How to Prepare a Floor for Liquid Screed
How do I prepare a floor for liquid flow screed?
Floor preparation for liquid flow screed is a five-stage process: clear the substrate of all debris, install separation or insulation layer, fit underfloor heating if required, fit perimeter expansion strip, then complete final pre-pour checks. Each stage is critical — skipped steps cause cracking, debonding or curling.
Step 1 — Clear and clean the substrate
Remove all dust, debris and loose material from the substrate. This prevents contamination of the underlayer and ensures the separating membrane lies flat. Sweep, vacuum if necessary, and check for any sharp protrusions that could puncture the membrane.
Step 2 — Install the separation or insulation layer
Lay a polythene separation membrane (1000-gauge minimum) across the entire floor area with 100 mm overlaps and taped joints. Where insulation is specified, lay PIR or EPS boards close-butted to the perimeter before the membrane goes down.
Step 3 — Fit underfloor heating pipework (if applicable)
UFH pipework must be installed by a competent engineer, secured at the correct centres for your heat source, with manifolds positioned for access. Pressure-test and balance the system before pouring — once the screed covers the pipes, fixing errors are extremely expensive.
Step 4 — Fit perimeter expansion strip
A 10 mm closed-cell foam expansion strip runs around the full perimeter of the room and against any rising elements (pipes, columns). This allows the screed to expand and contract without cracking against rigid edges.
Step 5 — Final pre-pour checks
Confirm: substrate level checked, datum points marked at the required finished screed level, doorways and openings sealed, the room is closed to other trades during pour and for 48 hours after, and the property is at minimum 5°C for the next 72 hours. Once the screed is down, see our drying times guide for when you can walk on it and accept floor finishes.
Why does proper preparation matter?
Liquid screed is unforgiving of preparation faults — debris causes weak spots, missing perimeter strip causes edge cracking, incorrect membrane causes bonding failure. Every pour we arrive on site to find one or more of these missed. We will pause the pour rather than work over bad preparation.