CHAPTER 6

Color Cement Relief Tiles

TO BEGIN A RELIEF TILE, a model should first be planned on clay or modeling wax. A pencil pattern is first made on paper and this paper is placed over the layer of clay or wax and a pencil tracing will produce an indented pattern of the subject on the clay or wax underneath.

TO MODEL THE SURFACE a wooden modeling tool, such as is used by sculptors, or a leather modeling tool or even small whittled pieces of wood can be used. In producing raised portions the clay or wax scraped to produce low parts can be used and care should be taken not to produce too great a relief as a tile design should not appear detached.

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.

TO MAKE THE PLASTER CARVED MODEL trace the design onto a smooth slab of plaster of the right size that has been cast on a smooth surface. If a larger piece of plaster than the desired size is used it can be cut down.

TO CUT PLASTER SECTIONS an old saw can be used or several strokes of a knife on the surface until about one-quarter of the thickness has been cut, and a similar cutting on the reverse side, just opposite to the cutting on the first side will enable the plaster to be broken easily. Or by laying it on a straight edge with the line of cutting over the edge, a quick pressure with the hand will snap the two pieces apart.

AFTER THE DESIGN IS TRACED a chiseled nail point, nut pick or other hard edged point is used for scraping the surface of the plaster, modeling it or carving it to the desired shapes. Naturally it will be found that plaster can only be taken off and not added on and that all reliefs must be produced from the surface downward, that is the natural surface will be the maximum height and all variations in the surface produced below that.

BACKGROUND TREATMENTS are produced where a design appears in low relief against a background. The background may be stippled with the tool point or lines scraped or crossed lines used to create interesting background qualities.

TO BUILD UP PLASTER SURFACES, roughen the surface onto which more plaster is to be placed and mix fresh plaster and place it on with a small spoon or with the brush. After this is dry it can be carved or scraped with the tools used in the modeling of plaster.

TO FINISH THE PLASTER CARVING, it is dried, shellaced, and used for casting just the same as the other relief forms described. To preserve casts from receiving injuries to their surfaces they should be wrapped in paper with a card against their face and placed with face toward the wall in a cupboard or shelf, when not in use. Where a mold has been repeatedly used and the shellac become worn, the mold should be carefully dried and the shellac coating renewed.

A CONVENIENT CLAY TO USE for relief work is the powdered fire clay secured in most hardware stores and is the clay used for lining grates, furnaces and similar purposes. This clay is convenient in that only the amount needed may be mixed up for use, leaving the balance of the powdered fire clay always in good condition.

RELIEF TILES DESIGNED FOR FLOOR SURFACES or for wall surfaces are best where they do not contain deep relief as they will not catch dust or dirt and will be better unified with the remaining surfaces.

SPECIAL TREATMENT FOR RELIEF FLOOR TILES is required in that the cement should be compact and clean sand should be used mixed with just enough water to cause the two to adhere to each other and this should be tamped into the mold well up against the face of the plaster tile to pack the mixture firmly and cause it to form into a durable surface.

TO HARDEN CEMENT TILES or pottery they should be placed in water so that the water will complete the chemical action producing the stone-like quality of successful cement work. If the tile is removed and dried and again placed in water it will increase the hardness.

AFTER THE TILE IS HARDENED it is dried thoroughly and brushed well with a brush. It may be waxed or first given a thin coat of shellac and then waxed. Shellac should never be applied until the cement tile is thoroughly dry, as otherwise the shellac will remain sticky.