The problem of repairing old concrete floors is faced by many residents of Khrushchev. Over the years, the surface of the screed wears out, becomes covered with cracks. Usually, a floor covering laid on top does not make it possible to notice a defect in time. This leads to the formation of large cracks and chips. And only by undertaking to dismantle the old coating can you discover hidden problems. Therefore, before laying a new linoleum or laminate, it is necessary to repair the floor screed.
Damage to a concrete floor screed does not happen by itself. For this, there must be reasons contributing to the appearance of one or another type of defect:
Repair of the screed depends on the type of defect. The most common screed defects are cracks and chips. In addition, hidden voids and delaminations can form. They are detected by tapping with a metal rod.
A dull sound indicates the presence of voids. If the area of the damaged area is more than 30%, it is advisable to replace the old screed with a new one. A smaller area of damage can be repaired.
The area to be repaired must be cleaned prior to repair. Expand the crack with a chisel and a hammer to a depth of 1 cm. In cross section, the recess should look like a cone with a narrow part at the bottom. Then the site is re-cleaned and dedusted.
To do this, use a vacuum cleaner or sandblaster. The surface of the recess is treated with an epoxy primer diluted with a solvent (1:10) and allowed to dry. This is necessary for a stronger bond between the base and the repair compound. The gap is then filled with mortar. After the mixture has dried, the surface to be repaired is sanded and cleaned.
After cleaning the repaired area, the crack expands with the help of an angle grinder (grinder) to a depth of 5 cm. To do this, deep grooves are made on both sides of the gap. Then, with the help of a chisel and a hammer, all chipped concrete is removed, the crack deepens. Further, the repaired area is dedusted and covered with a primer epoxy composition.
The solution is applied in two, and if necessary, in three stages. It depends on the size of the crack. If the crack is too wide, it is necessary to install metal brackets. To do this, cuts are made across the recess with a depth of 2 and a width of 1.5 cm. After adding a repair mixture to these cuts, reinforcement is laid. Then the entire recess is sealed with mortar. The final step is grinding the repaired surface.
The exfoliated area is cleaned around the perimeter to a depth of 2 cm using an angle grinder. All concrete inside the cavity to a depth of 2 cm is removed using a perforator. The resulting recess is dedusted with a sandblaster or vacuum cleaner and primed. Then the recess is filled with repair mortar and leveled. After the composition has hardened, the surface to be repaired is ground and cleaned flush with the floor.
Attention! Deepenings of more than 5 cm are filled with a solution in several stages.
Over time, subjected to daily exposure, the screed begins to dust. This happens even if the floor covering is laid on the screed. To prevent excessive dusting, it is necessary to dedust the surface.
A good helper in eliminating this defect will be special mixtures such as Elakor or Ashfor. It is only necessary to choose the brand of the composition. The choice depends on the load to which the floor is subjected.
Before applying the composition, the concrete surface is thoroughly cleaned. For better adhesion, you can sand the floor. After removing the dust with a vacuum cleaner, impregnation is applied with a roller. Modern compositions not only help to remove dust from the screed, but also to increase the wear resistance of the surface.
There are times when the concrete floor screed peels off from the base. The resulting voids adversely affect the wear resistance of the screed. This problem can be solved without resorting to drastic measures. By tapping the entire surface with a hammer, the location of the voids is determined. In these places, the hammer will make a dull sound.
Having thus determined the contours of the delamination zones, holes with a diameter of about 16 mm are drilled in these places with a step of 240 mm. Filling the construction syringe with a low-viscosity repair compound, pour it into the holes. This is done gradually so that the composition fills the entire cavity. A day after the operation, you can start applying a protective coating.
Quite often, before laying the laminate, an uneven base is detected. Differences in height do not allow to carry out the desired. Therefore, first of all, it is necessary to align the screed. Most easy way correct the situation - apply.
Before using the composition, the surface must be prepared. Remove dust and rinse twice with soda solution. The base gets wet. The mixture is prepared in small portions, applied to the floor and leveled. The needle roller removes air bubbles from the composition.
Rolling the surface of the screed to remove air bubbles
The listed actions are good if the area of the damaged surface does not exceed 30%. Otherwise, it is advisable to replace the floor screed. Before replacement, the coating is polished. With the help of special mixtures, heavily polluted areas are cleaned. The prepared base is covered with a primer. If the repair is carried out in rooms with high humidity, it is necessary to use a water-repellent compound.
The self-levelling compound is prepared and applied in small batches. After each application, the surface of the composition is rolled with a spiked roller. This helps to remove air bubbles that reduce performance characteristics coatings. The thickness of the layer can be from 5 to 10 cm.
The service life of the repaired screed depends on the correctness and thoroughness of these works. The quality of the materials used also plays an important role. No wonder they say: "The miser pays twice." Don't skimp on materials. Only in this case, the time for a new repair will not come soon.
Screed- this is an intermediate layer in the construction of floors between the base and the finishing floor of the room.
Leveling ties serve to level the base, to give a given height (or slope) to the floor plane. For the screed device, they use: cement-sand mortar, lightweight and cellular concrete, ready-made dry mixes for self-leveling floors, self-leveling mixes.
The minimum thickness of the cement-sand mortar screed is 30mm. For screeds with a thickness of less than 20 mm, ready-made dry mixes are used. For a layer less than 5 mm, self-leveling compounds are used.
Thermal insulation screeds serve to provide thermal insulation of the room from the base. Thermal insulation is carried out with a density of about 170 kg/m³ or foam plastic with a density of at least 30 kg/m³.
In the case of underfloor heating, an insulating layer is necessary to prevent the spread of heat into the room below.
Dry floor screed is made of special gypsum-fiber or cement-fiber boards. Such slabs are laid on a dry backfill (sand, expanded clay fraction 1-5mm, perlite) or polystyrene (expanded polystyrene), which perform a leveling function.
Before backfilling, the base is covered with a film with an overlap between pieces of film of at least 20 cm to protect the screed from moisture. The film should go on the walls 20 cm above the level of the future floor. Along the walls around the entire perimeter, an insulating tape made of polyethylene foam is laid. The tape is used for soundproofing and for compensating for the linear expansion of the laid slabs.
The thickness of the backfill must be at least 2 cm. Level the backfill along the guides using the rule.
Then the plates are mounted. The plates are stacked on top of each other with an overlap and fixed in special grooves with self-tapping screws. Before this, the joints are coated with glue.
After laying the plates, cut off the protruding parts of the film and insulating tape.
A dry screed is used to repair old floors or flooring on wooden floors that are afraid of a large number moisture.
The advantage of a dry screed is the simplicity and speed of its installation, the possibility of laying floor covering already a day after the installation of the screed plates.
A screed is satisfied if:
it is necessary to level any element of the floor under the coating;
give the floor a given slope;
form a durable layer along non-rigid (or fragile) floor elements.
Before pouring cement screed it is necessary to check and close the gaps and joints between the floor and walls, between the floor slabs. After that, the floor surface is dedusted. It is necessary to remove oil stains, paint residues.
For the installation of a cement-sand mortar screed on a concrete underlying layer, reinforced concrete floor or waterproofing layer on a surface cleaned of debris and dust, beacon rails are laid through 1.5-2 m with a height equal to the specified thickness of the screed (usually 3-5 cm).
Used as a beacon rail wooden bars of appropriate thickness, galvanized profiles UD, CD, intended for installation or steel pipes desired diameter that are used repeatedly.
The level of the top of the lighthouse hreek is determined by the marks that are made on the walls using a level or a simple water level. Then, the marks of the top of the lighthouse are set using a tape measure or a measuring ruler and, if necessary, the underlying layer is leveled.
In accordance with the marks applied to the wall, beacon rails are installed, which are laid on the fixing marks from the solution, embedding them until required level. To maintain a predetermined level, dry cement is poured onto the marks, which accelerates the hardening of the marks. To create screed slopes, beacon rails are installed with a slope.
With the help of the rule, the correct laying of the beacons is checked.
The surface of the underlying layer is moistened immediately before laying the cement-sand mortar. Humidification prevents excessive suction of moisture from the solution and increases the strength of the screed.
The solution is laid between two lighthouse rails in strips through one and leveled with a rail-rule, which is supported on two lighthouse rails, and after removing the lighthouse rails, on the edges of the previously laid screed strips that have hardened. In the missed strips, the solution is placed 24 hours after the laying of the first strips.
A freshly laid screed is protected from moisture loss by covering it with matting, film, shields, etc. and watered for 7 days at least once a day. At high temperatures (above 15 ° C), the screed is watered twice a day, this will avoid the appearance of cracks.
You can usually walk on a freshly laid screed after 24 hours. The screed gains full strength after 28 days.
The clearance between the 2-meter control rail and the surface of the screed to be checked must not exceed:
2mm for screeds for coverings from parquet, linoleum and other rolled synthetic materials;
6mm for screeds for other coatings.
The deviation of the screed plane from the horizontal or the specified slope is 0.2 of the corresponding room size, the maximum deviation is not more than 50 mm.
Irregularities on the surface of the screed. Large irregularities are knocked down (or hollowed out with subsequent embedding), small ones are ground with an abrasive tool.
Cracks in the screed. Occur as a result of the drying of the screed (very fast drying) or the use of poor-quality mortar. Cracks are embroidered, primed and sealed with mortar.
Detachment of the screed from the base. Cut out a "bubbling" area, remove dust and moisten the base, re-fill with a solution.
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The cement screed is the outer layer of the subfloor. Over time, for many reasons, it wears out, but the floor covering laid on top does not give time to determine the defects that have arisen. In the process of its replacement, when the foundation is exposed, the hidden problems of the floor become apparent, and it becomes necessary to repair the cement screed. How it is done, you will learn from this article.
The floor screed is subjected to tremendous stress from the weight of the floor covering, furniture and equipment, as well as dynamic influences from falling objects and walking people. Therefore, the service life of an expensive floor repair largely depends on its condition. The money invested in this event can be wasted if a screed deprived of attention makes itself felt.
Reliable information about the state of its surface can be obtained only after the floor is completely cleaned of old coatings, debris and dust. To determine the degree of damage to the screed, there are such criteria:
For a simple repair of the screed at home, a mixture that can be made independently from available and inexpensive materials is quite suitable. It consists of PVA glue, water, sand and cement. To prepare a repair mortar, you must first dilute the PVA glue in water in proportion to 1: 3, and then add a dry mixture of cement and sand 3: 1 to the resulting emulsion.
The composition should be mixed at minimum speed for 5 minutes using an electric drill with a mixer nozzle. After the process is completed, it is recommended to immediately immerse the mixer in water poured into a bucket and rinse well when the tool is in operation.
If the cracks in the screed are deep, this composition will not work. To repair it in this case, you will have to buy a special thixotropic liquid for concrete. Store-bought mixes are mainly mixed with water, and home-made formulations are mixed with glue suspension. Ready mixtures can be replaced with tile adhesive.
All screed defects, such as small and deep cracks, delamination and dust formation, potholes and depressions, are eliminated different ways which we will consider below. In the meantime, it is necessary to prepare the following tools and materials for work: a puncher, a trowel and a rule, a brush, a grater and a paint roller, cement, a primer for concrete and a repair mixture.
To repair a cement-sand screed with minor defects, first you need to mark all problem areas with chalk, and then cut each crack and recess with a hammer and chisel a few millimeters deep and 1-2 cm wide along the edges. After that, you need to remove construction debris from the surface of the screed with a broom, and from the cracks - with a vacuum cleaner.
Cleaned cracks and recesses should be treated with a penetrating primer several times until it no longer soaks into the concrete. This procedure is necessary to increase the adhesion of the base with the repair mixture.
In the process of drying the primer, you can prepare the mixture according to the recipe described above. The resulting solution should fill the cut damage to the screed just above the general level of the rest of the surface, and after the mixture has hardened, sand the repaired areas.
Advice! If the thickness of the screed is small, it is better to cut the damage to its entire depth. In this case, the adhesion of the putty to the base will be better, and the further development of cracks will become impossible.
After the crack is cut, several strobes must be made across it, the ends of which will extend beyond the resulting cavity by 5-6 cm on each of its sides. Then, holes 2-3 cm deep should be drilled at the two ends of each strobe, and then debris should be removed and the cut cracks should be cleaned with a vacuum cleaner. Prepared recesses must be treated with a primer and left to dry.
Now it is necessary to prepare a mortar of sand and cement in a ratio of 3:1. Filling the crack should be done gradually in several stages. The first of them uses a liquid mixture, which needs to fill part of the cavity in depth so that it penetrates into the most hard-to-reach places notches.
Then you need to prepare a solution of medium density and fill it with a crack flush with the bottom of the transverse strobes. When it hardens, it is necessary to make staples tightening the crack from thick wire or reinforcement and mount them in the strobes so that the bent ends of the rods go into the drilled holes.
After that, a little plasticizer should be added to the solution and filled to the end of the cavity along with the staples. Then the surface in the area of the former crack must be leveled, and after the mortar has dried, it must be sanded. Now the repair of the crack in the cement screed can be considered complete.
Repair of delaminations can be done in two ways. In the first case, the entire damaged area must be cut out, and a new screed should be laid in its place. In the second, the exfoliated area is subjected to injections, during which a special binder composition on an epoxy or adhesive basis is introduced under it. The second method is less time consuming and faster. It makes sense to use it if the problem area is even and does not have through cracks.
After determining the places of delamination of the screed, they need to be outlined with a marker or chalk, then take a perforator or drill and install a drill or drill for concrete with a diameter of 16 mm in any of these tools. Drilling in places of delamination should be carried out for the entire thickness of the screed, keeping the distance between them 0.2-0.3 m.
When this work is completed, a primer must be poured into the holes obtained. It should moisten the entire internal cavity between the base and the screed layer. To speed up the drying process of concrete, you can use a building hair dryer.
It is important to correctly determine the material for screed injection. It must have good fluidity, because the repair mixture will have to be pumped under the screed using a plunger pump or a construction syringe. The cement-adhesive mixture will cost less, more expensive, but more reliable - low-viscosity epoxy.
Injections through the holes in the screed should be done gradually, allowing time for the repair compound to fill the entire space of the cavity. This procedure should be continued until the mixture appears on the surface of all drilled holes and its level does not stop dropping.
The screed must dry for 24 hours. After that, you can work with it further: primer, glue linoleum, lay tiles, and so on.
In this case, for repair, it is first necessary to cut through the pothole with a grinder equipped with a diamond disk along the damage perimeter to the entire thickness of the screed. Then, using a perforator or a chisel and a hammer, the concrete should be removed from the pothole. After that, the cavity must be cleaned of screed residues and dust, and then treated with a penetrating primer.
After the primer has dried, it is necessary to prepare a repair mixture and fill the pothole with it using a spatula. Without waiting for the mixture to dry, use a wide spatula and a rail to level it with the floor and leave it until the final polymerization. Grinding the problem area should be done so that the pothole filled with the mixture does not stand out against the background of the floor.
Important! At a depth of damage of more than 5 cm, the repair mortar should be applied gradually in several steps.
Gradually, the amount of dust increases, and it becomes impossible to simply sweep it away. Often it is a consequence of significant mechanical loads on the surface of such a floor and its "old age". In other cases, dust appears immediately after a month or two after the start of using a new screed. The reason for this is the low quality cement mixture and violations in the technology of its laying. If it is not possible to replace the screed, it can be repaired in the following way.
First you need to thoroughly clean its entire surface with a vacuum cleaner. If potholes and cracks are found at the same time, they must be repaired using the technology described above. After that, the screed must be sanded and cleaned again in the same way. Then the floor surface should be treated with a penetrating primer and allowed to dry. At the final stage of work, the entire screed must be covered in two layers with a polymer composition. If the room has high humidity, special water emulsifiers should be used for this purpose.
There is another way to eliminate dusting of the screed - this is its painting. In this case, the coating must be sufficiently wear-resistant, according to this parameter, the finishing material should be selected.
The cardinal method of such a defect in the screed is its reinforcement with fiberglass and subsequent pouring with a special self-leveling building mixture. To implement this method, the floor surface must first be cleaned with a vacuum cleaner, treated with a primer and allowed to dry.
After that, glue should be applied to the surface of the screed and the fiberglass should be laid with overlapping sheets. When the first layer of glue dries, the second layer must be applied to the resulting coating and allowed to dry completely. The floor can then be sanded or poured over the fiberglass with a self-levelling compound.
How to make a cement screed - look at the video:
The stresses that cause the appearance of cracks during the installation of a screed have a number of reasons that are associated both with a violation of the formulation of the mixtures, the technology for performing work and the mode of curing, and with the human factor.
Cracks in the screed are a defect that most often raises questions from the customer. Other screed problems: low strength, high humidity, non-compliance with the standard evenness of the base, heterogeneity of the material over the area, lack of adhesion to the underlying floor structure - all this can only be identified by an expert with the help of measuring instruments. But cracks are noticeable to any person who first encountered the repair or installation of the floor.
According to SNiP 2.03.13-88, a floor layer is called a screed, which serves to level the underlying floor layer or floor, give the floor covering on the floor a given slope, cover various pipelines and communications, and distribute loads on non-rigid underlying floor layers on the floor.
Reasons for the formation of cracks in the screeds
Cracks usually appear in areas of stress concentration. Stresses in the mortar layer during cement hydration appear mainly for the following reasons:
- violation of the technology for the manufacture of mortar screeds;
- performance of work without regard to various design features screeds;
- errors in the preparation of the mortar mixture;
- problems associated with the temperature and humidity regime of curing and drying of the mortar mixture;
- lack of qualified performers and the necessary equipment.
Let's take a closer look at each of these points.
1. Violation of the technology for the manufacture of mortar screeds. In domestic construction, the most common technology for the manufacture of mortar screeds is the "strip" casting of screeds along the guides.
As a result of the application of this technology, not a solid base layer is obtained, but a set of strips that are not connected to each other. Naturally, cracks form along the edges of the strips. This can be avoided by laying the mortar on all strips at the same time and removing guides or beacons immediately after leveling the mortar. Another screed device technology is laying the screed according to the level indicated on the walls by a special rule.
2. Performing work without taking into account the various design features of the screeds. The absence of damping (compensation) gaps along the walls and around the columns is one of the reasons for the formation of cracks in mortar screeds.
With thermal expansion bearing structures will put pressure on the mortar screed, and it will crack. Thus, during manufacture, the screed cannot be brought close to walls or columns, it is necessary to leave a gap of at least 10 mm.
At large areas mortar screed (for screeds on a separating layer > 40 sq. m), the assembly joints must be cut to a depth of 2/3 of the screed the day after the mortar has been laid. These seams are necessary for the predictable formation of cracks that occur due to shrinkage stresses. If the seams are not cut, then cracks will still form, but the direction, shape and number of cracks will be arbitrary, which will greatly complicate the work of repairing them. Mounting joints after the strength of the mortar screeds (28 days) are sealed using a special technology of "power closure" with two-component resins.
Errors in the "docking" of mortar screed structures of different thicknesses also lead to the formation of cracks. A typical example is heated floors.
If the heated elements and heat-insulating plates do not lie over the entire surface of the room, then the mortar screed will turn out to be of different thicknesses, which will lead to the formation of cracks in the future. In addition, tests of underfloor heating should be carried out after the mortar screeds have gained strength (28 days), within 25 days according to a special protocol in accordance with DIN 18365. After testing, newly formed cracks must be repaired.
The presence of communications in the base is a factor affecting the formation of cracks. This is due to the thickness of the screed above the pipeline. According to DIN 18365, the thickness of the screed above the pipeline must be at least 4.5 cm. If the screed is not thick enough, then cracks will form during the drying and curing of the mortar.
It is also necessary to say about expansion joints, the purpose of which is the prerogative of the designer. In public buildings with large areas, it is required, according to existing methods, to calculate and lay in the project expansion joints in the mortar screed, linking them to the floor design, since these joints remain mobile and are not covered by floor coverings.
3. Errors in the preparation of the mortar mixture. The main reason for the appearance of cracks in mortar screeds are shrinkage stresses resulting from uneven drying of mortar screeds in thickness and uneven curing. Due to contact with air, the top layer of mortar screeds dries and “shrinks” faster than the bottom one. In it, crystallization of cement stone occurs earlier. As a result of this process, microcracks are first formed, and then they expand and connect to each other.
Since water is involved in these processes, it is natural that its amount is one of the most important factors in the formation of cracks. For normal cement hydration, the water-cement ratio should be 0.3-0.4, but such a screed is very difficult to lay, and special equipment is required; in construction conditions, screeds are supplied by concrete pumps, bringing the water-cement ratio to 0.6-0.7. Such a screed is very easy to fill, but the strength is significantly reduced and there is a large shrinkage of the mortar screed (by the amount of evaporated water), which leads to the formation of a large number of cracks.
Sand is used as a filler for mortar screeds. This construction material available at any site. But the use of fine sand (up to 0.3 mm) leads to a decrease in the surface activity of cement (there is simply not enough cement). Accordingly, the strength of the mortar screed also decreases, which leads to the formation of cracks. For getting strong ties without cracks, it is necessary to use coarse sand - 4-8 mm (up to 70%) together with fine sand - 0.2-2 mm (up to 30%).
Strengthening mortar screeds with reinforcing meshes slightly reduces the risk of cracking, but the introduction of steel fibers into the mortar gives a very good result. Significantly reduces the risk of cracking by adding plasticizers to the solution, as well as the use of special dry mixes with already specified properties.
To block the formation of cracks, various vapor barrier materials can be used, which are applied (by roller) to the mortar screed 1-2 days after laying. But in this case, it is necessary that the manufacturer of the vapor barrier has a set of materials for further processing of the base and laying the floor covering. Otherwise, problems arise with the adhesion (adhesion) of the treated mortar screed with subsequent materials used for laying floor coverings.
4. Problems associated with the temperature-humidity regime of curing and drying of the mortar mixture. The formation of cracks in mortar screeds is strongly influenced by the temperature and humidity in the room, as well as the rate of change of these parameters. At low humidity there is a very rapid "exhaustion" of moisture from mortar screeds, which leads to a significant decrease in strength. High humidity prevents the screed from drying out and proceeding to the laying of the coating. Heat floor leads to an accelerated set of strength mortar screeds and the formation of a large number of cracks. Cracks in this case are formed due to the uneven manifestation of these parameters over the base area (local heating, draft). Low temperature delays the curing of cement mortars.
Under the influence external factors(draughts, sun, fluctuations in temperature and humidity) curing and drying of the screed may be uneven or too fast. In this case, the top layer, as a rule, dries out before it has time to gain strength. In order for the process to proceed evenly, the screed should be covered with plastic wrap on the second or third day after laying and left for one to two weeks.
The appearance of cracks in the screed can also be caused by chemical reactions: during the formation of cement stone, redistribution and crystallization of salts occur, which can lead to the formation of microcracks, but these processes are highly dependent on the presence of impurities (purity) in the local materials used (water, sand, cement) .
5. We should not forget about the human factor. The lack of appropriate qualifications for the masters, the necessary equipment and tools will certainly affect the quality of the work performed on the mortar screed. Before starting work, it is necessary to study the project in detail, conduct an examination of the base and conditions in the room where the mortar screed will be laid. When performing work, it is necessary to keep a work production log, in which the temperature and humidity conditions of the room are recorded, etc.
Before closing the cracks that have appeared, it is necessary to determine the cause of their formation, determine the design of the base, the presence of temperature, expansion and structural joints, clarify by what method and under what conditions the screed was made.
Also, by tapping, it is necessary to determine whether the cracks are superficial or extend through the entire thickness of the screed. A dull, "dense" sound indicates that cracks are moving along the surface. They can simply be puttied with the appropriate mixture. To do this, the crack is expanded and deepened, dust is removed (with a vacuum cleaner), primed and puttied with a special polymer cement putty. If, when tapped, the sound turns out to be sonorous, dust will come out of the crack, and the crack itself will “crawl”, then the screed has peeled off from the bottom of the base. In this case, the damaged area will have to be removed and repaired from a special polymer cement quick-drying mortar in its place.
A structure that is torn apart by a crack or generally represents separate parts (this is possible with a strip screed device) is repaired using the “forced closure” technology with two-component resins.
A crack passing through a temperature or expansion joint is not sealed. Here it is necessary to perform an expansion joint, the design and dimensions of which are agreed upon by the design organization leading this object.
If the cracks were formed due to the lack of structural seams near the walls and columns, then first it is necessary to cut through these seams, and then carry out repairs using the “forced closure” technology with two-component resins.
The reason for the formation of cracks must be identified and eliminated, otherwise, despite the repair and repair of cracks, after leveling the screed, laying the floor covering and starting to use the premises, new cracks will appear in the screed, which will eventually appear on the floor covering.
Repair of cracks and elimination of the causes of their occurrence are long and expensive operations, therefore, strict adherence to the technology for laying the screed, as well as the elimination of the causes of crack formation, will significantly save time and money when installing floors.
When performing capital repair work indoors for any purpose Special attention requires the technical condition of the floors. After long-term operation, the coating may have a number of defects, which can only be corrected by a major overhaul of the floor screed.
After a long use of the concrete floor, it can receive both minor damage and become covered with large cracks, which can be fixed only by a complete replacement of the screed.
The easiest way is to completely dismantle the existing coating to the very base and arrange a new screed. Such actions justify themselves if there are no more ways to restore the old screed. Under normal circumstances, this is unacceptable for a number of reasons:
Scheme of dismantling a damaged floor screed.
It would be more correct to remove the finished top flooring, clean the surface of the existing screed and visually examine it, determining the number and size of defects. In the process of studying the entire area of the concrete surface, it is recommended to gently tap with a hammer for the presence of hidden voids in the thickness of the screed as a result of delamination. A dull sound will accurately indicate the location of such a defect. After all damages and their number are determined, you can start choosing a way to eliminate them.
There are several types of wear on old concrete floor coverings:
Delaminations occur due to temperature changes and the effect of moisture on concrete.
Repair small cracks start by opening them in width and depth. For this, an angle grinder with a cutting wheel for stone and concrete is used. On both sides of the defect, the screed is cut in a circle to a depth of 5 cm so that after removing pieces of the old mortar, a rectangular groove 2-3 cm wide is obtained. It is cleaned and dust is removed to assess the sufficiency of the cut depth. If it turns out that the crack goes to the very base, then you will have to do the same work as in the case of through wide cracks.
Sequence of screed repair.
The cut groove is sealed after applying a primer to its walls, which will lead to dust removal and hardening of the existing concrete layer. It may be necessary to primer several times, especially when it is noticeable that the surface strongly absorbs the applied composition. To complete the last stage of the repair, you need to prepare a special cement-sand mortar on PVA glue. The recipe is as follows: glue is mixed with water in a ratio of 1:3, after which the mortar itself is mixed on this basis, the ratio of cement and sand is 1:3. Since the amount of work is small, it is best to do the mixing in a plastic bucket (possible from under the paint) with an electric drill with a mixing nozzle. If the latter is absent, you can use a piece of wire with a diameter of 6 mm, one end of which is bent up or in the form of a ring, and the other is fixed in the chuck of a power tool.
With the help of a trowel and a rule, the cut crack is filled, and the surface is smoothed, removing the remnants of the solution. Subsequent work can be carried out no earlier than 20 days after the end of the repair, this applies to all types of work to restore the screed. The same method can be used to repair potholes and other mechanical damage in the surface of the concrete screed.
The scheme of sealing cracks in a concrete screed.
Through wide cracks are expanded to the very base with a perforator, broken pieces of old mortar and dust are removed. For this purpose, it is best to use compressed air to blow out any excess debris. If a crushed stone pillow is found as a base, it will need to be compacted and filled with liquid cement milk at the cutting site, if possible. In this case, the milk should fall under the cut edges of the screed, after which you need to give time to solidify. base in the form reinforced concrete slab must be primed together with the edges of the resulting groove.
Further repair of the screed consists in filling the groove with a special compound. You can do this work by preparing the same solution as in the previous case, and smoothing it out with a rule. But it should be understood that cracks of this size do not occur in the screed just like that and can reappear, so it is recommended to withstand the technology. In this case, you should not save on self-preparation, it is better to purchase a ready-made thixotropic mixture for floor repair in trading network, at the same time buy a special damper cord-seal, this is used for the device of expansion joints.
After stirring, the entire cut-out niche is filled with the mixture, while vertical markers made of thin steel wire are installed along the entire crack. When the thixotropic mixture sets, the markers can be pulled out so that they come out more easily, they should first be lubricated with grease.
The next stage is the laying of a damper cord, under which a narrow groove 5 cm deep is cut. After this operation, the groove is sealed with a plastic sealant based on silicone or polyurethane. As can be understood from the technology, the result of such a repair is the construction of an expansion joint at the site of a large floor crack. Whatever the reasons for its occurrence, new defects will not appear in this place.
Layering of concrete in the thickness of the screed can be eliminated by injection. As soon as all places with this defect are found, it is necessary to drill holes in the screed within these areas using a perforator and a drill with a diameter of 12 to 20 mm, the distance between the holes is 250 mm. Next, they should carefully pour a special composition based on epoxy resins. If possible, it is better to use a syringe. Pouring should be carried out until all the voids and pores are filled, the process should be done intermittently, allowing the composition to soak into the concrete. Repairing a floor screed with this method is not difficult work, but it requires attention and patience. After the epoxy glue hardens, which will occur within a day, you can proceed to further work.
The weakened surface layer of the screed can be made stronger with modern building deep-penetrating compositions based on polyurethane. Such impregnations allow you to raise the grade of the screed solution from M50 to M300 to the required depth. After the floor is treated with polyurethane compounds, the formation of cement dust will stop, and a protective film up to 200 microns thick will appear on the concrete surface.
By performing restoration work on concrete flooring, you can significantly save money, which will inevitably be spent during the dismantling and installation of a new screed.
