A Quick Start Guide To Bricks – Types And Brickwork
In earlier days, bricks were hand-molded from moist clad and then and sunbaked. The quarrying of clay and manufacture of bricks requires a high-energy process, which involves the emission of carbon dioxide and other pollutants. However, well-constructed brickwork offers the long life of a structure with low maintenance.
The main constituents of brick are
- small quantities of chalk, lime,iron-oxide and other small constituents
The brick-making industry increases its effect and productivity by
- Effects of blending clays
- wide range of forming processes
- Adjustments of firing conditions
- Application of surface finishes
Standard size – referred in National Annex (informative) to BS EN 771-1: 2003 is 215 × 102.5 × 65 mm (length, width, height)
A standard brick weighs between 2 – 4kg
Types/forms of bricks
- Solid brick
- Frogged (frogged on one or both bed faces)
- Cellular (have cavities closed at one end)
- Perforated (perforations vary by size and number)
Special shapes of bricks
Shapes of bricks include Half-round coping, half-round capping, saddle-back coping, single bullnose stretcher, bull-nose doubleheader, double bull-nose stop, cow nose, cow nose stop, external angle, internal angle(dog-nose), plinth header, Radial stretcher, Tapered stretcher, etc.
- Copings and capping for parapet walls and free-standing walls
- Bullnose for corner details and for window reveals
- Plinths foe corbelling details
- Cants for turning angles
Appearance : Colors and texture
The colors range from the light buffs, greys, and yellows through pastel pink to strong reds, blues, browns, and deep blue/black. Colors depend mainly on the clay used, firing conditions, the addition of pigments to the clay, application of a sand-facing. Colors can be uniform or vary from a surface and from brick to brick.
Textures range from smooth, sanded to textured and deeply folded.
Unfired clay bricks :
They are used for internal non-load bearing applications. They require low energy input and a high potential for recycling. Also called Earth bricks.
Reclaimed clay bricks :
They are often used for aesthetic reasons.
Manufacture of Bricks
There are five main processes in the manufacture of clay bricks:
- Extraction of raw material
- The raw material is extracted from quarry and is transported to work place by road or conveyor belt. The raw material gets refine by removing top soil, rocks and any other unsuitable material. It is then grounded into fine powder and pigments are added to produce desired colors. Considerable amount of water is added to get the desired plasticity.
- Forming process
- Handmade bricks – wet clay is poured into wooden mounds on a bench. Other variations – pallet molding and slop molding.
- Soft-mud process – clay is mechanically thrown into pre-sanded molds.
- Pressed bricks – subjected to sequence of four pressings with steel molds. These bricks have a deep frog on one bed face.
- Extruded wire-cut bricks – clay with water content is fed into a screw extruder which consolidates the clay and extracts the air. Continuous columns are formed and are cut into bricks with series of wires.
- These bricks from wet clays are made to dry and shrink to prevent cracking and distortion. They are stacked in and passed through drying chambers.
- Intermittent and continuous kilns are used for firing process. For large scale production, continuous kilns are used whereas, intermittent gas fired kilns are used for specialized products.
- Packaging and distribution
- Bricks are shrink-wrapped into packs for easy transportation and are distributed.
Classification of Bricks
Variety of bricks
Three main varieties of bricks are
- Common bricks
- They have no visual finish. Used for general building works where brickwork is to be plastered and unseen.
- Facing bricks
- Gives attractive finish. The Surface may be smooth, textured, or sand faced. They are used for most visual work where pleasing and durable finish is required.
- Engineering bricks
- These are dense and vitreous with load-bearing characteristics and low-water absorption. classified as Class A and Class B.Used to support heavy loads and in places to reduce chemical attack, water absorption or impact damage.
As per ASTM C 902
In ASTM C 902, brick is classified into three weather classes, three traffic types, and three applications.
- Weather Resistance is evaluated according to physical properties, such as compressive strength, cold-water absorption, and saturation coefficient.
- Class SX is for uses where water-saturated brick is exposed to freezing.
- Class MX is for exterior uses where brick is not exposed to freezing.
- where as Class NX is for interior uses where brick will be sealed, waxed, or otherwise coated.
- Traffic performance of pedestrian and light-traffic paving brick is evaluated by its abrasion resistance. Two alternatives provided for measuring this characteristic are abrasion index and volume abrasion loss.
- Type I is for exposure to extensive abrasion, such as driveways and entrances to public and commercial buildings.
- Type II is for exposure to intermediate traffic, such as exterior walkways and floors in restaurants and stores.
- And Type III is for exposure to low traffic, such as floors and patios in single family homes.
- Three applications
- PS is for general use where units are installed either with mortar- or grout-filled joints between units in any pattern or without mortar joints, but only in a running or other bond pattern that does not require units manufactured to close dimensional tolerances.
- PX is for installations without mortar joints between units that require minimal dimensional variations because of special bond patterns or other special construction conditions.
- PA is for units selected for certain appearance characteristics stemming from variations in color, texture, and size.
Durability of Bricks
Factors considered for the durability of bricks:
- Type of unit
- Clay composition
- Dimensions and configurations
- Traffic performance
As per the standard freezing test, bricks are classified according to Freeze/thaw resistance as
- F2 – Masonry subjected to severe exposure
- F1 – Masonry subjected to moderate exposure
- F0 – Masonry subjected to passive exposure
Soluble salt content
Soluble salts can cause efflorescence causing it to expand and deteriorate by sulphate attack.
- Low (S2)
- Normal (S1)
- no limits (S3)
Efflorescence appears as white deposits on the surface of the brick. It is caused by moisture carrying salts from inside the bricks and mortar to the surface where the water evaporates leaving the crystalline salts.
Staining – The surface of brickwork may be stained by cement which is to be taken care of.
- Compressive strength
- Water absorption and suction
- Moisture and thermal movement
- Thermal conductivity
- Fire resistance
- Acoustic properties
The bonding, mortar color, and joint profile have a significant effect on the visual appearance of brickwork. The three-dimensional effects of decorative dentil courses and projecting corbelled features offer the designer further opportunities to exploit the effects of light and shade.
- Mortars – Mixture of cement/sand/lime or cement/sand with plasticizer. Give a bearing for the bricks and acts as a sealant for brickwork.
- Bonding – Stretcher bond, English bond, Flemish bond, English garden wall bond, Flemish garden wall bond enhances the visual appearance of brickwork.
- Joint Profiles – Standard range of joint profiles are struck or weather joint, curved recessed joint, flush joint, square-recessed joint.
Reinforcement is used either vertically or horizontally, wherein vertical reinforcement is possible in cavity walls.
Tile bricks replicate the visual effect of hung tiles. A profiled edge on each brick overhangs the brick course
below creating the tiled effect. Profiled bricks can create features with beautiful shadow effects.