Code of practice for external facings and veneers, Part I: Stone facing
1967 Edition

The code suggests several methods for attaching stone facings to masonry backing: (1) Mechanical projections on the stone units that embed physically into the backing wall; (2) Masonry bonding or keying where bonding stones or keys interlock the facing with the backing masonry; (3) A combination of both to enhance stability. Installation programming advises avoiding drilling in backing walls except at mortar joints aligned with fixing points. Integral bonding requires at least 15% of the facing area to be bonded stones extending about 10 cm into the backing, contributing structurally to the wall.

For bonded stone facings, the standard mandates that bonded stones constitute a minimum of 15% of the facing surface area and extend at least 10 cm into the backing wall. These stones must be evenly spaced, especially for smaller stone units where spacing should not exceed 60 cm horizontally and vertically. Non-bonded stones are limited to alternate courses or must be firmly secured with cramps rated for at least 180 kg tensile strength. The facing thickness should be a minimum of 9 cm and at least half the stone's height. Bonded facings are constructed simultaneously with the backing wall to ensure structural continuity.

IS 4101 Part 1 specifies metal cramps made from copper alloys containing zinc, tin, nickel, lead, or aluminium due to their high resistance to corrosion in damp environments and chemical attack from mortar or concrete. Stainless steel cramps are also recommended for their excellent corrosion resistance. Aluminium alloy H9 in W condition as per IS 737-1955 is acceptable. Galvanized mild steel is not favored for cramps because of its poor durability in such conditions.

For pointing joints, a mortar mix of cement : lime : sand in the ratio 1 : 2 : 9 is recommended, using crushed stone sand from the same stone as the facing units to ensure compatibility. For jointing large facing units, a 1 : 1 : 6 mix may be used if proven suitable for local exposure, accommodating dimensional changes better. Exposed joints should not exceed 6 mm thickness, while close butt joints should be limited to 1.5 mm. Mortar used for fixing should be free of fillers and chips, and stones must be adequately wetted before placement. Joint finishing often involves square recessed or weathered profiles.

Uniformity in slab size and absence of warping are vital to maintain alignment. Fixing cramps must be accurately positioned and not bent unless designed for such adjustment, as bending compromises strength. Holes in the backing wall might need enlargement for anchorage of load-bearing cramps, and factory-drilled dowel holes may require onsite modification. Joint mortar should be a weak composite (cement:lime:sand = 1:1:5 to 6) with joints between 6 and 12 mm thick. Continuous visual inspection during installation is essential to detect and correct misalignment.