Calculator · checked 29 October 2026
Screed calculator
How much screed your floor takes, when it should be dry, and when the heating can go on.
Figures checked against each source on 29 October 2026. How we check
Put in the floor area, the depth and the screed. The planner gives the volume and weight, a drying date to the usual 75% RH limit, and when underfloor heating can go on, using the makers' published figures.
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.
The rules behind the numbers
| Screed | Drying guide to 75% RH | Heating on from | Depth limits |
|---|---|---|---|
| Sand and cement | 1 day per mm to 50 mm, then 2 days per mm | About 21 days of drying first | 65 mm floating in a house (MPA) |
| Liquid, calcium sulphate (Gyvlon) | 1 day per mm to 40 mm, then 2 days per mm | 7 days, up 5°C a day | 35 mm floating; 25 mm over pipes |
| Liquid, cement-based (Roadstone FlowPlus) | 1 day per mm to 40 mm, then 2 days per mm | 14 days, max 45°C | 25 mm over pipes; no more than 80 mm |
| Fast-drying (Mapei Topcem, Ronacrete) | About 4 days | 4 days (Mapei) | Per the maker |
| Levelling compound (Larsen SLC 2000) | Per the bag | Per the maker | 5–30 mm; 1.6 m² per bag at 10 mm |
Sources: Ronacrete, Drying of Screeds; Roadstone FlowPlus cement liquid screed brochure (RS.BRO-19 Rev 01, March 2022); Gyvlon flowing screed general data pack (Anhydritec); Mapei Topcem technical data sheet; Mineral Products Association, Mortar Data Sheet 22: Screeds (Issue 3, October 2023); Designing Buildings Wiki, Screed over underfloor heating (last edited 15 September 2020); Goodwins: Larsen SLC 2000 floor levelling 25 kg; Cemfloor Complete technical data sheet (2023). Checked 29 October 2026.
Drying times are for good conditions: the building closed up, then ventilated, with no gas heaters. Depth matters most, because every millimetre past 40 or 50 mm takes about two days. That's why liquid screeds, laid thinner, are usually ready sooner, even though they dry at about the same rate per mm.
The test, not the calendar, decides when floor finishes go down. Ask the contractor who's doing the moisture test, and which method they use.
Questions people ask
How do I work out how much screed I need?
Area times depth. 50 m² at 65 mm is 50 × 0.065 = 3.25 m³. At 2,100–2,200 kg/m³ (Roadstone FlowPlus, Cemfloor), that's about 6.8 to 7.2 tonnes.
How long before I can tile or lay timber on screed?
When it tests at or below the maker's limit, usually 75% RH. As a guide: a 65 mm sand and cement screed takes about 80 days (1 day per mm to 50 mm under BS 8204-1, then 2 days per mm), a 40 mm calcium sulphate liquid screed about 40 days (Gyvlon), and a fast-drying screed about 4 days (Mapei, Ronacrete).
When can I turn on the underfloor heating?
Gyvlon calcium sulphate from 7 days, Roadstone FlowPlus from 14 days at no more than 45°C, Mapei Topcem after 4 days, and sand and cement after about 21 days of drying (Designing Buildings Wiki). Bring it up slowly and follow the maker's heat-up cycle.
How many bags of levelling compound do I need?
Larsen gives 1.6 m² per 25 kg bag of SLC 2000 at 10 mm. So 20 m² at 10 mm takes about 13 bags, at €31 to €34.99 a bag incl. VAT at Goodwins.
Why doesn't the calculator give a price for the whole job?
None of the Irish screeding contractors' websites we checked on 29 October 2026 publishes a price per m². The price comes from your floor: the area, the depth, the type of screed, access for the pump and what's under it. Get your floor priced and one screeding contractor who covers your county will give you a figure.
Sources (8)
Prices and facts on this page were checked against these published pages. We are not connected to these businesses.
- Ronacrete, Drying of Screeds: ronacrete.co.uk
- Roadstone FlowPlus cement liquid screed brochure: roadstone.ie
- Gyvlon flowing screed general data pack (Anhydritec): specifiedby.com
- Mapei Topcem technical data sheet: cdn.shopify.com
- Mineral Products Association, Mortar Data Sheet 22: Screeds: mortar.org.uk
- Designing Buildings Wiki, Screed over underfloor heating: designingbuildings.co.uk
- Goodwins: Larsen SLC 2000 floor levelling 25 kg: goodwins.ie
- Cemfloor Complete technical data sheet: cdn.shopify.com
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.