Short answer: for most homes a liquid calcium sulphate screed is the best screed for underfloor heating, because it flows fully around the pipes, can be laid thinner and conducts heat well, so the floor warms up faster and more evenly. A fibre-reinforced sand and cement screed is a reliable alternative, especially on small areas or where a cement-based floor is needed.
What makes a good UFH screed
- Full contact with the pipes: air gaps reduce heat output
- The right cover: enough depth to spread heat and resist cracking, but not so much that the floor is sluggish
- Low shrinkage: to reduce cracking as the floor heats and cools
Preparation checklist
- Pipes fixed securely so they cannot float during the pour
- System pressure-tested and kept under pressure while screeding
- Perimeter edge strip on every wall and around the manifold
- Slip membrane over the insulation, taped at joints
Commissioning the heating
Never run new underfloor heating at full temperature on a fresh screed. After the minimum curing period, the flow temperature is raised in small daily steps, held, and reduced again before floor coverings are laid. Your screeding contractor should give you the schedule for the product used.
Heat-up times compared
A thinner, denser screed with full contact around the pipes responds faster. In practice a liquid screed over underfloor heating usually warms a room noticeably quicker than a thick sand and cement screed, and is easier to run on a lower flow temperature, which suits heat pumps.
Heat pumps
Heat pumps work most efficiently at low flow temperatures, so good heat transfer through the screed matters even more. If you are fitting a heat pump, tell us early: the screed type and depth are part of getting the system to perform as designed.
Quick answers
Can I tile straight onto a screed over underfloor heating? Only once it is dry, the heating has been commissioned and the surface prepared. See when can you tile on new screed.
Should the heating be on during the pour? No. The system should be filled and pressure-tested, but switched off until the screed’s minimum curing period has passed.
Written by Ben Phillips, director of Chelmsford Floor Screeding Ltd, floor screeding contractors based in Billericay with 20+ years of experience across Essex and London. More about us.