Color Cement Handicraft

by Pedro J. Lemos; Reta A. Lemos

AVOID UNDERCUT SURFACES or overhanging edges on the finished model as this will result in locking of the cement cast with the plaster mold and breaking of the tile before it can be removed. A general checking over of the different parts before the plaster cast is made will avoid many of the overhanging parts going through as they can be easily located and corrected.

TO CAST THE PLASTER MOLD the clay or modeling wax is surrounded with the retaining bars and as the clay or wax needs no oiling the plaster can be mixed and poured into this mold. A slight jarring of the table or surface on which the mold is placed will cause the plaster to settle, producing a level surface and also cause any bubbles to break or come to the surface.

TO AVOID BUBBLE DEFECTS IN CASTING either with plaster or cement the plaster or cement mixture should be poured into the center location of the mold allowing it to spread gradually toward the sides and corners carrying the air in the grooves and low spaces, forcing it toward the edges. Once the surface is covered in this way the remainder of the mixture can be poured in more rapidly.

TO CORRECT BUBBLE DEFECTS that appear on the finished plaster or cement casting, scrape some of the plaster or cement from the back or sides where it does not matter and repair the flaws by pressing it into the holes. Where cement is repaired this way it should be permitted to dry for another day before it is placed into water to harden.

TO MAKE THE CEMENT RELIEF TILE in color the plaster cast made from the clay or wax model should be oiled after it has been shellaced and surrounded with the retaining bars. The color should be then mixed with the cement and water added to make it of a pouring consistency, it is then poured into the mold. After this color has set for awhile the back layer is added of concrete after the color of the first pouring has been carried up so as to produce color on the sides as well as on the face.

WHERE A NUMBER OF COLORS ARE USED the colors are mixed and dripped upon the oiled surface of the plaster mold before it is enclosed with the retaining bars, as the retaining bars would prevent free access to the surface with the brush. After the various colors have been placed, the plaster cast is then placed within the bars and the color being permitted to set, it is then backed with a layer of concrete.

THE CONCRETE BACKING MAY BE COLORED either with color throughout or with a topping of color to give it a finish. If corners are to be rounded or the edges trimmed in any way this color layer should be thick enough to permit trimming without exposing the under layer.

TO AVOID THE COLOR FALLING OUT in color relief work, the following should be observed. When preparing to pour in the backing, observe whether any of the color cement placed on the tile has become too dry. If so, it should be sprayed with a light coating of water or brushed with a brush full of water, and its upper exposed surface slightly roughened so that the backing will adhere firmly. If it becomes dry and smooth the second layer of cement poured onto it will come in close contact but not adhere, and later a change in temperature or jar of the tile may shake a portion of the design loose so that a color fragment will fall out.

TO AVOID COLOR PREMATURELY DRYING, the plaster cast should be placed in water for fifteen minutes at least before the color is placed into it. To permit free absorption of water the plaster tile should never be shellaced on the bottom but only on the sides and the top.

ANOTHER WAY TO MODEL A RELIEF DESIGN is to carve it on plaster direct without making the relief on clay or modeling wax. This method has the advantage of being proof against overhanging edges, though some care must be taken against undercut surfaces.