How to Pour Screed — Step-by-Step UK Guide

What You'll Need

Before You Start

• Determine your screed type — bonded (stuck to slab), unbonded (on DPM) or floating (on insulation). This determines thickness and preparation.
• Check the subfloor is clean, dry and free from dust, oil and loose material. Sweep and vacuum thoroughly.
• Set your finished level using a laser level or dumpy level. Mark datum points on the walls around the room.
• If installing underfloor heating, ensure all pipes are fixed, pressure-tested and the system is signed off before screeding.
• Use our Screed Calculator for material quantities and our Floor Levelling Calculator if you need to level an existing floor first.

Step-by-Step Instructions

Step 1: Prepare the Substrate

For a bonded screed, clean the slab and hack up the surface with a scabbling tool to provide a key. For an unbonded screed, lay a DPM across the entire floor, lapping up the walls by 100mm and overlapping sheets by 150mm with taped joints. For a floating screed on insulation, lay rigid insulation boards tightly together and cover with a polythene slip layer.

Step 2: Set Screed Rails

Place screed rails (50mm timber battens or steel screed rails) across the room at 1.5-2m intervals. Level them to your finished floor height using a laser level. Bed the rails on small mounds of stiff screed mix and allow to set. These guide your screed bar to the correct level.

Step 3: Apply Bonding Agent (Bonded Screed Only)

Brush SBR bonding agent (diluted as per manufacturer instructions) onto the concrete slab. Apply the screed while the bonding agent is still tacky — do not allow it to dry completely. Work in manageable sections.

Step 4: Mix the Screed

Mix 4 parts sharp sand to 1 part cement in a cement mixer. Add water gradually — the mix should be semi-dry. Test by squeezing a handful: it should hold together without releasing free water and crumble when pressed with a thumb. Over-wet screed shrinks and cracks.

Step 5: Lay the Screed

Tip the mixed screed between the rails. Spread it roughly with a shovel, slightly higher than the rails. Then compact it by tamping down with a wooden float or the flat of a shovel. Build up in layers if the screed is over 50mm thick — compact each layer.

Step 6: Level with a Screed Bar

Place the screed bar (a long straight edge) across the rails and draw it towards you with a sawing motion. This cuts the screed to the correct level. Fill any low spots, add more screed and pass the bar again. Repeat until the surface is flat and level with the rails.

Step 7: Remove Rails and Fill

Once the screed between rails has stiffened slightly (1-2 hours), carefully remove the rails. Fill the grooves left behind with fresh screed mix and trowel smooth. Compact and level to match the surrounding surface.

Step 8: Float the Surface

Use a wooden float to close the surface and bring it to a consistent finish. For a smooth finish (e.g. under vinyl or tiles), follow with a steel trowel. Do not over-trowel — this brings cement to the surface and creates a weak layer (laitance) that can debond.

Step 9: Cure the Screed

Cover the screed with polythene sheeting for the first 7 days to slow drying and ensure proper curing. In hot or draughty conditions, this is essential — rapid drying causes shrinkage cracking. Do not force-dry the screed with heaters or dehumidifiers during the initial cure period.

Step 10: Allow to Dry

After the 7-day curing period, remove the polythene and allow the screed to dry naturally. Ventilate the room but avoid draughts directly on the surface. Test moisture levels before applying any floor finish — use a moisture meter and follow the floor finish manufacturer limits (typically below 75% RH for tiles, below 65% for vinyl).

Common Mistakes to Avoid

• Too-wet mix: Over-wet screed shrinks as it dries, causing cracks and a weak surface. Always aim for a semi-dry consistency.
• Insufficient thickness: Screed that is too thin cracks under load. Bonded screed must be 25mm minimum; unbonded 50mm minimum; floating 65mm minimum.
• Skipping the bonding agent: On a bonded screed, without primer/SBR the screed will debond from the slab, causing hollow spots and cracking.
• Forced drying: Using heaters or opening windows during the first 7 days causes rapid shrinkage and cracking. Cure under polythene first.
• Applying finishes too soon: Laying tiles or vinyl on damp screed traps moisture, causing adhesive failure, mould and floor finish damage.

Cost Estimate (2026 UK Prices)

Use our Screed Calculator and Floor Levelling Calculator for exact quantities for your project.