Microcement and floor dilatation joints

One of the reasons why customers choose microcement is the ability to create a uniform surface without joints. This is because, thanks to the content of polymers, the microcement is quite flexible and does not require dilatation by itself. Usually, however, we recommend transferring the already existing dilatations also to the microcement layer, and even making the proper dilatation, when there is no such. Why is it so important?

What is floor dilatation joint?

Dilation is a cut in the floor, thanks to which you can minimize the effects of stresses arising in the concrete and thus avoid cracking. The concrete screed during setting and then during operation (e.g. when using underfloor heating and the associated temperature fluctuations) shrinks and expands, which can lead to the formation of cracks. Usually, expansion joints are cut at the door-sills, at windows and in rooms larger than 5m x 5m.

Dilation in the door-sill transferred to the microcement layer. Photo: Pracownia Betonu

Dilation in the microcement layer. Photo: Pracownia Betonu

Assessment of the quality of the substrate and existing dilatations

The substrate for the microcement should be of good quality. Before starting the proper application of microconcrete, and actually before accepting the order, the contractor checks the floor for cracks or microcracks. If they are, the place of their occurrence and the location of the dilatation should be analyzed. It often happens that the developer did not cut the appropriate amount of expansion joints or did not use them at all (!).

Crack due to lack of expansion joints in the balcony door-sill. Photo: Pracownia Betonu

Repairing expansion joints

Missing expansion joints must be cut, and cracks that are already visible must be secured. Usually, such cracks are “stitched” with steel rods and then poured with resin. The next step is to lay the reinforcing layer – FESTFLOOR Life base with mesh. Only after the base layer has dried, you can start applying the microcement. Preparing the floor for microcement in such a way as to protect it against cracking is quite time-consuming and that is why, among others, contractors value floors more expensive than, for example, walls.

Cutting expansion joints in microcement

When the microcement is dry, cut the expansion joint in the same place as the expansion joint in the screed. This task requires precision and good quality equipment. You cannot afford to make the slightest mistake, because every shortcoming will be very visible. This is where the laser, guide bar, concrete saw and multitool work best. Finally, the joint is filled with an expansion joint filler.
Such expansion of the expansion joint will provide protection against the transfer of excessive stresses to the surface of the microcement and, consequently, lifting and detachment of the floor at the location of the expansion joint (or missing expansion joints).
Microcement is a very flexible coating, but the stresses in floors (especially fresh ones) may be too strong and lead to damage.