US2662024A

US2662024A - Cementitious compositions

Info

Publication number: US2662024A
Application number: US213483A
Authority: US
Inventors: Wallace C Riddell; George B Kirk
Original assignee: Kaiser Gypsum Co Inc
Current assignee: Kaiser Gypsum Co Inc
Priority date: 1951-03-01
Filing date: 1951-03-01
Publication date: 1953-12-08
Anticipated expiration: 1970-12-08

Description

un' nz.

Patented Dec. 8, 1953 2,662,024 CEMENTITIOUS COMPOSITIONS Wallace 0. Ridden, Berkeley, and George B. Kirk,

Redwood City, Caliit, assignors, by mesne asuignments, to Kaiser Gypsum Company, Inc, a corporation of Washington No Drawing. Application March 1, 1951, Serial No. 218,488

11 Claims. (01. 106-109) This invention relates to cementitious compositions; and particularly to such compositions for use with gypsum wallboard, especially fg wng thejointsbet "'1 aces of the boards after installation.

I In order to produce a monolithic effect in a construction using gypsum wallboard it is necessary to treat the joints between boards, nail heads and any other surface defects so that a smooth, uniform surface results. Cementitious or adhesive materials have been proposed for these purposes in the prior art, but have had some disadvantages. Many such compositions have had a protein base, for example, but this 'type of adhesive requires considerable waiting time, for instance, to minutes, after mixing the dry powder with water, to allow the "protein to go into solution. In some commercial cements a marked change in con-- sistency occurs during the waiting period so that it is necessary to readjust the consistency by mix- 'ing in more dry powder to obtain a workable paste. A strongly alkaline pH is also essential in employing such a material. This strongly "alkaline condition is quite disadvantageous in application to wallboard because it is injurious to the paper covering of the board, resulting in weakening of the paper and marring its surface appearance. In other practices of the prior art, farinaceous substances have been employed in such compositions, but it has been necessary to use only small portions because of the increased tendency to cause cracks and checks in the surface, which remain even after the surface has 'been painted. The tendency to crack and check also occurs in the same manner with the proteincontaining materials which also shrink appreci- {Jbly in drying.

Ihe above disadvantages are overcome by the 'cementitious composition of the present inventionrand still fm-ther advantages are obtained. According to the present invention there is pro- -vided a eemeptitious cp msigon, or a cement 2!. leinl nhetueenjle l li and for providing a smooth, uniform surface for wall- ;boards,co n ta in 'n 1g from to deadburned 50 17 5? dextrin, i'r'om 5% .sum from 15 mica from of glaz. from 10% to 2 o o 10% -to 20 ,0 of and less than .0% of b s, iortlang cemen fiferably, the cementitious composi 1011 a 0 contains from 0.5% to 2% of a or from 0.2% to 1.0% of a dispersin aent, wetting agen or, advantageously, both of these g e en s. Alternatively, if desired, the wetting agent or the dispersing agent, or both, can be 2 added to the mixing water at the time and place of use of the composition.

The composition is employed as a finely divided powder, according to the usual good practice'in this art. In use, Will-m to asmo u andcan e app zed to the joint. r surface immediate y. e. g. h e oints between adjacent edges of wallboard or in covering nail heads or surface defects in the board. Any paste which remains unused at the end of a working day can be retempered, that is, mixed with water to the desired consistency, replacing water lost by evaporation, on the following day, and can be then employed in the same manner as freshly prepared paste. The cementitious paste is applied to the wallboard joint or surface and sets to a hagiygmpositionjn a short miter example ii about 2 to 3 hours, igpeni; i h w nnconnlncmldu in,lar ema t o @tting of the degtrin component: upon Luther 'ment slowly sets also, forming a strong mass of interlaced gypsum crystals, providing still further increased strength, hardness, and waterand heat-resistance.

The deadburned gypsum employed is Keene's cement or other deadburned gypsum w o so very slowly and is not sensitive to atmospheric moisture. Keane's cement, for example, is well known to the art and comprises a calu dmemww a m QLlZ OiE- 0 5 1% which after calcining is ground to substantially pass a mesh screen, and then usually a small amount of ac c elerator is added, for instance less than about 1% of aluminum sulfate or potassium .sulfate, or of each when both are added. Such material, because it sets slowly in the cementi- 'tious composition, provides late and increased strength in finely divided form in order to provide a smooth suri'ace when set. Suitably, this gypsum can be of a size to substantially entirely pass a 100 mesh screen. The dextrin component is, for example, a ggxtrinizemstarch. or it can be a mixture of dex 1' an a m or portion, up

na 11mm, e wei ht or h c mmp artiall inized starch which, for example, ca n c' ontE rom 217 a 5' 40% water-soluble a I J tXAMINtH ized starch are particularly advantageous because they provide desired bulkiness. In a preferred embodiment, a dextrin component as described i mployed l c aon pel by ei t of dextrin and 3 parts by weigh t g f partifll y deg;- ..trinized .starch, or modified corn flour as it is sometimes known in the trade, these weights being based on the total weight of the joint cement mixture. The dextrin is a product made, for example, by treating corn starch with acid in a water medium, with heating, to convert to dextrin. After the conversion is finished, the fluid is neutralized, dried and ground. Starches other than corn starch can be employed in making the dextrinized or partially dextrinized product. The starchy component gives a much harder and stronger early set in the composition of this invention.

The clay employed is a plastic clay, preferably commercial fire cla and is also used in finely divided form. It improves the workability of the paste so that it can be readily applied or "buttered on the surface to be treated.

Mica is also employed in finely divided form and it is of special advantage in a composition containing the hereinabove-defined amounts of dextrin component. The use of these high amounts of the dextrin component produces a strong and hard composition but, in the absence of the amount of mica defined, the dried cement exhibits shrinkage cracks or checking. It has been found that these cracks and checks are substantially entirely eliminated by the addition of the mica in the amounts shown, especially in cooperation with the amount of asbestos added. Furthermore, the adhesiveness of the composition is apparently improved by the mica addition. The asbestos fiber forms a fibrous mat in the composition which enables uniform drying of the composition with more uniform development of strength and desired surface characteristics, and ,aids in the prevention of cracking and checking upon drying.

A small amount of Portland cement, that is, less than 1.0%, and pre cm a out 0.2% to about 0.3%, is included in the composition. This acts to maintain a slightly alkaline reaction, which is found to prevent rusting of nailheads in contact with the cement, but at the same time the alkalinity is maintained well below that which causes damage to paper, especially the paper a liner or covering of gypsum wallboard. It is one theory of the operation of the Portland cement addition, but without intention of being limited by this theory, that this cement in the presence of water hydrolyzes slowly to form an amount of Ca(OH)z which maintains the desired alkalinity. At the same time Portland cement is stable when stored in air, whereas if an equivalent amount of calcium hydroxide were added in the mix, it would absorb carbon dioxide from the air to form the carbonate, reducing its effectiveness. The Portland cement irrthe co rppsiginpilthis iurTnupirisad edlin sufiicient qnaimla tain the alkalinity thereof atlrom more than pH 7.0 isiesstheirpn 8.0? when in the presence pf water.

Preferably a dis ersin a ent is also included -with the cementitious composition of this inefiective constituent. In this specification and claims the agent will be termed waste sulfite liquor. There can also be employed herein a purified lignin derivative of wood which has been digested with caustic soda or sodium sulfite, to

- produce cellulose pulp. This lignin derivative is preferably employed in the form of the watersoluble sodium salt. This lignin derivative and its sodium salt are described in a brochure entitled Indulin: Lignin from Pine Wood," published by West Virginia Pulp & Paper Company. Alternatively, also, there can be employed in this invention a dispersing agent which is a watersoluble salt of a condensed a l sulfonic acid, such as the sodium salt of condensed mononaphthalene sulfonic acid. The dispersing agent is preferably added in an amount of from about 0.5% to about 2.0% by weight, based on the total weight of the mix; and it can be added in the dry state, or an equivalent amount of liquid.

Preferably a wettin agent is also included with the above-desmtitious composition. The wetting agent can be included in the composition itself. Alternatively, the wetting agent can be incorporated in the tempering water, if desired, along with the dispersing agent described above, and this mixture can be added to the dry mixture of ingredients described above, to form the pasty mass for application to the wallboard joint or surface. The wetting agent is, for

example, an alk 1 ar 1 sulfonate, such as a WW lsu lfona te, afi'alE lated monoso mm c zene su onate, or the like. Any other desired wetting agent can be employed. The wetting agent wets out the paper liner of the gypsum board, promoting bonding of the cement thereto. The wetting agent is preferably added in an amount of from about 0.2% to about 1.0% based on the total dry weight.

It is an advantage of the present invention that the composition sets fairly rapidly to give a hard cement with a high early strength; and another advantage is that the deadbumed gypsum, or Keenes cement, sets more slowly providing continually increasing strength and a final very hard and strong product. It is believed that some of the Keenes cement combines with the sugars present in the dextrin or partially dextrinized starch to form insoluble calcium saccharate. which enhances the strength an ardness of the final product. It is a further and particular advantage of this composition that the incorporation of mica prevents cracking or checking so successfully that relatively large amounts of dextrin can be incorporated to give the enhanced early strength and hardness, and that the final surface is smooth and continuous, as desired. It is also an advantage that the material can be mixed with water and used immediately. Further advantages will be noted from the above description.

A specific example of a cementitious composition according to the present invention is as follows:

Per cent Keenes cement, substantially entirely passing 100 mesh 47.00 Dextrin 17.00 Partially dextrinized corn flour 3.00 Mica, powdered 15.00 Asbestos fiber, finely ground 10.00 F'ireclay, finely ground 7.00 Portland cement 0.25 Waste sulfite liquor (dry) 0.50 Wetting agent (alkyl aryl sulfonate) 0.25

The partially dextrinized corn flour used in this example is of such consistency that it requires, per 100 grams thereof, the admixture of from 500 to 600 milliliters of water to form a paste which will just pour.

The amounts in this specification and claims are expressed in percentages by weight, based on the total dry weight of the mixture, or, in other words, not including water employed in mixing. Where screen or mesh sizes are given herein, they are in meshes per linear inch, U. S. Bureau of Standards screens.

Having now described the invention, what is claimed is:

1. Cement for wallboard joints and surfaces containing from 35% to 50% of finely divided deadburned gypsum, from 15% to 20% of dextrin, from 5% to of finely divided clay, from 10% to 20% of finely divided mica, from 10% to 20% of finely ground asbestos, and a small amount of Portland cement, said Portland cement being present in an amount of less than about 1%, said percentages being based on the total weight of the mixture.

2. Cement for wallboard joints and surfaces containing from 35% to 50% finely divided deadburned gypsum, from to of dextrin, from 5% to 10% oi finely divided plastic clay, from 10% to 20% of finely divided mica, from 10% to 20% of finely ground asbestos, a small amount of Portland cement, said Portland cement being present in an amount of less than about 1%, from 0.5% to 2% of a dispersing agent, and from 0.2% to 1% of a wetting agent, said percentages being based on the'total weight of the mixture.

3. Cement as in claim 2 wherein said dispersing agent is dried waste sulfite liquor.

4. Cement as in claim 2 wherein said wetting ent is a sodium salt of anal}; l a l 5. Cement as in claim 2 containing from 0.2% to 0.3% Portland cement.

6. Cement as in claim 2 wherein the dextrln includes up to about 15% of the weight of this component of partially dextrinized corn starch.

7. Cement for wallboard joints and surfaces containing from to 50% finely divided deadburned gypsum, from 15% to 20% of dextrln, from 5% to 10% of finely divided plastic clay, from 10% to 20% of finely divided mica, from 6 A 10% to 20% of finely ground asbestos, a small amount of Portland cement and from 0.5% to 2% of a dispersing agent, said Portland cement being present in an amount of less than about 1%.

8. Cement for wallboard joints and surfaces containing from 35% to 5 finely divided deadburned gypsum, from 15% to 20% of dextrin, from 5% to 10% of finely divided plastic clay, from 10% to 20% of finely divided mica, from 10% to 20% of finely ground asbestos, a small amount of Portland cement and from 0.2% to 1% of a wetting agent, said Portland cement being present in an amount of less than about 9. Cement for wallboard joints and surfaces containing from 35% to 50% finely divided deadburned gypsum, from 15% to 20% of dextrln, from 5% to 10% of finely divided plastic clay, from 10% to 20% of finely divided mica, from 10% to 20% of finely ground asbestos, and a small amount of Portland cement, said Portland cement being present in an amount of less than about 1%, and having a pH of from more than 7.0 to less than 8.0 in the presence of water,

said percentages being based on the total weight of the dry mixture.

10. Cement for wallboard joints and surfaces containing from 35% to 50% finely divided deadburned gypsum, from 15% to 20% of dextrin, from 5% to 10% of finely divided plastic clay, from 10% to 20% of finely divided mica, from 10% to 20% of finely ground asbestos, a small amount of Portland cement, said Portland cement being present in an amount of less than about 1%, from 1% to 2% of a dispersing agent, and from 0.2% to 1% of a wetting agent, said percentages being based on the total weight of the mixture, said cement having a pH of from more than 7.0 to less than 8.0 in the presence of water.

11. Cement for wallboard joints and surfaces containing 47% of Keenes cement substantially entirely passing mesh, 15% finely divided mica, 10% finely ground asbestos fibers, 7% finely divided fire clay, 17% dextrin, 3% partially dextrinized corn starch, 0.5% dried waste sulflte liquor, 0.25% of a sodium salt of an alkyl aryl sulfonate and 0.25% of Portland cement, said percentages being based on the total weight of the mixture.

WALLACE C. RIDDELL. GEORGE B. KIRK.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,194,926 Anderson Aug. 15, 1916 1,858,369 Linzeli May 17, 1932 1,863,990 Nelson June 21, 1932 2,127,451 scripture Aug. 16, 1938 2,318,540 Talbert May 4, 1943 2,322,930 Gardner June 29, 1943

Claims

1. CEMENT FOR WALLBOARD JOINTS AND SURFACES CONTAINING FROM 35% TO 50% OF FINELY DIVIDED DEADBURNED GYPSUM, FROM 15% OF FINELY DIVIDED FROM 5% TO 10% OF FINELY DIVIDED CLAY, FROM 10% TO 20% OF FINELY DIVIDED MICA, FROM 10% TO 20% OF FINELY GROUND ASBESTOS, AND A SMALL AMOUNT OF PORTLAND CEMENT, SAID PORTLAND CEMENT BEING PRESENT IN AN AMOUNT OF LESS THAN ABOUT 1%, SAID PERCENTAGES BEING BASED ON THE TOTAL WEIGHT OF THE MIXTURE.