Screeding glossary
The words in screed specifications and quotes, in plain English.
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75% RH
The usual moisture limit before flooring, measured at the screed surface.
Bay
One area poured between joints. Limits run from 36 m² to 1,000 m².
Bonded screed
Stuck to a prepared base. Sand and cement: 25 mm minimum, 40 mm specified.
Bonded Screed Construction
Floor screed of 25 to 40 mm thickness laid directly onto a mechanically scabble-prepared structural concrete slab coated with a polymer or cement slurry bonding bridge.
BRE Screed Tester (Drop Weight)
Portable soundness test device that drops a 4 kg weight down a guide rod onto a 1000 square millimetre steel anvil to measure indentation depth in millimetres after four blows.
CT-C20-F4
A cementitious screed of compressive class C20 and flexural class F4.
Curling
Edges of a screed lifting as it dries.
Curling at Free Edges
Upward lifting of screed corners and bay joints caused by differential drying between the exposed top surface and the damp underside of a sand-and-cement bed.
D49 mesh
A light steel mesh used in sand and cement screeds; floating sand and cement needs it, or fibres.
Day Joint (Construction Joint)
Vertical stop-end formed where a screeding gang finishes work for the day, later keyed or dowelled where two separate pours meet.
Dry-Pack Semi-Dry Mix
Traditional 1:3 to 1:4 cement-to-sharp-sand screed mixed at low water content so a handful squeezed in a gloved palm holds its shape without free water weeping out.
Epoxy Damp Proof Membrane (Liquid DPM)
Two-coat solvent-free epoxy resin applied to a cementitious screed when residual moisture exceeds 75 percent relative humidity, allowing early installation of timber or vinyl flooring.
Expanded Metal & Polypropylene Fibre Reinforcement
Crack-control mesh or micro-synthetic fibres dispersed through a sand-and-cement screed to resist plastic shrinkage stresses during initial curing.
Fine Aggregate Grading (EN 13139)
Washed 0/4 mm concreting sharp sand specification required for durable floor screeds, distinct from soft plastering or bricklaying sand.
Fine concrete screed
A screed with aggregate up to 10 mm, mixed 1:4 to 1:5.
Floating screed
On insulation, separated from walls and pipes. Sand and cement: 75 mm, 65 mm in housing.
Floating Screed over Insulation
Screed laid onto a polythene slip membrane over rigid thermal or acoustic insulation boards, requiring a minimum thickness of 65 mm unheated or 75 mm over heating pipes in sand-and-cement.
Force drying
Drying with heat and dehumidifiers: from day 7 on calcium sulphate.
Forced-action mixer
A pan mixer with blades. Fast-drying screeds need a forced-action mixer; a free-fall mixer won't do.
I.S. EN 13813
The standard for screed materials, from NSAI in Ireland. It classes screeds by strength (C) and flexural strength (F).
In-situ crushing resistance
A screed's resistance to being crushed by traffic, tested with the BRE screed tester.
Laitance
A weak skin on calcium sulphate screeds, sanded off before flooring.
Levelling screed
A screed finished to a set level to take the final flooring.
Perimeter strip
Foam round walls and columns that lets a floating screed move.
Power Float Compaction
Petrol or electric rotary pan and blade machine run across freshly ruled sand-and-cement screed to compact the upper crust and leave a dense, smooth surface.
S.100
The Department of Agriculture's minimum specification for farm concrete: Mix A C35/45, Mix B C30/37.
Screed Rail ( Screed Batten )
Straight timber or steel profile bedded to laser level on dabs of mortar so the screeder can draw a straightedge across the bay to establish finished floor level.
Shrinkage Relief Saw Cut
Shallow mechanical cut chased 15 to 20 mm into a newly hardened sand-and-cement screed across thresholds and column lines to direct shrinkage cracking into a straight, fillable line.
SR1, SR2, SR3
Surface regularity classes named in BS 8204: 3, 5 and 10 mm under a 2 m straightedge.
Surface Regularity (SR1, SR2, SR3)
BS 8204 flatness classes measured beneath a 2 metre straightedge with a slip wedge: SR1 allows a 3 mm gap, SR2 allows 5 mm (the domestic norm), and SR3 allows 10 mm.
Unbonded screed
On a separating layer, not stuck to the base. Sand and cement: 50 mm minimum, 70 mm specified.
Unbonded Screed on Membrane
Sand-and-cement screed of at least 50 mm depth laid on a heavy polythene separating sheet over a concrete slab where bonding is impractical or damp protection is required.
Wearing screed
A screed that is itself the floor surface. Concrete wearing surfaces are BS 8204-2.
Wet-on-Wet Slurry Primer
Neat cement and SBR polymer bonding coat brushed into a dampened concrete subbase immediately before compacting a bonded sand-and-cement screed on top.
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