CHAPTER 3
Plain and Incised
Cement Tiles
A KNOWLEDGE IN MIXING CEMENT is the next step necessary in Color Cement Handicraft. The steps necessary toward mixing cement are simple, the main point being that the cement should be fresh. The student is cautioned to test the freshness of cement by seeing that no caked or hard lumps of cement are contained in the sack mixture. As formerly explained the cement should have a smooth, slippery feeling when passed between the fingers.
NEAT CEMENT is the term applied to cement mixed with water without the addition of any sand or gravel. Neat cement produces a very smooth surface and responds to reproducing every change in the surface of the model. It should be used on the surface only and not for the entire tile or pottery. If used without any sand or gravel, it is termed “too fat,” and has the fault of cracking sooner or later. Therefore neat cement is always backed up with a concrete mixture.
CONCRETE is a mixture of sand and cement, gravel and cement, or rock and cement. In all instances where such a mixture is made, the two parts should be _mixed dry_ before any water is added. Only enough should be mixed to meet immediate needs as it is not best to use cement that has stood so long that it has commenced to harden.
TO SECURE A VERY FINE SMOOTH SURFACE for tiles or pottery the cement should be used neat. It must be sifted dry through a fine sieve and enough water added to make it of easy working consistency. Then a mixture of two-thirds gravel or sand and one-third cement with water added may be used on the back of the tile or the inside of a vase and possibly again lined with a mixture of neat cement.
Cement or concrete can stand for an hour or two and again be used by adding more water and mixing thoroughly. This cannot be done with plaster and should be avoided with cement or concrete. If chemical action has commenced and the cement has partly set, it naturally will have lost much of its strength for second use.
A CONCRETE MIXTURE of one part cement and two parts sand or gravel will give good strength. The sand or gravel must be clean. If it contains any vegetable matter or other sediment, it should be avoided. To test your sand quality put a four-inch layer in an ordinary quart jar, fill with water within three inches of the top. Cover and shake well. Then permit the sand to settle. If the sediment or loam which remains at the top of the sand is one-half inch or more, the sand is not fit for use in concrete.
CEMENT MIXTURES ADAPTABLE TO VARIOUS USES are given below. These may be used for backing and reinforcing large problems, in garden pottery, garden furniture or walls.
1. RICH MIXTURE 1 part cement 2 parts sand 5 parts gravel
2. STANDARD MIXTURE 1 part cement 2 parts sand 4 parts gravel
3. MEDIUM MIXTURE 1 part cement 2½ parts sand 3 parts gravel
4. LEAN MIXTURE 1 part cement 3 parts sand 6 parts gravel
Cement and sand mixed dry first, then with water. The gravel is mixed wet with other mixture and thoroughly combined.
Builders use the Rich Mixture for columns and high stresses, and where water tightness is necessary.
Standard Mixture is used for arches, for tanks and sewers, and for machine foundations.
The Medium Mixture is used for piers, sidewalks, and heavy walls.
The Lean Mixture is used for walls, foundations and for unimportant work.
THE FIRST PROBLEMS IN CEMENT should be the casting of cement tiles without the use of color. As a beginning problem set the retaining bars around a six-inch square space and mix a neat mixture of cement and pour into the space so as to make about a quarter-inch layer. After this has set for about fifteen minutes pull some of the neat cement up the sides with a putty knife or strip of cardboard and then pour in the remainder of the tile concrete mixture of one-third cement and two-thirds sand. This will result in a tile with the top and sides surfaced with neat cement. The surfaces of the bars and the glass or other under surface have of course been properly oiled previous to the pouring.
BEFORE PROCEEDING WITH TILE MAKING it may be necessary to make a number of plaster bars to use as retaining walls. These are made as follows: Two strips of wood one-half inch to an inch thick laid parallel on a glass or other smooth surface that has been greased with oil. The distance between the strips of wood should be about ten inches, as the length will then serve for producing eight-inch tiles or any size under this dimension. The edges of the wood facing inward should always be oiled, the wood strips are held in position by small lumps of modeling wax pressed firmly into the outer edge of the wood so that it attaches it to the surface of the glass. This will leave a channel between the two wooden strips into which the plaster is poured. The two ends of the channel may be stopped with blocks of wood or blocked with wax or clay. As soon as the plaster is poured into the mold it should be evened by running a straight strip of wood or metal over it spanning the width of plaster. Run this back and forth to trim off the surplus, so that the plaster will have an even thickness when removed from its bed.
TO REMOVE THE PLASTER first remove the wooden strips and then tap the layer of plaster lightly on the edge with a hammer. This will loosen it. Then with a T square and sharp nail mark off bars five-eighths inch wide and also bars one and one-quarter inches wide. At least twelve bars of each width should be made. After drying for three days the bars may be sawed apart with any sharp saw, care being taken to hold the saw within the groove made by the nail. The edges of the bars may be further smoothed if necessary with a knife or file.
STRIPS OF WOOD WITH SURFACED SIDES can be used in the place of plaster bars and if oiled will release very easily from the plaster when used as retaining walls.
TO MAKE AN INCISED TILE in plain cement proceed as follows: Roll out clay or modeling wax to about one-half inch thickness and cut to the desired size of tile. Cover this smooth surface, place a design which has been made on thin paper and trace with a pencil. The paper should be held so as not to slip and the result should be a slight indentation of the design on the clay. These lines are then incised over with the incising tool to the desired depth, care being taken that no over-hanging edges remain on the edges of the incisions. The incisions should have sides slightly sloping inward and if the tool is correctly shaped it will produce such lines.
THE DESIGN should be planned to be at least one-half inch from edge and simple in construction. Avoid a tangle of ever crossing lines. A geometrical arrangement dividing the square into pleasing spaces will produce the best results.
Place the tile on a level surface and take four bars of the one and one-fourth inch plaster strips or wood, soak in water for fifteen minutes, wipe dry and oil. Now place the four bars so that the inside edges are against the wax or clay tile and fasten so that they are unmovable with modeling wax. The bars if placed with one end projecting past the bar meeting it at right angles permits their adjustment to any size tile under ten-inch dimensions. Onto this pour plaster-of-Paris, pour into the center letting it run toward the edges forcing all air ahead of it as it enters the incisions. Level off surface and remove the plaster cast from the mold as soon as it has hardened.
TO RELEASE THE PLASTER CAST first remove the surrounding bars and lift the plaster tile off the clay. The plaster tile will have the design in relief on the surface. If any clay is adhering to these relief lines, it is evidence that there are overhanging edges and such edges should be trimmed with a knife before the next step. The next step is as follows: After plaster tile is dry put it in water for a few minutes, then oil the surface well. Place back in the bars and repeat previous operations excepting that this time a cement mixture is used instead of plaster. A mixture of neat cement should be used half way up and permitted to remain for five minutes before the concrete (one-third concrete, two-thirds sand) is poured in for the remaining half.
IN MIXING SAND AND CEMENT it should be remembered that they should be mixed together thoroughly _while dry_ before any water is added. After the cement has been poured into the form, if it is to be used for floor or wall purposes, four small squares of cardboard should be pressed into the exposed cement which is the back of the tile. This should be done about fifteen minutes after the cement has been poured, when it is not too soft.
The tile may be removed after it has remained in the form for twenty-four hours. A thin cement mixture of another color may be made and brushed over the tile and the surplus removed, leaving the last color only in the incisions.
AN INTERESTING VARIATION is produced by cutting away the clay or wax between the incisions of the pattern to the depth of one-half inch or less, making a mold of this tile and in turn casting a concrete tile. The result will be a surface with relief section and low spaces, the relief being concrete and rough in texture.
These low spaces are then filled with a colored cement of another color, or neat cement, and brought to the level of the relief surface. Such a tile secures a pattern adaptable to tile walks, or any surface which is subjected to wear, in that the design is not only a thin surface layer, but a thick portion of color that will not disappear with the wearing of the surface layer.
A SIMPLE METHOD OF MAKING TILE MOLDS is to cut a design from a thick piece of cardboard or sections of a design, and glue these in proper position to carry out a design arrangement. These pieces should be cut with tapering sides so as to permit of proper “draught” or releasing conditions when the plaster cast is made for mold purposes.
The pieces of cardboard should remain glued until dried to avoid the moisture of the soft plaster moving the parts around.
WITHOUT THE USE OF COLOR a number of pleasing and varying textures can be secured with plain cement, as the gray color of the cement has an artistic quality, and it is well to become well grounded in the use of cement before combining color with it.
SEVERAL WAYS OF USING PLAIN CEMENT FOR TILES beside those already given are explained in the following descriptions. These are termed Traced Cement, Burnished Cement, Scraped Cement, Concrete Tile, Cement and Concrete Tile, Glazed and Dull Cement Tile, Glazed Relief Line Tile.
THE TRACED CEMENT TILE is made by pouring a half-inch mixture of concrete (one-third cement, two-thirds sand) into a mold made with the usual retaining bars of any desired dimensions. Over this concrete mixture a layer of about one-quarter of an inch of sifted neat cement mixed with water should be placed. At a certain degree of hardness this layer of neat cement will yield to a slight indentation or traced outline. This condition can be tested by touching the edge of the surface with a pencil point to see whether it is too hard or too soft. A good plan is to pour the mixture in the evening and it is generally in right consistency to work upon on the following morning. The surface should be nearly hard but still sensitive to pressure with a point.
HAVING PREPARED THE DESIGN on a piece of paper about the weight of business writing paper, the design is placed on the surface of the tile and kept in the same location while a blunt, soft lead pencil is traced over the pattern, pressing firmly to create a good indented line in the cement surface. The design for this work is best where the pattern is easily expressed in lines or outlined forms. The forms can be increased in strength by rubbing the pencil on the outer edge of the lines to be slightly modeled in separate appearance. When the design has been completely gone over, the tile is placed in water for several days, after which it is dried and a thin coating of color wash (see chapter on Surface Finishes) may be added to it which will further the pattern by coloring the traced lines.
THE BURNISHED CEMENT TILE is produced by casting a similar tile to the one made for the Traced Cement Tile and proceeding in the same manner, excepting that the spaces between the forms are burnished smooth with the dull pointed pencil or a smooth small stick. This results in some parts being burnished or pressed down while others remain in slight relief. A change in this is also produced by scraping the smooth surface off between the lines in certain places instead of burnishing it. This results in parts of the surface being of a different texture and also of a little different color, as the scraped parts are different in both these respects to the cement which has dried and remains untouched on the surface.
A SECOND BURNISHED TILE EFFECT is to pour a layer of neat cement first in the mold and a concrete mixture last. When this is hard enough to remove, and still soft enough to work upon (the neat cement layer having been in the bottom will dry with a dull finish and not a glaze finish as when flowed on as a top layer) it should be removed and the design traced upon this neat cement surface. If a leather tool or smooth hard point is used, certain parts as desired can be worked upon, smoothed down or pressed in, through the paper which will create a change of surface texture.
THE SCRAPED CEMENT TILE is where either the top neat cement or bottom cement layer has the design in line or form scraped out of the cement, the entire design being produced without a plaster mold being used. A sharpened nail or nut pick will make a good scraper and this scraping and pressing is done on the cement surface direct and not through a paper as in the two previous problems. This direct method of working upon cement surface is considered more thoroughly and more extensive applications made of it in the chapter on Carved and Modeled Cement.
THE CONCRETE TILE. Varying finishes may be secured in casting any cement tile by the kind of aggregate used with the cement. A rough irregular small crushed rock will give one kind of texture, while a round small white gravel will give another and each change will present different effects. Without going into extremes of finishes or having too many changes in the surface of a tile, pleasing effects can be secured by one to three changes of texture secured by putting different mixtures in different parts. This may be done by mixing and applying with a brush or spoon the different mixtures into the mold, placing the mixtures each in their proper section of the mold. The whole is then covered with the backing mixture resulting in the surface pattern appearing with the changes after the tile has been released from the mold.
Where a concrete mixture is to appear rough in texture, the sand or gravel and cement should be mixed dry, just enough water added to cause it to mix up to a damp consistency so that it can be shaped with the hand. This can then be put in the mold and tamped slightly with a block of wood to press it in true contact with the surface of the mold. This will result in a porous, open texture, producing good contrast with neat cement parts that have been previously placed or are to be added.
THE CEMENT AND CONCRETE TILE is made with plain cement producing added interest to the design by the two textures or surface finishes that occur between cement and concrete. The design for such a tile is best where the parts are separated either by an incision or a relief line. The plaster mold should therefore present separate portions, some of which can be considered for the cement parts and others for the concrete parts.
By mixing neat cement until it is of a thin mixture, the mixture can be placed on the mold wherever wanted by dripping it from a brush. Care should be taken in the use of a brush with cement that a wiping stroke is not used as such a stroke will remove the oil from the plaster surface and cause parts of the cement to stick to the plaster.
After the cement has been placed, a concrete mixture is made and poured into the space up to the desired height to produce the necessary thickness. This will at the same time fill in the remaining surface spaces of the tile.
THE GLAZED AND DULL CEMENT TILE is produced by filling in with clay or glued cardboard bits cut to shape, those parts that are to be glazed gray cement. Do not use modeling waxes or artificial clays for this part as the oil or grease in them will interfere with the glazed cement adhering to the surface in the final finishing.
After the cardboard or clay is dry a layer of neat cement is poured in, and backed with the usual concrete mixture. After the tile is released, the cardboard bits or clay is removed and cleaned out, the surface under it is roughened with scratched lines and the tile is put in water for an hour. The spaces are then filled with a mixture of neat cement and permitted to harden in a shallow tray of water.
TO MAKE GLAZED CEMENT SURFACE it is important that these steps be watched:
1st. That the surface be roughened wherever the glazed surface is to appear.
2d. That the tile be soaked in clean water until it has fully absorbed water.
3d. That a little dry neat cement be placed on the spaces to have glazed effect.
4th. That the neat cement should be sifted and dripped on with a brush and not gone over a second time.
5th. That the tile is taken out and dried and the glazed and dull neat cement will create the change of surface texture as planned.
A bloom or chalk-like powder often comes on the surface of tiles, but will disappear within a short time and need not cause any anxiety.
GLAZED RELIEF LINE TILE is made by casting either a neat cement tile or a concrete tile with a relief line design and then mixing a neat gray or color cement glaze and putting it onto the surface. The tile is shaken in a level position until the entire surface is entirely covered leaving a thin layer of the glaze in the spaces between the lines as well as slightly on the lines. The tile is set in a shallow layer of water to harden.
OTHER VARIATIONS IN TILE EFFECTS can be made by combining these methods and with the use of color in these different methods described, unlimited avenues are opened to the worker in color cement. It should be remembered also that most of these methods of surface treatment are also possible in other forms beside flat or tile surfaces. The student should know these methods of working with plain cement and concrete as they are the foundation of successful Color Cement Handicraft.