Infill block: definition and role in the floor

What is an infill block?

An infill block is a precast element, in concrete or fired clay, laid between the beams of a floor to fill the voids. It is the block in what is known as a beam-and-block floor.

It is not load-bearing in the strict sense. The beams take the loads; the block closes the space between them and acts as permanent formwork for the structural topping poured over the top.

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What is its role in a floor?

The system reads from the bottom up. The beams span from wall to wall, the blocks fill the gaps, then a reinforced concrete topping is poured over the whole assembly and ties it together.

The method is very common in Belgian housing because it allows decent spans without full formwork or a crane for solid slabs.

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Concrete or clay: what difference does it make?

The concrete block is heavier, more resistant to compression and cheaper. The clay block is lighter and behaves better thermally, since fired clay conducts heat less readily than concrete.

There are also insulating blocks, in polystyrene, whose primary purpose is to deal with the thermal bridge at the ground floor. For the screed, the practical difference lies mainly in the permissible load and in the flatness of the resulting substrate.

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What does it change for the screed?

A screed is never poured directly onto the blocks themselves: it rests on the structural topping, which is the real working surface. This is a frequent confusion on site.

Two points deserve attention. The topping often has mediocre flatness, which affects the average screed thickness to allow for. And a beam-and-block floor transmits impact noise well, which makes acoustic decoupling particularly useful in grouped housing. See our acoustic solutions.