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1950-51 Theatre Catalog, 9th Edition, Page 427 (405)

1950-51 Theatre Catalog, 9th Edition
1950-51 Theatre Catalog
1950-51 Theatre Catalog, 9th Edition, Page 427
Page 427

1950-51 Theatre Catalog, 9th Edition, Page 427

such a way as to be uniform in thickness and free from ridging or excessively heavy brush marks.

It is true that some commercial Portland cement paints exhibit smooth working qualities more on the order of oilvehicle paints. However, experiments indicate that even these paints should be applied with stiff-bristle brushes if the concrete is coarse textured.

When weather conditions are such as to cause the paint to dry rapidly it is advisable to work in the shade in so far as practicable. Such practice makes it easier to keep the surface uniformly moist for proper suction and helps prevent too rapid drying of the coat being applied.

The different constituents of Portland cement paint vary substantially in specific gravity with each other and with the water; consequently, to prevent segregation and maintain a uniform mixture, the paint should be stirred frequently in the bucket.

When painting concrete masonry or other porous concrete for the dual purposes of moisture-proofing and decoration, both coats should be vigorously scrubbed on in such a manner as to work the paint back into the voids and provide a continuous paint film free from pinholes and other openings through which water might penetrate. Tests of the rain resistance of painted concrete masorny walls indicate that paints applied with spray equipment provide less protection than scrubbed-on coatings. Spray application, therefore, is recommended only on dense concrete or interior surfaces or where paint is not required for waterproofing purposes.

The proper average film thickness and coverage rate is rather difficult to estimate for Portland cement paints because of the edect of diEerences in the texture of the concrete to be covered. However, considering smooth concrete surfaces, it appears that a two-coat film should average about 0.015 inch thick which will be obtained with a coverage rate of about 100 square feet to the gallon of mixed paint for the two coats. If the concrete is rough textured or if the paint contains coarse filler (No. 50 to 100 mesh) a film thickness of 0.025 to 0.035 inch and coverage rate of from 45 to 55 suuare feet to the gallon should be sought. TWO coats on very rough textured block may require as much as 1 gallon to 35 square feet of surface.

(luring-Proper hardening of films of this type depend upon the availability of moisture for chemical reaction with the Portland cement. The moisture in the concrete base, in the paint itself, and in the air is utilized for this purpose, but usually this is not enough. On most jobs it is practicable to sprinkle the painted surface two or three times a day with the same fog spray used for dampening the concrete and it is recommended that this be done between coats and for at least two days for the final coat starting just as soon as the paint has hardened sufficiently not to be damaged by the spray, usually about 12 hours after application. Damp curing in this or some other efTective manner must be provided in order to obtain the best results with Portland cement paints. It will improve the hardness and durability of the paint in every case, and in some instances will mean the difference between a satisfactory and a poor job.


A BRUSH FILLED WITH PAINT is shown in the top picture. Mortar joints should be pointed first (bottom picture) to insure a complete sealing of ioints. Thorough scrubbing is necessary to force the point into the open texture of the masonry. During the painting process. the point should be stirred from time to time so that it will be kept at a uniform consistency. Second coat can be applied in 24 hours.
1950-51 Theatre Catalog, 9th Edition, Page 427