Code of practice for laying in-situ terrazzo floor finish
1984 Edition

According to the standard, the terrazzo topping should be mixed with a binder composition of 3 parts cement to 1 part marble powder by weight. Aggregates are then added by volume relative to the binder mix, with proportions adjusted based on aggregate size: 1.75 parts for sizes 1 to 7 mm, and 1.5 parts for 7 to 25 mm. The base or under layer for vertical surfaces requires a stiff cement mortar mix of 1 part cement to 3 parts sand by volume, finished with a rough surface to ensure good bonding. Thickness recommendations include a base concrete layer not less than 100 mm, a cushioning layer at least 75 mm thick, and a combined under layer plus terrazzo topping thickness of minimum 30 mm for flooring and 20 mm for dadoes or skirtings. The terrazzo topping thickness varies with chip size, ranging from 6 mm for 1 to 2 mm chips, up to 12 mm for chips between 7 to 10 mm.

Preparation begins with a well-compacted sub-base of earth or preferably sand. Above this, a cushioning layer, typically lime concrete, is placed, followed by a base concrete layer of lean cement concrete (1:5:10 mix) finished to a true level slightly below the final terrazzo surface. For vertical surfaces like skirtings and dadoes, a stiff cement mortar mix of 1:3 (cement:sand by volume) is applied with a roughened finish to aid bonding. Once the base is ready, the terrazzo mix is laid over a prepared screed bed, compacted thoroughly by tamping or rolling, and trowelled to a smooth finish while allowing adequate intervals between trowelling to prevent cement rising and cracking.

The standard mandates use of permanent mineral-based pigments conforming to specified proportions to ensure color durability and consistency. Common pigments include red oxide of iron, carbon black, green chromium oxide, and yellow oxide of iron, among others. Pigments are blended with cement or white cement in precise mass ratios depending on the desired color. Uniform mixing is critical to prevent streaking or uneven coloration, and trial panels are encouraged to verify color accuracy before application. The matrix color is controlled by the pigment-to-cement ratio, with white cement often used for lighter shades.

Post-installation, the terrazzo surface should be compacted and trowelled smoothly, avoiding excessive early trowelling to prevent surface defects. Initial curing involves air drying for 12 to 18 hours, followed by wet curing through water ponding for a minimum of 4 days. If re-wetting is necessary after cleaning, the surface should dry for 12 hours before repeating wet curing. Grinding should commence not earlier than 2 days after laying for manual methods, and 7 days for mechanical grinding, to allow adequate setting of the matrix. The grinding process progresses through stages with increasing grit sizes to gradually smooth the surface without damaging the marble chips. Proper adherence to these procedures ensures a crack-free, resilient terrazzo finish.

Slip resistance is maintained by avoiding the use of soap and excessive polishing, both of which can render the surface slippery. Regular cleaning with water, supplemented occasionally by dilute oxalic acid solutions, is recommended to keep the floor clean without compromising grip. When applying wax or emulsion polishes, they should be used sparingly and carefully buffed with soft materials to preserve surface texture. Maintaining a slightly textured finish rather than an overly glossy one enhances safety by preventing slips. Additionally, thorough drying after cleaning helps reduce the risk of accidents.