Cement screed is an opportunity to make the floor flat and smooth, strong and durable, ready for finishing using even the most demanding materials (tiles, laminate, parquet, etc.). Pouring a cement-sand screed can be done independently - implementing all stages of the work with your own hands is quite possible, without loss of quality and aesthetics.
Cement-sand screed guarantees an almost ideal base; most often this option is chosen for leveling the subfloor (concrete floors in multi-storey and private houses, brick floors or soil). As a rule, the thickness of the filling layer is 3-8 centimeters, calculated in accordance with the requirements and strength of the floors, estimates and other parameters.
The application of a cement-sand screed is designed to level the surface, strengthen it, redistribute loads, create hydro/heat/sound insulation layers, lay communications inside, equip a “warm floor” system if desired, and solve many other problems. There are special types of cement-polymer screed, thanks to which you can create a beautiful and original decorative floor.
Features and Benefits
The weight of one square meter of cement screed 1 centimeter thick averages from 16 to 20 kilograms. Screeds using expanded clay or polystyrene weigh a maximum of 18 kilograms, self-leveling mixtures show a figure of 16 kilograms.
In cases where differences in the subfloor reach 3 centimeters or more, a cement-sand floor screed is the best option. The screed can be tied and firmly adhered to the base, or unbound (floating), when the layer is placed on an additional layer (usually a mixture of sand and expanded clay), which acts as thermal insulation and protects against moisture.
The thickness of the cement-sand screed can be different. On average, the area can support a weight of up to 300 kilograms. If you need to increase the strength and ability to withstand different loads, the screed is reinforced with steel rods or mesh. The frame is placed on top of the expanded clay layer or attached to special fasteners or sheets of plasterboard.
Sand-cement screed has a porous structure, due to which it can absorb moisture. Therefore, the layer inside the building must be insulated with a special membrane, or waterproofed with bitumen mastic.
It is quite possible to carry out all the work on arranging a floor screed with your own hands. The main thing is to do everything according to the rules and preliminary calculations. When the screed has hardened and gained full strength, it acquires a rich gray tint.
The layer should be even and dense. If cracks or chips appear on the surface, it means that the proportion of the components was violated or the pouring technology was not followed, or the rules for drying the screed were ignored.
The main advantages of cement-sand screed:
- High-quality leveling - for any type of decorative coating.
- Durability – the service life of a concrete floor is on average 50 years.
- The ability to disguise communications inside the screed - sewer, water pipes, wires, underfloor heating systems, etc.
- Strength - the screed can withstand any load from furniture, equipment, etc.
- Good sound insulation - the screed almost does not conduct sound, and if it is also accompanied by a layer of sound insulation, the effect is magnificent.
- Thermal insulation - the minimum thickness of the screed and itself retains heat well, but if necessary, you can lay a layer of thermal insulation, ensuring the best characteristics.
- Minimal shrinkage - provided that the cement for the screed has been chosen of high quality, and the mixing is done correctly with the correct proportions.
- Quite a low price when compared with alternative methods of flooring.
Among the disadvantages that sand-cement screed may have are the following: large weight (depending on the thickness of the layer) and considerable pressure on the floor, long drying time (during which no further work can be performed - and this is about a month), the difficulty of creating a perfectly flat surface with your own by hand (but you can pour a self-leveling mixture on top), a long and labor-intensive pouring process.
Carrying out preliminary calculations and a properly executed screed allows you to eliminate most of the shortcomings and achieve an excellent result in the form of a strong, durable, even floor that is ready for further finishing.
Installation of beacons
Many designs and methods can be used as beacons. Let's look at three, the most practical in my opinion. The first design is a standard beacon profile laid on mortar islands. The second is made from a PP guide profile; it does not require drying of the solution and the screed can be poured immediately after installation. The third is the formation of a beacon from the solution itself, the method is relevant on very thin layers of 0-10mm.
Beacon profile
The most common beacon profiles, convenient for use in screeds, are 6 or 10 mm thick. For these purposes, it doesn’t matter at all whether they are aluminum or steel. 10 mm beacons are more practical - they are more rigid and require fewer attachment points. In most cases, you can get by with this profile.
Installation consists of setting the control screws to the desired height of the screed minus 10 mm (-6 mm) after 60-70 cm. The screws prevent the profile from sliding below the specified level and significantly simplify installation, and also increases accuracy.
Regardless of the type of beacons, the lines where the profiles will pass are first marked. The distance between the beacons is taken to be slightly less than the length of the rule, so that at any point on the floor the rule lies on at least two profiles. Standard 3 m profiles can be extended in length if required. It is most convenient to use the 1.5 m rule, with a distance between beacons of 1-1.2 m.
When the beacon lines are marked, holes are drilled along the lines for dowels with self-tapping screws. The screws are screwed to the required height, taking into account the thickness of the profile. It is better to do the alignment of self-tapping screws using a laser level. In the absence of a laser, the outermost screws are placed on the line using any available means, a thread is pulled between them and the remaining screws are already aligned along the thread.
When all the screws are exposed, mortar cakes are placed on them and the beacon profile is recessed into the mortar until it touches the screws. The solution protruding above the profile is carefully removed. Installation is complete and pouring is done the next day.
There is an alternative to the “wet” installation of the beacon profile - installation on clips. The profile is installed on special plastic fasteners without fixing with mortar. The disadvantage of this installation is that the fasteners do not have the proper strength and need to be installed much more often, ideally every 30 cm. And yet, the beacons turn out to be “thin”.
First of all, self-tapping screws are installed, as in the “wet” version, only more often. When installing self-tapping screws, similar to the first option, you need to take into account the thickness of the profile itself, but now you also need to take into account the thickness of the plastic clip - 1-2 mm. Then the main parts of the fastener are put on the screws, the profile itself and the whole result is fixed by the second part of the clip.
Quick installation on PP profiles
The method is used when there is no time to wait for the beacons to set. The disadvantages include a minimum layer of 30 mm and the need to dismantle the profile after pouring, followed by sealing the seams. It should also be taken into account that the solution will be separated by beacons and the seams are a weak point. The method is not applicable in floating screeds.
The process of setting the screws is identical to that described above, with the difference that the caps are installed to the entire height of the screed being poured, without taking into account the thickness of the beacons. In addition, next to the exposed screws, one hole is drilled for the fixing screw. When the limiting screws are in place, the ceiling PP profile is laid on the caps, and the profile is secured on top with fixing screws. You can fill the screed immediately. The next day the profile is removed and the seams are sealed.
Lighthouses from solution
To be more precise, from tile adhesive or a thickly applied self-leveling floor, the usual mortar is too weak to abrasion. The material is selected based on the speed of setting and availability at hand. Mortar beacons are relevant for layers of 0-10 mm, when the beacon profile is too thick.
For the work you will need the same PP ceiling profiles. The algorithm of work is the same, with the difference that the profile is installed in the form of an inverted letter “P”. The solution is poured into the resulting gap between the profile and the base. After setting, the profiles are removed and poured.
Beacons for thick layers
When pouring expanded clay concrete into layers of more than 10 cm, the limiting screws are needed too long, the mortar cakes are huge. You can get out of this situation by using bricks, placing them in the places where the beacons are attached.
Since the bricks must be laid on the mortar, to save time on setting, self-tapping screws can be eliminated. However, without self-tapping screws, accuracy can deteriorate significantly; it all depends on the skill of the master.
Types of cement screeds
There are many options for making floors made of cement-sand mortar. The proportions of the components can be different, you can add various additives and plasticizers, choose a polymer-cement screed and make floors with a 3D effect, etc. But there are two main types of screed arrangement: tied and untied screeds, as well as floating.
A bonded type cement screed is installed when pouring a layer of up to 4 centimeters. In this case, the base becomes a single monolith with walls and floor. The rough foundation needs to be prepared - cracks must be sealed, large holes, bumps and pits must be eliminated. Small defects with a difference of up to 3 centimeters can be left.
Before making a cement-bonded floor screed, it is advisable to go over the base with a wire brush to improve adhesion. The filling composition should resemble sour cream in consistency and hardens within 20 minutes after installation. Large premises are filled in stages. The screed takes up to 40 days to dry, maintaining the temperature and humidity conditions under the film.
An untied screed must be mounted on an already ideal surface. The base should not absorb moisture. The layer when installing this type of screed can be 5 centimeters or more. Before pouring, no primer is used, nor are methods for increasing adhesion.
A floating screed is installed when you need to make a layer of 5-8 centimeters. Cementing does not involve contact of the screed with the subfloor, since heat/waterproofing and different materials are installed between the layers. Typically, reinforcing mesh is used; fiber fiber is added to the solution, which increases the strength of the layer and eliminates the risk of crack propagation.
A floating (including reinforced) screed does not involve too much weight, since, despite its considerable thickness, it is poured using a semi-dry technology: the solution is mixed with a reduced volume of water, so it resembles wet sand in structure more than a liquid mixture.
Preventive action
A large area of the screed will inevitably crack in the future under temperature and mechanical stress. To avoid such problems, expansion joints are used. To do this, shallow slits are cut out in the still uncured solution.
The entire area of the room is divided into small sections. And the width between the seams should be between 3 and 4 meters. And in long and narrow rooms this figure decreases to 2. Seams are extremely necessary in the area of passages from room to room.
If a board or laminate is used as a finishing coating, then the cracks can be left empty. When tiling, the seams are filled with sealant. Otherwise, they will take all the moisture from the solution. And when screeding for “warm floors,” it is necessary to use reinforcing fiber and plasticizers.
Thickness and calculation of floor screed
The composition of the cement-sand mortar is simple and unchanged: cement, sand, water. Approximate calculations are given below (they may vary depending on the required floor characteristics and the brand of cement used).
The weight of a cubic meter of solution reaches 2000 kilograms. On average, a cubic meter of mixture contains 450 kilograms of cement and 1,300 kilograms of sand. A screed 1 centimeter thick requires 20 kilograms of solution - which means the consumption of components is 4.5 and 13 kilograms, respectively.
If you don’t want to prepare concrete with your own hands and think about what kind of cement is needed, what ratios of materials, etc., you can purchase a ready-made dry mixture. Its cost will be higher than a solution prepared independently, but the result will be of high quality, with the properties and parameters of the finished coating established by the standards.
In addition to cement, it is important to choose the right sand - without impurities (clay, silt, dust) that reduce the strength characteristics of the future screed layer. Usually they take washed river sand, or, in extreme cases, quarry sand.
To fill a standard screed, you will need to purchase a primer - its consumption is about 350 milliliters per square meter of surface. Thanks to the primer, it will be possible to ensure high-quality adhesion of the base and mortar, guaranteeing the strength and reliability of the screed.
Stage II. Determining the curvature of the existing base
A linear level, plumb lines or more modern devices such as optical or laser levels will help you. There is only one goal: to determine the topography of the base, mark the zero mark, find the highest point of the floor and calculate future costs - how much will need to be bought to make such a floor screed.
The simplest device for measuring floors is a level. They don’t need any special skills to use - it’s a simple glass flask with an air bubble, which they use to navigate. The flask is mounted in a wooden ruler, which we pick up.
Dry mixes
Do-it-yourself cement floor screed can be done using ready-made dry mixtures. Their main advantage is the absence of the need to calculate the proportions of the components included in the composition and, as a result, stability of characteristics and excellent results. The manufacturer prepares the mixture, the foreman’s task is to calculate the required volume of the mixture to complete the work and mix the solution on site, adding water.
Dry building mixtures are also distinguished by their ease of preparation, density, plasticity - they are comfortable to work with, they often demonstrate improved characteristics due to the introduction of various additives, plasticizers, etc. into the composition. All you need is to look at the mixture consumption in the instructions, purchase the required number of bags (25-50 kilograms each), add water according to the instructions and work.
Mixtures for screeding using dry and semi-dry technology are available on the market. Thus, the polycement mixture is more convenient to work with due to its elasticity; it is often used in industrial and civil construction to create new structures and restore existing ones.
Self-leveling mixtures for floor screed are very popular - you just need to pour this solution onto the surface, it will distribute itself evenly and perfectly evenly. True, it does not guarantee high strength and is inferior to dry mixtures reinforced with metal fiber fiber. The self-leveling mixture option is ideal for residential premises where the load on the floor is light. Lightweight concrete mixtures are also used here.
The modern market offers a large selection of dry mixtures of domestic and foreign production. The range is very wide and choosing an option even for fairly specific requirements is not difficult. While cement for floor screed one way or another assumes certain properties and parameters, ready-made mixtures can give very different effects due to the introduction of various components into their composition.
An example of such a product would be the Knauf Ubo mixture from one of the best manufacturers in the segment (German company Knauf). This is an ideal option for preparing CSP, which has a density that is 4-5 times greater than that of classic concrete. The screed is resistant to any temperature changes and is perfect for installing underfloor heating systems. Provides good sound insulation due to the introduction of polyethylene modifiers into the composition.
To fill one square meter you need about 5 kilograms of the mixture. And this choice is justified for pouring in a residential area due to the ease and simplicity of installation and the excellent performance characteristics of the floor.
Waterproofing
Before you prepare the solution for pouring the floor, you must complete the main step - installing a waterproofing layer. This is especially true for premises in private households, when flowing groundwater is very close. Waterproofing will prevent water from getting from the soil into the poured solution, which can cause oversaturation with moisture and uneven drying. The same applies to the rapid release of water from the fill into the lower floors and rooms. If this layer is not completed before the concrete floor is installed, this will negatively affect the drying process of the solution, the final quality and reliability of the surface of the future floor.
The technology of floor screeding in an apartment involves the use of a certain set of materials for the waterproofing layer. These include:
- Roll waterproofing. The most common of them is roofing felt. But it has a vulnerable area, which is the joint of the sheets. This means that they should not be joined, but should have an overlap of at least 15 cm. Some commercially available rolls have a special fastening element along the edge that allows individual sections to be fully and reliably connected to each other.
- Liquid waterproofing. Bitumen mastic is one of the most expensive. But in the end, they provide an excellent result that almost nothing can compare with. Ideal for rooms with high humidity, such as bathrooms.
- Film for waterproofing. It is not uncommon to use conventional polymer film. It only needs to have a certain thickness in order to meet all the qualities of the layer being arranged.
The choice of a specific option will depend on the size of the wallet, the desired items, as well as the specific case and condition of the room as a whole.
DIY cement screed
Before cementing the floor, it is necessary to carefully study all stages of the work. First of all, the base needs to be prepared for pouring, and then just lay the screed. All stages are important, so each one needs to be given enough attention.
Preparatory work
First you need to mark the future screed, determining the layer height and evenness. To do this, it is best to use a laser or ordinary construction level. Laser helps to correctly install beacons, which will ensure faster leveling of the mixture and a high-quality result.
The laser level is placed on the base, the beam is projected, and the horizon line is determined. Then, 30 centimeters from the wall and with the same step, a parallel line is further marked, portions of the solution are laid out along it, with a profile on top. You can use special beacons on the clamps. The poured mixture is then equalized using the beacons or profile. But before that, a number of important works need to be completed.
Stages of foundation preparation:
- Removing the old screed.
- Cleaning the surface from dirt, debris, dust.
- Apply an adhesion primer using a roller/brush.
- Filling with a layer of expanded clay and sand (if necessary, thermal insulation is laid), the thickness of which is up to 10 centimeters. Compaction of the layer with moisture.
- Design, installation of pipes, wires and other communications that are planned to be laid in the screed.
If there are too serious irregularities (which exceed the planned thickness of the screed), it is necessary to eliminate them: fill cracks, fill potholes, cut off bumps, etc.
Preparing the mixture
Before concreting the floor, prepare the solution needed for the screed. There are several ways to obtain a cement-sand mixture: purchasing ready-made dry mixture and mixing it on site, ordering the required volume of liquid mortar from the factory (this service is available both in Moscow and in the regions), independently determining the proportions of the components and preparing concrete.
If you choose the option of preparing the mixture yourself, then take cement and sand in a ratio of 1:3, fill it with water until the desired consistency is obtained. Next, the solution is poured onto the floor, leveled along the beacons, and allowed to harden.
The process of preparing semi-dry screed:
- Lay polyethylene film on the ground, pour cement and sand on top of it, mix with a shovel in the direction from bottom to top, trying not to disturb the shape of the cone.
- Make a hole in the center of the cone, pour water into it and mix everything.
- Without stopping mixing the components, pour the dry mixture around the edges, trying not to break the integrity.
- When the mass becomes thick, it is ready for installation; it must be used within 20 minutes.
- Leveling the screed within 1.5 hours.
To create a wet cement-sand mixture, high grade cement is used. Take a third of a bag of cement onto a bag of sand and fill it with water (about the same amount as the binder taken). The easiest way to do the mixing is in a container with a volume of 25-30 liters.
During the preparation of the mixture, you need to control the color of the solution - it should be gray: too dark indicates an excess of cement, red indicates too much sand.
Fill
Before pouring begins, the room must be covered around the perimeter with damper tape, which will protect the screed from moisture, temperature changes, and pressure. Laying the mixture begins from the corner farthest to the door, one person pours and smoothes the solution, the second at this time prepares the next portion. It is best to fill the base with an area of 30-50 centimeters at a time (this is the step at which beacons are laid).
Adjacent zones of two pours are mixed to a depth of 10 centimeters. The strip at the doorway is done last. The screed hardens within 2-3 hours, acquiring 50% strength after 2-4 days. Full ripening depends on the thickness of the screed and the volume of water in the mixture. On average, in ordinary residential premises the screed hardens by 1 centimeter per week.
Every day the screed is sprayed with water to prevent the top layer from quickly hardening while the bottom layer is still soft. 1.5 hours after pouring, the surface can be leveled by sliding on wedges; the bumps that appear later are knocked down manually.
Rub the solution with a mixture of cement and sand in equal proportions with the addition of water. During grouting, the surface should be sprayed generously with water.
Stage V. Preparatory work
To separate the screed from the walls, attach a damper tape. It’s easy to calculate its quantity: this is exactly the perimeter of the room.
The process itself is simple. Lighthouse slats need to be placed in a row. Install the first beacon from the wall at a distance of several centimeters, and each subsequent one in increments of 50-100 cm. After installing the beacons, lay out the mixture and level it using the rule. Once the mixture is so hard that it can be moved freely, remove the slats.
You can make beacons for the sand-cement mixture yourself. To do this, buy inexpensive 10 mm plaster beacons and 30 kilograms of gypsum plaster for them at a hardware store. For each lighthouse we make four supports from plaster - and this will be enough so that nothing bends while working with the rule. And the most durable adhesion of beacons is from Rotband, if you mix it in small portions. Just place the mortar in small slaps next to the screws, between them, and a little higher. Then attach the beacon, slowly lowering it until it touches everyone. Check the resulting plane.
You will be surprised, but many masters of their craft manage to arrange such screeds without beacons at all:
Types of expansion joints
During the operation of buildings, it shrinks due to temperature fluctuations, different thicknesses of the concrete floor and other operational errors. The same applies to a poured concrete floor, which may also begin to crack during the drying process. To avoid all this on a concrete floor, expansion joints must be present. Although this is not provided for or stated in the building codes and regulations.
The following types of expansion joints in concrete floors are distinguished:
- Insulating. They are performed along walls, possible decorative elements in the room (columns), around foundation protrusions for equipment. These seams are designed to prevent the transfer of deformations to the screed from the structure itself.
- Structural. They are issued in those places where the day's work of pouring the solution has been completed.
- Installation of shrinkage joints for concrete floors. Allows you to avoid the appearance of chaotic cracks on the screed during the drying process. If cracks appear, they appear only in a given direction. This is achieved by creating straight planes of slack.
Construction of deformation layers
Concrete pouring procedure
Before pouring, you need to check the temperature in the room. Pouring the floor with concrete should be done at a temperature from +5 to +30 degrees, since concrete loses its properties in the cold.
The solution is applied to the floor, starting from the far corner of the room . They pour it between two lighthouses. The rule rests on the beacons and moves along them, performing leveling by removing excess solution. This procedure helps to get rid of air bubbles that are saturated with the solution. Having finished with one sector, you must immediately move on to another. It is necessary to level the concrete base without stopping to prevent the appearance of cold seams, which reduce the strength of the finished screed.
After completion of work, it is not recommended to move on the surface. The beacons are removed after 3–4 days. After their removal, the recesses are carefully sealed with mortar. For the first 3 days, the base is watered and covered with film. These manipulations will protect it from drying out. The film is removed from the surface after 10–14 days. To better retain moisture inside the cement layer, it is recommended to cover the film with sand or wet sawdust. The minimum drying time is 28 days.
Preparing for leveling
For the floor to look great, it needs to be leveled, and for this you need to carry out preparatory work. You can prepare it as follows.
- Check the condition of the base.
- Select alignment method:
– using a screed made of sand and cement;– “dry” method;
– self-leveling mixture.
- Carry out the necessary work to eliminate unevenness, cracks, chips, taking into account the base material (concrete, wood).
- Take measurements of the room.
- Install the subfloor; if it is already installed, check the quality of its characteristics at the moment.
- Install beacons and take appropriate measurements.
After completing the preparatory work and eliminating all detected base defects, you can begin leveling the floor using one of the selected methods.
Before you start leveling the floor, you need to prepare it
