Why does a screed need movement joints?

A screed moves. It shrinks as it dries, then expands and contracts with temperature fluctuations. If you try to stop it, it won't give up: it will crack. The whole art lies in creating planned lines of rupture rather than suffering them.

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Three types of joints not to be confused

The perimeter joint is the simplest and most overlooked. Made of a perimeter strip compressible material, it runs along the entire perimeter of the room, against walls, columns, and thresholds. It allows the screed to breathe and cuts off the transmission of impact noise to the structure.

The control joint divides large areas into independent zones. It is also systematically placed in every doorway, where the screed narrows and becomes fragile.

The structural joint follows an existing joint in the main structure. It must pass through the entire thickness, including insulation, and is non-negotiable.

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How often?

For a traditional cement screed, the standard practice is to divide areas of about 30 to 40 m², with a strip length rarely exceeding 8 meters and shapes as close to a square as possible. L-shapes, narrow corridors, and inside corners must always be cut.

An anhydrite screed completely changes the game: since its shrinkage is very low, it allows for surfaces of several hundred square meters without intermediate joints. This is a decisive advantage for large open spaces. In all cases, the manufacturer's specifications take precedence over general rules.

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The case of underfloor heating

With underfloor heating, thermal stress increases and the zones become smaller. One rule is set in stone: a heating loop must never cross a joint without being protected by a sleeve. Each delimited zone must be supplied by its own loop, which must be decided at the layout planning stage, not on the day of the pour. The decoupling complements this system by preventing any rigid contact with the support.