How to make a lightweight floor screed?

In cases where the arrangement of a traditional concrete floor is not possible due to its excessive weight, a lightweight screed is used. Especially often such a need arises when carrying out repair work in buildings with wooden floors or if necessary screed thickness exceeds 50 mm.

Currently, several methods are used to reduce the mass of the concrete floor, but their principle remains unchanged - components are added to the composition of the building mixture that reduce the specific gravity of concrete with minimal loss of its strength.

Types of lightweight screed

The most popular ways to reduce the mass of a concrete screed is to add fine fractional components to the solution, the density of which is much less than the density of the cement-sand mixture. First of all, such additional components include expanded clay, perlite, expanded vermiculite, etc.

Expanded clay

This is a fairly common material in construction, obtained by firing clay. Expanded clay perfectly copes with the functions of insulation or drainage material. Due to the porous structure, expanded clay crushed stone or sand has a small specific gravity, therefore expanded clay concrete is actively used to reduce the mass of building structures.

As for the lightweight floor screed, today its most common type is expanded clay concrete. Also, on the basis of this material, fine-grained mixtures are made, the density of which is much lower than the density of concrete.

Advantages of using expanded clay in concrete mortar:

• Expanded clay is not afraid of aggressive chemical influences, it is not subject to the appearance of fungi.
• The mortar used has a high setting and drying speed.
• Provides excellent sound and thermal insulation.
• It is easily leveled to obtain a flat surface or a technologically necessary slope.
• Provides slight shrinkage.

However, laying a lightweight screed using expanded clay has significant drawbacks associated with the need for additional leveling of its surface and a significant thickness.

A large number of different types of claydite-based mixtures are presented in construction stores, the use of each of them requires strict adherence to the requirements of the manufacturer's instructions, since the wrong choice of percentage components of the components that make up the solution significantly affects the quality of the screed.

Perlite

For the preparation of building mixtures with a low specific gravity, expanded perlite is used, which is obtained as a result of a sharp heating of this substance.

Advantages of a screed with the addition of perlite:

• Due to the fact that this material does not spring when laying the solution, working with mixtures based on it is quite simple.
• The high strength of such concrete is achieved due to the reaction of perlite with lime, which is released during the hydration of cement.
• Good breathability.
• Excellent heat-insulating and sound-proofing properties of perlite concrete significantly increase these qualities of the final structure.
• Increased fire safety provided by the heat resistance of perlite.

The preparation of a mixture based on perlite involves the preliminary mixing of all its ingredients without water, which is added at the very end.

Styrofoam

This gas-filled material, obtained on the basis of polystyrene, is characterized by an extremely low specific gravity, as well as a low price and low thermal conductivity.

The advantages of building mixtures with expanded polystyrene used for floor screed:

• Resistant to aggressive chemicals and moisture.
• High thermal insulation.
• Small cost.
• Long service life of the screed.

Such a screed requires increased protection against mechanical damage.

Vermiculite

This material belongs to the group of hydromicas. When heated, it significantly increases in volume and acquires a porous structure, which significantly reduces its specific gravity. In this way, expanded vermiculite is obtained.

Since this material has the ability to absorb moisture well, then in the process of preparing vermiculite concrete for floor screed, you should carefully monitor that the amount of water is minimal, but sufficient for the convenience of working with the solution.

Required Tools

To perform work on laying lightweight concrete screed with any of the listed materials, use the following tool:

1. A container for preparing a solution or a concrete mixer.
2. Drill with a suitable nozzle for preparing the mixture.
3. Construction hydraulic level.
4. Lighthouses.
5. Putty knife.
6. Rule.

Work order

1. Preparatory stage. The first step is to prepare the floor surface. To do this, it is cleaned of dust, as well as chemical and organic contaminants. A thorough inspection is carried out to identify and remove loose parts of the old concrete. Next, the floor is primed in 1 or 2 layers.
2. Installation of beacons. With the help of a hydraulic level or a building laser, the zero point of the future subfloor is determined, marks are made on the walls of the room and beacons are installed on it.
3. In order to increase the strength of a lightweight screed, a reinforcing mesh can be used.
4. Preparation of a building mixture, which must be carried out in strict accordance with the required proportions. It should be remembered that in order to obtain a high-quality mixture, a large amount of water is not required, its content should not exceed 25% of the total volume of the solution. The resulting material must be used very quickly (for various types of mixture - from 0.5 to 1.5 hours)
5. The solution is applied to the floor surface with a spatula, a rule or a vibrating screed is used to level it. Most of the materials used in the installation of a light screed have significant shrinkage. Therefore, when applying the building mixture on the floor surface, its layer thickness should be 1-1.5 cm higher than the installed beacons. The thickness of the lightweight screed should not be less than 3 cm.
6. Within 2-14 days the screed dries up. All this time, its surface should be covered with polyethylene and regularly (every 12 hours) wetted with water.

Thus, the use of additional components in the solution is not associated with too significant financial costs, however, it can significantly reduce the mass of the concrete floor and, consequently, the load on the floors. In addition, this technology makes it possible to achieve an improvement in a number of technical characteristics of the screed and is quite simple to use it for self-repair of an apartment.

It should be remembered that a light screed is still inferior to traditional concrete in strength, therefore, in order to improve the performance of such a floor, it is necessary to apply a leveling layer of high-strength building mixture on its surface.