Screed types · checked 29 October 2026
Liquid screed
Calcium sulphate (anhydrite) flowing screed: how deep, how it's laid, how long it takes to dry, and what has to happen before the floor goes down.
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Figures checked against each source on 29 October 2026. How we check
Liquid screed is a flowing screed, pumped into the room and levelled while it's wet. The classic liquid screed is made on a calcium sulphate (anhydrite) binder. It flows round heating pipes, cures without being covered and can go down much thinner than sand and cement.
Gyvlon lists 35 mm as the minimum floating depth in a house and 25 mm as the minimum cover over heating pipes. It dries at about 1 mm a day for the first 40 mm. Before tiles or timber go down, the surface has to be sanded, tested and primed.
In Ireland "liquid screed" also covers flowing screeds on a cement binder, such as Roadstone FlowPlus. Those behave differently, especially at the floor-finish stage: see cement-based liquid screed.
Screed planner
Plan your screed
Put in your floor and the day it's laid. You get the volume, the weight, when it should be dry enough for floor finishes, and when the heating can go on, from the makers' own figures.
Drying times are for good conditions, closed up and ventilated. The floor is tested before finishes go down, not guessed. None of the Irish screeding contractors' sites we checked publish a price per m², so the price comes from your floor.
What it's made of
Gyvlon's screeds use a calcium sulphate binder that is a by-product of making hydrofluoric acid, mixed with aggregates and additives and made to BS EN 13813. They're batched at ready-mix plants and arrive in truck mixers or mobile mixers. BS 8204-7 is the code of practice for pumpable self-smoothing screeds.
Calcium sulphate screed is laid in Ireland. Precision Floor Screed, for example, says the Ultraflo hemihydrate screed it lays is supplied throughout Ireland, with a minimum depth of 30 mm.
Sources: Gyvlon flowing screed general data pack (Anhydritec); Precision Floor Screed (Ultraflo hemihydrate screed); Cemfloor Complete technical data sheet (2023). Checked 29 October 2026.
Depths
| Construction | Gyvlon minimum |
|---|---|
| Bonded | 25 mm |
| Unbonded | 30 mm |
| Floating, residential | 35 mm |
| Floating, commercial | 40 mm |
| Cover over heating pipes | 25 mm minimum, 30 mm nominal |
Source: Gyvlon flowing screed general data pack (Anhydritec). Checked 29 October 2026.
Gyvlon's advice is that where the floor zone is deeper than these figures, the extra should go into more insulation, with the screed kept to the minimum. Thinner screed dries sooner.
- Floor finish Goes down once the screed is sanded, tested and primed.
- Calcium sulphate screed From 35 mm floating in a house; 25 mm minimum over the pipes.
- Polythene At least 500 gauge, lapped 100 mm and taped, so the screed can't leak through.
- Insulation Flat and firm, with no rocking.
- Slab The concrete base.
On the day
- Building closed in.Roof on, and any missing doors or glazing sealed with polythene, insulation or ply.
- Edge strip round every wall.At least 8 mm closed-cell strip, 10 mm with underfloor heating, pushed into the corners without stretching.
- Insulation and polythene.Boards flat and firm, overlaid with at least 500 gauge polythene lapped 100 mm and taped. Gyvlon warns never to use the foil tape that comes with insulation boards.
- Pipes fixed and tested.Underfloor heating pipe clipped or stapled at least every 400 mm so it can't float, and pressure tested, preferably with water, before the screed goes in.
- Pour and level.The screed is pumped in and levelled while wet. Gyvlon puts output at up to 1,500 m² a day.
Source: Gyvlon flowing screed general data pack (Anhydritec). Checked 29 October 2026.
After the pour
Keep the building closed and free of draughts for the first 48 to 72 hours. You can walk on the screed after 24 to 48 hours, and load it after 7 days. After that, warmth and ventilation dry it: Gyvlon says dehumidifiers can go in from 72 hours and the underfloor heating can be used to force-dry it from 7 days. Gas heaters and other fossil-fuel heaters should be avoided, because they add moisture to the air.
Drying time
In good conditions a calcium sulphate screed dries at 1 mm a day up to 40 mm and half a millimetre a day after that. Gyvlon's own example: a 50 mm screed takes 40 days for the first 40 mm and 20 days for the last 10 mm, 60 days in all.
Source: Gyvlon flowing screed general data pack (Anhydritec). Checked 29 October 2026.
Before the floor finish goes down
- Sand it. Calcium sulphate screed can form a surface laitance. Gyvlon says it must be sanded before any bonded floor finish, with an orbital sander and vacuum and 60 grit, just before the floor goes down.
- Test it. The screed has to be at or below 75% RH (0.5% moisture), measured with a hygrometer, carbide test or oven test.
- Run the heating first. Where there's underfloor heating, it has to be commissioned and run before floor coverings go down, however dry the screed seems.
- Prime it. A primer seals the surface and keeps cement-based adhesives and smoothing compounds from reacting with the calcium sulphate. Gypsum-based adhesives and compounds are also made.
Source: Gyvlon flowing screed general data pack (Anhydritec). Checked 29 October 2026.
Bays and joints
| Floor | Max bay | Max length | Max shape |
|---|---|---|---|
| Underfloor heating | 300 m² | 20 m | 6 : 1 |
| Unheated, floating or bonded | 1,000 m² | 40 m | 8 : 1 |
Gyvlon also asks for a joint between separately controlled heating zones and at door thresholds, a joint between heated and unheated screed, and a joint over every structural movement joint.
Source: Gyvlon flowing screed general data pack (Anhydritec). Checked 29 October 2026.
Heat transfer
Gyvlon gives its screed a thermal conductivity of 2.2 W/m·K against 1.1 W/m·K for sand and cement, and its Thermio+ screed a certified minimum of 2.3 W/m·K. A screed that conducts better, and sits thinner over the pipes, responds faster to the heating.
Sources: Gyvlon flowing screed general data pack (Anhydritec); Gyvlon Thermio+ technical data (Anhydritec). Checked 29 October 2026.
Questions people ask
How thick is liquid screed?
Gyvlon's calcium sulphate screed: 35 mm minimum floating in a house, 40 mm commercial, 30 mm unbonded, 25 mm bonded, and at least 25 mm over heating pipes.
How long does liquid screed take to dry?
About 1 mm a day up to 40 mm, then half a millimetre a day, in good conditions. Gyvlon's example is 60 days for 50 mm. Dehumidifiers and running the underfloor heating from day 7 speed it up.
When can you walk on liquid screed?
After 24 to 48 hours, according to Gyvlon. It can be loaded after 7 days.
Does liquid screed need sanding?
Calcium sulphate screed does: Gyvlon says it must be sanded to remove laitance before bonded floor finishes, then primed. Cement-based liquid screeds such as Cemfloor don't need sanding to remove laitance.
Can you tile onto liquid screed?
Yes, once it's dry to 75% RH, sanded and primed. The primer stops cement-based adhesive reacting with the calcium sulphate.
Sources (4)
Prices and facts on this page were checked against these published pages. We are not connected to these businesses.
- Gyvlon flowing screed general data pack (Anhydritec): specifiedby.com
- Precision Floor Screed (Ultraflo hemihydrate screed): precisionfloorscreed.ie
- Cemfloor Complete technical data sheet: cdn.shopify.com
- Gyvlon Thermio+ technical data (Anhydritec): gyvlon.co.uk
Get your floor priced
Four taps about the job and one screeding contractor who covers your county rings you. Or call 087 162 1846, lines open 8am to 8pm.