Qualities / properties of good building stones

QUALITIES / PROPERTIES OF GOOD BUILDING STONES

1. Structure

Stone should be homogeneous and crystalline in structure. The finer the crystalline texture, the stronger is the stone. Surface of a freshly broken stone should be sharp, clean and bright.

2. Appearance

Appearance is important for face work of structures. The stone should be of uniform colour in appearance. Light coloured stones resist weathering action in a better way than darker ones. Also, the stone should be free from cracks, cavities, flaws or patches of material.

3. Hardness and Toughness

The building stone should be hard and tough to withstand rough weather. If the stone is used in road work, it should be hard enough to resist wear and tear as in pavements, etc.

4. Weight

Whether a heavier or a lighter variety is to be used for a structure depends on the nature of the structure and the stresses it has to withstand.

5. Crushing Strength or Compressive Strength

It depends upon density. Stones of igneous origin are stronger than sedimentary. In structures like arches, dams, etc., the stones should be tested for compressive strength.

6. Ease of Working

The stone should be easily workable i.e., should be easily cut, carved and dressed. Soft stones like limestone and sandstone are easier to work into carvings than hard granite.

7. Porosity

It depends upon the voids. The less porous a stone is the less moisture it can absorb. It is more useful for building purposes. Porous stones are destroyed by disintegration and decomposition.

8. Water Absorption

A good stone should not absorb water more than 0.6% by weight after one day's immersion.

9. Durability

Durability is the power of resisting atmospheric influences like smoke and atmospheric acids polluting the air in industrial areas. Durability depends on the chemical composition, physical structure and resistance to weathering.

10. Weathering

Weathering is the disintegration produced by physical changes and the decomposition produced by chemical changes at the surface of the stone by atmospheric agencies. Variations of temperature, mechanical abrasion due to wind, frost, etc., are the physical agents while hydration, oxidation and carbonation are the chemical agents.

11. Acid Resistant:

A good stone should be acid-resistant.

12. Resistance to Fire

Fire causes the destruction of stones due to (i) different coefficients of linear expansion of the constituent minerals and (ii) poor heat conductivity of stone.