Expanded clay is expanded baked clay. Inside there is a porous formation, outside there is a sintered shell.
Expanded clay was successfully used before the advent of modern insulation materials as a high-quality and inexpensive heat insulator. In some cases it is still used in this capacity. When working on floor screed, the material is used for leveling and as a mortar filler. It consists of fired, foamed clay granules of different fractions and shapes.
Advantages:
- Thermal insulation qualities. Within 0.07 – 0.16 W/(m*K). For comparison: foam plastic 0.031 - 0.04, mineral wool 0.045 - 0.07, reinforced concrete 2.0 - 2.04;
- Mechanical load. Compressive strength from 0.6 to 5.5 MPa. For comparison: foam plastic 0.03 - 0.4 MPa, concrete 5 - 60 MPa and higher;
- Moisture resistance. Water absorption 8 – 20%. Staying in water for a long time does not destroy the material;
- The material is fireproof. Non-flammable, does not emit any toxic substances when exposed to high temperatures;
- Biologically inert. Does not rot and is not a breeding ground for microorganisms;
- Rodents do not grow in expanded expanded clay. The mobility of the backfill does not allow making moves and making nests;
- Noise absorption. Achieved only when added to a cement screed, and not when dry backfilled;
- Over a long period of time, the properties of high-quality material do not deteriorate. In many old buildings (more than 50 years old), during demolition, expanded clay is discovered, with which nothing happened;
- The properties are not affected by temperature changes in any climatic zones;
- Low cost and availability;
- The work does not require any special tools or skills. A floor screed with expanded clay is essentially no different from a standard floor screed.
Flaws:
- For insulation, a large screed thickness is required. A layer with expanded clay less than 10 cm thick is ineffective;
- Dry floor screed with expanded clay is dangerous if water gets into the expanded clay layer. The material itself will not be damaged, but moisture under the concrete will remain, which can lead to increased dampness inside the room and the formation of mold.
Not just any expanded clay is suitable for floor screed. Depending on specific cases and places of application, it is recommended to use different brands. Which expanded clay is better in a particular case is determined by the following parameters: layer thickness, laying method (fill layer or expanded clay concrete), presence of water, etc.
There is GOST 32496-2013 for the characteristics of expanded clay grains. However, manufacturers may not adhere to it, producing products to their own specifications or simply not maintaining the standard. In particular, when purchasing material from an unknown manufacturer, there is a risk of purchasing material with an increased background radiation. At least there are such warnings.
The main parameter is the grain size of the fractions: 5 – 10, 10 – 20, 20 – 40 mm. Also somewhat conditionally divided into:
The first two types are used as thermal insulation material. It is possible to make a screed with expanded clay sand, but only as a porous filler for concrete. In this case, the characteristics of the concrete coating will not differ much from ordinary concrete in terms of thermal insulation.
Using expanded clay for floor screed
In terms of thermal insulation qualities, the material is inferior to a number of modern insulation materials: expanded polystyrene, mineral wool and other foamed, porous and fibrous synthetic insulation materials. This becomes especially critical in rooms with low ceilings. For reliable thermal insulation, the expanded clay layer should be 10 cm or higher, while using polystyrene foam, 5 cm is sufficient (in specific situations it may be less).
In what cases is it advisable to use expanded clay:
- To reduce the pressure of the screed on the base. Expanded clay concrete is much lighter than conventional concrete;
- In cases where the insulated floor will experience significant weight loads: garages, industrial premises, etc.;
- Installation of “warm” floors. It is convenient to place heat-conducting communications directly on the expanded clay. In this case, the material will also act as a thermal insulation cushion. With this technology, the “warm” floor equipment should be above the heat-insulating pad (recessed level with it, but no more). Between the heat conductors and the finished floor there should be as few heat-insulating elements as possible (a thin layer of regular screed, self-leveling floor, decorative finishing). Nevertheless, it is better to use modern insulation materials - extruded polystyrene foam or, in extreme cases, polystyrene foam;
- Situational for leveling the surface, reducing concrete consumption. It is usually cheaper to level with various construction waste or soil. The quality is better than soil, clay or construction scrap. Does not require additional compaction, practically does not shrink.
For screeds with expanded clay, three methods and their combinations are used:
- Expanded clay concrete. When mixing concrete mortar, expanded clay is introduced in different proportions and different fractions depending on the purpose;
- Backfill. Expanded clay is not mixed with concrete, but simply piled on (a thermal insulation layer, leveling, like a filler). This layer can subsequently be either isolated from liquid concrete or concrete poured directly onto it;
- "Dry" screed. In fact, this is a layer of expanded clay covered with sheet flooring material (gypsum fiber, plywood, chipboard, fiberboard).
Expanded clay concrete
To obtain an insulating layer, a thickness of expanded clay concrete of at least 10–15 cm is required. No preliminary preparation of the base is required before pouring. The exception is large uneven ground (holes, dips), which are recommended to be filled and compacted first. Waterproofing is also done on the basis of general construction indications. Those. if there is a need to hydroprotect the structure from groundwater or high humidity.
The process of laying expanded clay concrete screed is identical to the process of laying conventional screed. The only differences are in the preparation of the mixture.
Advice! If the thickness of the screed is more than 6 cm, then for simplification it is poured in two layers. The first layer does not reach 4 - 5 cm to the floor level. The second layer is leveling.
Stages of expanded clay concrete screed:
- Floor level markings. Marking can be done using a building level or a water level (preferred).
Marking using a water level. First, a level is marked at any convenient height along the entire perimeter of the room. Then the required distance is measured from these marks.
- Preparing the base (if necessary). Filling holes, leveling large uneven areas. Waterproofing measures. It is sufficient to use polyethylene film as waterproofing. It is advisable to place the film with a slight overlap (10 - 15 cm) if several strips are laid down. It is also advisable to make small allowances on the walls up to the width of the screed.
Waterproofing with polyethylene film.
- Installation of fittings (if necessary). Multilayer filling simplifies the installation of reinforcement. In this case, the reinforcement is placed before the leveling layer is poured.
Installation of reinforcing mesh.
- Installation of beacons based on fill level. Beacons can be made using any method and installed on a base using a solution (gypsum solutions can be used to speed things up). Instead of specialized beacons, you can use any straight profiles (for example, a wall profile for plasterboard). You can also make the rule yourself from a piece of board.
Installation of beacons on the solution.
- An edge damper tape is installed along the walls. Serves to compensate for temperature fluctuations. Sold in different types, including with a self-adhesive side. You can also attach it to the wall using any method: double-sided tape, glue, stapler.
Fixation of the damper tape is only necessary at the time of pouring; durability of the fastening is not required.
- Preparation of expanded clay concrete. Factions and type depend on the goals. The insulation properties are higher for large fractions of gravel. Crushed stone and expanded clay sand are used for thin leveling layers. The proportions are approximately 1 cement (M400), 3 construction sand, 4 expanded clay. Expanded clay is pre-soaked in water; without being saturated with moisture, the granules will float to the surface of the concrete.
- Filling and leveling according to the beacons. When pouring in multiple layers, to obtain a homogeneous screed, it is recommended to pour the leveling layer immediately after the first layer.
The method is used both as an independent screed and as one of the layers in multi-layer pouring. Under tiles, self-leveling floors on this screed are quite sufficient.
Backfill
Something between dry screed and expanded clay concrete. Also, depending on the purposes, different fractions and types are used. For thermal insulation, the expanded clay layer must be at least 10 cm, and the gravel fraction must be at least 20 mm. For leveling, smaller fractions, crushed stone and sand are preferable. It is not advisable to use the backfill method if there is a high risk of direct water ingress. Moisture insulation, if necessary, on the first and semi-basement floors is required.
In fact, this is a screed device for expanded clay:
- Floor level markings.
- Preparing the base (if necessary).
- Installation of beacons based on fill level.
- Backfilling and leveling the expanded clay layer. Sometimes, to improve the insulation properties, you can additionally lay a layer of waterproofing from the liquid solution - a regular polyethylene film. It is advisable to spill the top layer of expanded clay with a liquid solution so that it does not float up when pouring the screed and it is convenient to install beacons. The only plus is that expanded clay will not float when pouring a sand-cement screed if the solution is too liquid. The polyethylene film also prevents the granules from floating.
- Installation of fittings (if necessary).
- Pouring sand-cement screed along the top. It is recommended to dilute the solution thicker, possibly in smaller batches, or to prevent the granules from floating using the above methods.
The method is also used as an independent screed, and as part of multi-layer “pies”.
Dry screed
There are two types of dry screed:
Technology:
Advice! It is not necessary to do the entire room at once. Can be done in parts according to the size of gypsum fiber board sheets. In this case, fewer beacons will be required, making it more convenient to move along the laid floor. Otherwise, to move, you will either need to start laying from the entrance, or create islands for moving along the poured expanded clay (in this case, it is enough to temporarily lay gypsum fiber sheets).
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According to reviews, the easiest and most accessible way to level the floor yourself is to install an expanded clay concrete layer. Screeding a floor with expanded clay with your own hands can be done in two ways. The choice of one method or another depends on the purpose of the room and the characteristics of the base. Detailed video instructions from our article will help you strictly adhere to the technology for performing expanded clay concrete leveling. To understand what price your screed will cost, you should do a calculation. You can also find out how to do it correctly here.
Advantages of screed with expanded clay
Expanded clay is an environmentally friendly, durable and practical material that can improve the heat and sound insulation characteristics of the floor. Expanded clay concrete screed is used if it is necessary to significantly raise the floor level. The strength of expanded clay mixture is not lower than that of cement mortar. In addition, the solution has the following advantages, provided that the proportions of its preparation are observed:
- good vapor and air permeability;
- frost resistance;
- resistance to elevated temperatures;
- the material is not subject to burning, rotting and corrosion;
- the low weight of the solution facilitates its transportation and installation;
- expanded clay concrete allows you to reduce the load on the floor;
- the material copes even with significant unevenness of the base.
An equally important advantage of such a solution is that the floor screed with expanded clay can be laid with your own hands.
When is expanded clay concrete used?
The installation of expanded clay concrete screed is simply irreplaceable in some cases:
- If the height of the leveling layer is 10-15 cm, then the use of pure cement mortar or concrete is impossible due to too much load on the floor slabs. In this case, all that remains is to make a composition with expanded clay.
- Sometimes even a low screed is too heavy to install over an existing floor, for example, in an old building. In this case, installing a low expanded clay concrete layer will help not load the floor.
- When leveling wooden floors with wet screeds, it is also better to use a lightweight solution. In this case, the expanded clay leveling layer can be combined with a layer of foam or other lightweight materials.
- The price of cement is not small, so in order to reduce the cost of the screed, expanded clay is used as a mortar filler. According to reviews, it is cheaper to do expanded clay leveling than to use cement mortar. But don't forget to keep the proportions.
Choosing expanded clay for mortar
Expanded clay comes in different fractions. Accordingly, its price also differs. The choice of fraction of this material is made according to the type of work. So, based on the diameter of the elements, expanded clay is divided into the following types:
- expanded clay sand – fraction size from 0.1 to 5.5 mm (this material is often used when installing dry floor screed);
- round and oval expanded clay has dimensions of 5-40 mm (obtained in the process of swelling of clay);
- The particle size of angular expanded clay can be up to 4 cm.
The last two types of granular material are used to make concrete and cement-sand screeds. If you want the leveling layer to not shrink too much, it is better to use expanded clay of different fractions. To understand how much material you need to buy, you can do a simple calculation or use an online calculator from the Internet.
Advice: to create a leveling layer with expanded clay, it is better to choose granular material with a size of 5 to 20 mm.
Preparing the base
Before laying expanded clay concrete screed, you need to prepare the base:
- The evenness of the floor must be measured using a building level.
- Then, using a laser device, the screed level is marked on the walls of the room.
- Beacons are installed starting from the highest point of the base. In this place the screed should not be less than 6 mm.
- All beacons are leveled (see video).
Drywall profiles, slats, boards or pipes can be used as beacons. They are usually placed on mortar heaps or beds. According to reviews, it is better to lay it on cement or gypsum mortar.
Dry method of arranging expanded clay leveling
To make a dry expanded clay screed, you need to purchase fine-grained material. Further work is carried out in this order:
- Preparation of the base and installation of beacons is done as described above.
- Expanded clay is poured onto the floor and leveled so that the height of the expanded clay layer is 2-2.5 cm below the expected screed level. Most likely, you will not achieve a perfectly flat surface, but it is necessary to maintain horizontality. You can calculate the amount of expanded clay using the online calculator on the building materials website.
- Now, using a level, check the evenness of the backfill.
- To ensure better adhesion of the expanded clay layer to the screed, water it with cement laitance. As a result, a film will form on the surface of the granular backfill, which will protect the material from shrinkage due to the absorption of moisture from the screed.
Tip: cement mortar is made from water and cement in a 4:1 ratio, that is, you need exactly twice as much water as to prepare a regular cement mortar.
- Fill the screed. We prepare an ordinary cement-sand or concrete mortar with our own hands, pour it in and level it over the surfaces using the rule. The height of the layer should be such that the mixture, when leveled, is aligned with the upper border of the beacons. To do this, place the rule on the guides and pull it towards you, leveling the mixture.
- Every other day, the beacons can be removed, and the resulting voids can be primed and sealed with fresh mortar. The floor surface in these places is rubbed with a trowel (see video).
Wet expanded clay concrete leveling
After reading reviews online, you can understand that this installation method allows you to reduce the time it takes to install the screed. The work is carried out in this order:
- First the first layer is made. To do this, expanded clay is mixed with the solution. It is difficult to specify exact proportions for mixing. And calculation will not help here. There should be just enough water to evenly wet the surface of the expanded clay. Sand and cement are added gradually until a non-dry, thick, homogeneous mass without lumps is obtained.
- We lay the solution on the floor in such a thickness that it does not reach 2-2.5 cm from the expected level of the screed. We level the mixture (see video).
- Now, without waiting for the mixture to dry, fill in the finishing layer of ordinary cement-sand mortar.
- Carefully level the top layer using the beacon rule.
- Every other day we remove the beacons and fill the voids with a solution after preliminary priming.
Video instructions for performing expanded clay leveling:
Calculation of expanded clay concrete
To find out how much expanded clay you will need for a screed, you need to make a simple calculation. The proportions of materials may be different, but keep in mind that the more expanded clay you add, the warmer but less durable the screed will be.
Calculation of the proportion of expanded clay per leveling layer can be done taking into account the bearing capacity of the base, the required thermal insulation qualities of the floor and the thickness of the structure. The optimal ratio of strength and thermal conductivity of the leveling layer is achieved when expanded clay makes up half of the total volume of the solution. When calculating the price and volume of expanded clay, keep in mind that it is supplied in bags, but is calculated in liters.
Expanded clay concrete is the same cement mortar that is used to fill the screed. But since the coarse aggregate is not heavy crushed stone, but expanded clay granules, the floor is warmer. Expanded clay is quite fragile and is not suitable for fully leveling actively used surfaces. Its main purpose is to create a light heat and sound insulation layer that does not seriously increase the load on the base.
To make expanded clay concrete with your own hands, you will need expanded granules with a particle size of 5-10 or 5-20 mm with a bulk density of 600-700 kg/m3. Fine sand is not as effective, but is used for fine pouring up to 30 mm. Large fractions are more often used for dry and semi-dry screeds. The final choice depends on the loads on the future floor:
1. The best results are shown by mixtures where all particle size classes from 5 to 40 mm are present in equal proportions. In this case, the screed turns out to be a little denser and heavier, but quite strong. At the same time, cement consumption is reduced.
2. To reduce the load on the floors, expanded clay is chosen larger. A finished screed with a large thickness may shrink over time, but this is the only way to level out serious differences in the surface, reaching 10-15 cm.
3. If the concrete thickness is small and there is a need to get rid of shrinkage phenomena, there is only one option left - fine expanded clay sand.
As for cement, you cannot save money here, since it only depends on it how tightly the expanded clay granules adhere to each other. At a minimum, it should be a binder with brand strength M400, but you can also use the more expensive PC M500. The main thing is that Portland cement should be produced without substitute slag additives.
Increased demands are also placed on fine-grained aggregates, since they can also influence the strength characteristics of expanded clay concrete. This is ordinary quarry sand, but it must be sifted and washed. To reduce the density of the screed and increase its thermal insulation properties, it is better to choose larger sand fractions.
Since the finished solution does not have sufficient mobility (its characteristics correspond to the lowest class P1), plasticizing additives are introduced into it to improve the workability of the mixture. You can use air-entraining modifiers such as SDO, which additionally porous the cement matrix. But it’s cheaper and easier to pour liquid soap into the concrete mixer yourself at the rate of 50-100 ml per PC bucket.
Proportions for different brands
To determine the scale of work, you will need to measure the area of the room and calculate the height of the future layer of expanded clay concrete. The pouring volume is the amount of clay aggregate in cubic meters, which should be used as a basis for further calculations. A “warm” monolith can be obtained in different densities - from 1000 to 1700 kg/m3 (although it is better to use the most durable coatings for the floor), and the proportions for the screed will change accordingly.
| Density of expanded clay concrete, kg/m3 | Weight per cubic meter of mixture, kg | ||
| Expanded clay M700 | Cement M400 | Sand | |
| 1500 | 560 | 430 | 420 |
| 1600 | 504 | 400 | 640 |
| 1700 | 434 | 380 | 830 |
If the expanded clay is well moistened, 140-200 liters of water per cube of solution will be enough for such proportions. If soaking is not effective enough, the amount of liquid can be increased to 300 l/m3.
Traditionally, builders use a simplified ratio to obtain expanded clay concrete of grade M100 strength - optimal for constructing a “warm” screed on their own. To do this, take 1 part of cement:
- 3 hours sand;
- 4 hours of expanded expanded clay;
- 1 hour of water.
With such proportions, you can even purchase sand cement, where the bulk materials are in the ratio 1:3. If you need a stronger screed, you simply choose a different preparation recipe for it:
| Brand of expanded clay concrete | Cement | Sand | Expanded clay |
| M150 | 1 | 3,5 | 5,7 |
| M200 | 2,4 | 4,8 | |
| M300 | 1,9 | 3,7 | |
| M400 | 1,2 | 2,7 |
When working with cement of a higher grade M500 and screeding in domestic premises with operational loads no higher than average, it is recommended to use the following ratio of components per cube of expanded clay:
- 295 kg of cement;
- 1186 kg of coarse sand;
- 206 liters of water.
Light screeds are prepared from expanded clay with a density of 200-300 kg/m3 without adding sand. Here you will need to make a solution with the following ratio:
- 720-1080 kg of expanded clay granules;
- 250-375 kg of cement;
- 100-225 liters of water.
Expanded clay is poured into the container first. Before this, the granules need to be soaked in water so that they are saturated with moisture and then do not pull it out of the concrete. After adding a little more liquid, sand cement is poured into the mixer trough or drum, thoroughly mixing the solution. With the correct proportions of expanded clay concrete, all granules during the manufacturing process should become the same gray color - without brown spots.
If the mixture does not seem fluid enough, you can add a little more water to it. If there is excess moisture, you should not add dry components, as this will not allow them to be mixed until homogeneous and will deteriorate the quality of expanded clay concrete, violating the cement ratio. In this case, it is better to let it brew a little, then stir again.
Cooking should be done quickly and without delay. As soon as the granules are completely covered with cement slurry, the composition must be immediately poured onto the base, leveling it along the installed beacons. A solution with expanded clay aggregate sets faster than ordinary concrete, but within a week you can move freely on such a floor. The final strength gain occurs within 28 days.
Features of working with expanded clay concrete
Before pouring, you must lay waterproofing on the floor or coat it and the lower part of the walls with bitumen mastic. Otherwise, moisture will be absorbed into the base, preventing the cement from gaining the required strength. Such a fill will turn out to be non-monolithic and very fragile - it will creep under load and gather dust. Also, a damper tape should be secured around the perimeter of the room to compensate for thermal expansion. Upon completion of the work, the expanded clay concrete screed will require additional protection from moisture evaporation. To do this, it is covered with a film on top, which can be removed after a couple of days.
The finished layer of “warm” concrete needs final leveling - preferably with preliminary grinding. From above it is filled with an ordinary sand cement solution no more than 30 mm thick (without adding gravel). This is enough to hide irregularities, but not to worsen the thermal insulation characteristics of the rough base. The final filling is carried out according to the beacons, carefully leveling the mixture according to the rule. The slats are carefully removed the next day, and the remaining traces are sealed with fresh compound.
Semi-dry screed is another option for insulating and leveling the floor using expanded clay, allowing you to treat small areas one after another. In this case, dry expanded clay granules are poured onto the prepared base with installed beacons - to such a height that 20 mm of the beacon profile remains uncovered. They are poured with liquid cement mortar (milk) on top and compacted, gluing the expanded clay grains together. After a day or two, the surface is filled with a finishing screed - preparing concrete for it is no different from the “wet” method already discussed.
Expanded clay concrete floor screed - a step-by-step description of the work of making an expanded clay screed on a concrete base.
This type of screed is the most durable, but also the most labor-intensive.
If you decide to lay tiles, laminate or linoleum on a concrete base, then you naturally need a flat and smooth surface.
If we take simply a concrete floor in a multi-story panel building as the initial option, then it rarely meets the definition of “smooth and even surface.”
In order to level it, it is necessary to make a screed, i.e. lay a layer of cement-sand, cement-gravel or cement-expanded clay mixture.
The first 2 options are suitable if you make the screed thin, no more than 2-3 cm, or lay it on the ground, for example, in a garage, basement, shed - i.e. where it will not destroy the ceiling between floors, since the weight of such screeds is very significant.
If you need to significantly raise the floor level, by 10-12 cm, for example, in order to join the “tiled” floor in the kitchen with the level of the wooden floor in the corridor, then expanded clay concrete screed is the most correct choice.
Here again there are 3 options:
- You can simply scatter a layer of expanded clay, approximately 8-10 cm, over the entire surface of the floor, level it and pour a layer of sand-cement mixture on top.
- Spread a layer of expanded clay over the concrete base, level it, and pour a very liquid cement solution on top - “cement milk”. Wait until it “sets” and pour the sand-cement mixture on top, which is then leveled.
- Initially, make an expanded clay-sand-cement mixture, lay it in a layer of the required thickness on a concrete base, and after this mixture has hardened (about a day), lay a leveling sand-cement screed.
In the above example, option 3 was chosen as the most durable (but also the most labor-intensive).
Step-by-step implementation of expanded clay floor screed
We take a container in which you can place at least 3 buckets of expanded clay, a bucket of sand, a bucket of cement. Mix the mixture with a shovel (if you don’t have a concrete mixer), gradually adding water until a homogeneous mass is obtained.
We begin to lay it in an even layer from the farthest corner of the room, gradually moving towards the front door. To control the uniformity of laying, it is necessary to have some kind of probe with a mark at the required level. In this case, a wooden stick with a notch at 9 cm was used.
We spread a portion of the mixture, tamping it on top with a block, and pierce it in several places with a probe to obtain a layer of the same thickness.
Attention! You can lay a screed on a concrete floor without waterproofing if you are absolutely sure that there are no holes or cracks in this foundation through which water from the screed can leak to your neighbors below.
Therefore you need:
- pre-seal all cracks in the ceiling;
- lay waterproofing in the form of overlapping polyethylene strips, taping the joints so that these strips extend onto the walls just above the future top level of the screed.
Having laid the expanded clay mixture, wait until it “sets” (1-2 days). Then we begin preparations for laying the leveling sand-cement screed.
Making a leveling sand-cement screed
At a hardware store we buy several beacons (specially molded strips of metal 3 m long). On the frozen expanded clay mixture, we install beacons on raised surfaces using mortar so that the surface of the beacon is horizontal (check with a level).
The beacons must be installed in the form of an inverted letter “T” (the beacons remain embedded in the screed forever).
All beacons are aligned strictly horizontally using a level. When the solution on which the beacons are installed has set, pour the sand-cement mixture between the beacons and level it using the rule (you can buy a tool in a store, or you can use a piece of a flat metal corner, as in the example described).
Leveling is that you lay the rule on the beacons and, moving it from side to side, “pull” the surface of the mixture towards you, stepping back (hence the name “screed”).
As the screed dries (after about 2-3 days), its surface must be evenly moistened with water so that the screed does not crack. During the drying process, the screed shrinks slightly; complete drying occurs after 4 weeks. If you need a perfectly flat surface, you can fill the screed with self-leveling flooring. In the described example it was not necessary, since tiles were laid on the screed and a perfectly smooth surface was not necessary.
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?
- 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.
- 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.
- The sealed bag should be placed on a piece of pipe or strong lath.
- Use a knife to cut through the top of the bag.
- Use a pipe to lift it and place the two halves in a vertical position.
- 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.
- 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.
- 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