Where durable natural stone is not available at reasonable cost, artificial stone, also known as cast stone becomes the choice. Artificial stone is made with cement and natural aggregates of the crushed stone and sand with desired surface finish. Suitable colouring pigments may be added. However, colouring should not exceed 15% by volume. Cement and aggregates are mixed in proportion of 1:3. Artificial stone can be moulded into the most intricate forms, cast into any size, reinforced to have higher strength, are most suitable for face work, grooves, rebates, etc., can be cast easily and are economical. Some of the artificial stones available are as follows.
1) Concrete Blocks
These are cast at site in the construction of piers or cast in moulds for steps, window sills, etc.
2) Ransom Stones
These are prepared by mixing soda silicate with cement to provide decorative flooring. These are also known as chemical stones. These have compressive strength of about 32 N/mm2.
3) Victoria Stones
These are granite pieces with the surfaces hardened by keeping immersed in soda silicate for about two months.
4) Bituminous Stones
Granite and diorite are impregnated with prepared or refined tar to form bituminous stone. These are used for providing noise, wear and dust resistant stone surfaces.
5) Imperial Stones
Finely crushed granite is washed carefully and mixed with Portland cement. The mix is moulded in desired shape and then steam cured for 24 hours. The cured blocks are immersed in silicate tanks for three days. These stones are similar to Victoria stones.
6) Artificial Marbles
It can be either pre-cast or cast-in-situ. These are made from portland gypsum cement and sand. In the precast variety, the cast-stone is removed after three days. On the fifth day of casting these are treated with a solution, liquid fluorite of magnesia. It is then washed and wrapped in paper for 24 hours and then once again treated with the liquid. After one month the stone is polished by rubbing emery over the surface with a linen rag ball dipped in mixture of lime water and silicate of potash and then the process is repeated without emery. It is used for external works. Cast-in-situ variety is made by laying the mix on canvas, in thickness about 1.5 mm more than the required thickness of the stone. The surface is rubbed over and the air holes are filled with mix. Grinding is done by hand or machine. The surface is then rubbed with a polishing stone. Final rubbing is done with a ball of wool moistened with alum water dipped into a 1:3 mix of hartshorn powder and diatomite.
7) Garlic Stone
It is produced by moulding a mixture of iron slag and portland cement. These are used as flag stones, surface drains, etc.
0 comments:
Post a Comment