DRESSING OF STONES

Generally the stones obtained after quarrying have a rough surface and are irregular in shape. The process of bringing the stones to a regular shape and required finish is known as dressing. The purposes of dressing are as follows:

1. To set the stones in a regular shape and appearance.
2. To prepare the stones for a suitable site for easy handling and transport.
3. To make hammer-dressed surface, tooled surface, polished surface, rubbed surface or cut-stone surface to suit a particular stone masonry.
4. To secure proper bedding in stone masonry.

Two types of dressing are in use, viz., quarry dressing and site dressing. Quarry dressing is one where the stones are dressed at the quarry and sent to the work site. Site dressing comprises of dressing the stones at the site to the specific size and type. Proper choice depends on the quality of labour at the quarry, distance of the quarry and work site, etc.

2.9 DURABILITY OF STONES

Durability of stones depends on the environment at which they are constructed. For proper durability assurance, it is necessary to know the agencies which deteriorate stones and to take adequate steps to preserve the quality of stone during its lifespan.

2.9.1 Deteriorating Agencies of Stones

Various agencies which are responsible for the deterioration of stones are discussed below.

1. Rain

Rain is one among the main causes for wetness on stones. This wetness is dried by the sun. The process of wetting and drying go a long way in deteriorating the stone. Gases and acids contained in rain water may have damaging effect on stones.

2. Climate

Climate is another factor which causes deterioration. In hot climates there are frequent changes in temperature which result in deterioration. Similarly, stones exposed to cold climate causes freezing of water in the pores resulting in expansion, which causes splitting of the stone. Hence, porous stones should be avoided in cold regions.

3. Wind

Wind laden with grit and dust strikes the stones and causes wear of the stones. Also the impurities in the atmosphere along with moisture penetrate into the pores due to the wind and causes dampness resulting in deterioration.

4. Vegetation Growth

Vegetation growth along the cleavages of joints of stones secretes certain acids by the roots, and thereby cause deterioration. The presence of moisture in roots causes further decay.

5. Chemicals

Chemicals of different kinds move and react due to the usage of different stones such as limestone and sandstone. Such movements of chemicals from one to the other cause deterioration.

6. Living Organisms

Living organisms sometimes cause holes to form in the joints of stones and cause instability to the structure. Further, these holes provide room for the accumulation of moisture and thereby deteriorate the stones.

2.9.2 Preservation of Stones

Preservation of stones is intended to protect the structure against the action of weathering agents and also to protect the good appearance of the face work. The durability of stones increases remarkably if the stones are properly preserved. Preservation is effected in the following ways:

1. Voids existing in the pores are filled properly.
2. Preservation of stones by coating with suitable oils like coal tar, linseed oil, etc.
3. Entry of moisture into the surface of the stones is to be avoided.
4. Stones with carbonate of lime should be discouraged from use in industrial towns.
5. Brick masonry with a combination of limestone and sandstone or magnesium limestone and granular limestone should not be laid close to each other.
6. Building materials which are inactive with stones should be used.
7. Growth of plants on the joints of stones should be prevented.