FAQ

Liquid screed can be applied over insulation (floating application), either thermal or acoustic, at a depth of 40mm in domestic applications and 40mm in commercial applications.

When used with underfloor heating, the minimum cover required over the pipe is 30mm, in accordance with BS EN 13813:2002.

The preparation required for liquid floor screed is no different from that required for traditional sand and cement screed — although it must be done correctly, not “what people try to get away with”.

Typical ground floor build-up:

• DPM
• Structural slab
• Insulation
• Vapour barrier
• Floor screed

With underfloor heating:

• DPM
• Structural slab
• Insulation
• Vapour barrier
• Underfloor heating loops
• Floor screed

On upper floors using beam and block or concrete planks, a DPM may not be required, but a vapour barrier is still essential.

The vapour barrier is not primarily related to ground moisture. It is required by insulation manufacturers such as Celotex and Kingspan to prevent contamination from the screed.

It also acts as a separation layer to minimise cracking if movement occurs beneath the screed. For this reason, roll-format vapour barriers are preferred over folded sheets, which can introduce creases and stress points.

Underfloor heating screed is not a specific screed product. More accurately, it should be described as screed suitable for underfloor heating.

Gypsum-based liquid screeds are ideal for underfloor heating due to their strength, allowing reduced screed depths while maintaining performance.

Typically, liquid screed can be laid at around 50mm total depth with underfloor heating, compared to approximately 75mm for traditional sand and cement screed. This improves heating responsiveness and can help preserve headroom.

Sand and cement screed:

British Standards recommend 1 day per mm for the first 50mm and 2 days per mm thereafter. For example, a 65mm screed may require up to 80 days to dry.

In practice, 4 weeks is often a sensible minimum, but moisture levels should always be checked before laying impermeable floor coverings.

Liquid (self-levelling) screed:

Drying times are significantly reduced due to reduced thickness and improved drying characteristics. Dehumidifiers can also be used to accelerate the process safely.

Ceramic tiles, natural stone, slate, marble, limestone and similar materials perform extremely well due to their high thermal conductivity.

Most other floor coverings are also suitable when specified and installed correctly. Expansion gaps, flexible adhesives and appropriate underlays are essential.

Yes — both engineered and solid timber flooring can be used successfully with underfloor heating when properly specified.

Engineered boards are particularly suitable due to their stability and reduced movement. Solid timber is also acceptable, although narrower boards are recommended.

Moisture control and acclimatisation are critical. Flooring should only be laid once screeds, plaster and internal finishes have adequately dried.

Yes, provided the correct carpet and underlay combination is chosen.

The combined tog value of the carpet and underlay should not exceed 2.5 tog to ensure efficient heat transfer.