What is liquid screed?
Liquid screed is a floor screed mixed wet enough to flow. It's pumped into the room, finds its own level, and is knocked flat with a dappling bar instead of being compacted by hand.
There are two kinds: calcium sulphate screeds (anhydrite or hemihydrate), and cement-based liquid screeds and cement-based liquid screed, which behave more like a traditional screed once they've set.
Free, no obligation. One local screeding contractor prices it, not five.
What it's made of
Both kinds are a binder, fine aggregate, water and admixtures, batched at a plant or from bags. The binder is the difference.
| Calcium sulphate | Cement-based | |
|---|---|---|
| Binder | Calcium sulphate. Anhydrite is a by-product of making hydrofluoric acid; hemihydrate comes from flue gas desulphurisation | Cement with a flowing admixture |
| Colour when wet | Red or pink fluid (a thin calcium sulphate screed+) | Dark grey fluid (cement-based liquid screed) |
| Laid | Floating, unbonded or bonded | Floating or unbonded (cement-based liquid screed); cement-based liquid screed also bonded |
| Surface skin | Anhydrite can leave laitance that is sanded off; hemihydrate and low-laitance mixes don't | Light abrading and cleaning (cement-based liquid screed); no sanding (cement-based liquid screed) |
| Standard | BS EN 13813, laid to BS 8204-7 | I.S. EN 13813, laid to BS 8204 (cement-based liquid screed); EN 13813 (cement-based liquid screed) |
How it goes down
- Ready the floorInsulation flat, a perimeter strip round every wall, polythene over the insulation lapped and taped, heating pipes clipped and pressure tested. The full checklist.
- Set the levelTripods or levelling pins set to the finished height across the room.
- Pump it inFrom a truck mixer or a mobile mixing vehicle, through a hose. A crew can lay up to 1,500 m² of calcium sulphate a day, or 2,000 m² of cement-based, against about 150 m² of sand and cement.
- Dapple it
Bars pushed through the wet screed in two directions to release air and level it (cement-based liquid screed asks for two passes at 90 degrees).- Leave it closed
No draughts, sun or heating for the first 24 to 48 hours (cement-based liquid screed), 48 to 72 hours, or 7 days with windows and doors closed (cement-based liquid screed). Foot traffic after 24 to 48 hours. - Dapple it
Where it works, and where it doesn't
- Underfloor heating. It flows round the pipes with no voids and can be 25 mm over them. Heating and liquid screed.
- Big, open floors. Fewer joints than sand and cement: bays up to 1,000 m² on an unheated floor.
- A flat finish. Calcium sulphate reaches SR2 under BS 8204, and cement-based easily reaches SR1.
- Not to falls. A liquid screed can't be laid to falls. A shower floor or a drained area needs a different screed.
- Not as a wearing floor. Cement-based liquid screed is non-structural and non-wearing: it's the layer under the floor finish.
Every screed type, liquid and otherwise, is compared on floorscreeding.ie.
Liquid screed poured by the contractor who takes your call
Calls on this site ring JAM Floor Screeding: James Mulhall, based in Portlaoise, 25 years laying floors. Lines open Mon to Sat, 7am to 6pm. These are his jobs.
“JAM were punctual, professional and efficient and did an outstanding job on pouring our new floor as part of a renovation. Very highly recommend!”
“Excellent work, laser level finish, neat and tidy worker, highly recommend.”
“Top class work by james and his crew, highly recommend”
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What is liquid screed questions
What is liquid screed made of?
A binder (calcium sulphate, or cement with a flowing admixture), fine aggregate, water and admixtures, mixed wet enough to flow and self-level.
Is liquid screed the same as self-levelling compound?
No. A levelling compound is a few millimetres on top of a floor. Liquid screed is the floor layer itself, normally 25 mm or more.
How soon can I walk on liquid screed?
After 24 to 48 hours. It can take load after 7 days.
Can liquid screed be laid to falls?
A cement-based liquid screed can't. Use a sand and cement screed where the floor has to fall to a drain.
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