Stone masonry blocks walls
• The drawbacks of random rubble masonry, common in many hilly areas, are the excessive use of stones, mortar and labour, also its non-uniformity and the risk of water penetration. By precasting the stones into uniform concrete blocks these drawbacks are eliminated.
• The technique, developed in India, basically involves steel moulds, a plate vibrator and trowels. A concrete casting platform and the inner surfaces of 4 or 5 battery moulds are oiled. The moulds are arranged side by side on the platform. Into each mould 2 or 3 stones are placed, with the flattest side of each stone resting on the casting platform. Gaps between stones or between stones and mould should be at least 15 mm.
• A concrete mix of 1: 5: 8 (1 cement: 5 sand: 8 graded course aggregate of 10 mm and less) is filled into the moulds, compacted with the plate vibrator, and finished with a trowel. The blocks are demoulded 5 to 10 minutes later (depending on the climatic conditions), water cured for two weeks and kept dry for another two weeks.
• The bottom face with the exposed stone texture forms the external face during construction. The blocks, typically 29 x 19 x 14 cm (l x b x h), are used in conventional masonry construction, permitting single brick thick walls (20 cm) for 3-storeyed buildings. Special blocks with recesses for reinforcement can be used, thus also achieving earthquake resistance Further information: Bibl. 22.01.
The precast stone elements consume slightly more cement in the production and laying of the blocks, than random rubble masonry, but waterproofing is achieved without or with far less plastering. Thinner load-bearing walls are possible and the construction time is greatly reduced. Even earthquake resistance can be achieved, which must be rated higher than the costs of construction.
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