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Stone Masonry - General Care and Cautions |
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Though, construction of stone masonry, for all that simplistic look, has some underlying principles for better and quality construction; they are listed below.
- The rock should be sound, attractive, and free of defects, weathering products, dust and organic and greasy matter.
- For more stable configuration, bigger pieces of stone must be used at the bottom of wall, while the smaller ones at the top of wall.
- Dry stones must not be used in masonry. They readily absorb water from mortar, and affect hydration of cement. They should be thoroughly watered or preferably be soaked in water for a few hours before using in masonry.
- Rocks should be arranged in masonry such that the joints or planes of sedimentation / metamorphosis must not be aligned with the line of load acting on the wall.
- Freshly quarried rocks with clean surfaces are better for bonding and strength.
- The thickness of mortar joints in masonry wall must be kept uniform and limited to the least possible (around 1 cm), in both horizontal and vertical directions.
- The mortar to be used for masonry work needs to have good plasticity for better workability. To achieve this, air entraining agents (which cause air bubbles) or plasticisers may be added. The good old lime mortars have these properties but not the strength of cement to withstand modern structures. A special masonry cement, which has both these advantages, may be used for large-scale masonry works.
- The mortar joints in successive rows must not be aligned vertically, to avoid formation of a week plane.
- The facing and backing of masonry wall must be connected with large header or through or bond stones of length equal to the thickness of wall at regular intervals. The horizontal and vertical spacing of such rocks must not be more than 1.5 m and 1.0 m respectively, to arrest splitting tendency of walls.
- When dressed stones are used uniformity of size, unless specifically required, is an important criterion.
- Stones used for ornamental works like wall surfacing must be fine grained.
- In random rubble masonry, where rocks of different sizes and shapes are used, making a compact mass of rocks with minimum quantity of mortar holds key. The skill and judgment of mason in arranging rocks of different shapes and sizes is more important for the strength of wall than the strength of rocks used.
- The arrangement of stones in masonry should be such that there is good interlocking between stones with minimum voids.
- No masonry wall shall be raised for more than a metre in height, in one day. When it reached around two metres of height, it is better to give it a 7 day curing before laying any lintels, beams etc., or continuing to raise it further.
- Plumb line must be checked regularly to ensure the verticality. For battered walls, the specified batter can be ensured by using triangular batter template, along with the plumb bob.
- Joints and junctions of wall shall be properly bonded and be raised at once. If joining of another wall at a later stage is in evitable, teething (protruding rock faces) must be left in the completed wall for full height of wall to be built later.
- Frames of doors and windows must be put in position preferably before completion of wall.
- Sufficient number of holes must be left in masonry, when necessary for supporting scaffolding. They should be properly filled before plastering on both faces finishes.
- The contact surfaces of columns, beams, slabs, old masonry etc., must be chipped, scraped, thoroughly cleaned and watered before laying masonry for proper bonding.
- The stone masonry wall shall be raised almost uniformly along its length, to prevent unequal settlements of foundations. For very long walls, the ends must be left stepped to follow on later, instead of leaving a vertical face.
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