On account of its decorative and good wearing properties, this terrazzo flooring is becoming very popular these days and is being commonly provided in offices, schools, hospitals, residential buildings, banks etc. Terrazzo is a concrete surface with special aggregate of marble chips (or other decorative material) mixed with white and/or coloured cement in proportion of 3:1 (three marble chips : one cement). The aggregates are exposed by grinding the surface mechanically or manually. The terrazzo flooring may be laid in different thicknesses. The construction of 40 mm. thick flooring is described below.
The operations of the preparation of sub-base and laying of base concrete are carried out in similar manner as described earlier in case of cement concrete flooring. The 40 mm. thick flooring will consist of a 6 mm. thick layer of terrazzo topping and 34 mm. thick under layer of cement concrete 1:2:4. Prior to laying flooring, the whole area is divided into suitable panels by use of dividing strips (made from copper, brass, aluminium or glass) of thickness not less than 1.5 mm. and width not less than 25 mm. In order to reduce the risk of cracking, the area of one panel should not exceed two square metre.
The surface of base concrete should be cleaned of all dirt, mortar dropping debris etc. and then wetted with water. Prior to laying the cement concrete under layer, the wet surface of base concrete is smeared with a coat of neat cement slurry to ensure proper bond between the base concrete and flooring.
The concrete under layer is then spread, consolidated, levelled and finished to a slightly rough surface. When the under layer has hardened sufficiently, already prepared plastic terrazzo mixture is laid over the treated under-layer of concrete and compacted thoroughly by tamping or rolling. The terrazzo mixture consists of one part of cement (white or coloured) or a mixture of the two mixed with two to three parts of marble chips with water just sufficient to make it a workable mix. During tamping or rolling, it should be ensured that at least 80% of the finished surface should show exposed marble chip aggregates and if necessary additional marble chips may be added during the of tamping or rolling to satisfy this condition.
After tamping or rolling, the surface is floated and troweled and left to dry out for 12 to 18 hours. After this period the surface is cured under standing water for 2 days.
Thereafter surface is subject to first grinding by machine by use of carborundum stones of coarse grade. (No. 60). The whole surface is then scrabbed using plenty of water. All pores and holes (if any) are then filled with cement grout (using the same coloured cement as in the original mix for terrazzo topping) and the surface coated with neat cement grout of cream like consistency. The surface is again cured for five to seven days and second grinding is carried out by machine by using carborundum stones of fine grade (No. 120). In the similar manner, the surface is cleaned and repaired as before and cured again for a period of 4 to 5 days and subjected to third grinding by machine by using carborundum stones of 320 grit size.
The finished surface is finally worked with dilute oxalic acid solution. The floor is finally polished by floor polishing machine fitted with felt or hessian bobs, till it shines.