A mosaic needs to be "contained" within a frame, otherwise, the tesserae will pop off at the edges. The frame may be a real wood or metal frame or simply an area filled in with cement surrounding the mosaic.
FINISHING AND CARE
A good method to clean a mosaic is to simply brush the mosaic surface with a soft brush (a shoe brush). To bring out the colors of marble and stone, the mosaic surface can be polished with WAX or with MOSAIC WET. After a mosaic is set, you can GRIND your marble/stone mosaic by hand with sandpaper if it is small or with an electric grinder. You could also grind smalti but the result is not so good because it would affect their brilliance. To clean your mosaic, DO NOT USE muriatic acid.
GROUTING
Wall mosaics are usually not grouted because their beauty lies in the uneven aspect of their surface. Floor mosaics, which will be ground, may be grouted by spreading a watery mix of cement on the surface of the mosaic. When the thin layer of cement has set, the mosaic can be ground so that the surface will be very smooth.
To grout the surface of a mosaic without grinding it, pour a small amount of liquid cement mix so that it fills in the interstices and remove the amount in excess from the tesserae with a wet sponge, and later with a bristle brush.
In ancient mosaics, the lime under-bed was always colored (under-painted) to match the color of the mosaic surface. One option to reduce the intensity of white lime/cement is to "distress" it by "painting" the surface with some WATER mixed with DRY POWDER PIGMENTS. The lime/cement interstices will absorb the color and when it is dry you can brush the surface clean.