What is a dry screed, why it is needed and what the minimum thickness should be

Dry screed is a simplified approach to floor leveling that eliminates the need for concrete. Instead, it utilizes lighter materials like expanded clay or vermiculite. This leads to quicker and easier work. The advantages and disadvantages of this method, along with the process of installation, are elaborated in the provided article.

The essence and structure of dry screed

To begin with, it is essential to comprehend the concept of dry screed. It is a commonly used technique for leveling floors that eliminates the need for pouring cement-sand mortar. In other words, it is a simplified method that differs greatly from the traditional concrete floor installation. Dry floor screed can be described as a leveling process comprising of five layers:

1. Separating – this layer is directly placed on the concrete or other substrate. Its purpose is to provide moisture protection, typically achieved using a vapor barrier or polyethylene film. On wooden bases, bituminous, corrugated, or perforated paper is used.
2. Edge tape – this layer is laid in the gaps between the floor’s edges and the wall surface. It serves as a soundproofing element.
3. The dry floor screed can be described as a leveling layer that forms the foundation of the entire structure. It is composed of fine fractional material with a moisture content of 1%, typically expanded clay sand with particles measuring no more than 5mm. However, due to its tendency to settle over time, it is advisable to use a mixture of branded bulk flooring.
4. If the surface does not have significant flaws or height differences of more than 10mm, polystyrene foam slabs can be used instead of dry backfill. Not only do these slabs provide an even surface, but they also offer thermal insulation properties.
5. The final layer is the finishing layer, which consists of gypsum fiber sheets that serve as a base for flooring. One of the most reliable options is glass panels with connectors, which can be easily installed by yourself.

Pros and cons of the technology

The description indicates that dry screed is a multilayer construction that does not require pre-mixing of mortar, unlike concrete. This technology offers several notable advantages:

• Lightweight and suitable for any type of flooring
• Provides a flat surface
• Easy installation process without messy procedures
• Saves time as it does not require waiting for drying
• Offers good heat and sound insulation
• Allows for immediate installation of the finish coating once the screed is complete

Dry screed materials

Dry screed is a simplified technology for leveling the floor, using loose compositions made of various components. The main options include:

1. Medium fraction claydite, which is a good insulator and has a lightweight and porous surface. This affordable material is commonly used for screeding, with a weight of 250 to 600 kg per cubic meter.
2. Vermiculite, another lightweight material with low density. It weighs only 160 kg per cubic meter. It’s important to use vermiculite that has undergone swelling for flooring purposes.
3. Perlite, a natural material that is a volcanic rock. It’s known for its lightness and durability.
4. Compevit – a material made of rounded expanded clay with a cross section of no more than 4 mm. It has high density and does not sag over time, ensuring a consistent surface.
5. When considering dry screed, it is important to understand that in certain situations, it is possible to omit the backfilling process. If the floor surface is sufficiently level, placing polystyrene foam slabs will be enough.

By understanding what dry screed is and its various applications, it becomes clear that backfilling may not always be necessary. In cases where the floor surface is already even, laying polystyrene foam slabs can suffice.

Step-by-step instructions for laying

In order to start working, it is essential to measure the room and determine the minimum thickness needed for the dry screed. This requirement is dependent on the quality of the surface – the more even it is, the less filler will be required.

On average, the thickness ranges from 30 to 50 mm. However, the minimum requirement is 15 mm. If the floor has significant defects, it is advisable to choose a thickness with a reserve of 50-60 mm. It is important to note that the material consumption per square meter is between 54 and 75 kg (based on a 30 mm thickness of dry floor screed).

Once the calculations have been completed, the work can commence. The main steps are as follows:

1. Prepare the foundation – remove any debris and clean the surface. If there are any imperfections, fill them with a dry mixture to ensure a relatively even floor.
2. Place a sheet of heavy-duty polyethylene film on top of the foundation, making sure it overlaps by at least 25 cm. Create a 10-15 cm overlap on the walls as well.
3. Secure the edge tape in the gaps between the walls and the floor.
4. Install the beacons around the perimeter using a construction level.
5. Pour the mixture, focusing on achieving the desired thickness for the dry screed. Begin from the highest point of the floor (use a level to determine the height).
6. Smooth out the pile according to the level and compact it using a rubber mallet.
7. Install the finishing layer – you can use two-layer gypsum-fiber boards for this, securing them with adhesive.

1. It is recommended to allow 2-3 days after completing the specified task before installing the floor covering. This will ensure that the screed is fully cured and capable of withstanding years of use.