Choosing screed for underfloor heating

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Insulation should be laid beneath the UFH system to ensure that the heat always rises upwards and is not absorbed into the underlining base. Wall abutments will prevent the heat bridging into the perimeter walls.

Semi dry screed such as traditional, reinforced or fast drying is the ideal choice for underfloor heating. Manufacturers and suppliers generally recommend a depth of 60mm to use with their systems, which is the standard depth for traditional screed. This depth works well with the flow of heat from the UFH system as it retains the heat for longer compared to thinner depths, making it more energy efficient.

Sand and cement screed are more economical especially on smaller sites then self-levelling screeds, which were created to cover vast areas. Anhydrite, (also known as liquid, poured, flow or self-levelling) was created specifically to cover industrial spaces at speed and 2000 square metres a day can be poured. It is generally only on larger sites that anhydrite is more cost effective in comparison to traditional screed.

Screeding should take place as soon as possible after an underfloor heating zone is laid and pressure tested. Care must be taken to protect the pipe work whilst working. The best practice is to use a screed pump as the machine delivers the mixture via hoses, ensuring that the pipe work is not damaged. The mixture must be well compacted around the pipes to make certain that there are no voids or hollows. 

Utilising a laser level ensures that the floor is always level. 

The floor should be allowed to cure and dry naturally until full strength is reached as per British Standards and manufacturer's instructions. The full drying time of the floor will depend on the depth and products used. 

Fast drying screeds will allow for the early laying of floor finishes, early foot trafficking and let the heating system be used earlier. 

Ceramic tiles bond well with semi dry screed.