Handbook on Masonry Design and Construction
1991 Edition

The handbook recommends several masonry units: Common burnt clay bricks for general use with compressive strength from 3.5 to 35 N/mm² (IS 1077:1976), heavy-duty bricks (engineering bricks) for structural works with strength ≥ 40 N/mm² (IS 2180:1970), perforated and hollow clay bricks offering lighter weight and improved insulation (IS 2222:1979, IS 3952:1978), sand-lime bricks for areas lacking bricks or stones (IS 4139:1976), and concrete blocks for economical multi-storey construction (IS 2185 Part 1:1979). Stones such as granite, basalt, sandstone, and limestone are covered under IS 1597 parts 1 and 2, with granite favored for durability. Laterite stone blocks (IS 3620:1979) and precast stone blocks (refer to CBRI notes) are also included. Selection depends on availability, compressive strength, durability, cost, and ease of construction.

Mortar selection depends on strength needs, exposure conditions, and type of masonry units. Cement mortars typically range from 1:3 to 1:8 cement-to-sand ratios, with richer mixes prone to shrinkage and leaner mixes being harsh. Lime mortars use lime-to-sand or pozzolana ratios of 1:2 to 1:3, offering good workability and low shrinkage but slower strength gain. Cement-lime mortars combine cement, lime, and sand in ratios like 1:1:6 or 1:2:9 to balance strength and workability. Exposure dictates use of hydraulic lime or cement-lime mortars for durability. Recommended mixes vary by location and load, for example, foundation masonry may use richer mixes while internal walls use leaner ones. Mortar retempering is allowed once within time limits depending on mortar type.

Design must address the effects of load eccentricity and wall slenderness, as eccentric loading increases buckling risk and reduces load capacity. The handbook introduces a Stress Reduction Factor (ks) to account for combined eccentricities, with maximum combined eccentricity occurring around 60% of wall height. For eccentricity-to-thickness ratios (e/t) up to 1/24, only axial compression is considered with allowable stress up to 1.25 times masonry compressive strength. Between 1/24 and 1/6, bending stresses are included without tension. Above 1/6, tension may occur on one side, so the effective compression area is reduced and eccentricity limited practically to t/3. These considerations ensure safe and economical design.

The handbook advises constructing masonry arches by building symmetrically from both ends, inserting the keystone last at the center. Skew backs must be precisely cut to ensure radial bearing of end voussoirs, and any defects should not be patched with mortar. The arch should be kept moist during construction to prevent premature setting, using slow-setting mortar to enhance bonding. For multiple adjacent arches, keystones are inserted only after adjacent arches have reached at least 25% completion to counteract side thrust. Dome construction techniques resemble those for arches but are less extensively covered due to their infrequent use.

To mitigate cracking and moisture issues, the handbook recommends using masonry units complying with standards and curing concrete blocks for at least 28 days to allow initial shrinkage. Control of drying shrinkage, thermal movements, differential strains, and foundation settlement is essential. Proper handling, storage, moistening before laying, and use of suitable mortar with adequate curing and finishing are critical. Good workmanship includes correct mortar mixing, controlling brick suction rate (~2 kg/min/m²), avoiding thick or uneven joints, and preventing disturbance after laying. Walls exposed to moderate or severe conditions should be plastered on both sides, preferably with cement-lime or lime mortar for enhanced resistance. Filling joints fully and designing walls according to exposure severity further improve durability.