Liquid Screed for Underfloor Heating: How It Works

Liquid screed is commonly used with warm-water underfloor heating because it flows around the pipework as it is poured, surrounding the pipes and creating an even base for the floor finish. It suits most modern floor build-ups with underfloor heating, but the right product and depth depend on your project.

Cotswold Flow Screed installs pump-applied liquid screed over underfloor heating across Gloucestershire, Worcestershire, Warwickshire and the Cotswolds from our base in Evesham. This guide explains how liquid screed and underfloor heating work together and what to plan before the pour.

Why liquid screed is commonly used with underfloor heating

Warm-water underfloor heating pipes sit within the screed layer, so the screed needs to surround them fully. Liquid screed is poured rather than raked into place, so it flows around and under the pipework and levels itself across the floor.

This makes it a practical choice for extensions, new builds and renovations where heating runs across large or open-plan areas. Traditional sand and cement screed can also be used over underfloor heating, and the team can talk through how the two compare for your floor.

How the floor build-up fits together

A typical floor with underfloor heating and liquid screed is built up in layers. From the bottom up, it usually includes:

1. Base slab or subfloor, which needs to be sound and reasonably level
2. Insulation boards, laid tight together across the floor
3. Polythene barrier, laid and taped over the insulation so the screed cannot run underneath
4. Perimeter expansion foam, fitted to all walls and vertical features
5. Underfloor heating pipes, fixed securely to the insulation or a pipe system
6. Liquid screed, poured over and around the pipes
7. Floor finish, such as tiles, timber or vinyl, once the screed is ready

Your architect, builder or heating designer will set the exact build-up. If you are unsure how the layers fit your floor, send the details to the team and they can advise.

Gyvlon or Cemfloor over underfloor heating

Cotswold Flow Screed installs two types of liquid screed, and both are used over underfloor heating:

• Gyvlon anhydrite screed, a calcium sulphate-based screed developed for use with underfloor heating and commonly chosen for homes and commercial buildings.
• Cemfloor cementitious screed, a cement-based alternative often chosen where an anhydrite screed is not suitable. Cemfloor Level Plus is available where floor height is limited.

Which one suits your project depends on the floor build-up, the depth available, the floor finish you plan to lay and your build programme. The team will recommend a product when you request a quote.

How much screed goes over the pipes

The screed needs enough cover over the heating pipes to protect them and spread heat across the floor. Each manufacturer sets a minimum cover for its product, so the total depth depends on which screed is used and how the floor is built up.

Depth also affects the amount of screed your project needs, and so the cost. Our guide to how much liquid screed costs explains how depth and floor area drive the price. If you know the finished floor level from your drawings, include it with your enquiry and the team will confirm the depth.

Before the pour: who does what

A smooth pour depends on the heating and the screed being prepared in the right order. On most projects the work splits like this:

• Heating installer: fixes the pipes securely so they cannot lift when the screed is poured, connects the manifold and pressure-tests the system before the pour.
• Screed preparation: the polythene barrier and perimeter expansion foam need to be in place. You can fit these yourself or add them to your Cotswold Flow Screed order.
• Cotswold Flow Screed: carries out a pre-installation site visit, usually the day before the pour, then pumps and levels the screed.

If you are fitting your own barrier and expansion foam, it needs to be finished before the pre-installation site visit. See Other Services for the preparation work we offer.

After the pour: drying and bringing the heating on

There is no fixed drying time for liquid screed. It depends on the product, the depth of the pour, ventilation on site and the floor finish going down afterwards.

Underfloor heating is usually brought on gradually once the screed has had time to cure, following the screed manufacturer's guidance. Your heating installer will set the commissioning process, and the team can advise on screed aftercare, including sanding where it is needed before the floor finish is laid.

Heating by Underfloor Heating Technologies, screed by Cotswold Flow Screed

Cotswold Flow Screed installs the screed only. Heating design, supply and installation is carried out by our sister company, Underfloor Heating Technologies. Where a project needs both, the two teams can coordinate the heating installation and the screed pour.

Get a quote for screed over underfloor heating

Cotswold Flow Screed covers Gloucestershire, Worcestershire, Warwickshire and the Cotswolds from Evesham. Send your location, floor area, the finished floor level or screed depth if known, and the type of heating system, and the team will come back with a quote based on your project. Request a quote online or call 01386 577010.