Mortars & Masonry works

Stone masonry is the construction of walls with stones bonded with mortar, or sometimes dry. It is classified into rubble masonry and ashlar masonry.

1. Rubble masonry

Stones are rough, roughly shaped, with irregular faces.

• Random rubble: Stones of irregular shape and size, as obtained from the quarry. Two types: uncoursed (no regular courses; cheapest) and coursed (levelled at 300 to 600 mm intervals).
• Square-snecked rubble: Roughly squared stones of different heights, with small stones (snecks) in the gaps.
• Coursed rubble (first, second, third sort): Stones roughly hammer-dressed, laid in courses of equal height. First sort: stones are dressed, height 150 to 300 mm; second and third sorts are less regular.
• Dry rubble: Without mortar; for boundary walls and retaining walls.
• Polygonal rubble: Stone faces dressed to irregular polygon shapes, joints at several angles.
• Flint rubble: Flint stones.

2. Ashlar masonry

Stones are finely dressed, with all faces and joints chisel-dressed to uniform sizes, laid with thin joints (3 mm).

• Ashlar fine: Very fine, with joints about 3 mm; best finish.
• Ashlar rough-tooled: Faces roughly tooled.
• Ashlar rock-faced (quarry-faced): Face left rough with a chisel-drafted margin.
• Ashlar chamfered: Edges chamfered at 45°.
• Ashlar block-in-course: Stones of different sizes arranged in courses.

 Random rubble        Coursed rubble        Ashlar
  _/\_  __           |____|__|____|        |____|____|
 |  \/_|__|          |__|____|__|_|        |____|____|
 (irregular)         (courses levelled)     (fine joints)

Comparison

Typical rules: through stones at 1.5 m intervals, wall thickness at least 350 mm, and good bonding with 1:6 cement-sand or mud mortar.

Mortar is a paste of binding material (cement, lime or mud), fine aggregate (sand) and water, used to join bricks or stones, and for plastering and pointing. A good mortar should have the following properties.

1. Workability: It should be easily mixed, spread, and applied without segregation; it should stay plastic long enough for placing.
2. Adhesion (bond strength): Good bond with bricks, stones and the surfaces.
3. Strength: Sufficient compressive strength to carry the load of masonry. Cement mortar 1:4 has 7 to 8 N/mm² at 28 days (IS 2250).
4. Durability: Resists weather, moisture, frost and chemicals.
5. Water retentivity: It should not lose water rapidly to dry bricks; this keeps the hydration complete.
6. Setting time and hardening: Initial set not before 30 minutes (cement); it should harden at a suitable rate.
7. Imperviousness: Low permeability so that water does not enter the wall.
8. Fire resistance.
9. Low shrinkage and cracking.
10. Economy, and good appearance of the joints.
11. Proper fineness of sand (graded, free of clay, silt, organic matter).

A cavity wall is a wall made of two separate leaves (skins) of masonry, usually brick or block, separated by a continuous air space (cavity) of 50 to 100 mm, tied together by metal ties.

Construction

• Outer leaf (103 or 115 mm) takes weather; inner leaf (100 to 230 mm) carries the load.
• Cavity width: 50 to 75 mm (normally up to 100 mm).
• Wall ties: Galvanised steel or stainless steel ties (vertical twist, butterfly or fish-tail type) placed at 900 mm horizontally and 450 mm vertically, staggered, with a slope downward to the outer leaf; with drip.
• DPC: Placed at the base, at openings and below the top of the wall, with a flashing, so water in the cavity is thrown out; weep holes at 1 m centres in the outer leaf at the bottom.
• Cavity is kept clean, and it is closed at the eaves, openings and top by a ring beam or a solid closer.
• Insulation can be fitted in the cavity.

 Horizontal section:           Vertical section:
 |outer|  cavity  |inner|        roof slab
 |_____|<-50mm->|_____|         |  |   |  |
   tie ------------ tie         |  |   |  |
                                ==DPC====(weep hole)
                              plinth

Merits

1. Prevents rain penetration and dampness.
2. Good thermal insulation (cool in summer, warm in winter).
3. Good sound insulation.
4. Prevents the formation of efflorescence, and saves on material in outer leaf (fine brick).
5. Light structure with the same stability.

Demerits

1. Costlier than the solid wall, by about 20 %.
2. Needs skilled work and supervision; mortar droppings can bridge the cavity.
3. Takes more time.
4. Ties can transfer moisture if badly placed.
5. Needs extra DPC and details at openings.

Manual mixing of cement mortar is done for small works, when a mixer is not available. For a 1:6 cement-sand mortar (1 part cement to 6 parts sand by volume), the steps are as follows.

Materials and tools

Cement (OPC 43 grade), clean river sand (passing a 4.75 mm sieve, free from silt and organic matter), clean water; a watertight platform (masonry or steel sheet, 3 m × 3 m), shovels, trowels, a gauge box, buckets.

Procedure

1. Measure the sand: Measure the volume of sand with a gauge box (e.g. 6 boxes for 1 bag of cement; 1 bag of 50 kg = 0.035 m³).
2. Spread the sand: Sand is spread in a uniform layer, 150 to 200 mm thick on a clean, hard platform.
3. Add cement: The cement is spread evenly over the sand.
4. Dry mixing: The sand and cement are mixed with shovels by turning the heap over at least 3 times, until the mix is of a uniform colour.
5. Making a crater: The dry mix is made into a ring with a hollow at the centre.
6. Adding water: Water is added slowly in the centre (about 20 to 25 % by weight of the dry mix, to get a workable consistency), without letting it escape.
7. Wet mixing: The mix is turned and re-mixed 3 to 4 times with a shovel until it is uniform and has the correct consistency.
8. Use: The mortar is used within 30 minutes of mixing (before the initial setting). Hardened mortar must not be re-tempered. Unused mortar is discarded.
9. Cleaning: The platform and tools are cleaned after use.
10. Curing: The finished work is cured for at least 7 days.

 1. sand layer   2. + cement   3. dry mix
 ~~~~~~~~~~~~~   ===========   (turn x3)
 4. crater -> add water -> turn x3-4 -> mortar

Brick masonry is the construction of walls from bricks bonded with mortar. A typical specification (as per Nepal Standard and IS 2212) is:

Materials

• Bricks: First-class, well burnt, uniform in colour, shape and size (traditional Nepali brick 230 × 110 × 55 mm; IS standard 190 × 90 × 90 mm), with compressive strength not below 3.5 N/mm² (NS 1:2060: 7.0 for class A); water absorption not more than 20 %; free from cracks, lime and soluble salts.
• Mortar: Cement-sand 1:4 to 1:6 (as in the drawing) for ordinary work; sand clean and graded, passing a 2.36 mm sieve; water clean.

Workmanship

1. Bricks are soaked in clean water for at least 2 hours (until the bubbles stop) before use.
2. Bricks are laid in English bond or Flemish bond in full mortar bed, with frogs upward; vertical joints are filled completely, and stretcher and header joints are broken (no vertical alignment); the minimum overlap is a quarter of the brick.
3. Joint thickness: 10 mm (not more than 12 mm and not less than 6 mm); joints are raked to a depth of 10 to 15 mm for plastering or pointing.
4. Work is carried up evenly in all parts; the maximum height of a day's work is 1.0 to 1.5 m; the wall is kept plumb and level by plumb bob, spirit level and string line.
5. Toothing of 150 mm is left at the end of a day; the junction of walls is made with proper bond.
6. A wall is kept wet by sprinkling water and cured for 7 to 10 days; it should be protected from rain and sun.
7. DPC at plinth level; lintels and sill bands as designed; no chasing after completion.

Measurement and payment

Measured in cubic metres (m³), with deductions for openings; the rate includes materials, labour, scaffolding and curing.

Random rubble masonry

Stones of irregular shape and size, as obtained from the quarry, are laid without courses; small stones fill the gaps.

• Uncoursed random rubble: stones used as they come, roughly shaped with a hammer; bond stones (through stones) every 1.5 m² of wall.
• Coursed random rubble: work is levelled at about every 300-350 mm height to form rough courses.
• Joints are irregular, mortar 1:6 (cement-sand) or mud/lime mortar; thickness of wall at least 400 mm.
• Cheap, suitable for foundations, boundary and retaining walls in hilly areas of Nepal.

   ____ ___ _____ __
  /    \   \     \  \   irregular stones,
 /__ ___\___\_____\__\  no regular courses
 \  /   /  / \    /
  \/___/__/___\__/

Coursed rubble masonry

Stones are roughly dressed and laid in courses of equal height in each course; height of courses may differ from course to course.

• First sort: face stones squared with hammer, courses 150-300 mm high, joints thin (about 10 mm); all courses levelled.
• Second sort: stones roughly dressed, joints thicker; courses not so regular.
• Third sort: stones hammer-dressed lightly, used for ordinary walls.
• Bond stones 1 per m² of face and quoin stones at corners; stronger and neater than random rubble.

 +------+---+-----+--+   course 1 (h1)
 +--+-------+----+---+   course 2 (h2)
 +-----+-----+--+-----+   course 3 (h3)

Ashlar masonry

Stones are finely dressed to exact rectangular blocks with fine joints (3-6 mm) and laid in regular courses; it is the best and costliest stone masonry.

• Ashlar fine: every face chisel-dressed, joints 3 mm; used for monumental buildings.
• Ashlar rough-tooled: faces roughly tooled, joints up to 6 mm.
• Ashlar rock-faced (quarry-faced): face left rough with a dressed margin around.
• Ashlar chamfered: edges chamfered at 45 degrees, giving a V-joint.
• Block-in-course: blocks of equal height dressed; backing of rubble.

 +------+------+------+
 +---+------+------+--+   regular courses,
 +------+------+------+   thin joints

A retaining wall is a structure built to hold back (retain) earth, water or other filling at a level difference, preventing it from sliding or collapsing; it is used for hill roads, terraces, basements, bridge abutments and embankments.

Types

• Gravity wall: stone, brick or plain concrete; resists by its own weight.
• Cantilever wall: RCC stem and base slab; weight of soil on the heel helps stability.
• Counterfort wall: RCC wall with vertical ribs (counterforts) at 2.5-3.5 m behind the stem; for height above 6 m.
• Buttress wall: like counterfort but the ribs are in front.

Forces acting on a retaining wall

1. Self weight $W$ of the wall (and weight of soil on the heel), acting at the centroid, downward.
2. Active earth pressure $P_a$ from the retained soil, acting horizontally at $H/3$ from the base:

$$P_a = \tfrac{1}{2} K_a \gamma H^2, \quad K_a = \frac{1-\sin\phi}{1+\sin\phi}$$

3. Surcharge load on the backfill, which adds pressure $K_a q H$.
4. Water pressure if the backfill is saturated (reduced by weep holes and drains).
5. Passive resistance of soil in front of the toe (generally neglected or reduced).
6. Base reaction (bearing pressure) and friction at the base, which resist sliding.

        backfill
   ---------------+
        |         |  <- surcharge q
        |  wall   |
   P_a->|  (W)    |
        |_________|
      toe  heel
        base reaction

Stability checks

• Overturning: $FS = M_R/M_O \ge 1.5$ (2 for gravity wall).
• Sliding: $FS = \mu \Sigma W / P_a \ge 1.5$.
• Bearing pressure within safe bearing capacity, no tension at base (resultant within middle third).

Weep holes (100 mm at 2-3 m c/c) and a granular filter behind the wall drain the backfill.

Given: plastering area $= 100\ \text{m}^2$; thickness $= 12$ mm; mix 1:6 (cement : sand).

Step 1: Wet volume of mortar

$$100 \times 0.012 = 1.2\ \text{m}^3$$

Step 2: Dry volume (add 27% for dry bulk, voids in sand and wastage)

$$1.2 \times 1.27 = 1.524\ \text{m}^3$$

Step 3: Cement and sand (sum of ratio $= 7$)

$$\text{Cement} = \frac{1.524}{7} = 0.218\ \text{m}^3 \approx 6.3\ \text{bags (0.0347 m}^3\text{ per bag)}$$ $$\text{Sand} = \frac{6}{7} \times 1.524 = 1.306\ \text{m}^3$$

Answer: Cement = 0.218 m³ (about 6.3 bags of 50 kg = 314 kg); sand = 1.306 m³.

Given: plastering area $= 200\ \text{m}^2$; thickness $= 10$ mm; mix 1:5 (cement : sand).

Step 1: Wet volume of mortar

$$200 \times 0.01 = 2\ \text{m}^3$$

Step 2: Dry volume (add 27% for dry bulk, voids in sand and wastage)

$$2 \times 1.27 = 2.54\ \text{m}^3$$

Step 3: Cement and sand (sum of ratio $= 6$)

$$\text{Cement} = \frac{2.54}{6} = 0.423\ \text{m}^3 \approx 12.2\ \text{bags (0.0347 m}^3\text{ per bag)}$$ $$\text{Sand} = \frac{5}{6} \times 2.54 = 2.117\ \text{m}^3$$

Answer: Cement = 0.423 m³ (about 12.2 bags of 50 kg = 610 kg); sand = 2.117 m³.

Mortar is a workable paste obtained by mixing a binding material (cement, lime or clay) and a fine aggregate (sand, surkhi or cinder) with water in a fixed proportion. It is used to bind bricks or stones in masonry, to fill joints and to make plaster, pointing and flooring finishes. It hardens with time and gives strength and stability to the masonry.

Examples: cement mortar (1:4, 1:6), lime mortar, cement-lime (gauged) mortar and mud mortar.

Functions of mortar

1. Binds bricks or stones together into a single unit.
2. Spreads the load evenly over the bedding of units.
3. Fills the gaps between units, so wind and rain cannot enter.
4. Gives a level bed so that the masonry is straight and plumb.
5. Provides decorative effect in plaster and pointing, and protects the wall surface.
6. Takes up small movements and gives bond strength.

Properties of good mortar

• Workability: easy to mix and spread, remains plastic long enough to lay the unit.
• Water retentivity: keeps water long enough, so bricks do not suck it out.
• Adhesion: good bond to bricks/stones.
• Strength: adequate compressive strength (cement mortar 1:4 about 5 N/mm² at 28 days).
• Durability: resists weather and chemical attack.
• Setting: should set neither too fast nor too slow.
• Low shrinkage: no cracks on drying.
• Impermeability and cheapness.

Given: brickwork volume $= 10\ \text{m}^3$; brick size 57 mm x 115 mm x 240 mm (nominal, without mortar); mortar joint $= 10$ mm; mortar 1:4 (cement : sand).

Step 1: Size of brick with mortar

$$(0.25 \times 0.125 \times 0.067) = 0.002094\ \text{m}^3$$

Step 2: Number of bricks

$$N = \frac{10}{0.002094} = 4776.1 \approx 4777\ \text{bricks}$$

Step 3: Volume of bricks without mortar

$$4777 \times 0.24 \times 0.115 \times 0.057 = 7.515\ \text{m}^3$$

Step 4: Wet volume of mortar

$$10 - 7.515 = 2.485\ \text{m}^3$$

Step 5: Dry volume of mortar (add 27% for dry bulk, voids in sand, wastage and shrinkage)

$$2.485 \times 1.27 = 3.156\ \text{m}^3$$

Step 6: Cement and sand for 1:4 (sum of ratio $= 5$)

$$\text{Cement} = \frac{1}{5} \times 3.156 = 0.631\ \text{m}^3 = 909\ \text{kg} \approx 18.2\ \text{bags (50 kg, 0.0347 m}^3\text{ each)}$$ $$\text{Sand} = \frac{4}{5} \times 3.156 = 2.525\ \text{m}^3$$

Answer: Mortar required for 10 m³ brickwork = 2.48 m³ (wet) or 3.16 m³ (dry); this needs about 0.631 m³ cement (18.2 bags) and 2.52 m³ sand; bricks = 4777 nos.

Given: brickwork volume $= 10\ \text{m}^3$; brick size 57 mm x 115 mm x 240 mm (nominal, without mortar); mortar joint $= 10$ mm; mortar 1:6 (cement : sand).

Step 1: Size of brick with mortar

$$(0.25 \times 0.125 \times 0.067) = 0.002094\ \text{m}^3$$

Step 2: Number of bricks

$$N = \frac{10}{0.002094} = 4776.1 \approx 4777\ \text{bricks}$$

Step 3: Volume of bricks without mortar

$$4777 \times 0.24 \times 0.115 \times 0.057 = 7.515\ \text{m}^3$$

Step 4: Wet volume of mortar

$$10 - 7.515 = 2.485\ \text{m}^3$$

Step 5: Dry volume of mortar (add 27% for dry bulk, voids in sand, wastage and shrinkage)

$$2.485 \times 1.27 = 3.156\ \text{m}^3$$

Step 6: Cement and sand for 1:6 (sum of ratio $= 7$)

$$\text{Cement} = \frac{1}{7} \times 3.156 = 0.451\ \text{m}^3 = 649\ \text{kg} \approx 13\ \text{bags (50 kg, 0.0347 m}^3\text{ each)}$$ $$\text{Sand} = \frac{6}{7} \times 3.156 = 2.705\ \text{m}^3$$

Answer: Bricks = 4777 nos.; cement = 0.451 m³ (about 13 bags); sand = 2.7 m³.

Faces of a brick

A brick (standard 240 x 115 x 57 mm) has the following faces and parts:

• Stretcher (side) face: longest vertical face, 240 x 57 mm, shows in a stretcher course.
• Header (end) face: the small end face, 115 x 57 mm, shows in a header course.
• Bed (top / bottom) face: the horizontal face, 240 x 115 mm, on which mortar is spread.
• Frog: a depression (about 10 mm deep) in the top bed which holds mortar.
• Arris: the edge where two faces meet.

           240 (length)
      +----------------+
     /|               /|
    / |  top (bed)    / |  57
   +----------------+  |  (height)
   |  | header face |  |
   |  +-------------|--+
   | /  stretcher   | /  115 (width)
   +----------------+

Mortar for 1.5 m³ brickwork in 1:4

Given: brickwork volume $= 1.5\ \text{m}^3$; brick size 57 mm x 115 mm x 240 mm (nominal, without mortar); mortar joint $= 10$ mm; mortar 1:4 (cement : sand).

Step 1: Size of brick with mortar

$$(0.25 \times 0.125 \times 0.067) = 0.002094\ \text{m}^3$$

Step 2: Number of bricks

$$N = \frac{1.5}{0.002094} = 716.4 \approx 717\ \text{bricks}$$

Step 3: Volume of bricks without mortar

$$717 \times 0.24 \times 0.115 \times 0.057 = 1.128\ \text{m}^3$$

Step 4: Wet volume of mortar

$$1.5 - 1.128 = 0.372\ \text{m}^3$$

Step 5: Dry volume of mortar (add 27% for dry bulk, voids in sand, wastage and shrinkage)

$$0.372 \times 1.27 = 0.472\ \text{m}^3$$

Step 6: Cement and sand for 1:4 (sum of ratio $= 5$)

$$\text{Cement} = \frac{1}{5} \times 0.472 = 0.094\ \text{m}^3 = 136\ \text{kg} \approx 2.7\ \text{bags (50 kg, 0.0347 m}^3\text{ each)}$$ $$\text{Sand} = \frac{4}{5} \times 0.472 = 0.378\ \text{m}^3$$

Answer: Mortar = 0.372 m³ (wet), 0.472 m³ (dry); cement 0.094 m³ and sand 0.378 m³; bricks = 717 nos.

First class brickwork in 1:6 cement-sand mortar

First class brickwork is masonry built with first class bricks (well burnt, uniform in size, shape and colour, free from cracks, crushing strength not less than about 10 N/mm² and water absorption not more than 15-20%), laid in cement sand mortar 1:6 with a proper bond (English/Flemish), joints of 10 mm thickness, full mortar beds, vertical joints staggered, bricks soaked before laying, and the wall kept wet for curing for at least 7 days. It is used for important walls of buildings.

Materials for 10 cum (10 m³) brickwork except bricks

Given: brickwork volume $= 10\ \text{m}^3$; brick size 57 mm x 115 mm x 240 mm (nominal, without mortar); mortar joint $= 10$ mm; mortar 1:6 (cement : sand).

Step 1: Size of brick with mortar

$$(0.25 \times 0.125 \times 0.067) = 0.002094\ \text{m}^3$$

Step 2: Number of bricks

$$N = \frac{10}{0.002094} = 4776.1 \approx 4777\ \text{bricks}$$

Step 3: Volume of bricks without mortar

$$4777 \times 0.24 \times 0.115 \times 0.057 = 7.515\ \text{m}^3$$

Step 4: Wet volume of mortar

$$10 - 7.515 = 2.485\ \text{m}^3$$

Step 5: Dry volume of mortar (add 27% for dry bulk, voids in sand, wastage and shrinkage)

$$2.485 \times 1.27 = 3.156\ \text{m}^3$$

Step 6: Cement and sand for 1:6 (sum of ratio $= 7$)

$$\text{Cement} = \frac{1}{7} \times 3.156 = 0.451\ \text{m}^3 = 649\ \text{kg} \approx 13\ \text{bags (50 kg, 0.0347 m}^3\text{ each)}$$ $$\text{Sand} = \frac{6}{7} \times 3.156 = 2.705\ \text{m}^3$$

Answer: Cement = 0.451 m³ (about 13 bags of 50 kg); sand = 2.7 m³.

Properties of mortar

1. Workability: easy to mix, spread and lay without segregation.
2. Water retentivity: holds sufficient water, so bricks do not absorb it quickly.
3. Adhesion and bond strength with brick/stone.
4. Strength: adequate compressive strength (1:4 cement mortar $\approx$ 5 N/mm²).
5. Durability: resists weather, frost and chemicals.
6. Proper setting time and low shrinkage.
7. Impermeable and economical.

Cement and sand for 10 cum brickwork

Assumptions: brick 240 x 115 x 57 mm (nominal), 10 mm joints, mortar 1:4 (cement : sand), dry volume = 1.27 x wet volume.

Given: brickwork volume $= 10\ \text{m}^3$; brick size 57 mm x 115 mm x 240 mm (nominal, without mortar); mortar joint $= 10$ mm; mortar 1:4 (cement : sand).

Step 1: Size of brick with mortar

$$(0.25 \times 0.125 \times 0.067) = 0.002094\ \text{m}^3$$

Step 2: Number of bricks

$$N = \frac{10}{0.002094} = 4776.1 \approx 4777\ \text{bricks}$$

Step 3: Volume of bricks without mortar

$$4777 \times 0.24 \times 0.115 \times 0.057 = 7.515\ \text{m}^3$$

Step 4: Wet volume of mortar

$$10 - 7.515 = 2.485\ \text{m}^3$$

Step 5: Dry volume of mortar (add 27% for dry bulk, voids in sand, wastage and shrinkage)

$$2.485 \times 1.27 = 3.156\ \text{m}^3$$

Step 6: Cement and sand for 1:4 (sum of ratio $= 5$)

$$\text{Cement} = \frac{1}{5} \times 3.156 = 0.631\ \text{m}^3 = 909\ \text{kg} \approx 18.2\ \text{bags (50 kg, 0.0347 m}^3\text{ each)}$$ $$\text{Sand} = \frac{4}{5} \times 3.156 = 2.525\ \text{m}^3$$

Answer: Cement = 0.631 m³ (about 18.2 bags); sand = 2.52 m³.

Mortar

Mortar is a paste of binding material (cement or lime), fine aggregate (sand) and water; it is used to join bricks or stones, fill joints and plaster surfaces. Common types are cement mortar (1:3 to 1:6), lime mortar, cement-lime (gauged) mortar and mud mortar.

Estimation of mortar requirement

The mortar needed depends on the volume of masonry and the volume of units in it.

1. Find the volume of brickwork $V$ (m³).
2. Find the size of a brick with mortar, e.g. $(240+10)\times(115+10)\times(57+10)$ mm, and the number of bricks $N = V/\text{volume of one brick with mortar}$.
3. Volume of bricks without mortar $= N \times 0.24 \times 0.115 \times 0.057$.
4. Wet volume of mortar $= V -$ volume of bricks.
5. Dry volume $=$ wet volume $\times$ 1.27 (to account for voids in sand, shrinkage and wastage).
6. Divide by the mix ratio $1:n$: cement $= \dfrac{\text{dry volume}}{1+n}$, sand $= \dfrac{n}{1+n}\times\text{dry volume}$.
7. Convert cement to bags: 1 bag (50 kg) $= 0.0347$ m³.

Worked example (10 m³ brickwork, 1:6)

• Bricks $= 10/(0.25\times0.125\times0.067) \approx 4777$.
• Brick volume $= 4777 \times 0.0015732 = 7.515$ m³.
• Wet mortar $= 10 - 7.515 = 2.485$ m³; dry $= 2.485 \times 1.27 = 3.156$ m³.
• Cement $= 3.156/7 = 0.451$ m³ ($\approx$ 13 bags); sand $= 3.156 \times 6/7 = 2.705$ m³.

For plaster: mortar volume $=$ area $\times$ thickness $\times$ 1.27 (dry).

Masonry work

Masonry is the construction of a structure by building up units such as bricks, stones or concrete blocks, bonded together with mortar. When the units are bricks it is called brick masonry; when they are stones it is stone masonry. A good masonry has strong bond, plumb and level courses, full joints and proper curing.

Materials for 20 cum brickwork in 1:6 mortar

Given: brickwork volume $= 20\ \text{m}^3$; brick size 230 mm x 110 mm x 55 mm (nominal, without mortar); mortar joint $= 10$ mm; mortar 1:6 (cement : sand).

Step 1: Size of brick with mortar

$$(0.24 \times 0.12 \times 0.065) = 0.001872\ \text{m}^3$$

Step 2: Number of bricks

$$N = \frac{20}{0.001872} = 10683.8 \approx 10684\ \text{bricks}$$

Step 3: Volume of bricks without mortar

$$10684 \times 0.23 \times 0.11 \times 0.055 = 14.867\ \text{m}^3$$

Step 4: Wet volume of mortar

$$20 - 14.867 = 5.133\ \text{m}^3$$

Step 5: Dry volume of mortar (add 27% for dry bulk, voids in sand, wastage and shrinkage)

$$5.133 \times 1.27 = 6.519\ \text{m}^3$$

Step 6: Cement and sand for 1:6 (sum of ratio $= 7$)

$$\text{Cement} = \frac{1}{7} \times 6.519 = 0.931\ \text{m}^3 = 1341\ \text{kg} \approx 26.8\ \text{bags (50 kg, 0.0347 m}^3\text{ each)}$$ $$\text{Sand} = \frac{6}{7} \times 6.519 = 5.588\ \text{m}^3$$

Answer: Bricks = 10684 nos.; cement = 0.931 m³ (about 26.8 bags); sand = 5.59 m³.

Random rubble masonry

Rough irregular stones, in the shape in which they come from the quarry, are laid without any definite courses; mortar (1:6 cement-sand or lime) fills the gaps and smaller stones fill the voids. Through (bond) stones are placed at about 1.5 m spacing for bonding the wall thickness. Minimum wall thickness is about 400 mm.

• Uncoursed: no courses at all; cheapest.
• Coursed: levelled at 300-350 mm height to get rough courses.

    ___ ____ __ ___
   /   \    \  \   \   irregular stones, thick
  /__ __\____\__\___\  and irregular joints
  \  /  /   /\   /
   \/__/___/__\_/

Dry rubble masonry

Rubble stones are laid without any mortar; stability depends on proper interlocking and weight of stones. Large stones are used at the bottom and bond stones across the thickness.

• Stones are carefully selected and fitted; small stones (chinking) wedge the gaps.
• Wall thickness is large (about 600 mm at base) and height is limited.
• Used for temporary works, boundary walls, retaining walls in hilly regions and terraces where economy is important and drainage is needed.

   ___  ____  ___
  |   \/    \/   |   stones interlocked,
  |__/\  __  /\__|   no mortar
  |  \ \/  \/ /  |
  |___\_/\__/\___|

A bond is the arrangement of bricks in courses so that vertical joints of successive courses do not coincide (no continuous vertical joint), which distributes load and gives strength. Common bonds:

1. Stretcher bond

All bricks are laid as stretchers; each course is shifted by half a brick. Used for half-brick thick partitions and boundary walls.

 +-----+-----+-----+
 +--+-----+-----+--+
 +-----+-----+-----+

2. Header bond

All bricks are headers; courses shifted by quarter brick (using three-quarter bats). Used for curved walls and one-brick thick walls.

 +--+--+--+--+--+
 +-+--+--+--+--+-+

3. English bond

Alternate courses of headers and stretchers; a queen closer after the first header at the quoin. It is the strongest and most commonly used bond.

 H H H H H H     header course
 S S S S S       stretcher course

4. Flemish bond

Each course has alternate headers and stretchers; queen closer next to the quoin header. Looks attractive but is a little weaker than English bond.

 H S H S H S
 S H S H S H     (stretcher centred over header)

5. Others

• Garden-wall bond: three stretchers between headers in a course.
• Raking bond: inclined bricks for thick walls.
• Dutch bond, Rat-trap bond (cavity, economical).

Rules: use whole bricks, break vertical joints, 10 mm joints, lap of at least 1/4 brick.

English bond corner (1 brick thick wall)

Courses alternate between a header course and a stretcher course.

• Header course: a header at the quoin (corner), then a queen closer next to it, then headers along both walls.
• Stretcher course: a stretcher at the corner of one wall runs through, and the other wall butts against its end; stretchers are placed in two rows, with the inner row broken by a header-closer.

Course 1 (header course) PLAN        Course 2 (stretcher) PLAN
 +--+-+--+--+--+--+--+               +-------+-------+-------+
 |H |Q|H |H |H |H |H |               |   S   |   S   |   S   |
 |  | |  |  |  |  |  |               +-------+-------+-------+
 +--+-+--+--+--+--+--+               |   S   | S/closer| ... |
 | H  |                              +-------+
 +----+                              |   S   |
 | Q  |  wall B                      +-------+   wall B
 +----+
 | H  |
 +----+

Elevation: the face of the wall shows alternate courses of headers and stretchers, with perpends (vertical joints) in alternate courses falling over each other (every second course).

Flemish bond corner (1 brick thick wall)

In each course headers and stretchers alternate; a queen closer is placed after the first header at the quoin.

Course 1 PLAN (outer face wall A)     Course 2 PLAN
 +--+-----+--+-----+--+              +-----+--+-----+--+
 |H | S   |H | S   |H |              | S   |H | S   |H |
 +--+-----+--+-----+--+              +-----+--+-----+--+
 | S|                                | H|
 +--+   wall B                       +--+  wall B
 | H|                                | S|
 +--+                                +--+

Elevation: headers and stretchers alternate in the same course, and the header of one course lies over the centre of the stretcher below.

Points of difference: English bond is stronger (more headers in alternate courses), uses fewer bricks with a queen closer at the quoin; Flemish bond gives a better appearance but needs more bats and is slightly weaker.

Parapet wall

A parapet is a low wall (0.6-1.0 m high) built above the roof or terrace edge along the sides. It protects people from falling, hides roof slopes and carries the coping, and also helps in fire control. It is built of brick, stone or RCC, 115-230 mm thick, with a coping (RCC or stone, projecting about 40 mm with drip groove) on top and a DPC at the base to stop water seeping into the roof.

    ===========  coping (drip)
    |         |
    |parapet  | 0.9 m
 ===|=========|==== roof slab

Gravity retaining wall

A wall of stone, brick or plain concrete which resists the earth pressure by its own weight. It is trapezoidal in section with a wide base; the front face is battered. Used up to about 3-4 m height. Weep holes drain the backfill.

      |\
      | \ earth
    P_a->|   \
      |  W   |
      |______|
        base

RCC counterfort retaining wall

For high walls (above 6 m), a thin RCC stem and base slab are strengthened by vertical triangular ribs (counterforts) spaced 2.5-3.5 m c/c behind the wall. The stem acts as a continuous slab spanning between counterforts, and the counterforts act as T-beams cantilevering from the base slab. The weight of backfill over the heel helps stability. It is economical for greater heights as it saves material compared with cantilever walls.

 PLAN                SECTION
 stem ===========     |\_ counterfort
  |  |  |  |  |       |  \
 counterforts          |___\___ base slab

Basement

A basement is the storey of a building that is wholly or partly below the ground level, used for parking, storage, services or shops. Its walls must resist earth pressure and ground water, so they are built as retaining walls (RCC, 200-300 mm) with a waterproofing (tanking) layer. Requirements: damp-proof floor and walls, drainage around the wall, adequate ventilation, lighting and fire exits, and a proper ramp or stair.

Waterproofing methods: integral waterproofing compound, bituminous membrane, cement plaster with water-proofer, and drainage (French drain, sump pump).

Retaining wall

A retaining wall holds back earth where the ground level changes suddenly. Types are gravity, cantilever, counterfort and buttress walls. It must be designed against overturning, sliding and bearing failure under active earth pressure $P_a = \tfrac12 K_a\gamma H^2$ acting at $H/3$ from the base. Weep holes and filters behind the wall prevent build-up of water pressure.

   backfill      ground level
  ------------+
    |         |
    | wall    |   basement wall retains soil
 P_a|--> W    |   on the outside
    |_________|
        footing

Plastering is the covering of walls, ceilings and other rough surfaces with a layer of mortar to protect them and give a smooth, decorative finish. The mortar must be workable, adhere well and be durable.

Mortars used

Practice

• Thickness: 12 mm for internal brick walls, 15-20 mm external, 6 mm for ceilings and 6 mm second coat (two-coat work).
• Surface is cleaned, wetted and raked joints for key; plaster applied between level guides (screeds).
• Cured for at least 7 days.

Sand should be clean, well graded and free from clay and silt.