Concrete glossary
The words in concrete quotes, drawings and dockets, in plain English.
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A142 & A193 Steel Fabric Mesh
Welded high-tensile steel wire sheets (6 mm wires at 200 mm centres for A142; 7 mm wires for A193) set on plastic chairs in the upper or middle third of a slab to control drying shrinkage cracks and spread wheel loads.
A393 mesh
Welded steel fabric of 10 mm bars at 200 mm centres, sold in 4.8 × 2.4 m sheets.
Air-entrained concrete
Concrete with tiny air bubbles mixed in to resist freeze/thaw damage. S.100 asks for at least 3.5% on exposed yard slabs using Mix B.
Blinding
A thin layer of fine material on the hardcore that fills the voids so nothing sharp punctures the membranes.
Bull Float & Magnesium Darby
Long-handled magnesium alloy floats pushed across freshly screeded concrete immediately after strike-off to embed coarse aggregate slightly, flatten ridges, and bring up cream before bleed water rises.
C25/30 & C30/37 Strength Classes
Standard European and Irish EN 206 compressive strength ratings where the first number is the 28-day cylinder strength and the second is the cube strength in N/mm2; C25/30 suits domestic slabs and C30/37 or C35/45 suits heavy yard and agricultural work.
Clause 804 Granular Sub-Base
Well-graded crushed rock aggregate (0 to 31.5 mm) spread and compacted in 150 mm layers with a vibrating roller or plate compactor beneath a concrete driveway, shed base, or yard to create a free-draining, non-frost-susceptible foundation.
Contraction (Crack-Control) Joints
Straight saw-cuts or grooved joints formed to one-quarter or one-third of the slab thickness at regular 3 m to 4.5 m bay spacings within 12 to 24 hours of pouring so natural drying shrinkage cracks neatly along the straight joint line.
Cover
The depth of concrete over the steel, set by the exposure class and design life.
Curing
Keeping the moisture in new concrete so it gains strength: polythene, wet coverings, a mist spray or a curing compound.
D20
20 mm maximum aggregate size. D10 and D14 are the smaller ones.
Damp-Proof Membrane (1200 Gauge Polythene)
A heavy-duty polyethylene sheet (minimum 300 microns) laid over a 50 mm sand blinding layer beneath internal house floors and insulated shed slabs to block ground moisture from rising into the concrete.
Damp-proof membrane (DPM)
A sheet under or over the slab that stops ground moisture rising, continuous with the damp-proof courses in the walls (TGD C).
Defective Concrete Products Levy (DCPL)
A 5% levy on the value of certain concrete products at first supply, since 1 September 2023 (Revenue).
Dowel Bars (Debonded Movement Dowels)
Smooth mild-steel bars (typically 16 mm or 20 mm diameter, 450 mm long) cast half-bonded and half-sleeved across day-work construction joints and expansion joints so adjacent concrete bays stay level under vehicle axle loads while still sliding horizontally.
Expansion Joint & Compressible Filler Board
A full-depth isolation gap (12 mm to 20 mm wide) filled with closed-cell polyethylene or bitumen fibreboard and sealed on top with flexible polyurethane sealant where a new concrete slab meets house walls, gate piers, or manhole frames.
Exposed Aggregate Concrete
A decorative driveway and patio finish where a surface retarder is sprayed onto the freshly floated concrete and pressure-washed off the next day to reveal natural washed quartz, granite, or limestone pebbles.
Exposure class
The I.S. EN 206 code for the conditions concrete faces, e.g. XC1 dry inside, XC2 many foundations, XF3 horizontal surfaces exposed to rain and freezing.
Ground-supported (ground-bearing) floor
A concrete floor slab laid on compacted hardcore and carried by the ground. TGD C: at least 150 mm of concrete on at least 200 mm of hardcore.
Hardcore
Compacted granular fill under a slab. TGD C grades it under S.R. 21: T1 Struc (0/32 or 0/40 mm), T2 Perm (4/40 mm, gas permeable) and T3 Blind (0/4 mm).
Helicopter Power-Floated Finish
Polishing a stiffening concrete floor or shed slab with walk-behind or ride-on rotating steel trowel blades to produce a dense, hard-wearing, dust-free smooth surface for workshops, garages, and commercial units.
High Radon Area
An area where the EPA predicts more than 10% of homes are above 200 Bq/m³.
Pattern Imprinted (Stamped) Concrete
A poured concrete driveway or patio coloured with surface-hardening pigment, dusted with antique release agent, textured with interlocking polyurethane cobble, slate, or ashlar mats while still plastic, and sealed with acrylic resin.
Polypropylene Micro-Fibres & Structural Macro-Fibres
Synthetic fibres dosed directly into the ready-mix truck drum to hold plastic concrete together during the first 24 hours (micro-fibres) or add post-crack toughness across yard and industrial floor bays (macro-fibres).
Power float
A machine with blades turning on a pan that gives a slab a smooth, dense, level finish.
Pyrite
A mineral that can make hardcore swell. TGD C points to S.R. 21 Annex E for limiting it.
Radon barrier
A fully sealed, low-permeability membrane over the whole footprint, required in High Radon Areas (TGD C).
Raft foundation
A reinforced slab, typically 150 to 300 mm thick, under the whole footprint, used on poor or variable ground.
S.100
The Department of Agriculture's minimum specification for farm concrete: Mix A (C35/45) for silage, Mix B (C30/37) for the rest.
Slump (consistence)
How easily fresh concrete flows, from S1 (10 to 40 mm) to S5 (220 mm and over).
Slump Class (S2, S3 & S4 Workability)
The consistency and flow measurement of fresh ready-mix concrete; S2 (50 to 90 mm slump) suits kerbing and steep driveway gradients, S3 (100 to 150 mm) is standard for hand-placed slabs, and S4 suits pumped concrete pours.
Standby radon sump
A sump under the slab with pipework to outside, so radon can be extracted later if a test shows it's needed. Expected in every new floor (TGD C).
Strength class (e.g. C25/30)
The I.S. EN 206 label for concrete strength: characteristic cylinder and cube strength at 28 days, in N/mm².
Strip foundation
A continuous strip of concrete under a load-bearing wall. TGD A: at least 200 mm thick, 400 to 650 mm wide on good ground.
Tamped & Brushed Non-Slip Finish
Drawing a stiff bristle yard brush or wooden tamping beam across a fresh concrete driveway or farm yard at right angles to the direction of travel to leave crisp micro-ridges that shed rainwater and give tyres and livestock safe grip.
Trench fill
A strip foundation with the trench filled with concrete to within about 150 mm of ground level.
U-value
How much heat passes through a floor, in W/m²K. TGD L 2022: 0.18 for a new dwelling's ground floor, 0.15 with underfloor heating.
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