Why Use Expansion and Control Joints?

An expansion joint creates a deliberate gap in the screed that allows the material to expand and contract freely as temperatures change, without that movement causing cracks in uncontrolled locations. Screed expands as it heats up and contracts as it cools, and without somewhere for that movement to go the internal stresses build up until the floor cracks. Expansion joints direct that movement to a predictable location where it can be managed rather than letting it open up randomly across the finished surface.

Expansion joints are needed in all liquid screed floors, but they become particularly important where underfloor heating is present, since the repeated heating and cooling cycles create more movement than a floor without UFH. They should be fitted around the perimeter of every pour, at junctions between rooms, in L-shaped and T-shaped floor plans where different areas meet, and wherever underfloor heating pipes pass through a doorway. The larger the pour area, the more important it is to subdivide it with control joints.

An expansion joint is designed to accommodate movement across the full width of the screed, typically fitted at the perimeter and between separate pour areas. A control joint, sometimes called a crack inducer, is designed to weaken the screed along a specific line so that if cracking does occur it happens there rather than elsewhere. In practice the two are often used together: expansion joints at the boundaries of a pour, and control joints to manage movement within a larger poured area.

Across doorways and thresholds, at any structural column bases, and at any junction between a smaller area and a larger one such as a corridor meeting a room. In floors with underfloor heating, expansion strips should also be placed wherever the UFH pipe crosses from one zone to another or passes through a doorway. Getting the positioning right at the installation stage is far easier than dealing with uncontrolled cracking afterwards.

Yes, and in most cases you should. The Metex Vertical Control Joints are designed specifically to sit over UFH pipes without needing to be notched around them, which keeps installation straightforward and avoids any risk of damaging the pipe during fitting. It can be configured to work at either 40mm or 45mm screed depths by rotating the strip, and positions accurately with dedicated clips rather than relying on adhesive backing.

Without expansion joints the screed has no controlled outlet for the movement caused by temperature changes and drying shrinkage. The result is usually cracking, which can range from minor surface crazing to significant structural cracks that open up under the finished floor covering. In a floor with underfloor heating the repeated thermal cycling makes this outcome more likely and the cracks more pronounced. Retrofitting expansion joints after a floor has cracked is not straightforward, so getting them in during installation is always the right approach.