Self-leveling screed, the solution for reduced thickness

01/07/2020 – The design phase is that in which the client, with the technical – professional help of the designer, begins to give concrete form to what was initially only an abstract image of his future home. Unlike a new building, in the context of a renovation, the design freedom could be more limited, because it goes to operate on an already existing context.

For example, a client wishes to equip his home with a floor heating and / or cooling system, intervention that provides which provides for the demolition of the existing screed and the reconstruction with radiant typology. To obtain a radiant screed, considerable thicknesses are required.

What happens if there are quota problems available? If the thicknesses are not enough, will you have to give up the idea of ​​having a floor heating / cooling system?

The solution is there, and it is the low thickness radiant screed: a different way, compared to the traditional radiant screed, to meet particular needs such as limited availability of height, but not only, this solution can also be adopted in those contexts in which the construction sites available are very small, such as the center city ​​or for work on high floors.
Photo: © Viega Italia

Self-leveling, types and characteristics

A low thickness radiant screed is made through the self-leveling screeds. A self-leveling screed consists of very fluid mortars whose workability is such as to allow flattening with limited or no manual intervention.

The self-leveling screed can be anhydrite-based (chalk), or a cement base. It is combined with a radiant flooring system, composed of insulating radiant panels e piping, of which the self-leveling screed constitutes the final and closing part. When the self-leveling is cast on site, its fluid consistency allows it to adhere perfectly to the geometry of the radiant panels. A radiant system can be realized starting from only 30 mm, excluding the coating.

As with any product, even with a low thickness radiant screed made with self-leveling, you need to know the peculiarities to appreciate the requirements and know any limits of applicability.

Photo: © Laterlite

Self-leveling, low thermal inertia and mechanical resistance in reduced thicknesses

The reduced thickness determines a low thermal inertia, that is, the ability to respond quickly to requests for changes in temperature throughout the day. On the contrary, in the traditional radiant systems, consisting of insulation and cement screed, the high thickness of the screed takes in the heat generated by the heating pipe and gradually releases it to the floor surface, giving the impression of a “reactive slowness” of the system.

The time that a radiant floor takes to reach the surface temperature is about one hour, much less than traditional radiant systems. It is clear that the lower it will be thermal inertia, the lower the energy consumption, the higher the reaction speed.

But a low thickness screed is also resistant? Will it support the flooring over time?
The self-leveling screed it manages to “equate” a traditional one with little thickness because once hardened it is more compact. There compactness gives mechanical resistance, which preserves the characteristics and integrity of the flooring.

But it is necessary to verify, after drying, if there is presence of bleeding, or the presence of dust on the surface, a phenomenon to which a self-leveling agent could be subject. Gluing a flooring on a bleeding layer, not correctly removed, can give rise to detachment phenomena. It is therefore necessary to remove the bleending layer, vacuum the dust and apply a primer on the surface of the screed.

Photo: © Rossato Group

Self-leveling, speed of installation, workability and lightness

A self-leveling screed, thanks to the fluid consistency, the laying speed and the workability, allows to cover large surfaces, but at the same time does not allow the creation of slopes.

At the same time it is much lighter compared to a traditional sand – cement screed. For this reason it is suitable for use when working on homes where the existing floor cannot be overloaded excessively due to a set of factors, such as reduced thickness, very large spans, the age of the floor itself, etc. It is also used on existing flooring if the substrate presents the requirements for the overlap.

The low thickness radiant screed collides with the factor humidity. Whether it is based on anhydride or cementitious, it must not present humidity or, at least, not exceed the values ​​defined by the regulations. The anhydride-based screed made of gypsum must be laid in rooms with a residual humidity of less than 0.5%. The self-leveling cement-based screed, on the other hand, must not be used for substrates subject to continuous rising damp.

For these reasons, the insertion of one must be envisaged both in the design and execution phases vapor barrier of suitable thickness in the radiant floor system, to be placed between the self-leveling screed and the underlying layer; alternatively, after careful technical evaluation, a suitable person two-component epoxy primer against rising damp.

Its a self-leveling screed can be laid moisture resistant floors, such as the ceramic o la natural stone and non moisture resistant floors, such as the parquet and the so-called resilient floors. In all cases, for radiant floor systems, UNI-EN 1264-4 prescribes that before proceeding with the laying of the cladding, the first ignition cycle of the system must be performed which must be carried out only after 4 days from the complete drying of the screed. .