In order to obtain finishes of a pleasing texture and to avoid the monotony of the dashes and the difficulties of execution of the float finishes, a number of finishes have been developed by specialists and manufacturers of colored stucco. Color tones are introduced, and with combination of colors and methods of finishing there are unlimited possibilities as to number of surface effects which can be devised. One of these finishes has been named "floated rough cast." The wall is prepared for a rough-cast finish, and then the high points are lightly smoothed off with a plasterer's wood float. This finish lends itself readily to a two-color combination. First, the finish coat of one color is applied and partially floated and while still plastic another color is dashed on and then the high points smoothed off and the two colors blended together. Another has been called the "sponge-float" finish and is produced by carefully working the plastic finish coat with a softwood float drawing the float away from the surface at random. The suction between the float and the stucco gives a roughness of surface which is between the extremes of the roughness of the wet dashes and the smoothness of the sand-float finish. When executed in colored stucco, it gives a very acceptable finish.
Fig. 25. - This six-room house built of hollow tile walls with an exterior finish of stucco is comfortably placed on a 45-foot lot. (Copyright - Architects' Small House Service Bureau, Inc., Plan 6-B-27.)
Although the name "exposed aggregate" has been applied to the ordinary troweled or floated surface which is given a final scrubbing treatment with brush and water or a cleaning with an acid wash, the name will be used here in connection with a finish which should be more properly designated as a surface-treated concrete. The exposed aggregate finish is obtained by applying a finish coat which in itself is a concrete with miniature aggregate. The cement and fine sand bear a definite relation to the coarse aggregate which predominates the mix. The coarse particles have to be sized and proportioned to the fine material in keeping with the architectural features of the building and in accordance with the effect which it is desired to produce when the structure is viewed from a given distance. Usually the coarse particles are of one size from 1/8 to ¼ inch and upward and are proportioned into the mix to give a maximum density. This coating is applied and after it has stiffened the surface film of cement and finer aggregate is removed by gentle brushing with a wire brush and then the coat is left to harden and dry out. Next, it is washed with dilute acid and clean water. By removing the cement and fine particles the color of the surface is determined by the color of the aggregate and its texture by the size and shape of the coarse particles.
While this treatment ranks first as a stucco finish, it is also the most difficult of stuccowork to plan and execute. By the use of colored aggregates the most beautiful of color tones can be obtained and due to its density and texture many of the common structural defects are eliminated. To carry out the work successfully requires the selection, grading, and proportioning of the aggregate from a knowledge of size effect and color tone, and to obtain a uniformity of appearance over the entire surface requires the highest type of workmanship in the application and finishing of the coat.