What is the best way to do mosaic work with ceramics or marble?
Mosaics usually consist of units about one inch square glued on the bedding side to nylon net or on the face side to paper to make up sheets one foot square. These sheets can be laid out and pregrouted with a mix of two parts portland cement and three parts limestone dust or else masonry cement and water. The bonding face should be kept clean. It is preferable to choose a kind of mosaic that has an intermediate suction rate. Too high or too low a rate of water absorption will result in a poor bond to the mortar. Mechanical keys are generally useless and sometimes harmful because they interfere with bond by entrapping air. It is more effective to depend on a good mortar proportioned with one part of cement to four parts of sand by weight and containing a latex admixture of 15 to 20 percent of solids by weight of cement. Styrene-butadiene, non-water-sensitive polyvinyl acetate, or polyvinylidene chloride latexes are useful. If lightweight aggregate concrete is to serve as the substrate the mortar should be made with one percent methyl cellulose in the mixing water to improve its moisture retention. To apply the mosaic the adhesive mortar should be applied to a depth of about 1/8 inch over about one square yard of concrete. The mortar surface may be left smooth or very lightly scored. The pregrouted sheets are rolled or beat onto the mortar using a wooden block, rubber roller or other effective tool. If there is paper on the face of the mosaic this should be removed after the mortar has hardened, and the joints should be pointed with the same mortar except made with a finer sand. The surface should be washed when the pointing mortar has hardened.