Stones
The stones also used for masonry should be hard , durable , tough , and sound , free from weathering , defects like cavities , cracks , sand holes , injurious veins , patches of loose or soft materials etc. The stones should be obtained only from approved quarry.The stone should be obtained by quarrying large massive rock and not by breaking small size.Boulders having rounded faces.
Rocks from which building stones are obtained , are divided into three groups :1- Igneous rock
2- Sedimentary rocks
3- Metamorphic rocks
1- Igneous rock
It has been formed by agency of heat , the molten material subsequently become soli
ified.The cheif building used in steps , facing work , walls etc.However , it is unsuitable for carving work.It is more suitable for heavy engineering works such as docks , break waters, light houses , masonry bridges and piers.2- Sedimentary rocks
It has been formed chiefly through the agency of water.Most of these have been derived from breaking up of igneous rocks whose particles are conveyed and deposited by stream and accumulated to form thick strata that have been subsequently hardened by pressure.The principles building stones in this group are lime stones and sand stones.Lime stones
They consist of particles of carbonate of lime cemented together by a similar material.These are used in floors , steps and walls.Sand Stones
These are composed of consolidate sand and consist chiefly of grains of quartz united by cementing material. Sand stones is the most widly used building stone for steps , facing work ,columns , walls etc..3 - Metamorphic rocks
These rocks form a group wich embraces either igneous or sedimentary rocks which have been changed from their original form by either pressure , or heat , or both.The common building stones that fall under this category are slates and marbles.Slates easily spilt along natural bedding planes.They are not very suitable for masonry work.They are used for roofing work ,sills damp proof course etc.Marbles can take fine polish.Since they are costly , they are not used for masonry work.These are used for flooring , facing work , steps ,ornamental work etc..Marbles can beeasily sawn and carved.
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