Stone & Brick Masonry

Masonry

Masonry is construction with individual units (stones, bricks, blocks) laid and bound together with mortar. Stone masonry is used for foundations, walls, retaining walls, piers, abutments, dams and architectural facings where good stone is locally available.

Technical terms

Classification of stone masonry

1. Rubble masonry

Stones of irregular sizes and shapes (as obtained from the quarry or roughly dressed) laid in mortar. Economical but lower strength than ashlar.

2. Ashlar masonry

Stones finely dressed to regular shapes and sizes, laid in courses with fine, thin joints (often about 3–6 mm). Strong, attractive, but costly.

3. Composite masonry

A combination of different masonry types or materials — e.g. stone facing with brick backing, stone and concrete — for economy and appearance while using cheaper backing.

General principles of construction

1. Use hard, durable, well-seasoned stones free from defects; wet stones before laying to avoid absorbing water from mortar.
2. Lay stones on their natural bed (bed perpendicular to the pressure); in arches the bed is radial; in cornices vertical.
3. Provide through (bond) stones at regular intervals (commonly about 1.5–2 m apart in each course and at every course or alternate courses in height) or headers overlapping from both faces where full-length stones are not available.
4. Break (stagger) vertical joints in successive courses — avoid continuous vertical joints.
5. Face stones should tail well into the wall (length into the wall at least equal to height); hearting solidly filled with stones, spalls and mortar — no hollow spaces.
6. Use the largest stones in the lower courses, at corners (quoins) and jambs.
7. Use mortar of suitable proportion (commonly cement mortar 1 : 6 for rubble work); joints fully filled.
8. Raise walls uniformly throughout their length — limit the height raised in a day; stagger (rack back) junctions for later work.
9. Keep walls plumb and courses level; check with plumb bob and spirit level.
10. Cure masonry by keeping it wet (commonly at least 7 days for cement mortar).
11. Protect fresh work from rain, frost and hot sun.
12. Provide weathering and throating on projecting courses; coping on parapets.

Tools used in stone masonry

Trowel, spirit level, plumb bob and plumb rule, straight edge, square, mason's line, mallet and hammers (spalling hammer, club hammer), chisels (pitching tool, punch, point, claw tool, drafting chisel, boaster), scutch, gauges and templates.

Joints in stonework

Stone masonry compared with brick masonry

Quantity estimation

Stone masonry is measured in cubic metres (m³). For rubble masonry, quantities of stone and mortar per m³ of masonry are taken from standard data of the relevant schedule of rates — for rough estimates, rubble masonry is often assumed to need about 0.3–0.35 m³ of wet mortar per m³ of masonry, with the remainder stone (allowing for voids in stacked stone).

Worked examples

Frequently tested points

• Header — length across wall; stretcher — length along face; through (bond) stone — full thickness.
• Quoins at corners; corbel projects to support loads; coping on top of walls; throating drips water off.
• Hearting fills the interior; spalls fill gaps in rubble.
• Rubble masonry: uncoursed random, coursed random, squared rubble (uncoursed/coursed/regular coursed), polygonal, flint, dry rubble (retaining walls on hill roads).
• Ashlar masonry: finely dressed stones, thin joints — ashlar fine, rough tooled, rock/quarry faced, chamfered; block-in-course intermediate.
• Principles: natural bed, through stones at intervals, staggered joints, solid hearting, largest stones at bottom and corners, uniform raising, curing.
• Joints: rebated, tongue and groove, cramped (metal cramps), dowelled, joggled.
• Stone masonry — stronger, more durable, heavier, thicker walls, more skill; brick masonry — faster, thinner walls, easier alterations.

Terms in brickwork

Rules for bonding

Bond is the arrangement of bricks in successive courses so that vertical joints do not coincide, distributing loads and binding the wall together.

1. Bricks should be of uniform size; length about twice the width plus one joint.
2. Lap should be at least one-quarter brick along the length of the wall and half a brick across the thickness.
3. No continuous vertical joints in the face or within the thickness.
4. Stretchers are used mainly on the faces; the hearting should be filled with headers as far as possible.
5. Minimum use of bats; closers are placed next to quoin headers to develop lap.
6. Vertical joints in alternate courses should be in the same vertical line (perpends).
7. Each alternate header should be centrally placed over the stretcher below (in appropriate bonds).

Types of bonds

English bond versus Flemish bond

Construction practice and precautions

1. Use good-quality bricks (well burnt, uniform); soak bricks in water before use (to prevent absorption of water from mortar) but lay them surface-dry.
2. Lay bricks with frogs upward on a full bed of mortar; fill all vertical joints ("buttering").
3. Keep mortar joints uniform — commonly about 10 mm.
4. Build walls plumb and courses level using a mason's line, spirit level and plumb bob; check with a straight edge.
5. Raise the wall uniformly along its length; limit the height built in a day (commonly about 1 m or less) to allow mortar to gain strength; use racking back rather than toothing at junctions where possible.
6. Break joints according to the bond; use closers at quoins; avoid excessive use of bats.
7. Cure brickwork by keeping it moist (commonly at least 7 days for cement mortar).
8. Rake joints (about 10–12 mm deep) while mortar is green if the wall is to be plastered or pointed.
9. Provide holdfasts for door and window frames, and bond walls at junctions.
10. Protect fresh work from rain, hot sun and frost; do not load newly built walls prematurely.
11. Leave scaffolding holes only as permitted and fill them afterwards.

Reinforced brick masonry and brick nogging

• Reinforced brick masonry (RBM) — steel bars or hoop iron embedded in mortar joints or grouted cores to resist tension, shear and seismic forces — lintels, slabs (reinforced brick concrete), walls in earthquake zones.
• Half-brick walls (partitions) are often strengthened with hoop iron or reinforcement in every third or fourth course.
• Brick nogging — brickwork filling a framework of timber or concrete posts and rails (panel walls).
• Earthquake-resistant masonry — horizontal RCC bands (plinth, lintel, roof bands) and vertical reinforcement at corners and junctions as per IS 4326.

Strength of brickwork

The strength of brick masonry depends on:

• Compressive strength of bricks and mortar grade (masonry strength is less than brick strength).
• Workmanship — filling of joints, joint thickness (thicker joints reduce strength), wetting of bricks, bond.
• Slenderness ratio of walls and columns — effective height (or length) ÷ effective thickness; higher slenderness reduces permissible stress (stress reduction factor).
• Eccentricity of loading.
• Shape and size of units.

IS 1905 (Code of practice for structural use of unreinforced masonry) gives basic compressive stresses for masonry based on unit strength and mortar type, stress reduction factors for slenderness and eccentricity, area reduction factors, limits on slenderness ratio (commonly up to about 27 for walls in cement or cement–lime mortar), and minimum wall thicknesses.

Defects in brick masonry

Quantity of bricks and mortar

Worked examples

Frequently tested points

• Stretcher — length along face; header — length across wall; lap ≥ ¼ brick; perpends aligned in alternate courses.
• Queen closer — half width (cut lengthwise); king closer — one corner cut; bats cut across width.
• Racking back preferred over toothing.
• Stretcher bond — half-brick walls; header bond — curved walls and footings; English bond — alternate header and stretcher courses, strongest; Flemish bond — headers and stretchers alternate in each course, better appearance.
• Garden wall bonds: 1 header course (or header) per 3–5 stretchers.
• Raking bond (diagonal, herring-bone) for thick walls; stack bond non-load-bearing.
• Practice: soak bricks, frog up, 10 mm joints, raise uniformly (≈ 1 m/day), cure ≥ 7 days, rake joints for plaster.
• Half-brick partitions with hoop iron every few courses; RCC bands for earthquake resistance (IS 4326).
• IS 1905: masonry strength depends on unit strength, mortar, slenderness and eccentricity; slenderness limit about 27.
• Defects: efflorescence, sulphate attack, cracking, dampness.
• Modular bricks: 500 per m³; wet mortar about 0.25–0.30 m³ per m³.