You got to know Luc Wouters from previous issues. He is Technical Account Manager Floor Technology for Belgium at Bostik, a specialist in adhesive systems. Together with him we go over the following issues: homogeneous finish, smooth surface, tension-free, fast drying time even with higher layer thicknesses, no danger signs and ergonomics.

"You don't really make it easy for me, actually all these things overlap to a greater or lesser extent," Luc Wouters responds spontaneously at the start of the interview. "So finishing is one thing, but tension-free is something completely different. And when we talk about danger signs, we also need to define this further. After all, a levelling compound is often cement-bound, which means you always have to wear gloves, it remains a chemical product after all."

Fast drying time

The ideal opener seems to be ' fast drying time'.

"On the one hand, there are the standard levelling compounds and, on the other, there are the quick-drying variants. With the standard levelling compounds, you have to define the various, different maximum permissible layer thicknesses, which can go up to 20 mm or more. In this context, I can give the following maxim: if the layer is up to 5 mm thick, then you may - still if the levelling compound has been applied correctly - sand afterwards after 24 hours of drying and then install the floor. If the layer thickness is higher than 5 mm, then the waiting time is at least 48 hours and you have to take a moisture measurement just to be on the safe side."

"In practice, you often don't have that time, especially with projects it may have to be done faster. Suppose, for example, that it concerns fitting rooms in a shop. Then, of course, the operator wants them to be usable again as soon as possible and, consequently, the fitting out has to be quick. In this case, quick-drying levelling compounds provide golden service, as they are designed to allow same-day installation of floor coverings. Thus, this means that you arrive at the site in the morning, levelling and then you can install things like carpet or vinyl after only 4-5 hours of drying. You can assume with these quick-drying levelling products that all suppliers have this stuck in their range, which makes sense. You have to be able to offer a product that guarantees that the work can be completely finished in just one day."

Luc Wouters immediately raises a warning finger about these quick-drying levelling products: "Quick-drying may well do what it says, but if you do the work on your own, you may be disappointed. If you work alone and need to level 250 m², someone not named Superman will never keep up and you will see a lot of 'transitions' where freshly applied levelling compound no longer 'blends' well with the levelling compound applied just before, because the first applied one is already starting to harden. Which illustrates that these quick-drying variants are ideally suited to rather small areas."

Tension-free

Luc Wouters then indicates that he wants to talk about stress-free. For him, though, that is a difficult keyword to cover. The reason, he says, is that several things can cause tension in the levelling compound when it is dry.

"If you want a stress-free end result, you have to follow some rules," he raises a cautionary finger. "For example, you must never lose sight of the fact that if you are levelling, you must never do so right up to the walls, you must place edge strips. Such edge strips are not only related to possible impact sound, they are just as important for stress-free working. The necessary expansion joints in the screed must also be incorporated in the levelling compound. As a performer, you are obliged to follow the rules of the art. Especially with cement-bound levelling compounds, this has to be factored in with due care."

Homogeneous finish and smooth surface

The subsequent keywords homogeneous finish and a smooth surface our interlocutor prefers to treat together. For this, he points out that within the same brand, there are levelling compounds with different compressive strengths, which is expressed in Newton per mm².

"What you can pretty much take as a rule of thumb is that in an area that is intensively walked on, such as the entrance to a sports hall or a shopping centre, a level should be used with a compressive strength of at least 30 Newtons. The harder the levelling compound is, the higher the compressive strength. In this respect, the harder the levelling compound is, the less dust is released when sanding. As a result, your floor can withstand more intensive walking and has a smoother surface than a cheap version. In other words, you can finish perfectly. A smooth surface is particularly important for large projects where, for example, PVC is glued to the subfloor. That substrate must be perfectly even, otherwise you will immediately see the unevenness. The floor covering itself is of course a perfectly homogeneous product, but when you glue it, PVC follows any unevenness in the substrate."

Ergonomics

Throwing it over the bow of ergonomics, we hear that this is actually simple: "You have a number of ways to apply levelling compound and it is almost always done standing up with a squeegee, so this is not really problematic. What does often happen on somewhat larger projects is that a pump is used. You set the water dosage on that, after which you can cut out bags of levelling compound almost continuously. You apply the levelling compound with a gut suspended from the pump."

"Following on from this, I like to revisit how to achieve a smooth surface. For this, it is best to use a puncture roller. That way you get the air bubbles out of your levelling compound and no air is trapped. With this pricking roller, you roll crosswise twice, after which your levelled floor shines like a mirror!"