Sand and Cement Screed: Bonded, Unbonded and Floating Explained
- Screeding.com
- Apr 22
- 2 min read
Sand and cement screed — sometimes called traditional screed — has been used in UK construction for decades. It remains the go-to choice for many applications, particularly where bond strength is critical or where liquid screed is impractical. There are three installation methods, and choosing the right one matters enormously.
Bonded Screed
Bonded screed is mechanically and adhesively fixed to the structural substrate below. The base is scabbled or shot-blasted to open the surface, then a bonding agent — typically SBR latex or epoxy primer — is applied before screeding. This creates a strong key between the screed and the base. Minimum depth is 25–40mm. It is the thinnest option and is used in commercial settings where floor loading is high and depth must be minimised. Not suitable over insulation.
Unbonded Screed
Unbonded screed sits on a polythene slip layer that separates it from the structural base. This is used where the substrate cannot be adequately prepared for bonding, or where differential movement is expected. Minimum depth is 50mm to prevent curling and cracking. Commonly specified in new-build residential projects and commercial refurbishments where bonding is impractical.
Floating Screed
Floating screed is laid over a compressible layer — typically thermal or acoustic insulation. Because the screed is unsupported at its base, it requires the greatest minimum depth: 65–75mm. Used extensively in projects with underfloor heating, and for acoustic floors in flats and apartments where sound insulation must meet Building Regulations.
When to Choose Sand and Cement Over Liquid Screed
Sand and cement is often the better choice when bonded application is required over an existing substrate, when small areas make liquid screed pump hire uneconomical, or when the programme allows for longer drying times. For large open areas, liquid screed is generally faster, thinner, and more cost-effective. Not sure which is right? Use our Screed Advisor tool for a recommendation in 60 seconds.