Q: How would I go about making mosaics like the Ancient Romans did?
A: “Mosaic” is a term that includes various techniques for covering walls, objects, and sculpture with diverse materials, ranging from ceramic, to stone, and glass. The ancient Sumerians evolved a technique called “cone mosaic” which involved setting thousands of fired ceramic cones (point in) to embellish walls and columns in their temples and palaces. The Romans took the mosaic technique to a degree of perfection unsurpassed to this day, using it mainly for floors.
The Roman pictorial technique survived in the Eastern (Byzantine) Empire, and was later reintroduced to Italy, where it is still practiced to some extent. Anything from broken crockery, to pebbles sorted for color, to cut ceramic tiles can be used to cover surfaces, but if a pictorial effect is desired the easiest way to proceed is by using “smalti”, small (20mm) glass tiles that are easily cut with a nipper (a pliers-type implement with cutting jaws perpendicular to the handle). Be sure to wear eye protection while cutting any tile.
In the S.F. Bay Area, a source for smalti is Tilecraft Ltd. in San Rafael, 415-456-0282. They come by the sheet, adhered to a fabric base which soaks off in warm water, about 1.3 square feet to the sheet. Although hundreds of colors were available in living memory, now they can only order 50 colors, and stock about 20. If particular colors or shapes are needed, a potter or glassblower could probably make small tiles to order.
The tile can be adhered to a plywood base with mastics applied with a fine notched trowel, but it is preferable to work on solid concrete. Either a mortar can be applied about 1 inch thick over expanded metal lath (galvanized) which is nailed to the surface, or an existing concrete wall can be primed with admix (a glue that can also be added to mortar). Then “thinset” concrete (a proprietary adhesive concrete) is applied with a notched trowel to a small area and the mosaic tile is pushed onto the area covered, making sure the thinset does not come up to the level of the fronts of the tiles (you don’t want it showing through the grout).
To make things go quicker, it is possible to adhere the tiles ahead of time to clear contact paper laid on top of your pattern. Make sure to lay out the pattern in reverse, as the fronts of the tiles will be facing down. This way, you can pre-make your mosaic in squares about one foot on a side (don’t get much bigger or they will become unwieldy) and press the entire square onto the wall. Remove the contact paper after the thinset has gone off and the tiles are firmly attached to the wall. The mosaic is then grouted: a mixture of fine sand, cement, colorant, and water is forced into the spaces between the tiles (always leave at least 1/16 inch between tiles and try to keep the spacing consistent)—you can of course use proprietary grouts which are available in a wide range of colors. Make sure to keep sponging the surface until every trace of grout is off the fronts of your tiles—this is much easier to do before the grout sets.