Drywall Coating Composition

A dry powder was prepared according to the following formula:

The calcium carbonate was the high purity, ultrafine products old by Omya, Inc. under its trademark Omyacarb. Its bulking value is 0.0444 gallon per pound.

The calcined kaoline used was the product sold under the trademark Snow-Tex 45 by the Texas Industrial Minerals Company. Its bulking value is 0.0465 gallon per pound and its oil absorption value is 40-42 lbs. per 100 lbs. by the spatula rub out method of ASTM D-281-31.

The attapulgus clay as Attagel M-8214 from Engelhard Minerals and Chemical Co. Its bulking value if 0.0508 gallon per pound.

The titanium dioxide was the rutile type sold by American Cyanamide under its Unitane OR-600 trademark. Its bulking value is 0.0293 gallon per pound.

The mica has a bulking value of 0.0418 gallon per pound. Sold by United States Gypsum Company under the designation P80F-K, its mean particle size is 22.8 microns, as determined by Stokes sedimentation by sedigraph, and 97.5% by weight is smaller than 150 microns.

The sodium potassium aluminum silicate is available from Indusmin, Ltd. under its trademark Minex 7. It has a bulking value of 0.0459 gallon per pound.

The vinyl acetate/ethylene copolymer used was a redispersible powder sold by Air Products and Chemicals, Inc. under its trademark Airflex RP-245 which contains about 10% each of an inert filler and polyvinyl alcohol by weight. Thus, the copolymer itself, constituted about 5.4% of the powder of this example. The bulking value of the RP-245 powder is 0.1091.

The ethyl hydroxyethyl cellulose was the Bermocoll E-351 water soluble cellulose ether solid in powder form by Berol Kemi AB. The average number of hydroxyl groups in each anhydroglucose unit that have been replaced by hydroxyethyl groups is 1 and the average number of ethyl substituents per unit is 0.9. The Brookfield viscosity of a 2% aqueous solution at 20.degree. C. is from 4000 to 6000 cps as measured with a type LV viscometer and a No. 3 spindle at a speed setting of 12. With a specific gravity of 1.33, the bulking value of the cellulose ether is 0.0903 gallon per pound.

The powder of this example, having a pigskin volume concentration of 74.6% as calculated from the bulking values, was added to water with stirring in the proportion of 25 pounds of powder to 2.5 gallons of water. A cage type paddle mixer driven by a 3/4 inch drill motor at 550 r.p.m. was used to disperse the powder to the water. The thick, lump-free slurry was then diluted with 4 gallons of water. The resulting paint was ready to use about 15 minutes after the powder was first added to the water. It was strained through a sock in keeping with standard practice before being sprayed through an airless spray gun having a 0.019 inch atomizing tip onto a newly erected drywall having joint tape and joint compound at the seams between each panel. The result was a monolithic undercoat with no joint flashing visible under critical lighting. The wall was painted with a finish coat later without sanding the undercoat.

The procedure of Example 1 was followed generally except that the paint was applied with a roller with similarly good results.