Terrazzo

MOUSTURE TESTING: Before installing terrazzo, the concrete slab that will serve as the substrate must be tested for moisture levels. This is to ensure that the slab is dry enough to bond with the terrazzo and prevent future problems such as cracking, bubbling, or discoloration. The recommended test is the ASTM-F-2170 probe test, which measures the relative humidity of the slab. The acceptable threshold is usually 75% to 80%. If the slab is too moist, a moisture mitigation barrier may be applied to reduce the vapor transmission.

CONCRETE PREPARATION: The concrete slab must also be checked for proper level tolerance, which is usually 1/8 inch in 10 feet. If the slab is uneven, it must be leveled with a fill epoxy or other suitable material. The slab must also be cleaned of any dirt, dust, oil, grease, or algae that could interfere with the adhesion of the terrazzo. This can be done by shot blasting, grinding, or scrubbing the surface with a dilute muriatic acid solution. Any cracks or joints in the slab must also be repaired with a flexible membrane or filler to prevent them from reflecting on the terrazzo surface.

FLOOR LAYOUT: The design and pattern of the terrazzo floor must be laid out on the slab using divider strips. These are thin metal strips that separate different colors and sections of the terrazzo, as well as control the expansion and contraction of the material. The divider strips are fastened to the slab with nails, screws, or epoxy, and can be bent or cut to create various shapes and curves. The divider strips also serve as guides for pouring the terrazzo mix.

BASE COAT APPLICATION: The base coat is the layer of cement or epoxy that holds the terrazzo aggregates together. The base coat is mixed according to the manufacturer’s instructions, usually with a ratio of one part resin to two parts hardener. The base coat is also tinted with the desired color of the terrazzo. The base coat is applied to the slab with a trowel or a squeegee, covering the entire surface and filling the spaces between the divider strips. The base coat is then smoothed and leveled with a roller or a power trowel. The thickness of the base coat is typically 3/8 inch or 1/4 inch, depending on the type of terrazzo system.

AGGREGATE BROADCAST: The aggregate is the material that gives the terrazzo its appearance and texture. The aggregate can be marble, glass, or other natural or synthetic chips of various colors, sizes, and shapes. The aggregate is broadcast or sprinkled onto the wet base coat, covering the entire surface and creating the desired pattern. The amount of aggregate used depends on the desired density and coverage of the terrazzo. The aggregate is then pressed into the base coat with a roller or a trowel, ensuring that the chips are evenly distributed and embedded.

GROUT COAT: The topcoat is the layer of clear resin that seals and protects the terrazzo. The topcoat is mixed and applied in the same way as the base coat, covering the entire surface and filling any gaps or voids. The topcoat is then smoothed and leveled with a roller or a power trowel. The thickness of the topcoat is usually 1/16 inch or less, depending on the type of terrazzo system.

CURING & GRINDING: The terrazzo must be allowed to cure or harden before it can be polished. The curing time depends on the type of resin and the ambient temperature and humidity, but it is usually between 24 and 72 hours. After the terrazzo is cured, it is ground with a machine that uses diamond abrasives to remove the excess resin and expose the aggregate. The grinding process also removes any imperfections or unevenness in the surface and creates a smooth and flat finish. The grinding is done in several passes, starting with coarse grits and ending with fine grits. The grinding is usually done wet to reduce dust and heat.

POLISHING & SEALING: The final step is to polish and seal the terrazzo. The polishing is done with a machine that uses finer diamond abrasives to create a glossy and reflective surface. The polishing is also done wet to reduce dust and heat. The polishing is done in several passes, starting with medium grits and ending with very fine grits. The polishing also enhances the color and clarity of the terrazzo. After the polishing, the terrazzo is sealed with a protective coating that prevents staining, scratching, and water damage. The sealer is applied with a mop, a roller, or a spray, and allowed to dry. The sealer may need to be reapplied periodically to maintain the appearance and performance of the terrazzo.