What Is Screed?

Screed is a thin layer of cementitious material applied over a structural concrete slab or insulation to create a smooth, level floor surface. It provides the final surface for floor coverings such as tiles, carpet, vinyl, or laminate to be laid on.

Types of Screed

• Traditional sand and cement screed — A 3:1 or 4:1 (sand:cement) mix laid at 25–75 mm thickness. The most common type in UK domestic construction. Can be bonded (stuck to the slab), unbonded (laid on a DPM), or floating (over insulation).
• Self-levelling compound — A pourable compound that finds its own level. Used for thin applications (2–10 mm) to smooth out minor imperfections before tiling or laying floor coverings.
• Flowing (liquid) screed — Calcium sulphate or anhydrite-based, pumped into place. Ideal for large areas and underfloor heating installations. Faster to lay than traditional screed but needs longer drying time.
• Fast-drying screed — Modified cement screed with additives to reduce drying time. More expensive but allows floor coverings to be applied sooner.

Typical Thicknesses

• Bonded screed: 25–40 mm minimum
• Unbonded screed (on DPM): 50 mm minimum
• Floating screed (over insulation): 65–75 mm minimum
• Self-levelling compound: 2–10 mm

Drying Time

The general rule for traditional sand and cement screed is 1 mm per day for the first 40 mm, then 0.5 mm per day after that. So a 50 mm screed takes approximately 60 days to fully dry. Floor coverings should not be laid until the screed is fully dry (moisture content below 75% RH for most coverings, or below 0.5% for anhydrite screeds).