Building materials glossary

What the terms on a steel, cement, roofing or waterproofing quote actually mean. Each entry links to the guide that explains it in depth.

A

AAC block(एएसी ब्लॉक): Autoclaved aerated concrete block, a light grey block made from fly ash or sand, cement, lime and an aerating agent. It is light, easy to cut and lays with thin jointing mortar. AAC blocks are covered by IS 2185 (Part 3). Read the guide
Annealed wire(बाइंडिंग तार): Soft, heat-treated black iron wire that bends and twists easily by hand. It is the usual material for binding wire used to tie TMT bars. Read the guide

B

Backer rod: A round foam rope pushed into a joint before sealant is applied. It stops the sealant sticking to the bottom of the joint and helps it keep its shape. Read the guide
Bag (50 kg)(बोरी): The standard pack in which cement is sold in India. Quantities for slabs, plaster and brickwork are usually worked out in 50 kg bags. Read the guide
Barbed wire(कांटेदार तार): Galvanised fencing wire with sharp twisted barbs at intervals, strung between posts to keep out animals and trespassers. It is the cheapest fencing option, compared with chainlink and weldmesh. Read the guide
Beam (ISMB): A horizontal member that carries load across an opening and passes it to columns or walls. In steel work an I section such as ISMB is used, and in concrete work it is a reinforced concrete member cast with the slab. Read the guide
Binding wire(बाइंडिंग तार): Soft annealed wire used to tie reinforcement bars at crossings before concreting. The common choice is about 18 gauge (SWG). Quantity is usually estimated per tonne of steel. Read the guide
BIS ISI mark: The mark of the Bureau of Indian Standards on a product, showing the maker holds a BIS licence for that Indian Standard. For TMT bars it relates to IS 1786. Check that the licence is valid and the plant name matches the tag. Read the guide
Block jointing mortar: A factory-mixed powder of cement, fine sand and polymer additives used to lay AAC blocks in thin joints. It needs far less material than ordinary mortar. Read the guide
BMT: Base metal thickness, the thickness of the steel alone in a roofing sheet, without zinc or paint. It is a more honest measure of strength than TCT. Read the guide
Brass (unit)(ब्रास): A unit of volume used for sand and gitti in North India. One brass is 100 cubic feet, about 2.83 cubic metres. Weight per brass varies with the material and moisture. Read the guide
Brickbat coba(ईंट कोबा): A traditional terrace layer of broken brick pieces laid in mortar over the slab, then grouted and finished. It gives slope and some protection from sun and rain, but adds dead load, and it is not a waterproof layer by itself. Read the guide
Bundle weight: The total weight of a bundle of TMT bars, which depends on bar diameter, length and number of bars. It is used to check what was actually delivered. Read the guide
BWG: Birmingham Wire Gauge, an old table that links a gauge number to a diameter in mm. For some numbers it differs from SWG, so always confirm the mm thickness on the bill. Read the guide

C

Cement grade: A number such as 33, 43 or 53 giving the minimum 28-day strength in MPa of a standard cement and sand mortar cube. It is not the strength of the concrete you make. Read the guide
Cementitious coating: A cement-based waterproofing coat, often with polymer additives, brushed or sprayed on. It suits bathrooms, tanks and basements where there is little movement, and is less flexible than PU or bitumen systems. Read the guide
Chainlink(जाली तार): Woven wire diamond mesh, usually galvanised or PVC coated, used for fences around plots, farms and sports areas. It is stronger than barbed wire and cheaper than weldmesh. Read the guide
Channel (ISMC)(चैनल): A C shaped rolled steel section with a flat back, which makes it easy to bolt or weld other parts to it. Used for purlins, frames, gate posts and supports. Read the guide
Colour coated sheet(कलर कोटेड शीट): A roofing or cladding sheet made from galvanised or galvalume steel with a baked paint layer on top. It looks better and resists weather longer than plain GI, and is sold with a manufacturer warranty. Read the guide
Cover block(कवर ब्लॉक): A small concrete or plastic spacer placed under or beside reinforcement so the bars sit with the right concrete cover around them. Without it, bars sink to the shuttering and rust early. Read the guide
Cover width: The width of a roofing sheet that actually covers the roof after side overlaps. It is smaller than the overall sheet width, and sheet count must be worked out from it. Read the guide
Crest: The raised top ridge of a profiled roofing sheet. Screws on metal sheets are usually fixed through the crest into the purlin below, while valleys are the low channels where water runs. Read the guide
Curing(तराई): Keeping fresh concrete or plaster moist after casting so cement can gain strength. Most site specifications ask for at least 7 days of regular wetting. Curing continues after the shuttering is removed. Read the guide

D

d²/162: A shortcut formula for the weight of a TMT bar in kg per metre, where d is the bar diameter in mm. It is used to check whether a delivery is underweight. Read the guide
Damp proof course (DPC)(डीपीसी): A waterproof layer built in near plinth level to stop ground moisture climbing into walls. A missing or failed DPC is a common cause of rising damp. Read the guide
Development length: The length of bar that must be embedded in concrete so it can grip and carry its full stress. Lap lengths are based on it, and the drawing gives the value for your job. Read the guide
Dholpur stone(धौलपुर पत्थर): A sandstone quarried near Dholpur in Rajasthan, usually in cream, beige and light pink shades. It is widely used for flooring, cladding and boundary walls. Read the guide
Dry volume factor: The extra factor applied when converting a wet volume of concrete or mortar to dry materials, because loose dry materials shrink when mixed. The common factor is 1.54, meaning 54 per cent extra, though some designers use about 1.52. Read the guide
Ductility: The ability of a steel bar to stretch and bend a good deal before it breaks, giving warning in an overload or earthquake. D grades such as Fe500D are specified for higher ductility. Read the guide

E

Efflorescence(नमकीन सफेदी): The white, powdery or crusty deposit left on walls, bricks and stone when salts dissolved in water come out as it evaporates. It is a sign of moisture moving through the material. Read the guide
Elongation: How much, as a percentage, a bar stretches before it fractures in a tensile test. It is reported on the mill test certificate, and D grades must meet a higher minimum than plain grades under IS 1786. Read the guide
EPDM washer: A rubber sealing washer, usually bonded to a steel carrier, fitted under a roofing screw head. EPDM resists sun and ozone and stays flexible, which keeps the screw hole watertight. Read the guide

F

Fe500(एफई 500): A grade of TMT bar under IS 1786 with a minimum yield strength of 500 N/mm². Plain Fe500 does not carry the extra ductility requirements of the D grades. Read the guide
Fe500D(एफई 500डी सरिया): A TMT bar grade with 500 N/mm² minimum yield strength and the D (ductile) requirements. It must reach higher elongation and a higher tensile to yield ratio than plain Fe500. It is the usual choice for houses in North India. Read the guide
Fe550D(एफई 550डी सरिया): A ductile TMT bar grade with 550 N/mm² minimum yield strength under IS 1786. It is stronger than Fe500D, so it can allow slightly less steel where the engineer permits. Read the guide
Fly ash brick(फ्लाई ऐश ईंट): A brick made from fly ash, cement or lime and sand, pressed and cured rather than fired. It is uniform in size and uses a thinner mortar joint than a clay brick. Read the guide

G

Gauge: A number used to describe the thickness of sheet or wire, where a higher number means a thinner material. SWG and BWG are the two scales used, and the same number can mean different mm values on each. Read the guide
GC sheet(टीन की चादर): Galvanised corrugated sheet, a zinc coated steel sheet rolled into a wavy profile for sheds and roofs. It is often called GC or GI corrugated sheet. Read the guide
GI: Galvanised iron, steel coated with a layer of zinc to slow rusting. It is used for roofing sheets, wire, pipes and fittings. Read the guide
Gitti(गिट्टी): Crushed stone aggregate used in concrete, commonly sold by the brass or by weight. Sizes such as 10 mm, 20 mm and 40 mm suit different jobs. Read the guide
GP sheet(जीपी शीट): Galvanised plain sheet, a flat zinc coated steel sheet used for ducting, gutters, flashings and fabrication. It is the flat version of the corrugated GC sheet. Read the guide

H

Heat number: A batch code stamped or recorded for a lot of steel that was melted together. It links a bundle of bars to its mill test certificate. Read the guide

I

IS 1489: The Indian Standard for Portland pozzolana cement (PPC). Part 1 covers fly ash based PPC, and its minimum 28-day strength is 33 MPa. Read the guide
IS 1786: The Indian Standard for high strength deformed steel bars and wires for concrete reinforcement, which covers grades such as Fe500D and Fe550D. It sets strength, elongation, chemical and mass tolerance limits. Read the guide
IS 2062: The Indian Standard for hot rolled structural steel used for beams, channels, angles and plates. Quote it when ordering fabrication steel so the grade is clear. Read the guide
IS 269: The Indian Standard for ordinary Portland cement (OPC). Check the current BIS edition for the grades it covers. Read the guide
IS 456: The Indian Standard code of practice for plain and reinforced concrete. It sets rules for cover, lap length, mixes and curing. It asks that a tension lap be at least the development length and not less than 30 times the bar diameter. Read the guide
IS 808: The Indian Standard that gives the dimensions and section properties of hot rolled steel beams, channels and angles. Weight charts for ISMB, ISMC and ISA are based on it. Read the guide
ISA angle(एंगल): Indian Standard angle, an L shaped rolled steel section with equal or unequal legs. Used for frames, trusses, gate work, lintels and bracing. Read the guide
ISMB(आई बीम): Indian Standard medium weight beam, an I shaped rolled steel section named by its depth in mm, such as ISMB 150. Used for beams, lintels and heavy frames. Read the guide
ISMC(चैनल): Indian Standard medium weight channel, a C shaped rolled steel section named by its depth in mm, such as ISMC 100. Used for purlins, frames and supports. Read the guide

J

J hook and U hook: Bolt type fasteners used to fix roofing sheets to purlins where a self-drilling screw is not used. The J hook grips an angle purlin and the U hook is used with pipe or round sections. Read the guide
Jaali(जाली): A perforated screen or mesh used for ventilation, privacy and decoration. In stone it is a carved pattern, in metal it is welded or woven mesh for gates, windows and fencing. Read the guide

L

Lap length(ओवरलैप): The length over which two bars overlap so that load passes from one to the other. As a rough rule of thumb many sites use 40 to 50 times the bar diameter, but the structural drawing governs. Laps should be staggered. Read the guide
Lintel(लिंटल): A beam placed over a door or window opening to carry the wall above. It can be reinforced concrete or a steel section such as an angle or channel. Read the guide

M

M20(एम 20): A concrete grade with 20 MPa characteristic compressive strength at 28 days. A nominal mix for M20 is 1:1.5:3 of cement, sand and gitti by volume, and it is the usual grade for house slabs and beams. Read the guide
Mild steel (MS)(एमएस): Low carbon steel used for plates, angles, channels, pipes and fabrication work. It is not the same as ribbed TMT reinforcement bars. Read the guide
Mill test certificate(एमटीसी): A document from the steel mill giving the chemical and mechanical test results for a heat of steel, such as yield, tensile strength and elongation. Match its heat number to the one on the bundle tag. Read the guide

N

Nominal mix: A concrete mix given as fixed volume ratios of cement, sand and gitti, such as 1:1.5:3 for M20. It is used on small jobs where mix design and testing are not done. Read the guide

O

OPC: Ordinary Portland cement, cement with no added fly ash or slag. It gains strength early and is covered by IS 269. Read the guide

P

Plain cement concrete (PCC): Concrete without steel reinforcement, used as a levelling bed under footings and floors. Common ratios are 1:4:8 and 1:5:10. Read the guide
Polycarbonate sheet: A light, tough translucent plastic sheet used for skylights and roofs where daylight is wanted. It is lighter than glass and does not shatter like it. Read the guide
PPC: Portland pozzolana cement, made by blending Portland cement with fly ash or other pozzolana. It is covered by IS 1489, and is widely used in general house construction. Read the guide
PPC vs OPC: OPC gains strength faster early on, while PPC gains it more slowly but continues over time and usually gives a finer, cooler mix. Both work for house construction when properly cured. Read the guide
PU waterproofing: A polyurethane liquid membrane that cures into a flexible rubbery layer. It handles small cracks and movement better than cement-based coatings, and is used on terraces and balconies. Read the guide
Purlin(पर्लिन): A horizontal member laid across rafters or trusses that supports roofing sheets. In sheds it is often a channel, angle or box section, and sheets are screwed to it. Read the guide

R

Red stone(लाल पत्थर): A red to reddish brown sandstone, commonly used for boundary walls, steps, paving and cladding. It is hard wearing and suits outdoor use. Read the guide
Rising damp(सीलन): Ground moisture that climbs up a wall by capillary action, usually from the base. It leaves stains and efflorescence, and plastering over it only hides it for a while. Read the guide

S

Sandstone(बलुआ पत्थर): A sedimentary stone made of compacted sand grains, quarried in Rajasthan and elsewhere in colours from cream to pink and red. It is used for flooring, cladding, paving and walls. Read the guide
Seismic zone: A region on the Indian earthquake map, from II to V, that sets design shaking. The Uttar Pradesh State Disaster Management Authority lists Amroha, Moradabad, Meerut, Hapur and Bijnor completely in zone IV, which is a reason to prefer ductile D grade bars. Read the guide
Self-drilling screw(सेल्फ ड्रिलिंग स्क्रू): A screw with a drill-bit point that makes its own hole in a steel purlin, so no pre-drilling is needed. It is now the standard fixing for colour coated and trapezoidal metal roofs, used with an EPDM washer. Read the guide
Shuttering(शटरिंग): The temporary mould, made of plywood, steel plates or planks, that holds wet concrete in shape until it hardens. It is held up by props, and removal timing depends on span. Read the guide
Stirrup(रिंग): A closed loop of thin bar placed around the main bars of a beam or column. It resists shear and holds the main bars in position. Read the guide
Stripping time: The time after casting when shuttering and props can be removed. Side forms come off earlier than slab props. For typical slabs props are commonly kept about 7 days for spans up to 4.5 m and 14 days for longer ones, but follow your engineer. Read the guide
SWG: Standard Wire Gauge, a long-used British table matching a gauge number to wire or sheet thickness. A higher SWG number means thinner material. Read the guide

T

TCT: Total coated thickness, the thickness of a roofing sheet including steel, zinc and paint on both sides. It reads higher than BMT, so ask which one the dealer is quoting. Read the guide
Thin bed mortar: A thin layer of adhesive, about 3 mm, used to join AAC blocks instead of a thick cement mortar bed. It gives faster, cleaner laying. Read the guide
TMT bar(सरिया): Thermo-mechanically treated bar, a ribbed steel reinforcement bar with a hard outer surface and softer core, made by quenching and self-tempering. It is the standard reinforcement for concrete and is known locally as sariya. Read the guide

U

Ultimate tensile strength (UTS): The highest stress a bar carries in a tensile test before it breaks. It is reported on the mill test certificate and, for D grades, must be a set ratio above the yield strength. Read the guide

V

Valley: The low channel between two crests of a profiled roofing sheet, along which rainwater runs. It is also the name for the line where two roof slopes meet. Read the guide

W

Weldmesh(वेल्डमेश): Panels or rolls of wire welded at every crossing in a square or rectangular grid. It is described by wire diameter and grid spacing, and used for fencing, gates, plaster reinforcement and some slab work. Read the guide

Y

Yield strength: The stress at which a steel bar begins to stretch permanently. The number in Fe500D or Fe550D is the minimum yield strength in N/mm² (MPa). Read the guide

Z

Z120: A zinc coating class meaning at least 120 g/m² of zinc, counted across both faces together. A higher class such as Z275 gives longer life in humid or ammonia-rich places like dairy and poultry sheds. Read the guide
Zinc coating(जिंक कोटिंग): The galvanising layer on GI roofing sheet and wire that protects the steel from rust. It is stated as a class or in g/m², such as Z120 or Z275. Read the guide

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