How to prepare wooden floors for screeding. Screed on a wooden floor under tiles - design rules. Laying flooring along joists on a primer

Wooden floors are quite reliable and durable, but they themselves do not last forever. Over time, it becomes necessary to additionally lay the screed on the prepared wooden base.

Concrete screed is usually applied to a wooden floor only in cases where it is necessary to level it under some kind of coating.

If the wooden floor cannot be completely restored, then this leveling method is used.

In fact, the screed is considered as a surface element, the base of which is intended for a concrete floor with subsequent laying of the covering. The main purpose of the screed is to level the floor surface. Depending on what kind of coating should be, the following types of screed can be distinguished:

• for wooden floors;
• for installation of a heating system;
• dry and semi-dry screeds;
• concrete screed.

This is often done before laying ceramic tiles, polymer floors, or when installing a heated floor system, but we will look in more detail at the features and laying of concrete screed on a wooden floor.

Before you begin laying a concrete screed, you should prepare the necessary materials and tools:

For large volumes of leveling work, a concrete mixer is indispensable.

• plastic film;
• sand;
• cement;
• epoxy putty;
• acrylic sealant;
• plasticizer;
• construction beacons;
• moisture-resistant primer;
• polyurethane foam;
• steel mesh;
• hammer;
• level;
• mixer for mixing the solution;
• self-tapping screws;
• nails;
• screws;
• putty knife;
• roller, brushes;
• scotch;
• with sand.

Sequence of laying concrete screed

The technology for laying concrete screed includes the following steps:

The most accurate level markings can be obtained when using a laser level, but it is quite possible to carry out alignment with the help of beacons using a regular building level

• to start work, it is necessary to dismantle the old covering and install additional logs, since after the pouring process the screed will become much heavier and will sag greatly;
• if there are rotten boards, then they need to be removed and new ones laid in their place. This replacement is usually carried out on old floors;
• seal cracks and irregularities. When large gaps form, polyurethane foam is used, the joints are coated with acrylic sealant, and then smoothed with epoxy putty. Epoxy putty is also used when filling small gaps between boards;
• the next stage is sealant treatment. This operation is performed after the putty and foam have dried. Next, apply a waterproofing primer using a roller or brush in two layers. This primer is used to simultaneously cover the lower part of the walls (approximately 10-15 cm). Then a waterproofing film is laid with a spare overlap of 10 cm on the wall. After that, a steel mesh is placed on the film and screwed in place;
• Next, markings are carried out and beacons are installed. The most accurate level markings can be obtained when using a laser level, but it is quite possible to carry out alignment with the help of beacons using a regular building level;
• start preparing the solution, observing the following proportions: the capacity of clean sand is 3-4 parts, cement grade 400 is 1 part. Then clean water and special plasticizers are added to the solution, which provide the screed with the highest quality.

The cement mortar is mixed in a large plastic container using a drill and a special mixing attachment. After thorough mixing, the solution is left to settle for a short time, after which it is mixed again.

The material consumption should be approximately 15 kg/sq.m. m with a screed thickness of 1 cm. In the absence of a plasticizer, ordinary washing powder can be added to the solution so that a handful of powder corresponds to 100 liters of water.

Using the beacons as a guide, the solution is poured onto the floor. It is necessary to fill the entire floor at once, since it is unacceptable to perform this operation in parts.

The beacons are removed from the set solution, and the same solution is poured into the formed grooves. That's it, the screed is ready.

Leveling with self-leveling mixture

Any finishing coating must be laid on a smooth and level surface. This problem can be solved with self-leveling mixtures, the solution of which easily spreads and is distributed around the entire perimeter, forming a smooth surface.

Preparation of the solution

Work on leveling a concrete floor using a self-leveling mixture must be carried out very quickly, because its drying speed is high

Many experts argue that it makes no sense to make a screed on a wooden floor - it is too cumbersome, and there are a lot of materials available for dry leveling of the base. But in some cases it is necessary to give the floor a certain rigidity and level it in height using concrete mortar. This technology exists and determines how to make a screed on a wooden floor. It has its own characteristics that must be taken into account during the work process.

What you need to know about wooden structures

Despite all their undeniable advantages, wooden structures have a significant drawback, which is their shrinkage. When the humidity regime changes, wood changes its size, increasing or decreasing in volume, shrinking in height, stretching or shortening in length. For this reason, screeding on new boards is strictly prohibited. Leveling the wooden base can only be done after three years of use of the flooring.

The design of a wooden floor involves laying joists on which floorboards are mounted. It is worth noting that it is advisable to make a screed on them only if the logs lie on brick columns, the height of which is at least 30 cm. If the logs are located directly on the floor slabs, then it would be wiser to dismantle the floor boards and make the screed in the traditional way .

What you need to know about screed

The design features of laying the screed on a wooden floor mean that it is completely isolated from the lower layer of the base and is in no way connected to it. From this follows its name - untied screed.

After the concrete mortar has completely hardened, the screed turns into a stone slab that is not subject to any linear changes, which cannot be said about the wooden base on which it is poured. If the wood and the concrete layer are “connected,” then the instability of wooden structures under conditions of changing humidity conditions will cause cracks to appear on the surface of the concrete, followed by its destruction. In this regard, a special technology has been developed that determines how to make a screed on a wooden floor so that it is not connected to either the base or the walls.

Basic principles of leveling a wooden floor

The technological process of installing a screed on a wooden base consists of creating a waterproof layer between the moving wood and the monolithic concrete layer. To create such a border use:

• plastic film separating the screed from the wooden floor;
• damper tape that cuts off the concrete layer from the surface of the walls.

This method allows you to get a floating leveling slab that is not connected to wooden structures - neither to log or cobblestone walls, nor to the floor board. The screed, in this case, will not be exposed to “moving” wood, as a result of which it will not crack or crumble.

To avoid the appearance of fungus on the surface of the wood, it is treated with an antiseptic and a primer with a water-repellent effect. Only after this is it possible to lay plastic film on the wooden base.

Contact with polyethylene has a negative effect on wood, so bitumen mastic or materials impregnated with bitumen are widely used as waterproofing for wooden structures. But not in the case of a screed poured onto a wooden floor. Here, polyethylene film is most appropriate for certain reasons:

• it does not stick to concrete;
• the wooden base underneath can swell and shrink without consequences;
• the boundary between the screed and the floor prevents the wood from drawing moisture from the concrete mortar during the setting process, as a result of which depressions are not formed;
• concrete does not absorb moisture from wood, and therefore there is no need to worry about cracks appearing.

How to make a screed correctly

Work on the screed installation begins with preparing the base:

• remove boards;
• check lags - replace those that do not inspire much confidence;
• additional logs are installed if the step between them is less than 40 cm;
• floor boards are returned to their place and secured to the joists with self-tapping screws, damaged floorboards are turned over or replaced with others;
• check the floor for squeaks - if necessary, identify the cause and eliminate it;
• the cracks formed between the boards are sealed with sealant and wait for its final setting;
• treat the wood with an antiseptic if it does not have a paint coating, as well as with a water-repellent primer.

Next, determine the level to which the screed will be poured. Using a laser device, mark the “horizon” on the wall at a height of approximately 50 cm from the floor, set equal distances down and draw a line defining the level of the top of the screed.

The distance from the drawn line to the surface of the wooden floor should correspond to the average thickness of the future screed (usually 5-7 cm).

The next stage is the installation of insulation, resulting in a waterproof pallet. For this:

• A damper tape is laid along the walls along the entire perimeter, a couple of centimeters wider than the thickness of the screed. It is attached with glue or double-sided tape;
• a polyethylene film is laid with an overlap of at least 10 cm on adjacent canvases and with an overlap of at least 15 cm on the walls. The laid layer should not have folds or punctures, much less holes. Patches are applied to accidentally torn film, and all joints are taped.

A metal profile is placed on top of each concrete strip and pressed into the mortar until it is flush with the line previously marked on the wall.

If it is necessary to lay reinforcement mesh, the work is carried out in several stages. First, the first layer is poured, after it hardens (about a month) the reinforcement is laid, and only after that the beacons are placed. To speed up the process, fiber fiber is added to the concrete solution, which provides strength to screeds whose thickness is more than 5 cm.

At the final stage of the screed installation work, the mortar is poured and leveled along the beacons, which are removed after a day, and the grooves are filled with concrete. As it hardens, the screed is sprayed with water for a week and covered with polyethylene so that it can evenly part with moisture.

After the screed has completely dried, the process of installing it can be considered complete.

Today there are many floor coverings, however, time-tested wood has not lost its relevance and is still very popular. As a result, many home owners decide to install wooden planks on top of a concrete screed. This procedure is not too complicated, but it requires certain knowledge, so next we will look in detail at how to install a wooden floor over concrete.

General information

Often, before making repairs, people wonder which floors are better - wooden or concrete?

At first glance, concrete floors may seem more practical for the following reasons:

• They do not rot, and as a result are more durable;
• Over time, they do not begin to creak, unlike a wooden floor;
• They have good strength.
• They are moisture resistant, etc.

However, it is no secret that a concrete floor is colder than a wooden floor and, of course, less comfortable. As for the disadvantages of plank flooring, such as a tendency to rot or loosen and squeak, if modern installation technologies are followed, they cease to be a problem.

Therefore, when deciding which floor to lay - concrete or wood, you should take into account the operating conditions. For example, in a bathroom or kitchen it is more advisable to use a concrete screed covered, for example, with tiles. But in a living room or bedroom, where comfort and coziness come first, it is more advisable to cover the floor with wood.

Technology of laying wooden floors on concrete

Now let's take a closer look at how to lay a wooden floor on a concrete base.

It should be said right away that there are several installation technologies:

• Gluing boards to concrete;
• Laying on joists;
• Laying on plywood;

To choose the appropriate technology, you should familiarize yourself with each one, which is what we will do next.

Preparing the base

Before laying a wooden floor on concrete, you need to prepare the base, regardless of what installation technology will be used. Preparation consists of drying the screed if the floor was recently poured and leveling it. If the surface of the base has bumps, then they can be removed by grinding; if there are “pits”, then such a defect can be most easily eliminated using a self-leveling mixture.

Note! You can begin installation work only if the humidity of the screed does not exceed 3 percent.

At this stage, you should also make holes in the concrete for communications, for example, sewer or water pipes, cables, etc. The most effective method is diamond drilling of holes in concrete.

If the room area is large, then expansion joints should be made in the freshly poured screed. For these purposes, reinforced concrete is cut with diamond wheels. The final stage of preparing the base is coating the surface with a primer.

Impregnation will serve as waterproofing and will also prevent the occurrence of fungus and mold under the wooden floor. A one-component polyurethane primer mixture is usually used as a primer. After the primer has dried, you can begin installing the floor yourself.

Installation with glue

This technology involves installing boards directly onto a concrete base. Recently, it has been the most common way of laying wooden boards on a screed.

True, installation can only begin if the base complies with SNiP 3.04.01-87. If the concrete is loose or contains cracks, it is necessary to use special strengthening primers or cover it with a separating substrate, for example, Multimoll Vlies.

If it is intended to lay wide solid boards, then a modified elastic one-component polyurethane adhesive is used to glue the boards. Installation of narrow solid or engineered boards is carried out using two-component polyurethane adhesive.

The installation of a wooden floor on concrete in this case looks like this:

• First of all, you need to measure the room and cut the boards to the required length.
• Then, starting from the wall opposite the entrance, glue is applied to the surface of the base and leveled with a notched trowel. The layer thickness should be no more than 3 mm.
• Next, a board is laid on the glue-coated surface and pressed over the entire area.. In this way, 2-3 rows of boards are mounted. When laying boards, they must be tightly joined in the longitudinal and transverse directions; for this you can use tightening belts or wedges.
• After the glue has polymerized, the remaining boards are laid. In this case, the boards of the last row must be cut to width.

Note! A gap of at least 15 mm must be left between the walls and the coating.

The photo shows the lag installation diagram

Installation of floors on joists

This technology involves installing boards to wooden joists (rectangular beams). It can be used for boards with a thickness of 20 mm. Thinner boards should only be mounted on plywood.

The installation instructions are as follows:

• The joists are attached to the concrete floor using dowels and screws. In this case, their caps should be recessed several millimeters below the surface level. The axial distance between the logs should be 25-30 cm.

It must be said that there is another way to attach the logs - using adhesive and bitumen-containing mastics. This technology is justified if there is a possibility of damaging communications when drilling concrete.

• After installing the logs, it is necessary to level them. Places that protrude above the level must be removed with a plane. As a result, the deviation from the level should be no more than 2 mm per two meters.

• Next, along the walls you need to lay soft wood-fiber boards, which will serve as a soundproofing gasket between the floor and the wall.
• It is advisable to fill the space between the joists with heat-insulating material, for example, expanded clay or mineral mats.
• After this, the boards are installed, which are attached to the joists using self-tapping screws. Of course, nails can also be used for these purposes, but over time, such fastenings begin to loosen, resulting in a characteristic creaking sound when moving across the floor.

This technology is good because it allows communications to be carried out under the floor, as well as the use of insulation. However, the price of the structure increases, since in addition to the boards, it is also necessary to purchase beams.

Laying on plywood

A wooden floor on a concrete base can be laid using moisture-resistant plywood 12-18 mm thick.

In this case, the procedure is as follows:

• Standard sheets of plywood need to be cut into squares measuring 40x40 cm or 80x80 cm.
• The resulting fragments are laid diagonally towards the future coating. Moreover, the gap between them should be about 4 mm. The plywood is first glued and then shot with dowels.

A distance of about 10 mm should be left between the edges of the plywood and the walls. The sheets are laid offset according to the principle of brick laying, while the heads of the screws must be recessed by 3-4 mm.

• Before laying, it is rough sanded.
• The leveled base should be cleaned of dust.
• Then the boards are attached to the plywood using self-tapping screws.

That's all the main points of installing a wooden floor over a screed. It must be said that in some cases it is necessary to perform the operation in reverse, i.e. pour concrete over the wooden floor. Most often, in this case, a concrete screed is made over wooden joists.

To do this, metal corners are attached to the side walls of the joists, onto which a reinforcing mesh is laid, and the space between the joists is filled with expanded clay. After this, the concrete mixture is poured, which should be above the joist level.

This technology is used in old apartments, in which wooden beams serve as floors between floors.

Conclusion

Laying a wooden floor over a screed is a completely affordable operation that every home craftsman can perform. The only thing is that you must strictly follow the installation technology and do the work very carefully and accurately. In this case, the floor will be strong, smooth and durable ().

You can get more information on this topic from the video in this article.

Tiled and self-leveling floors on wooden floors cannot be made without a leveling screed.

Leveling a wooden base can be done using a wet cement-sand mortar, a semi-dry mixture with fiberglass, gypsum plasterboard, or Knauf floor slabs over a layer of insulation.

Figure 1. Screed on a wooden floor.

Features of the screed device for wooden floors

The cement-sand screed, after drying and gaining strength, turns into a monolithic slab that is not subject to linear changes. And wood has the ability to expand or shrink under the influence of humidity and temperature changes. The screed connected to the base, under the influence of unstable wooden structures, will become cracked and collapse.

Therefore, the main condition when installing a concrete screed on a wooden base is its isolation from wooden structures. So that the screed solution does not touch the wood of the walls and floor.

In addition, the screed should not put too much stress on the floor.

Preparing the base for the screed

Before deciding to pour a concrete screed over a wooden floor, carefully inspect the base. Check the condition of the joists and floor boards.

The wooden covering must be rigid and durable, without traces of mold or rot.

If the covering does not inspire confidence, you can strengthen it by installing additional joists, or replacing worn flooring boards.

Figure 2. Repairing a wooden floor.

Before installing a leveling screed on a repaired wooden base, we carry out the following preparatory measures:

1. Large cracks and junctions with walls are sealed with epoxy putty or polyurethane foam. After hardening, excess sealant is cut off and unevenness is sanded.
2. We clean the floor surface from debris and dust and treat it with an antiseptic and then with a primer twice.
3. We attach the damper tape to the walls along the perimeter of the room using double-sided tape. It will separate the concrete floor from the wooden wall. The tape should be 5-10 centimeters wider than the height of the screed.

You can use foam polystyrene or a wooden board for these purposes.

1. We lay a dense plastic film, at least 100 microns thick, separating the screed and the floor boards. We lay the film strips overlapping, fastening them together with tape, overlapping the walls by 15-20 centimeters.

Figure 3. Insulation of wood flooring.

We strictly monitor the integrity of the coating to ensure the tightness of the insulation. Moisture should not be allowed to enter the wooden floors both during the installation of the screed and during the operation of the coating.

1. A wet screed installed on a wooden floor must be reinforced. To do this, we lay a steel mesh with a 10x10 cell on the insulated surface. When pouring, the mesh should fall into the screed mass, so it is better to lay it on mortar supports.

Important!
A semi-dry screed does not require additional reinforcement, since the reinforcing fiber is contained in the solution.

1. Using a laser or hydraulic level, we mark the height of the screed. To do this, we transfer the horizon line to the wall. It can be at a height of one meter from the floor. Then, using measurements, we find the highest point of the floor and from there, adding three centimeters of screed thickness, we find the mark of the screed surface. We transfer this line to the wall around the perimeter of the premises.
2. We place guide beacons along the insulating layer, along which the screeds will be aligned. We make them from mortar, in the form of continuous strips, or a steel profile installed on slides of mortar. You cannot screw the profile to the base with self-tapping screws so as not to damage the integrity of the insulation.

We adjust the height of the beacons strictly according to the level, pressing the slats into the mixture or adding a solution under them.

We arrange the first row of beacons at a distance of 15-20 centimeters from the wall, and the next row - 1-1.5 meters from each other, but no more than the length of the rule.

Filling the screed can only begin after the beacon solution has dried.

Semi-dry screed device

Semi-dry screed is made from cement, sand, modifying additives and reinforcing fiber. The minimum amount of water required only to hydrate the cement is added to the mixture.

Such screeding must be carried out in strict accordance with manufacturing technology and building regulations. Following a certain sequence.

Preparation of the solution

The solution, in large quantities, is prepared at the construction site, in a pneumatic blower. This device performs the function of a mortar mixer and a concrete pump. With its use, there is no need for lifting mechanisms.

Figure 4. Production and supply of solution using a pneumatic blower.

All components of the solution are loaded into the device’s container in a certain sequence and mixed thoroughly. Under compressed air pressure, the mixture is supplied through a hose to the work site.

To ensure uniform distribution of the mixture flowing through the hose, special dampers are used.

The solution can be prepared directly at the installation site in a mortar mixer or in a container using a construction mixer.

It is better to use ready-made dry mixture in bags for such purposes.

If it is not there, we take cement and sand in a ratio of one to three and, stirring, gradually add fiber, at the rate of about 700 grams of fiber per cubic meter of solution.

At the end of the process, add a little water and mix until smooth.

You can make installation easier by adding plasticizers to the finished mixture.

Important!
We check the correct consistency by squeezing a small amount of the mixture in a fist. The finished solution should turn into a dense lump that does not release water when squeezed.

Screed device

The semi-dry mixture must be laid strictly according to the installed beacons, starting from the far wall of the room.

We level and compact the solution using a rule and a vibrating screed, carefully filling all the junctions.

Two hours after installation, the beacons can be removed and the resulting cavities can be sealed with a solution.

Figure 5. Grouting a semi-dry screed.

Sand the entire screed with a disc sander. Grind the corners and junctions with the walls using a trowel. At the same time, it is better to walk on a freshly laid screed using special concrete shoes to avoid pushing it through and damaging it.

If the room is more than 20 square meters, we cut expansion joints along the surface of the screed.

After grouting, the surface becomes perfectly smooth and even.

After a day you can walk on the screed, and after three to four days you can begin finishing.

Semi-dry screed is an ideal base for tiles or other covering on a wooden base.

It has many advantages over wet or dry screed:

• the finished coating is highly durable and abrasion resistant;
• due to the semi-dry porous structure, it is much lighter than a wet screed, its installation does not significantly load wooden structures;
• has high sound insulation and thermal performance indicators;
• the use of a minimum amount of water in a mixture with reinforcing fiber fiber eliminates the formation of cracks and shrinkage of the finished screed;
• dirty wet processes and the ingress of water from the solution onto the ceiling and lower floors are eliminated;
• Modern technology and efficient equipment make it possible to produce large volumes of semi-dry screed in a short time.

The permissible thickness of a semi-dry screed is from three to five centimeters.

It is possible to perform a semi-dry screed using a heated floor system.

In this case, it is necessary to lay expanded polystyrene on the wooden base, and then roll insulation with a foil layer.

Figure 6. Diagram of the installation of a heated floor system in a screed over a wooden floor.

Place the heated floor cable system on the insulation.

I recommend!
When installing underfloor heating systems in wooden houses, it is better to give preference to heating mats or an infrared heater in the form of a film with heating elements that can be laid on the finished screed in a layer of tile adhesive.

Wet screed

The screed using wet technology is made from cement and sand, in a ratio of 1:3 with the addition of water, to a plastic, creamy state.

Such a screed requires careful waterproofing of the base, preventing water from the solution from penetrating onto wooden structures.

The solution is prepared directly at the pouring site and laid in an even layer along the beacons.

It is undesirable to install a wet screed on a wooden floor for the following reasons:

• due to its heaviness, a wet screed requires a rigid and durable base;
• the wet process increases the humidity in the house, which is not desirable for wooden structures;
• with minor damage to the film waterproofing, water from the screed can get onto the wooden base and lower floors;
• a wet screed requires mandatory reinforcement, which additionally makes the structure heavier;
• The drying time and strength gain of the wet screed is 28 days;
• During the entire drying period, a wet screed requires care: protection from drafts and moisture.

Figure 7. Installation of a wet cement-sand screed.

Installation of dry screed on a wooden base

A dry screed consists of a layer of insulation and a rigid covering made of gypsum fiber board, gypsum plasterboard or special two-layer floor slabs of the Knauf system.

Expanded clay of different fractions, hard mineral slabs or Penoplex can be used as insulation.

Under the expanded clay we lay a layer of waterproofing made of dense polyethylene, 200 microns thick, so that it is not damaged when filling and compacting the expanded clay.

Important!
We place polyethylene on the walls 10-15 centimeters above the screed mark and secure it with construction tape. We lay the polyethylene strips overlapping and glue them together with tape.

We mark the height of the expanded clay layer using a laser level. We transfer the marks to the walls around the perimeter of the premises.

We install beacons from a metal profile for drywall. We check lighthouses strictly according to building level marks.

Pour a layer of expanded clay, carefully compacting and leveling with a long lath. We fill and compact the junctions with the walls.

Figure 8. Installation of gypsum fiber board screed on expanded clay.

A day later, we lay plasterboard sheets or floor slabs of the KNAUF system over the compacted expanded clay layer.

If using sheets, lay out the first layer on the expanded clay surface, leaving deformation gaps between the sheets of 1 millimeter, with offsets at the seams.

We cover the first layer with glue and lay the second layer of sheets on it, also moving the seams by at least 30-40 centimeters. We fasten the layers together with self-tapping screws.

When using ready-made Knauf panels, we lay them on a compacted surface and fasten them together using special locking joints.

Seams, joints and recesses from self-tapping screws are sealed with putty, sanded and coated with two layers of primer.

Advantages of dry screed:

• perfectly level base;
• excellent sound and heat insulation due to expanded clay;
• low weight does not require reinforcement of structures;
• the surface is ready for finishing immediately after installation;

Figure 9. Diagram of the installation of a gypsum fiber board screed on a wooden base.

The only drawback of dry screed with insulation is its large thickness, which does not allow its use in rooms with low ceilings.

Which screed to choose

If you have a strong and rigid wooden base, it is better to choose a semi-dry floor screed.

It will not load the floor too much; water from the screed will not get onto the wooden structures, even if the integrity of the waterproofing is damaged. Will create a reliable basis for laying any finished floor covering.

When leveling floors in old and dilapidated wooden houses, preference should be given to a dry coating. Dry screed is suitable if you need to insulate the floor of the first floor or the ceiling above an unheated basement.

If you decide to make a screed on a wooden floor, contact specialists who will help you choose the best option for leveling your floor and will carry out the work efficiently, quickly and professionally.

Screed on a wooden floor is not the best solution for installing a new floor. However, despite this opinion, if all technologies are followed, it is actually feasible. In addition, there are wooden floor structures that, being in good condition, are easier to fill with self-leveling flooring than to redo the entire floor structure.

This article will be useful for those who are building their own country house. Having made a self-leveling floor over a wooden one, it is easy to lay tiles in the bathroom or kitchen at home.

Information about septic tanks made of concrete rings will also be useful for owners of country houses. You can get information about septic tanks and place an order.

Wooden floor structures

Before you start talking about screeding a wooden floor, you need to understand the designs of wooden and plank floors.

It hardly makes sense to screed a wooden floor that is laid on joists and a 220 mm thick floor slab. The thickness of such a wooden floor is 70-77 mm and the best solution for such a floor would be to remove the wooden floor along with the joists and make a screed over the concrete floor slab.

Screeding a wooden floor makes sense if the floor joists are on high brick pillars. The height of such pillars can reach 30-40 cm (or more) and it is not possible to replace them with a screed. You can see two photos of schemes for such floors below.

It is precisely floors of this design that can be discussed as a possible basis for a screed.

Features of screed on wooden floors

Before deciding to screed a wooden floor, pay attention to the following:

A screed on a wooden floor is an unconnected screed, that is, the layer of such a screed will not be connected to the bottom layer of the base and will be an isolated layer of the floor, not connected to anything. This leads to some features of screeds on wooden floors.

Firstly, the wooden base for the screed must be very strong and completely motionless. Depreciation, which is so characteristic of a wooden floor, should be completely eliminated. If the wooden floor possibly vibrates, the screed above it will crack, which is unacceptable.

Secondly, depending on the selected material for the screed, the thickness of the screed can be quite thick. For example, when using a cement-sand mixture for screed, the thickness of the screed should be from 10-12 cm. The weight of such a screed will significantly increase the load on the wooden floor. If we take into account that the wooden floor is laid on joists, and there is a step between the joists (the distance between the joists), then as the load on the wooden floor increases, the distance between the joists must be reduced. In large rooms, the distance between the joists can reach 85 cm. Therefore, if you decide to make a cement-sand screed in a large room, you will have to dismantle the floor, reduce the step between the joists, install new joists and restore the wooden floor again.

It’s a lot of work, and perhaps you should think a hundred times before making a cement-sand screed on a wooden floor in a large room.

In order not to disassemble the floor and not reduce the distance between the joists, use not a cement-sand mixture, but, for example, anhydrite floor levelers. The thickness of such a screed is from 30 mm, the leveler does not require reinforcement and can be used for unbound screeds.

Third, A cement-sand screed on a wooden floor is made, always with a reinforcing mesh. This is done, again, to increase the strength of the screed. Moreover, fiberglass in the screed will not save you from using reinforcing mesh. That is, for a semi-dry screed, you will also have to make a reinforcing mesh with cells of 100x100 mm.

Conclusion. The use of cement-sand screed for large rooms with wooden floors is not justified by labor-intensive work. However. If the circumstances and conditions are such that it is impossible to avoid screeding a wooden floor, then to install the screed it is better to use a leveler suitable for independent screeding rather than using a cement-sand mixture. And in general, I would not consider a cement-sand screed as a priority for screeding on a wooden floor, although the use of a high-quality leveler will significantly increase the cost of the screed material.

Material for screeding on wooden floors

To make a screed on a wooden floor you will need the following material:

• Polyethylene film with a thickness of 200 microns, for waterproofing the screed layer from wood and walls;
• Mixture for screed. Read about choosing a mixture a little higher. If you choose a cement-sand mixture, then prepare a reinforcing mesh, preferably with a stainless steel coating. The mesh should not be in rolls. Why not in rolls?

You have to fix the reinforcing mesh on a wooden base, but you must not disturb the waterproofing, that is, do not tear the film. Think about how you will attach the mesh. At the same time, think about how you will attach the beacons for the DSP screed, because there is nothing to attach the beacons to, the base for attaching the beacons is polyethylene.

Why am I making these notes? In my opinion, it is better not to install a cement-sand screed on a wooden base in large rooms. The amount of work and problems will completely overshadow the result. Replace DSP with “Rovnitel” for isolated bases (unbound screed). For example, an anhydrite floor leveler.

Wood screed technology

The wooden floor must be strong, immovable, dry and not rotten. The same applies not only to the floor boards, but also to the joists and pillars on which it is laid. Rotten boards need to be replaced.

Important! Do not screed on a newly laid wooden floor; it may become deformed. The age of the wooden floor for screed must be more than one year when the floor is used in the range of home temperatures. Although I can’t imagine who needs to screed a new wooden floor.

The heads of the nails with which the boards are nailed need to be recessed a few millimeters so that they do not tear the layer of waterproofing film that needs to be laid on top of the boards.

If your apartment is on the ground floor and there is a basement or ground below you, then the seams between the boards need to be filled with epoxy putty. Epoxy putty is chosen because it does not allow moisture to pass through. The seams are sealed so that evaporation does not form between the film laid under the screed and the boards.

If the joints between the wall and the floor are wide, then seal them with construction foam, and on top with epoxy putty and liquid waterproofing.

After the putty has dried, polyethylene 200 microns thick is spread on the wooden base. Polyethylene is spread with an overlap of 10-15 cm on the walls. Two adjacent pieces of polyethylene are laid with an overlap of 20-25 cm. Seal the joint between the pieces of polyethylene with non-wetting mounting tape. Tape the overlaps to the wall with tape.

The polyethylene should lie flat, without folds. Under the polyethylene there should be a clean wooden base free of debris.

Preparation of the solution

Let me remind you that we make a screed from a mixture of leveling agent. We make the screed solution according to the instructions on the package. The leveler mixture is added to the water, not the other way around. The mixture is stirred mechanically with a mixer at low speed until it becomes thick sour cream.

How to check the thickness of the mixture

To check that the mixture is the correct thickness, find a container with a diameter of 70 mm so that it can hold 1 liter of solution. From this cylinder, pour 1 liter of solution onto a 50x50 cm plexiglass plate. The diameter of the spread solution should be 34-38 cm. This means that the density of the solution is correct. The density of the solution must be checked constantly.

Set the screed level

The unbound screed with leveler must be more than 30 mm. For a wooden floor, choose 50 – 60 mm. It is better to measure the level of the screed with a laser level. If the room is very small, a building level is sufficient. Using the laser level, draw a screed line along the wall and place benchmark beacons (levels on legs) along the floor surface.

Filling the screed

The finished leveling mixture is poured continuously over the entire surface of the floor from the far corner to the exit. Helpers will be needed for successful pouring. One dilutes the mixture, the second continuously pours the solution, the third levels the solution according to the level of the beacons and marks, using a special metal rod with oscillatory movements (raising and lowering the rod) along and across the cast surface.

Caring for a poured screed

There should be no drafts or low temperatures in the room with the screed. If you did use a solution from CPS, then cover the screed with polyethylene. The anhydrite self-leveling floor must be protected for 2 days from excessive insolation (direct rays of the sun), too high a temperature, drafts and water. After two days the room needs to be ventilated.

Some conclusions of the article

• Before screeding, evaluate the structure of your wooden floor;
• Cement-sand screed is very heavy and will put a lot of stress on the wooden floor, so you may have to reinforce the wooden floor;
• If possible, replace the DSP with a high-quality leveler for an independent screed;
• DSP screed on a wooden floor is cost-effective only for small rooms, kitchens, and bathrooms;
• Think a hundred times before using a screed on a wooden floor in houses with wooden floors, remember the load.

• And one last thing. If you plan to use tiles as finishing, replace the screed on the wooden floor, if possible in level, by laying cement bonded bonded boards (CSP).