Microcement and Floor Expansion Joints

One of the reasons clients choose microcement is the ability to create a seamless surface without joints. This is possible because, thanks to its polymer content, microcement is quite flexible and does not inherently require expansion joints. However, we usually recommend transferring any existing expansion joints to the microcement layer as well, or even creating proper expansion joints if the floor does not have them. Why is this so important?

What is a floor expansion joint?

An expansion joint is a cut in the floor that helps minimize the effects of stresses forming in the concrete, thus preventing it from cracking. A concrete screed shrinks and expands during curing and later use (for example, when using underfloor heating and the associated temperature changes), which can lead to cracks. Expansion joints are typically cut at door thresholds, near windows, and in rooms larger than 5m x 5m. These are known as expansion floors.

Dilatation transferred to the microcement layer | Contractor: Projekt Mikrocement

Expansion joint in the threshold transferred to the microcement

Assessment of Substrate and Expansion Joint Quality

The substrate for microcement should be of high quality. Before starting the actual application of microcement—and ideally even before accepting the job—the contractor should check the floor for cracks or microcracks. If any are found, it is important to analyze their location and the placement of expansion joints. It is quite common for developers to cut too few expansion joints, or sometimes not to include them at all.

Crack due to lack of expansion joint

Expansion Joint Repair

Missing expansion joints must absolutely be cut, and any visible cracks need to be properly secured. Typically, such cracks are “stitched” with steel rods and then filled with resin. The next step is to apply a reinforcing layer—FESTFLOOR Life base with mesh. Only after the base layer has dried can you proceed with the application of microcement. Preparing the substrate for microcement to protect it against cracking is quite labor-intensive, which is one reason why contractors often price floors higher than, for example, walls.

Cutting Expansion Joints in Microcement

Once the microcement has dried, we cut the expansion joint in the same location as in the screed. This task requires precision and high-quality equipment. There is no room for even the smallest mistake, as any imperfection will be highly visible. The best tools for this job are a laser, guide rail, concrete saw, and multitool. Finally, the joint is filled with expansion joint compound.

This approach provides protection against excessive stress transferring to the microcement surface, which could otherwise cause the floor to lift or become detached at the expansion joint (or where expansion joints are missing).

Microcement is a highly flexible coating, but the stresses that occur in floors-especially fresh ones-can be too strong and may lead to damage.