Why Liquid Screed Suits Underfloor Heating

As liquid screed is pumped across the floor it finds its own level, flowing into the gaps between pipe loops and clips rather than being tamped or raked into place. This reduces the likelihood of trapped air pockets directly beneath the pipe, which would otherwise act as insulating voids and create local cold or hot spots.

Encapsulation quality still depends on correct pipe fixing, adequate screed depth above the pipe crown, and a sensible pour sequence — the material's flow properties support good encapsulation but don't replace careful site preparation.

The thermal conductivity of the cured screed, its depth above the pipe, and the flow temperature set at the manifold all interact to determine how quickly and evenly a room warms. Your UFH designer's heat loss calculations and pipe spacing should already factor in the screed type being used.

Anhydrite (calcium sulfate) liquid screeds are widely used with UFH because of their good thermal conductivity relative to their density and their very low shrinkage, which suits the long, thin cross-section that sits over pipe runs. Cement-based liquid screeds are also used, particularly where wet areas or specific covering types make a cement-based product preferable, and both can perform well with correct design.

Neither screed type is inherently 'the UFH screed' — the choice generally comes down to project-specific factors such as covering type, moisture sensitivity of the build programme, and the designer's preference, and either can be pumped around pipework equally well.

Liquid screed's self-levelling flow is a genuine advantage, but it doesn't compensate for a poorly designed heat loss calculation, undersized pipe spacing, or a flow temperature that's mismatched to the covering. The screed forms the thermal bridge between pipe and room; the heating design still has to be right for the finished floor to perform as intended.

The manifold sets flow temperature and balances flow rate across each loop, and this balancing is done independently of the screed choice, but a consistent cover depth across the floor helps the balanced flows translate into even room temperatures rather than some loops running noticeably hotter than others at the surface.

Where loops of very different lengths feed from the same manifold, flow balancing at commissioning compensates for the resistance difference, but this only works reliably if the screed depth above each loop is broadly consistent, since a locally thicker pour can mask a well-balanced flow rate with a slower thermal response.

A sensible pour sequence follows the pipe layout rather than crossing it awkwardly, giving the screed a clear path to flow beneath loops without the pump operator having to work back over already-poured sections. This matters more on complex layouts with multiple loops feeding a single manifold.

Discussing pour direction with the UFH installer before the day, rather than deciding on site once pumping has started, avoids situations where an operator has to choose between a slower, more careful approach and one that risks leaving small voids near tight bends.