Masonry is the craft of shaping rough pieces of rock into accurate geometrical shapes, at times simple, but some of the considerable complexity, and then arranging the resulting stones, often together with mortar, to form structures. Stone Masonry use all types of natural stone: igneous, metamorphic and sedimentary; while some also use artificial stone as well.
Materials for stone masonry
- Stone should be procured from approved sources. The stones to be used is from boulders or rock quarrying of granite, quartzite, or similar materials having a minimum specific gravity of 2.4. The compression strength is not less than 400 kg/cm2 unless otherwise approved by the Engineer.
- For use in masonry work, the stone should hard, tough compact and durable, free from faults and cleavage.
- Stone masonry is dressed to the size and shape as shown on the Drawings or as required by the Engineer to fit the size of the wall lining or slab in the configuration as shown on the Drawings.
- Special Cement: Special cement should conform to the applicable standards.
- Sand: Sand for mortar used in the construction of stone masonry for walls, lining, paving etc. should be furnished by the Contractor in accordance with the provision of and in complete conformity with the stipulations and requirements for sand specified.
- Water: The water used for the preparation of mortar is free from objectionable quantities for silt, organic matter, alkali, sulfates, and other salts and other impurities, and will be subject to the approval of the Engineer.
- Mortar Composition and Mixing:
- Mortar for stone masonry should, except where otherwise directed by the Engineer, consist of one part Portland cement and three parts of damp loose mortar sand, by volume and sufficient water to produce the proper consistency for the intended use.
- Methods and equipment used for mixing mortar should such as will accurately determine and control an amount of each separate ingredient entering into the mortar and should subject to the approval of the Engineer. If a mixer is used, it is of approved design and the mixing time after all ingredients are in the mixer, except for the full amount of water, is not less than two minutes.
- Mortar is mixed only in quantities sufficient for immediate use, and all mortar not used within 30 minutes after adding water to the mix are discarded. Retempering of mortar is not allowed. Mixing troughs and pans are thoroughly cleaned and washed at the end of each day’s work.
Placing of Stone Masonry
- Stone used in masonry should properly be cleaned before placing and is approved by the Engineer.
- Stone should not be placed during rains sufficiently heavy or prolonged to wash the mortar from the masonry. Mortar already spread which becomes diluted by rain is removed and replaced before continuing with the work. Loads are not allowed on the stone before it is fully set.
- Stone to be used in masonry with mortar joints is moistened with water from three to four hours before they are used, or by a method which should ensure that each stone is thoroughly and uniformly wetted.
- Stone masonry are placed on properly prepared and firm foundations and in accordance with the Drawings or directions of the Engineer. Foundations used is approved by the Engineer before placing the masonry.
- Walls should uncoursed but include a bond stone of at least 0.3 m2 area showing on the exposed face and continuous through the wall for every m2 of the projected face.
- Full mortar coverage is provided on all non-exposed stone faces.
- Stone masonry constructed for a waterway are of the best standards of workmanship and objectionable matters in the masonry surface is removed by and at the expense of the Contractor. The smoothest practicable finished surface of the masonry is required whenever it is a part of a waterway, if not otherwise directed by the Engineer.
Pointing of Stone Masonry
- Where shown on the Drawings or directed by the Engineer, the Contractor should point masonry surfaces. Mortar for pointing, except as otherwise directed by the Employer’s Representative, is of the same composition as used for placing the masonry.
- In preparation of the pointing work, the joints at the exposed surface of stone masonry are raked out (before the mortar is set) or chiseled out. The surface is cleaned by wire brush and is moistened. Subject to the Engineer directions, the pointing is carried out as follows;
- Inside pointing should consist of a filling of joints to about 1 cm average depth from the face of the stone.
- Flat pointing should consist of joints to about 1 cm depth and height flush with the face of the stone.
- Raised pointing should consist of filling of joints to about 1 cm depth and height not less than 1 cm above the face of the stone.
- After raking the joints should be compressed with a printing tool. All tooling of joints should be done after the mortar has partially set but is still sufficiently plastic to bond. Stones with mortar voids visible beyond the depth of the raking is removed and re-laid with fresh mortar unless such voids can be completely filled by other methods as approved by the Engineer.
Curing and Repair
- Stone masonry including pointing is cured by water curing or other acceptable methods as approved by the Engineer.
- When curing by water the stone masonry is kept wet continuously for at least 4 days, unless otherwise specified by the engineer. Water used for curing shall meet the requirements of the specification for water used for mortar.
- If after completion, any stone masonry is out of alignment or not level or does not conform to lines and grades shown on the Drawings, it should be removed and replaced by the Contractor at his expense, unless the Engineer grants permissions in writing to patch or replace part of the defective area to his satisfaction.
Plastering Cement Mortar
The joints of the brickwork or stone should be raked out to a depth of 12 mm (1/2″) and the surface wall is washed and cleaned and kept wet for two days before plastering.
The materials of mortar, cement, and sand specified should be of standard specification. The Materials of mortar is first to dry mixed by measuring with boxes to have the required proportion as specified and then water added slowly and gradually and mixed thoroughly.
The thickness of plastering is as specified usually 12 mm (1/2″) to ensure uniform thickness of plaster. Patches of 5 mm x 15 cm (6″) strip 1 m (3 ft) apart or 10 cm (4″) wide plaster is applied first at about 2 m (6 ft) apart to act as a guide. First mortar is dashed and pressed over the surface and the brought to a smooth and uniform surface by means of float and trowel. Wall plastering should started from the top and worked down towards the floor. Ceiling plastering is completed before starting on wall plaster. All corners and edges are rounded and protected from rain, sun, frost, etc.
Measurement and Payment
- Stone masonry is measured for payment by the cubic meter. Quantities for payment will be computed from the lines and dimension shown on the Drawings.
- Payment for stone masonry is made at the unit price per cubic meter quoted therefore in the Bill of Quantities, which price is full compensation for all costs in connection with stone masonry except that separate payment is made for pointing of the masonry surface where required by the Engineer.
- Pointing of stone masonry surface is measured for payment by the square meter. Quantities for payment is the square meters of overall (gross) wall surface designated by the Engineer to have joint pointing.
- Payment for pointing stone masonry surfaces is made at the unit price per square meter quoted therefore in the Bill of Quantities.