Table of Contents
- 4.1 Composition of Good Brick Earth
- 4.2 Manufacture of Bricks
- 4.3 Qualities of Good Bricks
- 4.4 Tests for Bricks
- 4.4.1–4.4.5 Classification, Colours, Size
- 4.6 Fire-Clay and Fire Bricks
- 4.7 Brick Masonry Terminology
- 4.8 Bonds in Brick-Work
- 4.9 Comparative Merits: English vs Flemish Bond
- 4.10 Other Types of Bonds
4.1 Composition of Good Brick Earth
Figure 4.1 — Constituents of Good Brick Earth: Functions and Harmful Effects
4.1.1 Harmful Ingredients in Brick Earth
| Harmful Ingredient | Effect |
|---|---|
| Lime (in lumps) | Causes unsoundness. Lumps of lime → quicklime after burning; slakes and expands → splits bricks into pieces |
| Iron pyrites | Bricks get crystallized and disintegrated during burning |
| Alkalies (Soda & Potash) | Act as flux; cause bricks to fuse, twist and warp. Remaining alkalies → bricks absorb moisture → white/grey deposits on wall surface (efflorescence) |
| Pebbles | Will not allow clay to get mixed uniformly → weak and porous bricks |
| Organic Matter | Assists in burning. If not completely burnt → bricks become porous |
4.2 Manufacture of Bricks
Four distinct operations: (1) Preparation of clay → (2) Moulding → (3) Drying → (4) Burning
Figure 4.2 — Manufacture of Bricks: Four Steps with Kiln Comparison
Kiln Types (from source)
Bulls Trench Kiln
- Most widely used kiln in India; gives continuous supply; rectangular, circular or oval in plan
- Sections: 1-Loading, 2-Empty, 3-Unloading, 4-Cooling, 5-Burning, 6-Heating
- Stops functioning during monsoon (no permanent roof)
- Burning capacity: about 3 lakhs in 12 days
Hoffman’s Kiln (Flame Kiln)
- Circular in plan; divided into compartments/chambers; each chamber has fuel holes, main door, communicating doors and radial flue connected to central chimney
- Functions all year round (has permanent roof even during rainy season)
- Burning capacity: about 25 lakhs per season; higher quality bricks
4.3 Qualities of Good Bricks
- Table-moulded, well-burnt in kilns, copper-coloured, free from cracks, sharp and square edges
- Uniform in shape; standard size
- Give clear metallic ringing sound when struck with each other
- When broken/fractured show bright homogeneous and uniform compact structure free from voids
- Should not absorb water more than 20% by weight (1st class); 22% (2nd class) when soaked in water for 24 hours
- Sufficiently hard — no impression left when scratched with finger nail
- Should not break into pieces when dropped flat on hard ground from height of about one metre
- Low thermal conductivity; sound proof
- When soaked in water for 24 hours, should not show deposits of white salts when allowed to dry in shade
- No brick should have crushing strength less than 5.50 N/mm²
Do you know? Average crushing strength and tensile strength of hand moulded bricks are 60000 kN/m² and 2000 kN/m² respectively. The shearing strength of bricks is about one-tenth of the crushing strength.
4.4 Tests for Bricks
| # | Test | Method | Limit / Result |
|---|---|---|---|
| 1 | Absorption | Brick weighed dry → immersed in water for 16 hours → weighed again. Difference = water absorbed. | 1st class: ≤20%; 2nd class: ≤22.5%; 3rd class: ≤25% of dry weight |
| 2 | Crushing Strength | Compressed in compression machine until crushed | 1st class bricks: ≥10 N/mm²; 2nd class: <7.5 N/mm². No brick <5.50 N/mm² |
| 3 | Hardness | Scratch made on brick surface with finger or nail | If no impression left → sufficiently hard |
| 4 | Presence of Soluble Salts (Efflorescence) | Brick immersed in water 24 hrs; dried in shade; white deposits observed | <10% surface = slight; 10–50% = moderate; >50% = heavy = serious |
| 5 | Shape and Size | 20 bricks randomly selected; standard size 19×9×9 cm checked | Length 368–392 cm, Width 174–186 cm, Height 174–186 cm total for 20 bricks |
| 6 | Soundness | Two bricks struck with each other | Should not break; clear ringing sound produced |
| 7 | Structure | Brick broken; internal structure examined | Should be homogeneous, compact, free from holes and lumps |
4.4.1–4.4.5 Classification, Colours and Size of Bricks
Unburnt Bricks
- Sun dried — dried with heat received from sun after moulding
- Only for temporary and cheap structures; should not be used where exposed to heavy rains
Burnt Bricks — Four Classes
| Class | Description | Use |
|---|---|---|
| First Class | Table-moulded; burnt in kilns; standard shape; surfaces and edges sharp, square, smooth, straight; all qualities of good bricks | Superior work of permanent nature |
| Second Class | Ground moulded; burnt in kilns; surface somewhat rough; shape slightly irregular | Commonly used where brickwork is to be provided with coat of plaster |
| Third Class | Ground moulded; burnt in clamps; rough surface; irregular and distorted edges; give dull sound when struck together | Unimportant and temporary structures |
| Fourth Class | Over-burnt bricks with irregular shape and dark colour; very compact structure — sometimes stronger than first class | Used as aggregate for concrete in foundations, floors, roads |
Standard Size Data (India)
- Standard size
- 19 cm × 9 cm × 9 cm
- Nominal size (with mortar)
- 20 cm × 10 cm × 10 cm
- Traditional nominal size
- 23 cm × 11.4 cm × 7.6 cm
- Weight per brick
- ~3 to 3.50 kg (1 m³ brick earth = ~1800 kg)
- Min crushing strength
- No brick <5.5 N/mm²; 1st class ≥10 N/mm²
4.6 Fire-Clay and Fire Bricks
- Constituents: alumina 25–35%; silica 75–65%. Impurities (lime, magnesia, iron oxide, alkalies) should not exceed 5%
- Fire-clay classified by fire-resisting capacity: (1) High duty fire-clays (2) Medium duty fire-clays (3) Low duty fire-clays
- Fire bricks: usually white or yellowish white; weight ~30–35 N; compressive strength 200–220 N/mm²; water absorption 5–10%
- Used for lining interior surfaces of furnaces, chimneys, kilns, ovens, fire places
4.7 Brick Masonry Terminology
Figure 4.3 — Brick Masonry Terminology and Wall Elevation
4.8 Bonds in Brick-Work
Figure 4.4 — Main Types of Bonds in Brick-Work (from source)
4.8.1 English Bond
- Consists of alternate courses of headers and stretchers
- Vertical joints in header courses come over each other; vertical joints in stretcher courses also in same vertical line
- Essential to place queen closer after the first header in each header course
- A header course should never start with a queen closer — liable to get displaced
- In the stretcher course, stretchers should have a minimum lap of 1/4th of their length over the headers
- In walls having thickness equal to odd number of half brick (1½, 2½ brick thick), same course shows stretchers on one face and headers on other
4.8.2 Flemish Bond
- Each course consists of alternate headers and stretchers
- Alternate headers of each course centred over stretchers in the course below
- Every alternate course starts with a header at the corner
- Closers are inserted in alternate courses next to the quoin header
- Further divided into: Single Flemish bond and Double Flemish bond
4.8.3 Double Flemish Bond
- Every course presents same appearance both in front and back elevations
- Every course consists of headers and stretchers laid alternately
- Best suited for considerations of economy and appearance; enables one brick wall to have flush and uniform faces on both sides
4.9 Comparative Merits and Demerits of English and Flemish Bond
- For walls thicker than 1½ brick, English bond is stronger than Flemish bond
- Flemish bond renders better appearance of the face work — more attractive and pleasing
- Flemish bond is slightly economical as a number of bats can be used — renders use of broken bricks possible, but requires more mortar for additional joints
- Adoption of Flemish bond requires good workmanship and careful supervision — thus extra attention necessary to keep the vertical joints in alternate courses one above the other
4.10 Other Types of Bonds
| Bond Type | Description | Use |
|---|---|---|
| (i) Stretcher Bond | All bricks laid as stretchers. Overlap (usually half brick) by commencing each alternate course with a half brick bat. Used for half brick thick walls only. | Half brick walls only |
| (ii) Header Bond | All bricks laid as headers on the faces. Overlap (usually half width) by introducing a three-quarter bat in each alternate course at quoins. Better alignment — used for footings in foundations for better transverse distribution of load. | Footings, curved walls on plan |
| (iii) Garden Wall Bond | Suitably adopted for one brick thick walls which may act as a garden wall or a boundary wall | Garden walls, boundary walls |
| (iv) Facing Bond | Adopted for thick walls where facing and backing are desired to be constructed with bricks of different thickness. Bond of header and stretcher courses so arranged that one header course comes after several stretcher courses. | Thick walls with different facing/backing |
| (v) Raking Bond | Bonding bricks laid at any angle other than 0° or 90°. Arrangement helps to increase longitudinal stability of thick walls built in English bond. | Thick walls — longitudinal stability |
| (vi) Diagonal Bond | Best suited for walls 2–4 brick thick. Usually introduced at every 5th or 7th course along height of the wall. Bricks placed end to end so extreme corners are in contact with the stretchers. | Walls 2–4 bricks thick |
| (vii) Dutch Bond | Modification of old English cross bond; consists of alternate courses of headers and stretchers | General masonry |
Chapter 4: Bricks and Brick Masonry — Civil Engineering · Construction Materials
All technical data as per IS specifications and source material