Why a ‘Perfect Install’ Still Feels Lukewarm – The Screed Factor
Nothing beats that “feet-first” warmth from UFH, but only if it arrives promptly. For a builder or renovator, a sluggish system is a callback waiting to happen. You know the problem isn’t the install, but the system just isn’t responding. This is why screed thermal conductivity matters.
The issue isn’t the heat – it’s the transfer. That slab of standard screed over the pipes is behaving like a thermal barrier, creating a ‘lag’ that leaves the room cold when it should have heated up straight away. It’s all down to thermal conductivity.
This kind of problem is where our specialism makes a real difference. At Capital Screeding, we supply and install screeds, but we are specialists in high-performance liquid screeds designed specifically for UFH. Based in London, we support builders across Essex and the South East who need help to solve this issue. We’re trusted because we know thermal conductivity inside-out, and we know how to make your UFH perform.
What is Thermal Conductivity (and Why Does It Impact UFH)?
Thermal conductivity is a measure of how quickly and efficiently heat can pass through a material.
We experience thermal conductivity every time we stir a cup of tea with a metal spoon. It gets hot fast because of its high thermal conductivity. Replace it with a wooden spoon and, no matter the temperature of the tea, it will heat up very slowly because wood is an insulator and has a low thermal conductivity.
Your underfloor heating pipes are the equivalent of that hot cup of tea, and your screed is the transfer material that you need to heat up fast.
Traditional sand and cement screed acts more like the wooden spoon. It’s a poor conductor, so it creates a ‘lag’ by hoarding the heat instead of releasing it. Which is why conductivity is the most important metric for a UFH system that performs well.
Why Traditional Screed is Equivalent to the ‘Wooden Spoon’
Let’s stick with the wooden spoon/metal spoon analogy as a way to understand your UFH’s performance.
Traditional Sand & Cement - The 'Insulator'
So, why is sand and cement screed, applied by hand, the “wooden spoon” of your UFH system? There are two reasons:
It’s Very Thick – To achieve the necessary strength, it has to be laid at a depth 65mm to 75mm. This creates a dense barrier that the heat has to fight through.
It’s Full of Air – The texture and density of the material, and hand-application means it’s packed with tiny air pockets, or ‘voids’. Air is an excellent insulator.
These two factors mean the screed resists the heat from your pipes. It’s a “slow” material.
High-Performance Liquid Screed - The 'Conductor'
Specialist liquid screeds are the “metal spoons” of underfloor installation. Here’s why we wouldn’t use anything else:
It’s Denser – Liquid screed is self-compacting, so those insulating air pockets are eliminated.
It’s Thinner – Because it’s so much stronger, it can be laid thinner (as little as 40-50mm), so there’s less material for the heat to have to pass through.
It’s a Better Conductor – Liquid screed is a much better conductor of heat. Its high thermal conductivity means it is designed to transfer warmth, rather than hold onto it.
This combination means the heat from your pipes transfers to your feet quickly and efficiently.
“I’ve Already Got Traditional Screed. Do I Have to Rip It Up?”
This is the question we’re regularly asked so we know how frustrating it is to be in this position.
The honest, direct answer is that you can’t change the properties of the screed once it’s laid. It will always be a ‘wooden spoon’ – a material with low conductivity. No amount of adjusting the boiler or manifold will change how slowly that thick, dense slab of material heats up.
For a full-scale renovation where the UFH performance is the primary complaint, the only way to get that fast, responsive ‘metal spoon’ performance is to replace the screed.
There are, however, things you can do to manage the situation:
Upgrade Your Controls – A smart thermostat (like a Nest or Hive) can “learn” your screed’s lag time. It will schedule the boiler to come on 2-3 hours before you need the heat, so the room is warm when you need it.
Check Your Floor Finish – You can avoid exacerbating the problem. If you have a slow screed, putting a thick carpet and heavy underlay on top is the equivalent of adding a second insulator. Choose high-conductive finishes like LVT, laminate, or tiles instead.
The Capital Screeding Solution
Installing UFH is a big investment – you can’t afford it to be bottlenecked by your screed choice. As London’s specialist liquid screed installers, we will make sure your system has the perfect screed partner.
We supply and install advanced liquid screeds with the high thermal conductivity your project requires. For our clients in Essex and the South East, this means faster heat-up times, happier customers, and no complaints about sluggish floors.
Don’t leave your UFH performance to chance.
Talk to the screed specialists. Contact our London-based team today to talk through your UFH install in Essex or the South East. We’ll help you specify the right liquid screed to guarantee a fast, efficient system – 020 3369 3396
