Kick back and get a feel for the unsung hero beneath your feet.
When people consider underfloor heating (UFH), they often see a warm, inviting home. They think of cosy floors, no visible radiators, and fewer chilly mornings. But what actually makes it all work? One unsung hero is doing all the heavy lifting underneath those floorboards: liquid screed.
It’s not the flashiest part of a UFH system, but if you get it wrong, you’ll feel it on the floor—and the wallet. At Wright Readymix, we’ve been supplying screed to developers, builders, and contractors across the South West for years. Whether it’s a full-scale new build or a basement refurb, we know there’s no one-size-fits-all approach when it comes to screeding over UFH. In this guide, we break down what screed does, which type works best with UFH, and how to avoid the common pitfalls that cost time, money, and callbacks.
Key Highlights
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New UK data shows UFH with high-performance screed cuts energy use by up to 25% in new builds.
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Liquid flowing screed provides better thermal conductivity, quicker installations, and thinner depths. This makes it perfect for retrofits in tight spaces.
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Poor screed practices—like early heating or bad mixing—remain key causes of UFH failure and costly callbacks.
How Does Screed Work with Underfloor Heating?
Screed acts as the thermal bridge between your heating pipes and the finished floor surface. Once your UFH system is installed—usually laid over insulation boards—the screed is poured on top to cover the pipework and form a smooth, level base. It’s what transfers the heat up into the room and keeps it there.
But screed isn’t just filler—it’s a functional part of the heating system. The better it wraps around the pipes, the more evenly heat is distributed across the surface. That’s why thermal conductivity and screed thickness are key considerations in UFH projects.
Most setups call for a screed depth between 50mm and 75mm, depending on the material used and the build’s specific requirements. Too thick, and it acts like a heat sponge. Too thin, and you risk cracks or weak spots. Liquid screeds tend to perform best in UFH systems thanks to their ability to flow easily around the pipes and minimise air gaps. This helps improve heat transfer and speeds up response time.
Types of Screed for Underfloor Heating: Pros, Cons & Best Use Cases
Not all screeds behave the same under heat. Choosing the right one depends on your timescale, floor build-up, and what kind of performance your project demands. Below are the most common screeding options used in UFH installations—and when each one makes sense.
1. Traditional Sand and Cement Screed - The classic choice. This semi-dry mix is made with sharp sand and cement, typically at a 4:1 ratio. It’s manually applied and levelled with a trowel—great if you prefer a hands-on approach or need more control over the finish.
It’s a good all-rounder but less thermally efficient than newer materials. For it to work well with UFH, you’ll usually need to allow a 65–75mm depth. It also takes longer to cure, so it’s better suited to builds without tight handover deadlines.
2. Liquid Flowing Screed (Anhydrite/Gypsum-Based) - Flowing screeds are a go-to option in many South West new builds. They are self-levelling, fast to install, and ideal for UFH. They easily pour around heating pipes, which creates fewer air pockets. This improves conductivity, so heat travels to where it’s needed more quickly. Because of its density and flow, it can be laid thinner—around 50mm in many cases—saving time and materials. The only catch? Check compatibility with specific floor finishes, especially if they are moisture-sensitive. Also, make sure the surface is well-primed before tiling.
3. Fast-Drying Screeds - For projects on the clock, fast-drying screeds can be a lifesaver. Modified with additives, these options cure quickly—some within 3–7 days—so you can lay the final flooring much sooner. They're great for commercial jobs or phased housing developments where turnaround time is tight. Make sure to mix and apply the screed as specified. Otherwise, you might lose the speed advantage and face post-installation problems.
4. Fibre-Reinforced Screeds - If your project has big floor areas or you expect thermal movement, fibre-reinforced screeds add extra strength. Tiny polypropylene fibres are mixed in to improve tensile resistance and reduce shrinkage cracks. These screeds are ideal for areas where durability is key—think garages, open-plan layouts, or any UFH system running at higher output. They don’t replace proper jointing or curing, but they add a welcome layer of insurance against cracking.
Key Benefits of Screed for UFH: Why It Pays to Get It Right
Get the screed right, and the rest of the underfloor heating system works like clockwork. From energy performance to room comfort, here’s why screed plays a bigger role than most people realise.
1. Better Heat Distribution, Lower Bills - Screed acts as a thermal mass, absorbing heat from the pipework and releasing it gradually across the floor’s surface. Liquid floor screeds are especially good at this. They mould tightly around the pipes, eliminating air gaps and improving efficiency. That even coverage means the system can run at lower temperatures—often 35–45°C—instead of the usual 60+ you'd expect from radiators. According to the UK Green Building Council (2024), pairing UFH with high-performance screed can cut energy use by up to 25% in new homes.
2. Consistent Comfort Across Every Room - Because heat spreads out evenly under a screed layer, you avoid the typical hot-and-cold spots that plague radiator systems. No more freezing toes in one corner and boiling socks in another—it’s just a stable, warm environment from wall to wall. This is especially helpful in open-plan spaces. A steady temperature dramatically improves comfort and boosts heating system performance.
3. Works With Most Floor Finishes - Most standard flooring materials, like stone tiles, engineered wood, and carpet, work with screed. Just make sure the moisture content is right before installation. Liquid screeds usually dry faster. However, no matter the type, always check that the screed is fully cured before installing the final surface. Consider using a moisture barrier or insulation underlay for extra protection for wood or laminate.
Installation Considerations: What to Get Right Before the Pour
Laying screed over a UFH system isn’t just about tipping and trowelling. A bit of planning upfront makes the difference between a flawless floor and a cracked headache. Here’s what to lock down before, during, and after the pour.
1. Substrate Prep: No Shortcuts Here - Start with a clean, level, and dry base. UFH pipes should be properly secured, and insulation boards should be laid flat with no movement. Any gaps or uneven areas will cause heat inefficiencies and could lead to cracks down the line. Foil-backed insulation boards are widely used in South West developments. They reflect heat upwards and enhance energy retention. Seal the edges, tape the joints, and don’t forget perimeter insulation to allow for expansion.
2. Depth & Coverage: Match the Mix to the Build - Standard sand and cement screeds usually require 65–75mm, while flowing screeds can be applied as thin as 50mm—but always check the spec. Too much thickness slows response time, and too little can weaken structural performance. In retrofits with limited floor build-up, use high-performance screeds. They have better thermal conductivity and stay responsive even at shallower depths.
3. Drying Time: Resist the Rush - Don’t be tempted to fast-track your flooring. Traditional screeds dry at roughly 1mm per day, so a 70mm screed could take ten weeks to reach safe moisture levels. Fast-drying screeds cut that significantly but still need testing. Before applying any final finish, use a digital hygrometer or carbide bomb test to confirm safe moisture levels. When commissioning the UFH system, start at 20°C and raise it slowly—no more than 5°C per day—to prevent thermal shock.
4. Expansion Joints: Plan Ahead to Prevent Cracks - Large spaces or complex layouts need expansion joints to allow for movement. These should line up with structural breaks and fixed features like columns or walls. Cracks from thermal expansion are common in UFH floors, especially if joints are skipped or spaced too far apart. Don’t wing it. Stick to the layout guidelines. Consult your screed supplier or structural engineer if you have larger pours.
Common Mistakes (and How to Avoid Them!)
Even seasoned pros occasionally slip up, especially when timelines get tight or spec sheets get skimmed. Here are the top slip-ups we see with UFH screeds—and how to dodge them.
1. Flooring Laid Too Early - It’s tempting to crack on with the floor finish once the screed looks dry, but looks can be deceiving. Moisture trapped below the surface will cause trouble later—especially with timber or laminate. Always test moisture levels before laying any floor coverings. A digital meter will give you peace of mind—and help avoid warped boards, bubbled vinyl, or failed adhesives.
2. Poor Mixing or Ratios - If you're using traditional sand and cement, get the mix right—typically 4:1, with clean, sharp sand and just enough water to bind. Overwatering, lazy mixing, or winging the ratio leads to weak, brittle screed that won’t last a year. For specialist mixes like fast-drying or fibre-reinforced options, follow manufacturer guidance to the letter. Shortcuts here will cost you later.
3. Skimping on Insulation - Cutting corners on insulation is one of the biggest energy-wasting sins in UFH installs. Heat will always find the path of least resistance—and without good insulation below the pipes, it’ll go straight into the slab. Building Regulations Part L now require high-performance insulation in new homes. Even in retrofits, laying proper insulation boards can make or break your system’s efficiency rating.
4. No System Commissioning - Turning on the heating too soon—or ramping it up too fast—is one of the quickest ways to crack a screed. It causes rapid thermal expansion before the material is properly cured. Instead, start low. Begin at 20°C, increase slowly, and don’t exceed 55°C. Most systems are ready to be commissioned after 7 days (for liquid screeds) or longer for traditional mixes.
Why Choose Wright Readymix for UFH Screed Supply?
Many screed suppliers exist, but few grasp the challenges of a live building site. They often overlook tight deadlines and the need to get it right on the first try.
At Wright Readymix, we provide floor screed solutions designed for underfloor heating systems in the South West. Whether it’s a developer in Bristol working to Part L regs or a domestic installer tackling a retrofit in Dorset, get in touch. We’ve got the screed—and the know-how—to support your project.
We offer:
No call centre scripts. No guesswork. Just proper advice, dependable supply, and screed that performs under pressure.
Your Screed. Your Success. Your Call.
Choosing the right screed for your underfloor heating system is crucial. It impacts performance and longevity and helps you avoid expensive mistakes.
Key Takeaways
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The right screed boosts heat efficiency, comfort, and flooring fit, especially when it suits the building's needs.
Whether you’re running a site, installing for a client, or fitting out your own space, it pays to get this stage right. Limited slots are available, so secure your UFH-ready screed today. Call 0117 958 2090 or get in touch for a fast, no-obligation quote.
