I often get asked “just what is screeding?” In short, screeding (at least as practiced in the UK) is a thin, top layer of material such as sand or cement, which is poured on top of structural concrete or insulation. This material is then levelled and smoothed so it is the same height as the forms, or guides, that surround it. Imagine a person measuring a cup of flour, then using a knife to smooth the top. The flour is compacted and has a smooth top layer. This is screeding in its most basic form.
The most common use of screeding is in gardening and landscaping. The contractor pours concrete into the forms or guides and allows it to fill to a certain height. To ensure the concrete will be level when it dries, screeding must be done now. To do this properly, a tool such as a long piece of aluminium or timber, which is larger than the guides, is slowly moved over the guides. This tool is also moved in a back and forth motion while screeding to level and smooth the concrete, which ensures a perfectly level floor. There are also industrial tools available, which are ideal for use over larger areas.
There are four main types of floor screeding designs:
- Bonded screed
- Unbonded screed
- Floating screed
- Underfloor heating screed
Bonded Screed
This needs to be laid on a shot-blasted / scabbled concrete base, and be bonded using an adhesive such as PVA, SBR, epoxy resin or good old-fashioned cement.
Unbonded Screed
These are not bonded directly to the concrete base, but are intentionally debonded with the use of a DPM (damp-proof membrane).
Floating Screed
Floating screed is used on top of rigid insulation boards. It is recommended that the thickness of a floating screed should be between 65 and 90 mm.
Underfloor Heating Screed
A traditional sand and cement screed is an ideal choice of screed for underfloor heating. Under floor heating manufacturers and suppliers generally recommend a minimum screed depth of 60 mm to use with their systems.
The delivery, mixing, and pumping of screed is usually from a single vehicle which pours the screed directly from the mixing pan to the floor at a range of up to 60 metres. For smaller applications, the screed can be hand laid.
Screeding can be left bare to achieve a contemporary urban style to the building and it’s environment, similar to that in buildings by Japanese architect Tadao Ando, who is renowned for exemplary craftsmanship which evokes a Japanese sense of space. Alternatively other finishing materials can be applied on top.
