What is floor screed and why does an extension need it?

Screed is the smooth, level layer laid on top of the structural concrete slab to give a flat surface for tiles, LVT, or other flooring. Where there is underfloor heating, the screed also encases the pipes and spreads heat evenly across the floor.

Is liquid screed or sand-and-cement better for an extension?

Liquid screed is the right choice for any floor with wet underfloor heating because it flows to fully encase the pipes and dries very flat. Sand-and-cement is cheaper and fine for small floors without UFH, but it leaves gaps around the pipes that reduce heating efficiency.

How long does screed take to dry before tiling?

A typical liquid screed over underfloor heating takes several weeks, and on a cold or poorly ventilated UK site the real figure often runs to 60 to 90 days rather than the textbook rate. The gate is not the calendar but a moisture test, so the floor only goes down once the screed reads at or below the threshold.

What is laitance on a liquid screed?

Laitance is the weak, dusty surface layer that forms on anhydrite liquid screed as it cures. It has to be mechanically sanded off a few days after the pour before any flooring can be laid, and a good screed company includes this in their service.

Can you put a kitchen on anhydrite screed?

Yes, anhydrite screed works fine in a kitchen as long as the floor is sealed and the tiles and grout form a waterproof surface. It is sensitive to standing water though, so it is not suitable for rooms like bathrooms that regularly get wet.

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Phase 7 · Second Fix · Task 04 of 07

Screeding: The Floor You Never Knew You Needed

Liquid screed costs £18 – £34 per m²/m² and takes 8-12 weeks to dry, and both are easy to underestimate. Here's what to expect and how to manage it.

9 min readUpdated 2026Premium

Timeline infographic showing screeding milestones from pour day through foot traffic, UFH commissioning, moisture testing, and earliest tiling date for a 50mm screed

Prerequisites

Complete these first

If your floor has underfloor heating, it needs liquid screed, and that's where budgets slip. Some builders quote for the sand-and-cement screed they're used to rather than the specialist liquid screed the job needs, and liquid can cost roughly double. It's a different product at a different price, so if a screed line in your quote looks cheap, check which one it's actually for before you rely on the number.

Screed is the smooth, level layer that goes on top of your concrete floor slab. Your slab is structural, but it's not flat enough for tiles, LVT, or any finished flooring. The screed provides that flat surface. If you have underfloor heating, the screed also encases the heating pipes and distributes heat evenly across the floor.

Most homeowners don't even know screed exists until their builder mentions it. But it controls your project timeline more than almost any other single trade. A 50mm screed needs 8-12 weeks to dry before you can tile over it. Get the timing wrong and everything after it slides.

What this guide covers

01Liquid Screed vs Sand-and-Cement
02Why the Screed Quote Can Catch You Out
03The Anhydrite Question
04Installation Day
05The Long Wait
06Commissioning the UFH (and Why It Speeds Drying)
07Checking the Screed Before Tiling
08Expansion Joints and Cracking
09What This Means for Your Timeline
10Getting Quotes and Managing Cost

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