What is a screed board?
A screed board is either a levelling tool or a flooring panel. The tool is a flat, straight board or aluminium rule drawn across wet screed or concrete, usually along rails, to strike it off flat. The panel is a dry screed board, a rigid factory made sheet laid in place of a wet screed.
Which one someone means usually depends on who is talking. A screeder or groundworker means the tool. A builder planning a loft, a timber floor or an underfloor heating overlay usually means the panel.
The screed board as a tool
Wikipedia describes the tool as a flat board, sometimes called a screed board or floating screed, or a purpose made aluminium tool used to smooth and level materials. A concrete finisher uses it to cut off excess wet concrete and bring the surface of a slab to the right grade and smoothness.
In practice the board rests on two screed rails or level guides and is drawn along them, so the surface ends up at the height of the guides. Probst, for example, sells its rail sets without a board and describes the aluminium screeding board gliding over the rails. On a small floor a straight timber board does the same job, provided it is genuinely straight.
After the board has struck the screed off, the surface is closed with a trowel or a power float. The board levels; it does not compact. On a semi dry screed, compaction is a separate step that has to be done properly first.
The dry screed board as a panel
A dry screed board is a flooring panel that gives a solid, flat base without a wet trade. One widely sold example is Cellecta ScreedBoard 20, which its supplier describes as a 20mm calcium sulphate board made from recycled high density gypsum and reinforced with cellulose fibre. It weighs 25kg per m², the boards join with interlocking edges and no screws, and it can be laid over timber, steel and concrete floors, floating floors, existing joists or routed insulation.
The appeal is time. A dry screed board has no wet screed drying time, whereas a wet screed typically dries at about 1mm a day up to 40mm and more slowly beyond that, in good conditions. Boards are also used over underfloor heating, where the supplier says the board's high thermal conductivity helps the system run efficiently, and as acoustic layers; the supplier lists Robust Detail compliance for some separating floor types.
There are trade offs. A dry board is a proprietary system: the supplier's own tool list for ScreedBoard 20 names its adhesive and edge strip, and the board maker's rules decide which finishes and details are allowed. Over underfloor heating, the supplier warns that the heating must be pressure tested and must never be used to dry the adhesive.
Wet screed or screed boards?
| Wet screed | Dry screed board | |
|---|---|---|
| Typical depth | 25mm bonded to 65mm or more floating (sand and cement); from about 35mm floating (liquid) | About 20mm for a typical board |
| Drying time | About 1mm a day to 40mm in good conditions | None for the board itself |
| Weight | Heavier per m² at full depth | About 25kg per m² for a 20mm board |
| Best suited to | Ground floors, extensions, new builds, heated floors | Upper floors, timber structures, refurbishments where depth and weight are tight |
Swipe the table sideways to see every column.
Thickness figures are from the MPA data sheet and the Designing Buildings Wiki; board figures are the supplier's.
Common mistakes
- Using a bowed board as a straightedge. Every bow ends up in the floor.
- Expecting the board to compact the screed. It strikes off; compaction comes first.
- Choosing dry boards to save depth without checking the finish. The board maker's rules on adhesives, tiles and joints decide what can go on top.
- Drying adhesive under boards with the heating. The supplier of Cellecta ScreedBoard says never to do it.
How this relates to our services
We lay wet screeds: sand and cement, liquid and underfloor heating screed. We do not sell screed boards or tools. If you are weighing dry boards against a wet screed, tell us the depth you have, the structure underneath and what is going on top, and we will tell you honestly what a wet screed would need.
Sources
- Screed, Wikipedia, accessed 25 October 2026
- Probst AZL-EP screeding rail set, ULS Lifting, accessed 25 October 2026
- Cellecta ScreedBoard 20, JCW Acoustic Flooring, accessed 25 October 2026
- Post installation guidance, Gyvlon (Anhydritec), 2024
- Mortar data sheet 22: Screeds, Mineral Products Association, issue 3, October 2023
- Screed, Designing Buildings Wiki, accessed 25 October 2026
- Installation of Cemfloor screed, Cemfloor, accessed 25 October 2026
Part of our screeding glossary, which defines every term we use on site.