Proportions when laying expanded clay concrete for the floor. DIY expanded clay concrete floor screed Cement expanded clay screed

As mentioned above, the main material of this type of screed is expanded clay, which comes in several types:

• Crushed stone. This material is characterized by the largest fractions - from 5 to 40 mm. There is no recognizable oval shape. Expanded clay concrete with a crushed stone base is used for “wet” pouring.
• Gravel. This material has several categories regarding the size of the fractions. The first group is granules ranging in size from 5 to 10 mm. The second group is fractions from 10 to 20 mm in diameter. The third type of gravel is from 20 to 40 mm. All of the listed sizes are ideal for “wet” and “semi-dry” screeds.
• Sand. These particles are obtained by sifting expanded clay granules after heat treatment of the material. Size – less than 5 mm. Used for “dry” floor screed and pouring a thin layer.

Thus, you can decide what type of expanded clay granules to purchase in relation to the desired final results of the screed.

For example, to ensure good sound insulation of a room, it is advisable to use gravel for screeds with a height of 60 mm and above. You can also use crushed stone for a “wet” screed. The only difference with the “semi-dry” method is that the concrete solution with pre-soaked granules is mixed after placing the beacons. Moreover, the work is carried out simultaneously, and not in stages - that is, expanded clay concrete is poured into the gaps between the installed beacons, after which a leveling concrete layer is immediately applied.

You can sprinkle gravel mixed with sand directly under the floorboards. As a rule, the height of the logs allows for such filling.

How much expanded clay is needed to screed the floor is also a pressing question. A network of special trading platforms sells construction expanded clay, packaged in 50-liter packages. This amount is enough for 1 m2 of surface, taking into account the screed height of 40 - 50 mm. Based on this formula, you can easily calculate the amount of expanded clay for any area.

To insulate floors, especially on the first floors (above the basement) or in situations where the floor is generally located almost on the ground, you often make a do-it-yourself expanded clay concrete screed for thermal insulation. However, there are other, more powerful insulation materials, for example, the same extruded polystyrene foam, but its cost, compared to expanded clay, is too high, so most often they resort to a budget and, moreover, very convenient option.

Below we will talk to you about how this is applied in practice, and as a supplement we will watch the video in this article on the same topic.

How it's done

What is expanded clay

• Expanded clay is produced by firing clay or shale, resulting in a light porous building material, which can be in the form of crushed stone, but most often, these are oval granules, which can have a weight from 350 kg/m 3 to 600 kg/m 3 . Expanded clay sand with a fraction of up to 5 mm has the highest volumetric mass - up to 600 kg/m 3, a fraction from 5 mm to 10 mm - 450 kg/m 3, from 10 mm to 20 mm - 400 kg/m 3 and from 20 mm to 40 mm - 350kg/m3.
• It should be noted that this material, with a very high density, has excellent thermal insulation and noise-absorbing qualities, has excellent frost resistance, is fireproof, and its price is the lowest among all possible floor insulators. In this situation, it can be used both as a bedding and as a filler for expanded clay concrete.

Note. It should be noted that expanded clay absorbs water very quickly, but releases it for quite a long time, so the instructions recommend storing it in a dry, covered place where water does not flow. The moisture content of the material will subsequently affect the amount of water added to the solution.

Screed

In order to pour a layer of concrete screed with expanded clay, we need a flat base, and if it is a reinforced concrete floor, then we can say that the preparation has already been carried out before us, but most often such pours are done on the ground.

That is why, before we start screeding the floor, we will have to plan the base - there is no need for a mirror surface at all, but simply a flat area onto which sand and crushed stone can be poured. But after planning, the soil must be compacted, and if there are depressions, then fill them up so that the pillow lies evenly.

Now about the pillow - in this case you will need sand with crushed stone or the same expanded clay, but if we are talking about light, then, of course, it will be more logical if expanded clay is also used as a bedding, rather than crushed stone or gravel.

Now about the cut-off waterproofing - some recommend laying it on top of the pillow, but, judge for yourself, the wet bedding conducts the cold very well, so it is better to cut off the bedding itself from the ground, and not just the screed.

• Therefore, we will have a cake like this - a film (vapor-permeable or just thick cellophane, roofing felt in two layers) is laid on the ground (if it is rocky, then it needs to be leveled with sand so as not to damage the waterproofing).
• Then a layer of sand at least 20-30 mm thick, and then a layer of expanded clay (crushed stone), which also should not be less than 30-50 mm thick. The last layer can be poured at least a meter high - with this level you will have to level the rough base, onto which, in fact, the concrete screed with expanded clay of a certain fraction will be poured.

• Beacons are mounted directly on top of the backfill, but sometimes, to give the solution greater strength, a plaster mesh is laid on the floor, as in the top photo, or a sheathing is simply made from pieces of reinforcement, wire, and sometimes even from wooden slats.

Of course, the minimum layer thickness will also depend on the size of the fraction, but for the finest (5-10 mm) or even sand, the pouring thickness is not recommended to be less than 30 mm, but this, as a last resort, is better to stick to a minimum of 40-50 mm .

Before you start making the mortar, you should determine the proportions of the expanded clay concrete screed, but here it is difficult to say exact numbers - it all depends on the upcoming load and on the size of the fraction ().

But, nevertheless, you need to decide somehow, therefore, here you can be guided by the generally accepted ratios for residential buildings - 1/3/4, that is, for one part of M400 cement, 3 parts of sand and 4 parts of expanded clay will go.

Also, the proportions of expanded clay concrete screed can be determined by other ratios - for 30 kg of ready-made mortar (1 cement / 3 M400 cement) add 25 kg of middle fraction expanded clay. It is important to achieve a normal consistency of the solution, since a thick mixture is difficult to smooth out using the rule, and in a rare mixture, expanded clay floats to the top and making a mirror is almost impossible.

It is impossible to say here how much water you will need for the best consistency, as this will depend on the moisture content of the sand and expanded clay.

If everything is in order with the consistency, then when you pull the solution along the beacons as a rule, you will get an almost mirror-like surface and there will be practically no noticeable pieces of expanded clay (

To prepare a solution of expanded clay concrete for screed, approximately 25-20 bags are needed per 1 cubic meter.

Any person starting the construction of a house is faced with the issue of arranging subfloors. Under a warm floor you need to make a strong, monolithic, good foundation. Regarding sand-cement mortars, expanded clay concrete screed is considered the best. Its main filler is expanded clay, which is a granular material made from baked foam clay. Its appearance is presented in the form of granules.

Advantages and disadvantages

The advantages of the screed are achieved through firing technology, as well as the unique natural characteristics of clay.

Advantages:

• increased chemical resistance - does not rust, does not burn or rot;
• evens out large differences;
• suitable for any floor covering;
• moisture resistance;
• fire resistance;
• durability;
• a light weight;
• excellent thermal insulation and sound insulation properties;
• excellent resistance to fungal formation and rotting;
• environmentally friendly material.

Thanks to the above criteria, expanded clay concrete screeds are a durable and high-quality foundation for any type of floor covering.

Flaws:

1. Increasing the thickness of the floor.
2. Additional work is required, namely sanding the surface to achieve a smoother base.

A screed made of expanded clay is used to level a horizontal surface characterized by significant differences.

In addition, it gives the floor in the rooms the desired slope. It can be used both outdoors and indoors, as well as in industrial buildings.

Materials and tools

• metal container for stirring;
• level;
• mixer;
• Master OK;
• sand;
• expanded clay;
• plaster brush;
• cement.

Proportions for solution

The composition has different requirements, depending on the surface. The most common composition for the following: 30 kg of sand concrete and 25 kg of expanded clay. This mixture is ideal for public buildings. For residential buildings, the following composition will be optimal: expanded clay - 4 parts, sand - 3 parts, cement - 1 part.

In order to install the floor, it is necessary to make a mixture. To do this, expanded clay is poured into the container, approximately 1 cm more than the level of the top granules, and filled with water. Due to the fact that the material has a porous structure, it will absorb a certain amount of water. In order to speed up the absorption process using a mixer, the material is mixed.

The result is an expanded clay layer without moisture accumulation. Then sand concrete is added to it with continuous stirring. It envelops expanded clay particles. Since there are no exact proportions for such materials, the condition of the materials should be carefully monitored. Stop adding the cement mixture when the expanded clay granules acquire the color of cement.

Expanded clay concrete screed device

1. The working surface is prepared, which includes preparatory work for the base of the floor and the part of the wall that comes into contact with the screed. The floor is cleared of debris and dust, the recesses are sealed with plaster with a cement component. Wires that are on the floor must be removed.
2. They break the level marks and set the beacons needed for the expanded clay concrete screed. Using a water or laser level, marks are made at the desired height, a line is drawn, and a dye thread can be used. It is imperative to ensure that the lines in the corners connect. Then beacons are placed along the lines in increments of 50-60 cm. The beacons are fixed using cement mortar. And if necessary, then pieces of plaster or bricks can be placed under them. A day later, the next stage begins.
3. Expanded clay backfill. It is poured between the lighthouse slats and then leveled with a trowel. It is imperative to ensure that the backfill is slightly lower than the upper level of the beacons. And at least 2 cm between them. Expanded clay is poured with “cement milk” with light compaction, so that it does not “float” while the floor is being installed.
4. Filling is carried out one day after the above step. First, a cement-sand mortar is prepared and poured between two adjacent lighthouses. Alignment is done according to the level with a change in the angle of inclination (right/left, towards/away). The resulting puddles are leveled until they disappear and a perfectly flat surface is achieved.
5. After a day, the beacons are removed, and the solution is poured into the resulting voids. After an hour, the surface is watered with cement water and rubbed with a plaster float. If there is a need, then minor irregularities are ground using a solution.

You can walk on expanded clay concrete screed after 2 days. After 2 weeks you can already lay the floor covering. As a rule, complete drying occurs within 25-30 days, depending on the thickness of the screed, room temperature and humidity.

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Every owner of a house or apartment wants to have warm and smooth floors. Expanded clay concrete screed will help solve this problem. Its basis is expanded clay - an environmentally friendly material, which is granules of baked and foamed clay. In most cases, a screed made of expanded clay concrete is used to level the surface. It allows you to even out even large differences. In addition, expanded clay is a good heat and sound insulating material. Often, floors with this building material are used to hide communications or a “warm floor” system.

Advantages and disadvantages

The composition of expanded clay concrete includes expanded clay, concrete and sand. The components of the screed determine its advantages:

• high strength;
• durability;
• good thermal insulation;
• additional sound insulation;
• fire resistance;
• resistance to aggressive environments and chemicals;
• moisture resistance;
• not susceptible to rotting;
• light weight;
• environmental friendliness.

Expanded clay concrete does not ignite and is resistant to mechanical, chemical and other influences. In addition, its components resist the development of fungus and mold. Environmental friendliness and durability allow it to be used in residential areas. Expanded clay concrete screed allows you to level out large differences in floor heights. Compared to conventional concrete, such subfloors will be cheaper. And their low weight makes it possible to install them not only on the ground, but also in the attic and other places.

The main disadvantages of expanded clay concrete screed are the additional labor costs when pouring, as well as the need for grinding to obtain a smooth surface. But in this case, any material can be used to finish the floor: laminate, parquet, linoleum, and so on.

Proportions and preparation of solution

Depending on the desired brand of expanded clay concrete, the proportions of the components may differ. The strength of the screed is determined by the amount of cement in the solution.

The proportions of expanded clay concrete when used in public places can be as follows: for 50 kg of expanded clay you need to take 60 kg of sand concrete. To prepare it, you need to take sand and cement in a ratio of 3:1 (45 kg of sand and 15 kg of cement). If the thickness of the floor is about 5 cm, then the solution prepared from this number of components will be enough for about two squares of area. If the floor screed is performed in a residential area, then the proportions should be changed. You need to take four parts of expanded clay, three sand and one part of cement. The preparation of the solution must be carried out in a certain sequence.

• Expanded clay should be poured into a large container and watered. The granules absorb moisture well.
• Mix the solution and leave for a while. Drain off excess water and place the expanded clay in a concrete mixer.
• Add concrete and sand to it in the required proportions.
• Pour in water and mix everything.
• Expanded clay should acquire the color of cement, and the solution should acquire the appropriate consistency.

The consumption of the prepared solution depends on the proportion and thickness of the floor being laid. It can also be affected by the size of expanded clay granules. It is best to choose medium or fine material.

Methods for laying expanded clay concrete screed

Laying a screed with expanded clay is labor-intensive, but not difficult, so a person with a minimum of skills in this work can do it independently. There are three types of laying expanded clay concrete screed:

• wet;
• semi-dry;
• dry.

Each type has its own characteristics, but the preparation is always the same. The surface must be cleared of debris and strongly protruding parts must be removed. If there is a screed on the floor, it must be removed. All cracks and other defects must be repaired with cement mortar. The next step is laying waterproofing. For these purposes, bitumen mastic or film is used, which should extend onto the walls by about 15 cm. In addition, before pouring the screed, it is necessary to install a damper tape, as well as beacons at a distance of 50-60 cm from each other.

Wet method

If the floor screed is carried out using the wet method, then it is necessary to prepare expanded clay concrete. Its proportions depend on the location of application of the solution and other factors. The prepared solution is poured onto the prepared surface and leveled using the rule between the beacons. The main feature of a wet expanded clay screed is that the surface may not be smooth enough. Often it is necessary to fill the top thin layer, which will level the surface. In some cases, you can get by with sanding.

Semi-dry method

Semi-dry expanded clay concrete screed is laid in two stages. At the first stage, the floor is covered with dry expanded clay. Its level should be 2 cm below the subfloor level. Then it is poured with cement laitance, prepared from cement and water, and compacted to prevent swelling. Thanks to this, the expanded clay granules adhere to each other. All this is left for a day, and then the screed is completed. After setting, expanded clay is poured with concrete from a mixture of sand, cement and water, leveled using the rule and allowed to dry.

You can walk on the screed after two days, but it will take two to three weeks to dry completely.

Dry method

The floor is covered with dry expanded clay, as with the semi-dry method. It must be covered with plywood or drywall. The flooring is done in two layers so that the seams are well closed. A concrete screed is poured on top, thanks to which you can get a flat floor, ready for further finishing.

Regardless of the installation method, after two or three days the beacons installed before pouring are removed. The places where they were located must be sealed with cement mortar. During the drying process, the screed must be watered to prevent cracking. In some cases, the floor is covered with plastic film to retain moisture.

Expanded clay concrete screed is one of the few bases with universal properties, used in buildings and structures for various purposes.

Advantages	Flaws
Sufficient mechanical strength for all types of finishing floor coverings. Taking into account their characteristics, it is possible to adjust the properties of expanded clay concrete screed by changing the proportion of components.	A fairly large height reduces the volume of the premises.
Low thermal conductivity. Such screeds can be used both in underfloor heating systems and for conventional coatings. In all cases, a noticeable effect of reducing heat losses is achieved. Thermal conductivity indicators are regulated by the percentage of expanded clay and the height of the screed.	When preparing expanded clay concrete screed, you need to use bulk materials and water, as a result of which a fairly large amount of construction waste is generated.
High fire safety. Such screeds are considered a reliable barrier to open fire and are allowed by government regulators to organize and use them without restrictions.	The work is performed manually and requires significant physical effort.
Environmental friendliness. Expanded clay is a specially processed clay, a completely safe material for human health.	It takes at least 2–3 days to harden, which creates difficulties for the rhythm of construction work.
Low cost. Among all floor insulation technologies, expanded clay concrete screed is the cheapest.

Proportions and preparation of solution

The process of preparing the material has its own characteristics, and the proportions have a great influence on the final properties. Depending on the amount of water, the solution can be liquid, semi-dry or dry.

Liquid solution. There is so much water that light expanded clay floats up; after hardening, the heat-insulating material is concentrated in the upper part of the screed. Advantages - the screed is self-leveling. Disadvantages - for finishing floor coverings it is necessary to make a cement-sand screed, which increases the time of construction work and increases its cost. Another drawback is that a large amount of water significantly narrows the scope of application. Liquid expanded clay concrete screeds are recommended for insulation of attic spaces and various outbuildings. It is desirable that the floor slabs be reinforced concrete.

Semi-dry solution. The most commonly used material, the consistency of the solution allows the lightweight expanded clay to be evenly distributed throughout the entire volume. This screed is universally applicable and can be used on all types of floors and under all floors. Disadvantage: it requires a lot of physical effort, installation of beacons, and finishing grouting.

Dry screed. Feature - expanded clay is not mixed with the cement-sand mixture, but is laid dry on the base. A thin ordinary screed is made on top. Advantages: speed of production. Disadvantages: relatively low physical strength parameters.

Currently, ready-made dry cement-sand mixtures are available for sale; using them is much more convenient than buying the ingredients separately. In terms of price, they are somewhat more expensive, but if you take into account all the losses on travel and transportation, then there is no benefit in preparing it yourself. Savings on ready-made mixtures are also achieved due to the fact that it is impossible to accurately calculate the required amount of sand and cement; there will always be a surplus. And this is a direct loss of financial resources. The use of dry mixtures eliminates the occurrence of large unproductive losses of materials.

How to prepare the solution

It is recommended to add 2–2.5 parts of expanded clay to one part of dry mixes. If you want to prepare the solution yourself, then it is recommended to add three parts sand and four expanded clay to one part of the cement. The amount of water, as we have already mentioned, depends on what kind of solution is being prepared.

The mixture can be mixed manually or using an electric concrete mixer.

There is no point in using a mixer for several reasons. Firstly, it can only prepare a small amount of solution. Small portions significantly complicate the styling process. Secondly, each portion of the solution will have different proportions, which has a negative impact on the quality of the screed. Thirdly, the mixer cannot evenly distribute light expanded clay balls throughout the volume; most of them constantly end up in the upper part of the container.

The percentage of ingredients can be adjusted depending on the required final screed performance. If it is necessary to increase its strength, then the percentage of cement should increase and vice versa. To reduce thermal conductivity, more expanded clay should be given, but it should not be overused. Otherwise, the strength of the base will sharply decrease. The solution can be prepared indoors or outdoors; the specific decision is made taking into account the characteristics of the building and the capabilities of the developers.

Practical recommendation. If you plan to prepare a solution using ready-made dry mixtures, then it is better to do it indoors. Factory-made dry mixtures cannot be stored outdoors; they react extremely negatively to direct contact with water.

Preparation of beacons for expanded clay concrete screed

A very important point: the quality of the screed largely depends on the accuracy of the preparation of the beacons. It is better to make beacons under a laser level; if you don’t have one, you can use a water level. The work in this case will take more time, but will almost eliminate the possibility of error. Why? Each mark is placed separately on the wall using a water level; if there was an error on the first one, then it is leveled out by the others. The laser level works differently; it gives marks immediately along the entire perimeter of the room. Initially, an incorrectly positioned device causes the entire screed to be not horizontal, but with a slope. Keep this in mind, correcting the error later is time-consuming, difficult and expensive.

How to place beacons under a screed?

Step 1. Clear the room of construction debris and inspect the foundation. If there are large cracks on it, then they will have to be sealed, and work will continue only after the repair solutions have hardened.

Step 2. Cover the ceiling with plastic film or other waterproofing material. If the screed is done in non-residential premises on a concrete floor, then waterproofing is not necessary.

Step 3. Install the laser level. We have already said that this operation must be approached very carefully; all actions must be performed in strict accordance with the device manufacturer’s instructions.

Step 4. Check the distances from the ceiling surface to the laser lines. The minimum thickness of expanded clay concrete screed is approximately 5 cm. If it is made thinner, the strength will not meet current standards. The maximum thickness of the screed depends on the parameters of the room and the planned heat saving indicators. The thicker the expanded clay screed, the better the body is preserved indoors. It is recommended to cut down small protrusions on the surface of the ceiling. This is much more profitable than significantly increasing the thickness of the screed due to such problems.

Practical advice. The process of installing beacons will be much faster if you do not constantly check the distance between the guides and the laser beam with a tape measure or a simple template, but make a corresponding mark on the rule. This way you will simultaneously adjust the metal profile to the horizon level and adjust the thickness of the expanded clay concrete screed. This device allows you to set beacons without a bubble level; all the necessary functions are performed by a laser beam.

Step 5. Decide on the specific location of the beacons. The distance between the lines should be 15–20 cm less than the length of the rule. There is a gap of 30–40 cm between the outer beacons and the walls of the room. The lines should be directed towards the exit from the room. The distance between the stops for metal profiles is approximately 20–40 cm, specific values ​​depend on the parameters of the elements. One main condition must be met: the profiles should not bend under the rule during leveling of the screed, and during this process quite large forces can be applied to them.

Step 6. Prepare the metal slats and cut off missing pieces if necessary. Make a solution to fix the beacons. To speed up hardening, increase the amount of cement; the solution for beacons can be prepared in a ratio of 1:2. There is another way to speed up the hardening of the solution for slats. After placing the beacons, carefully sprinkle the surface of the mounds with dry cement; it will quickly absorb moisture. Remove the wet cement with a trowel or staple and repeat the operation. Thanks to these actions, you can start making the screed 15–20 minutes after installing the beacons.

To speed up the work, you can first prepare pads for the slats from various available materials. It is advisable to use pieces of bricks or pebbles of appropriate sizes. It is not recommended to use sections of plasterboard boards due to very low physical strength and moisture resistance.

Step 7 Place the pads in place, sprinkle some mortar on them and place the metal strip on top. Pay attention to the previously made beacon markings.

Step 8 Place a metal strip on a hill and a rule with marked marks on top.

Step 9 Gently press the metal profile until it is in the desired position. Constantly monitor the position of the laser beam on the rule using the marks. Hold the tool horizontally and, with little force, press the beacons to the desired level. If during work the profile sinks too much, then it should be raised, an additional portion of solution should be placed below and re-adjusted.

Step 10 Use a spatula or trowel to remove excess mortar from the surface of the planks. Use the same algorithm to place all remaining beacons. If you have the slightest suspicion of correctness, check the position of the slats again. To guarantee, it is recommended to apply the rule to the adjacent slats; the laser beam should be positioned exactly according to the marks previously made on it.

At this point, the work with the beacons is completed, after a short pause you can begin making expanded clay concrete screed.

Filling the screed

For example, we will take a classic screed - expanded clay is evenly distributed throughout the entire volume of the solution.

Practical advice. When purchasing expanded clay, pay attention to its quality.

What signs indicate bad material?

1. The balls are too different in size and have unequal weight. This indicates that during the production of the material the recommended technology was grossly violated. The large weight of the balls indicates that there are no air pores inside them, and the thermal conductivity does not meet the standardized parameters.
2. There are open pores on the surface. Very unpleasant marriage, do not buy such material. The fact is that water gets into these pores, it conducts heat well, and dries for a long time in a closed space. Such a screed will never meet expectations in terms of its performance characteristics.

To prevent cracking of the screed along the perimeter of the walls, lay a damper tape approximately five millimeters thick.

Step 1. Calculate the approximate amount of materials. This is easy to do if you know the area of ​​the room and the average thickness of the screed. You don’t need special precision; up to a kilogram you still won’t be able to determine the amount of materials. Buy them with a small reserve; the excess will always be useful later on at a construction site.

Step 2. Prepare the mixture. We have already mentioned that it is better to mix with a concrete mixer or shovel in a large container. If you don’t have either the first or the second, then prepare the solution in a bucket using an electric drill with a large whisk.

But be prepared for difficulties, the process is not that simple. Carefully monitor the overheating of the drill motor; when mixing a thick mass, it works with critically high loads. As soon as the tool body heats up, immediately stop stirring and cool the stator and rotor windings. Overheating of their insulation causes a short circuit, or at best significantly reduces the service life. After each overheating, the insulating properties of the special varnish decrease, and the situation is repeated progressively until a short circuit occurs.

Important. A common misconception among inexperienced builders is that electric tools need to be turned off to cool. This is not true. Of course, in this state they will cool down, but this will take a very long time. Professionals always cool electric tools while plugged in; the load is simply removed. All engines have an efficient air cooling system using built-in fans. Without load, no thermal energy is released, and a powerful air jet quickly removes excess heat.

There is no need to take the cement out of the bag with a shovel, this takes a long time, and the material will inevitably spill out a little. Experienced builders advise doing this differently.

1. The sealed bag should be placed on a piece of pipe or strong lath.
2. Use a knife to cut through the top of the bag.
3. Use a pipe to lift it and place the two halves in a vertical position.
4. Use a pipe to tear apart the uncut part of the package.

Now you can effortlessly lift half the bag of cement and pour it into a container for preparing the solution.

Do not forget that water is always poured first, then sand should be added, mixed a little, and only after that cement and expanded clay are poured out. Water is added in such a way that the expanded clay balls do not float, but are distributed throughout the mass.

Step 3. Gradually pour the prepared solution onto the floor, level it a little and level the plane using the rule. You will have to work in an uncomfortable position; use knee pads to make it easier. Do not throw too much solution at one time; you should easily reach the extreme point as a rule.

Practical advice. It is difficult to level an expanded clay concrete screed as a rule; the balls are lifted by the lower plane and leave deep grooves on the surface.

There are two ways to solve this problem.

1. The rule is not to keep it at a right angle to the guide rails, but to tilt it. During alignment, you need to pull it towards you and at the same time intensively move it left and right. Due to such movements, the expanded clay balls are sunk into the solution, and the surface usually remains flat.
2. Make a finishing screed on the surface with cement-sand mortar.

Make a specific decision depending on the type of finishing flooring you choose. There is no need to level anything for attic spaces. If you subsequently cover the screed with mineral wool and lay the floor on joists, then in this case the surface of the screed may have small depressions or protrusions. The screed will have to be corrected on laminate floors, parquet and all types of soft coverings.

To improve adhesion between a thin cement-sand screed and hardened expanded clay, the latter should be moistened generously with water before work. The fact is that concrete quickly absorbs moisture; an insufficient amount of it will not allow the top screed to gain the required strength. Professionals advise pouring dry cement onto a generously wetted screed and using a broom to mix it well with the liquid. This technique perfectly replaces modern primers.

The quality of the screed will improve significantly if the surface is leveled not after the expanded clay concrete has hardened, but immediately after it has been leveled. The new solution will tighten all the recesses and grooves, material consumption will be significantly reduced, and work will be sped up. In addition, this technology ensures that the screed layers are completely monolithic, despite the fact that it is made from two different mixtures.

Final leveling of expanded clay concrete screed

If you have little practical experience in performing this type of work, then the next day you will have to correct the shortcomings of the screed.

Important. Be sure to check whether the material can support a person's weight. If not, then you need to wait another day.

The surface should be leveled using a rule and a grater. The metal slats of the beacons can be pulled out or left in the mass, make the decision yourself, the quality of the screed remains almost unchanged.

Step 1. Remove the metal slats from the solution. It has not yet reached maximum strength; the elements can be removed without difficulty.

Step 2. Press the rule firmly onto the surface and scrape off any uneven surfaces using a back and forth motion. Make sure that no indentations appear. As soon as tool marks appear on most of the surface, the base is considered level. Work as a rule not only parallel to the beacons, but also diagonally.

Step 3. Remove the dry mortar, moisten the surface, and level the screed with a float. If the recesses are too large, they should be filled with mass. Never use old mass for leveling; cement has already lost its ability to gain strength; diluting it with water is useless. Check the condition of the screed using a level or rule; there is no need to achieve ideal indicators. The maximum permissible difference in height for the most capricious coatings is 2 mm per linear meter; such parameters are easily achieved after several passes with a float. Start grouting from the far corner of the room and gradually move towards the exit.

At this point the work is completed. Further arrangement of the floor can begin only after the screed has reached at least 50% of its maximum strength; the cement mortar gains such parameters in 10–14 days, the specific time depends on the microclimate in the room. If it is very warm and dry, then the screed needs to be watered every day. Keep in mind that concrete hardening does not occur due to the evaporation of water, on the contrary, it is needed for the optimal occurrence of chemical reactions, as a result of which their solution turns into solid concrete.

Prices for expanded clay in screed bags

expanded clay in bags

Video - Leveling the floor with expanded clay concrete screed