Floating screed: features, calculation of materials, installation

Recommendation points

• Application and advantages of floating screed
• Definition of layers. Choice of materials
• Selection and calculation of components
• The order of work. Professional tricks
• Typical errors and their exclusion

The floating screed will help to properly prepare the surface for laying the flooring. You can not only reduce noise and keep warm, but also hide communications. Let’s talk about the professional approach to the definition of layers, the choice of materials and typical mistakes when installing a floating screed.

Application and advantages of floating screed

A layer of a mixture using cement, made separately from the lower base without a rigid connection with it, is called a floating screed. Usually the screed is laid on a film.

Use a floating screed when required:

1. Level the surface for the flooring.
2. Improve waterproofing.
3. Provide soundproofing to a room or compartment.
4. Provide the surface with shock-absorbing qualities, which is important for gyms.
5. Improve the thermal insulation characteristics of the room.
6. Reduce costs when choosing flooring.
7. Ensure long-term operation and ease of maintenance of the floor surface.
8. Hide communications.
9. Carry out the installation of a warm floor.

The use of a floating screed can be limited by the low threshold of the balcony door, floor load restrictions. The permissible distributed load on the floor slab can be found in the technical documentation for the building. For a rough calculation, the weight of the screed is 1 cm thick and an area of ​​1 sq. m equal to 20 kg. The minimum thickness of the screed can be 20 mm. In this case, the load characteristic of the floor can be no more than 150 kg / sq. m. The optimum thickness is 40 mm. The weight of other materials can be neglected, except pipes with underfloor heating.

Definition of layers. Choice of materials

To achieve the desired properties, the floating screed is mounted on specially prepared layers of heat-insulating, sound-insulating materials and a water-repellent film. In general, the layer scheme is shown in the figure.

1 – floor slab; 2 – a layer of waterproofing; 3 – a layer of sound insulation; 4 – thermal insulation layer; 5 – edge (damper) tape; 6 – wall; 7 – plaster; 8 – calcium sulfate / cement-sand screed

When using the entire set of layers and taking into account the height of communications hidden in the floor, the height of the floor from the surface rises by 120 mm. This is comparable to the threshold of a balcony door and is often higher. In this case, it is necessary to carefully determine the thickness of the layers and conduct installation work..

Let’s consider a common option. To preserve the properties of the insulation, a polypropylene film with a thickness of 1.2 mm is placed between the screed and the bottom layer. The same film is laid on the base to exclude moisture penetration between the joints of the material.

The following is used as a heat-insulating layer:

• expanded polystyrene brands PSB-S-35 … 50, M35;
• high density basalt wool;
• wood wool mats.

The layer thickness is from 5 to 40 mm, depending on the selected material and the planned effect.

For sound insulation choose the material “Izolon” PPE, “Shumanet”. Often, a positive effect can be achieved by using various insulation materials, laid in two or more layers. The thickness of the sound insulation layer is from 3 to 50 mm.

The screed is 40 mm thick. If the room is more than 20 meters on the long side, then it is necessary to lay a separating damper to relieve stress in the screed. For reinforcement, you can use fiberglass or reinforcing mesh.

If it is necessary to reduce the height of the surface for the flooring, choose materials with acceptable properties with their small thickness. For example, Izolon, 3 mm thick, is used as sound insulation. Foam polystyrene 20 mm thick is suitable as a heater. The thickness of the screed can be reduced to 20 mm. In this case, fiber from materials other than metal fiber is used as reinforcement. Such a thin screed requires special skill for its installation..

Selection and calculation of components

To determine the required amount of material for each layer, you need to know the surface area and layer height. When buying insulation and sound insulation, managers will indicate whether it is necessary to increase the amount of material to take into account its compressibility during installation. The instructions will indicate which layer of screed is required for the operation of the insulation. Usually a 60 mm layer is recommended .

For the screed, cement grade 500 is taken without ash additives. It is better to take plasticizers separately. It is convenient to determine the required volume and then recalculate the need for each component. The amount of plasticizer is calculated based on the data indicated on the package.

The mixture must be made at the rate of 1 part of cement to 4 parts of sand. In places with increased variable load, it is recommended to change the proportion by 1 to 3. You can only use washed construction sand, otherwise the screed will emit dust during operation and may be loose with deteriorated strength parameters. The amount of water, including that contained in the sand, is calculated at the rate of 15–20% of the mass of cement in the solution. Fiber is added strictly according to the manufacturer’s instructions, observing the proportion and the order in which the components are mixed. Otherwise, the reinforcing fiber may be unevenly distributed throughout the volume of the solution. Usually 600 g of fiber is consumed per 1 cu. m solution. A more traditional option is steel mesh reinforcement. Wire diameter 3 mm, mesh size no more than 60×60 mm. For screeds, you can use non-shrinking dry mixes. However, this increases material costs..

The order of work. Professional tricks

To carry out the work, you need to prepare tools and equipment:

1. Concrete mixer.
2. Shovels.
3. Buckets.
4. Master OK.
5. Rule length from 1500 to 2500 mm, preferably two.
6. Laser level.
7. Roulette.
8. Mittens or gloves.
9. Respiratory mask.

When working with basalt fiber or insulation, you must use separate gloves and a respirator.

The work includes the following stages:

1. Preliminary marking of the upper level of the screed.
2. Leveling the surface and laying the waterproofing layer.
3. Markup.
4. Mounting the damper edge.
5. Laying insulation and sound insulation.
6. Laying a layer of waterproofing.
7. Installation of compensation boundaries.
8. Installation of beacons and reinforcement (not performed when using fiber).
9. Screed laying.
10. Screed care.

The knobs and protruding mounting elements of the base are cut off. The existing significant gaps are closed. Carry out preliminary marking of the upper level of the screed on the wall. Then the film is laid and the surface is leveled with sand. The joint of the film is made with a margin of at least 200 mm and entering the walls to form a boat to the upper level of the screed with a margin of 100 mm.

After that, using a laser level, it is necessary to mark on the wall a layer of sound insulation and insulation. When laying these layers, the joints are glued with tape. Spread a film for waterproofing insulation from the screed. Place the damper tape against the wall. Further, beacons are usually installed for reinforcement. The mesh is placed in the middle of the screed layer, between the upper and lower plane. This is a laborious job, the insulation is movable and the beacons have to be checked many times and corrected. For this reason, experienced craftsmen work with fiber as a reinforcing element for screed mortar..

Professional advice.If there is experience in working with cement mixtures, with a screed thickness of 40 mm, the reinforcing layer is placed on a screed made with a thickness of 20 mm. The next layer of screed is laid on top of the reinforcement, making sure that the bottom layer does not have time to grab.

The screed is poured according to the exposed beacons. As a beacon, it is convenient to set a collar with guides from a profile for PN drywall. When approaching the edge of the site, the profile is removed. The laser level allows you to complete the work of installing the beacon quickly. Editing is carried out with a trowel and a rule. The maximum smooth difference in level of 1 cm is considered acceptable, but it is better to achieve more accurate styling.

After leveling, the screed is rubbed. In the process of grouting, beacons are removed and traces from the recesses are removed, the quality of work is checked by level.

When using non-shrinking dry mixes, the work is easier, since there is no danger of the collar hardening. A screed 20 mm thick is laid, then the next layer is reinforced and laid. With pin beacons, the pins are removed and the puncture site of the waterproofing is treated with silicone and rubbed with a screed solution.

After the screed has set and can be walked on, it must be covered with plastic wrap to retain moisture. During the first three days, if necessary, the screed is moistened with water using a spray bottle. After three days, you can safely walk on it. After 8 days, you can install windows and doors. After 25 days, the screed must be checked for levels and for clearance. If differences are identified, they are polished.

Professional advice.After 30 days, the surface of the screed must be treated with diluted PVA glue. This will significantly reduce dust formation during surface operation..

Typical errors and their exclusion

Scrupulous and high-quality installation of each layer eliminates almost all mistakes that are often made during installation work.

1 – installation without damper tape; 2 – high position; 3 – incorrect position of the insulation; 4 – film rupture; 5 – height difference of the screed

There are other errors that worsen the quality characteristics:

1. During work, when laying sound insulation and thermal insulation, gaps and gaps must not be allowed. The sound will pass through this bridge, the quality of thermal insulation will deteriorate sharply.
2. If the side length is exceeded by more than 20 m, expansion joints must be provided. Otherwise, when the temperature rises, the screed may form a bubble or load the partition, and crack in winter. This reduces the durability of the screed..
3. When reinforcing, the mesh is laid close to the surface or base of the screed. This leads to a loss of strength characteristics..