are so united that they are inseparable.

Caskets can be made according to our invention either as a wholeor in sections. In practice we have found that sections such as the sides and ends of caskets manufactured according to the It is understood that these above process and after aging may be assembled I into the finished casket. In such cases we have found the following to be a satisfactory assembly cement:

Calcined magnesite 27.0

Silex (SiOz) 30.0 Zonolite (expanded mica); 2.0 Plasticising flu 41.0

We have also found that wood flour can be 'successfully substituted in the above formula for the Zonolite. I

In the instances where this cementing composition has been used we have found that the without waiting for the initial setting period, the component parts can be assembled together by locking the molds or mold sections together, filling any spaces that may exist between adjacent faces of the sections with the backing composition mix and, if desired, forming fillets in the corners. As soon as the final setting period is completed the molds. may be removed and the casket set aside for the aging period.

With articles made according to this inven tion the surface decoration can be applied in any one of a number of diflerent ways after the aging period is completed. It may be painted by the brush method, or by spraying in any ordinary manner with the usual priming coat, paints, lacquers, enamels and varnishes, and finished off as is usually done with painted surfaces. The surface may also be treated with various finishing oils and lacquers without the application of any paint substance. If desired, the undecorated surfaces may have a coat of asphaltum or other water proofing material applied to the outer surface.

We have found that in the formation of the above plastic masses a solid solution results, which solution contains in suspension all of the filling ingredients used in the mix.

In the commercial form of calcined magnesite there is always present as an impurity a percentage of calcium, which is present in the original magnesite rock. The presence of this calcium would adversely affect the properties of the finished material because of its action either as calcium oxide (the form in which it is present in the calcined magnesite) or as calcium chloride, the form in which it would be present after reacting with the magnesium chloride of the plasticising fluid. Calcium oxide, if unchanged and present in the final material as 0210, would in the presence of water, form calcium hydroxide Ca(OH)2.

Any moisture, whether present in the atmosphere or in the soil surrounding the finished article, would so combine with this calcium oxide. The combination of calcium oxide and water would result in a large increase in volume and the generation of considerable heat. Those reactions should be avoided because the change in volume will cause warping during setting and after the material has set, will develop cracks in the material with resultant'loss in mechanical strength and appearance, while the generation of heat inside the body of the mass would destroy part of the body structure rapidly because there are not available the means of rapid dissipation of this heat.

The deleterious effects of calcium" present in the final product as calcium chloride are due, among other reasons, to basic chemical properties of calcium chloride, such as the fact that calcium chloride is a salt highly soluble in water. This action would result in the leaching of the calcium chloride from the mass with'accompanying weakening of the mechanical properties and spoiling of the appearance of the product because voids would be left in the resultant ma the water is'in the form of water vapor or in its common liquid state. When calcium chloride absorbs water it expands substantially and since assaeoe the material of the finished article has already or warp out of shape.

While it has heretofore been proposed to add magnesium sulfate to magnesia base cements, we have found that the addition of magnesium sulphate in making our original plastic mix results in the combination of the active calcium (present in the calcined magnesite) and the sulphate ion S04, so that there is precipitated in and throughout the mass calcium sulphate, or in other words. gypsum, a crystalline product unaffected by water. The viscosity of the mass at this time in our cases is such that the precipitated gypsum does not settle out of the mass notwithstanding its relatively high specific gravity but is at once imprisoned at its many points of formation by the surrounding highly viscous ma terial, and remains where it was formed.

After being placed in the mold, the entire mass begins its initial set, which is primarily a process of dehydration. The second set, which has already begun during this period of dehydration, is caused by the union between the calcined magnesite and the magnesium chloride of the plasticizing fluid. Both of these settings occur in the material which surrounds the insoluble gypsum and also the inert filling materials used.

As recited above, by the thorough mixing of the dry ingredients before the addition of the plasticising fluid, plus the further mixing during the addition of the plasticizing fluid, we obtain.

a uniform distribution of the calcined magnesite throughout the mass and" therefore a uniform distribution of the precipitated gypsum throughout the mass and in and around the cells of the filler materials, since the sulphate of our plasticising solution reacts in place with the active calcium of the calcined magnesite.

One important eifect of this distributed g psum on the mechanical properties of the hardened mass is that this finely dispersed gypsum forms a lattice work of crystals throughout the mass by which formation shocks, stresses and strains on the material of the finished product become evenly distributed over a wide area, thus preventing excess loading at any one point. The crystals of gyp um have a definite form, mechanical strength and certain elasticity to return to their original shapes after deformation by the application of a force below that necessary to rupture the crystals.

These desirable mechanical properties will be retained in the finished product because calcium sulphate is highly insoluble in water, so cannot combine with any water with which it may come in contact, is inert to soil, water, alkalis, and the normal organic acids, and will not react with substances ordinarily found in polluted atmos pheres, water or soil.

The distributed calcium sulphate lattice work adds to the inherent strength, resilience, etc., imparted to the finished product by the ingredients selected for the particular composition. Accordingly, objects made by these formulae have the ability to withstand mechanical shocks and strains such as might be encountered in the han dling thereof in the factoi'y, in shipping and transportation, and in use, which heretofore has not been true of magnesia base plastics, especially in articles of large size and thin cross section.

Having eliminated the possibility of the formation of calcium chloride and converted the calcium into an insoluble form, as well as either 'terial or articles made using filler ingredients which are inert and cel-' lular or organic filler ingredients which have been effectively rendered inert by coating the same with the cementing materials with or without the water-proofing emulsion, we have found that the finished material will have the property.

of mechanically holding in its poreswater and water vapor. The presence or absence of this water vapor will depend upon the relative humidity of the surrounding air. Air of high relative humidity will impart some of its moisture to the pores of our material. On the other hand, it has been shown by tests that in surrounding air of lower relative humidity, material made according to the above formulae after aging, will readily give up the water held in its pores to the surrounding air. If the surrounding air is held at zero percent relative humidity, all of this mechznically held water or water vapor will come ou Now in the case of burial caskets, containers,

may be subject to varying atmospheric and humidit conditions remain unaffected thereby and will return substantially to their-dry state.

In addition to all of the above materials being water-resistant as pointed out above, they are also shown by many tests to be resistant to acids, alkalis, and the organic chemicals normally used in the preparation of bodies for burial, to preserve the tissues thereof. Likewise, those organic acids which are the result of body decomposition do not aflect this material under normal service conditions.

above, attention was called to the fact that articles madefrom our composition will have outer surfaces of such character that they can be directly painted and decorated without further preparation, in the same manner that wood and metal are now finished. That is to say the surface is composed of materials that are chemically inert to paints, lacquers. varnishes, and other similar ingredients, and also to waxes;

Articles made according to the above formulae will have outer surfaces that are clear, clean, finely textured, smooth, and slightly porous, enalbling a firm bond to be formed between the paint or applied finished material and the surface of the article. The articles will have hard surfaces which will not be readily marred in handling, transportation and use.

It will be apparent that only a thin, film-like outer coating of surface material is needed to fulfill the objects outlined above for articles made according to our invention.

By reference to monolithic structures it will be understood that we are not precluding the use of reinforcing materials in the body of the maaccording to our invention. That is to say. we found that if a foreign body such as wood, fabric, or metal be inserted in this material while in its plastic state, the foreign body will be firmly bound within the material, and this is also true even though the foreign body is only slightly inrbedded in the surface of the material.

Modifications maybe made in the methods and apparatus herein described without. departing from the spirit and scope of our invention, and such modifications are intended to be covered by the appended breathing is likewise of advantage in that articles which We claim:

1. A magnesia base hardenaible plastic composition consisting of calcined magnesite,.pumice, diatomaceous earth. asbestos, silex, and an asphaltum emulsion, to which is added a plasticising fluid consisting of magnesium chloride. ma nesium sulphate and water. the ratio of water to magnesite being approximately 1:1.

2. A magnesia base hardenable plastic composition consisting substantia'lly oi calcined magnesite 22%. pumice 2 diatomaceous earth 6.1%, asbestos 4.1%, silex 1.0%, asphaltum emulsion 3.0%, and plasticizing fluid 41.8%, the plasticising fluid consistmg substantially oi magnesium chloride 37.4%, magnesium sulphate 8.2% and water 54.4%.

3. A magnesia base hardenable plastic composition consisting substantially of calcined magnesite 25.5%, silex 27.5%, diatomaceous earth 2.5%, and plastieizing fiuid'44.5%, the plasticising fluid consisting substantially of magnesium chloride 37.4%, magnesium sulphate 8.2%, and water 54.4%.

4. A magnesia base hardenable plastic composition consisting substantially of calcined magnesite 21.5%, silex 20.9%, hardwood sawdust 5.9%, asbestos 3.9%, wood flour 3.8%, and plasticising fluid 44%, the plasticising fluid consisting substantially of magnesium chloride 37.4%, magnesium sulphate 8.2%, and water 54.4%.

5. A hardenable plastic composition comprising the following ingredients within and inclusive of the proportions indicated:

Parts by weight Calcined magnesite 37.8 to 55.0 Silex 1.7 to 27.0 Asbestos fibre 3.0 to 48.0 Diatomaceous earth 10.5 to 16.0 Pumice 5.0 to 39.6 Asphalt emulsion 4.0 to 6.0

and a plasticising solution consisting of magnesium chloride, magnesium sulphate and water, 73.5 to 150 parts by weight.

6. A hardenable plastic composition comprising the following ingredients within and inclusive of the proportions indicated:

- Parts by weight calcined magnesite 40 Asbestos fibre (short) 21.0 to 48.0 Pumice 7.0 to 23.0 Asphalt emulsion 4.0 to 6.0

and a plasticizing solution consisting of magnesium chloride, magnesium sulphate and water, 100 parts by weight.

7. A hardenable plastic composition comprising the following ingredients within and inclusive oi the proportions indicated:

Parts by weight Calcined magnesite 40.0 to 45.7 Silex 30.0 to 50.0 Asbestos 5.0 to 10.0 Talc 5.0 to 12.0 Diatomaceous earth 4.0 to 5.0 Bentonite 5.0 to 15.0

and a plasticising solution consisting of magnesium chloride, magnesium sulphate and water, 80 to 100 parts by weight.

8. A hardenable plastic composition comprising the following ingredients within and inclusive oi the proportions indicated:

' Asbestos Parts by weight Calcined magnesite 38.4 to 55.0 Silex 37.3 to 39.5 Saw dust 10.0 to 18.0 Wood flour 3.0 to 6.8 Asbestos 2.0.to 7.0 Vegetable fibre 4.0 to 5.0 Pumice 15.0 to 20.0 'Ilalc 9.0 to 10.0

and a plasticising solution consisting of magnesium chloride, magnesium sulphate and water, 75.4 to 150 parts by weight.

9. A hardenable plastic composition comprising the following ingredients within and inclusive oi the proportions indicated:

Parts by weight Calcined magnesite 38.4 to 40.3 Silex 37.3 to 39.5 Saw dust 10.5 to 16.0 Wood flour 4.1 to 6.8 5.1 to 7.0

75.4 to 78.4 parts by weight.

10. A hardenable plastic composition comprising the following ingredients within and inclusive of the proportions indicated:

' Parts by weight Calcined magnesite 50.0 to 55.0 Saw dust 10.0 to 13.0 Wood flour 3 Vegetable fibre 4.0 to 5.0 Pumice 15.0 to 20.0 Talc 9.0 to 10.0

and a plasticizing solution consisting of magnesium chloride, magnesium sulphate and water, 73.5, to parts by weight.

11. A hardenable plastic composition comprising the following ingredients within and inclusive of the proportions indicated:

Parts by weight Calcined magnesite 45.0 to 53.5 Sllex 35.0 to 50.0 Wood flour 3.0 to 4.2 'Asbestos 3.0 to 3.2 Talc 6.0to 9.2 Diatomaceous earth 3 Bentonite 5 and a plasticizing solution consisting of magnesium chloride, magnesium sulphate and water, 81.8 to 96.0 parts by weight.

12. A hardenable plastic composition comprising the following ingredients within and inclusive of the proportions indicated:

Parts by weight Calcined magnesite 45.8 to 53.5 S1183 42.7 17050.0 Wood flour 3.8 to 4.2

ingredients within and inclusive of the proportions indicated:

Parts by weight Calcined magnesite 55.0 Silex 5.0 Asbestos 15.0 to 18.0 Pumice 22.0 to 25.0

Calcined magnesite 40.0to 45.0 Silex 30.0 to 40.0 Asbestos 5.0 to 8.0 Talc 8.0 to 12.0 Bentonite to and a plasticislng solution consisting of magnesium chloride, magnesium sulphate and water, 90.0 to 100.0 parts by weight.

16. A magnesia base hardenable plastic composition comprising substantially the following ingredients within and inclusive of the proportions indicated:

Parts by weight Calcined magnesite 40-55 Silex 5-10 Asbestos I 8-18 Pumice -25 and a plasticising solution consisting of magnesium chloride, magnesium sulphate and water, 100-150 parts by weight.

17. A magnesia base hardenable plastic composition comprising substantially the following 5 \ingredients within and inclusive of the proportions indicated:

Parts by weight calcined magneslte 45.0 to 48.0 Silex 35.0 .to 40.0 Wood flour 3.0to 4.0 Asbestos 2.0to 3.2 Tal 6.0t0 9.2 Diatomaceous earth 3.0 Bentonite 0to 5 and a plasticising solution consisting of magnesium chloride, magnesium sulphate and water, 90.0 to96.0 parts by weight.

18. A magnesia. base hardenable plastic composition comprising substantially the' following ingredients within and inclusive of the proportions indicated:

Parts by weight Calcined magnesite -60 Saw dust 8-12 Wood flour 21-4 Fibre 4.5

Pumice 10-20 Talc 9-10 and a plasticising solution consisting of magnesium chloride, magnesium sulphate and water, -130 parts by weight.

. MURRAY ,J. 'MacDONALD.

CHRISTOPIfltR S. SCHWENDLER. FREDERICK C. SCHWENDLER.