Repair of existing screed. Repair of concrete floor screed Repair of cement screed

A simple calculation of a conventional cement-sand screed M150 shows its suitability for modern flooring. For example, a piece of parquet stave measuring 40x250 mm, laid on a screed, must transfer static pressure weighing 15 tons to it so that the screed underneath it falls apart. And in order for the screed to be pressed through by a woman's stiletto heel, a woman must weigh 150 kg and at the same time stand on one leg, leaning only on the heel.

If your apartment had a cement-sand or expanded clay concrete screed back in Soviet times and is currently in in good condition, then there is no need to touch it: it is quite suitable for modern flooring. The maximum that needs to be done with it is to level it to “zero”, and even then not always. Dust on the top layer of screeds is not a sign of its destruction, it is a natural process of releasing calcified particles - it is eliminated by priming and not by replacing the screed.

However, it must be taken into account that despite static calculations, damage from stiletto heels in M150 ties made in the last century is indeed possible. Even graceful dancing women can easily damage a screed of such strength with stiletto heels if, for example, linoleum or carpet is laid over it. The hairpin is a terrible weapon! If it is not customary to wear shoes in the house, then in this case the tie is knocked out when moving heavy furniture. For the same reason, on uneven screeds, parquet rivets are knocked out of the tongue-and-groove locks and the rivets are pressed into the screed. Therefore, it is better to lay all types of floor coverings on M150 screeds through a stress-redistributing substrate. There is no need to lay a backing under ceramic tiles.

To determine the safety of the existing screed, first carefully remove debris, residues of adhesives, paint and other contaminants. During the cleaning process, the screeds produce it visual inspection. Ideally, the screed should have an even, uniform light gray color. Inspection reveals cracks and peeling of the screed. Then the screed is tapped with the end wooden block. The sound from the blows should be the same over the entire area of the screed - hard and ringing. If in some places the screed “boils” - the sound is dull (empty), it means that there are delaminations of the screed from the floor slabs.

First of all, the “swelling” of the screed is eliminated. There are several ways to eliminate peeling of the screed, but all of them will be inaccessible to a home builder, so the only option for you is to determine by tapping the boundary of the “bulge” and cut out the screed until it overlaps with a scarpel and a hammer, or with a hammer switch switched to “impact.” If the screed “bounces” over large areas, then it must be completely removed and thrown away. A screed that has peeled off from the base, even if it still holds, will certainly sag over time, occupy the void formed under it and pull the floor covering with it. In other words, a floor covering installed on a “bumping” screed will please you a little with its beauty, and then, sooner or later, it will fail.

Small area delaminations of screeds can be repaired (Fig. 32). To do this, the screed is broken at the point where it is detached from the ceiling. Then pieces of screed are removed from the broken hole, the hole is swept and dusted. Before applying repair mortar to the hole, the boundaries of the hole and the exposed surface of the floor slab must be primed. There are several ways to prime: water, cement laitance or primers.

Rice. 32. Repair of individual screed areas

When priming with water, the entire surface of the hole is wetted a large number water, but without puddling. Priming with water aims to wet the solution of the old screed around the hole and the concrete of the floor slab in order to saturate them with water open pores. Otherwise, these materials will “suck” the water from the repair mortar placed in the hole. Water, instead of participating in the setting process of the repair mortar, will go inappropriately. In addition, priming with water washes away dust from the hole that was not removed by a vacuum cleaner (if you don’t care for a vacuum cleaner, you can only get by with priming with water).

Priming with cement laitance saturates the pores with water and binds dust. Cement laitance is diluted from cement and water in a ratio of 1:2. When priming with water or cement laitance, the repair mortar is applied immediately after the primer, without waiting for it to dry (using the “wet on wet” method). Priming with cement laitance is preferable to priming with water. With this method, the cement in the primer is combined with both the repair mortar and the old screed.

Priming with special primers has a slightly different character. These primers are a kind of adhesives that react to molecular level both with the old coating and with a patch. For example, some primers penetrate into the pores of the old screed and into the pores of the floor slab and crystallize there, thus stopping the suction of water from the patch. The primer that does not get into the pores remains on top and also crystallizes, covering the surface on which it is applied with multidirectional scales.

Modern construction market offers a wide range of primers. They are divided into primers for absorbent, low-absorbent and non-absorbent substrates. Cement screed and upper part reinforced concrete slab floors are classified as weakly absorbent substrates. And on the labels of many primers it is written: “for concrete surfaces, plasters and screeds.”

It makes no sense to use expensive dry mixtures with high strengths for the patch, since the screed itself was made from M150 mortar. You can mix the solution yourself from sand and cement or use inexpensive domestic ready-made dry mixes. For the patch, it is better not to use the “Universal dry mixture M150”, because, reading the technical characteristics of the mixture (from some manufacturers), we see: it gains strength of 10 MPa (100 kg/cm²), which does not meet the requirements of SNiP. It is better to buy dry mixture M300 (Sand Concrete) - after hardening, its strength is also not very high, but it is intended specifically for screeds and is produced according to the relevant GOST. The dry mixture must be diluted exactly according to the instructions written on the bag, that is, if the manufacturer writes that the amount of water needed for mixing is about 0.15–0.2 liters per 1 kg of mixture, then that much water should be poured in, not more and no less.

Simple domestic mixtures, in addition to a major advantage - low price, have an equally major drawback - they do not contain polymer additives. This means that by mixing the mixture in its original form with the amount of water recommended by the manufacturer, you will get a hard, unworkable mixture, which will also set in the screed for almost a whole month (28 days). Therefore, you also need to buy a plasticizer and a hardening accelerator for the mixture. To install patches, it is not entirely necessary to buy a plasticizer, since the repair areas of the screed are small, and with effort, you can lay the mixture that is difficult to lay, but purchasing a hardening accelerator is required. Otherwise, the moisture content of the patch will for a long time exceed the values required for floor coverings. You can, of course, neglect the hardeners and dry the patch with heaters, but this will disrupt the normal setting of the solution. The hardeners of the solution do not speed up the setting time, they only form a crust on the surface, allowing further work to be carried out, and the setting itself is “driven inside the material” and continues there for the prescribed time. Artificial drying of the material removes water from the material, which becomes insufficient for normal chemical reaction grasping. In the process of caring for the patch, on the contrary, it must be covered with polyethylene to prevent premature evaporation of water and periodically sprayed with water from a spray bottle.

The simplest and most affordable setting accelerator is liquid glass(stationery glue). However, this set accelerator turns a hard solution into an even harder one and shortens its "life" time to 1-2 minutes. For high-quality work, it is better to purchase a branded setting accelerator, for example, “Plitonit-active accelerator”, which has plasticizing properties, that is, it will not only speed up the setting and hardening time of the mortar, but also make the hard mortar workable.

If the screed being restored is made with fillers, for example, the screed is made of expanded clay concrete, then expanded clay balls must be added to the Sand Concrete. The ratio of dry mixture to expanded clay is 1:2. To prevent the expanded clay from floating, weigh the patch down with a sheet of tin.

After installing the patches on the screed, we proceed to eliminating the cracks. If the entire screed is riddled with numerous cracks, then it is better not to repair it, but to completely remove it. If there are few cracks and the screed does not fall into pieces, then it can be repaired. The technology for repairing cracks is almost the same as the technology for installing patches on the “bulging” areas of the screed.

Cracks along their entire length are expanded (expanded with a scarpel or a hammer drill), debris is removed from them and they are primed. Then the repair solution is mixed and applied into the cracks. By the way, jointing cracks with a scarpel or a punch will immediately show the condition of the screed. On a reliable screed, working with impact tools will only chip off those places that are hit, while a bad screed will split in large pieces.

After installing the patches and repairing the cracks, we wait 9 days. Next, we carry out a geodetic check of the screed. We check its evenness using the “clearance rule” and the slopes with a laser or regular level. If the screed is smooth and the gaps are normal, then you don’t have to do anything with the screed; it is suitable for all types of parquets, laminates, solid boards linoleums and carpets laid in a floating manner. However, all of them must be mounted on a substrate, since old screeds made in Soviet times are not strong enough to fit modern floor coverings. The repaired screed is suitable for tiled floors in the condition in which it is - no underlay is needed.

If the screed is not horizontal or has gaps larger than normal, it needs to be leveled. A geodetic inspection with a laser level should show the unevenness of the screed, and the result of the inspection is recorded directly on the screed. By comparing the difference in elevation between the bumps and holes, you must decide on the method of leveling the screed.

The screed can be leveled with coarse levelers, laid in a layer from 10 to 50–80 mm, or with finishing levelers (“self-levelling”), as dry mixtures are called, laid in a layer from 1 to 10–20 mm.

If it is written on the bag with the mixture that it is used for screeds with a thickness of 10 to 50 mm, then the screed from them must be made of exactly these dimensions, that is, this screed cannot be pulled “to zero”: the thickness of its thinnest part must be at least 10 mm, and the thickest is no more than 50 mm. If the inscription contains the addition “and holes up to 80 mm high,” then this addition must be taken literally, that is, the height of the screed must be no less than 10 and no more than 50 mm high, but deeper holes up to 80 mm high are allowed, but this height is only acceptable, but the main one is still 50 mm. The same applies to finishing levelers.

The difference between coarse levelers and finishing ones is the size of the filler grains; in finishing ones they are finer. Coarse levelers are thicker; when laying them, they need to be “stretched” as a rule, setting the thickness of the screed using beacons or guide rails. With skill, these screeds can create a floor slope. Finishing levelers - liquid, approximately like syrup or kefir, they are stretched without beacons and slats - set the thickness of the screed with a wide spatula. This type of material is quite fluid and can flow into a low angle on an uneven base. There should be no holes in the base for the finishing leveler.

Based on the results of a geodetic inspection of the existing repaired screed, you must decide which of the “levelers” you will use for leveling: rough or fine, or both mixtures in turn. In most cases, you only need to use the finishing mixture, since a rough mixture will subtract 30–50 mm from the height of the room. However, finishing mixture There is a fairly strict limitation on the height of the screed. Therefore, high bumps need to be removed from the old screed mechanically. This can be done in two ways: the old-fashioned way - weld an ax to thick reinforcement or steel scrap and clean off the bumps; buy a grinding machine, abrasive wheels for it and grind off the bumps.

After removing the bumps, use an “axe crowbar” or a grinder to remove the entire top layer (old cement “milk”) from the old screed down to the screed filler. Practice shows that the best adhesion (sticking) of the top layer to the bottom layer is provided by a rough surface. Firstly, on a rough surface the adhesion area increases. Secondly, when grinding the old screed, cement particles are removed and aggregate is exposed (particles of sand, expanded clay, small crushed stone). Thus, the mixed cement of the upper screed adheres not only to its aggregate, but also to the aggregate of the lower screed. Thirdly, the bottom screed needs to be freed from dirt, which is only possible by grinding (removing the top layer) of the surface. If there was a defect in the installation of the screed and the top layer of the screed peels off, then, of course, it also needs to be knocked down.

After sanding, the screed needs to be swept and vacuumed. Next, we treat it with “cement-cement” type primers for poorly absorbent surfaces, or with universal primers. For a cement screed, it is better to use a cement-containing “self-leveling”; if we use gypsum, then we buy a separating primer of the “cement-gypsum” type, for example, “Grunt 2” (Plitonit). It is better to do double priming of the old screed. The screed has been lying on the floor for a long time and most likely it is dry; the first layer of primer will simply be “sucked in” by such a screed, without leaving a trace on the surface. Therefore, when the first primer crystallizes in the screed, it must be covered with a second coat of primer. Read the instructions for the primer for the time between the first and second priming, since some primer manufacturers require the first layer to dry completely, while others allow a “wet on wet” primer.

We dilute the leveling mixture (“self-leveling”) according to the instructions. When mixing the mixture, it is better to pour the mixture into water (80% of the total volume) and stir, then lumps will not form, and while mixing, add the rest of the water. If you work with a drill with a mixer attachment, do not turn the drill on at high speeds, stir the mixture at medium speeds, otherwise the mixer blades will capture air and bring it into the solution.

Rice. 33. Leveling the screed with a finishing leveler (leveling mixtures)

We begin to fill the screed (Fig. 33) from the far corner of the room in stripes along the far wall, backing towards front door. We install a temporary threshold in the doorway. Two people work, since the screed needs to be poured in one step over the entire area. One mixes the mixture, the other pours it out and smoothes it with a spatula. When laying the mixture, do not walk on the fresh screed, push it with a spatula to the side and towards you, but not under your feet. After pouring a strip of screed (width enough for your hands to reach), roll it with a needle roller or scrub it with a rake or a stiff brush to release air trapped in the solution.

After pouring, leave the screed for several hours (recommended by the manufacturer). After this time, walking on the screed to care for it is allowed. Courtship is about covering her up plastic film so that it does not dry out prematurely. When pouring the screed and in the process of caring for it, the room must maintain a stable room temperature and there should be no drafts, that is, the windows must be closed. Caring for a screed usually does not exceed three days, read on the bag, different manufacturers different period setting of ties.

In rooms whose area exceeds 20 m² or one of the sides of the screed is longer than 8 m, expansion joints must be left in the screed. The fact is that when the dry mixture, mixed and laid on the floor, sets, internal stresses arise in the solution that can break the screed. To do this, a large room is divided in half or into four parts and placed in these places wooden slats. In fact, not one, but two or four screeds are poured in the room. When the ties have set and you can walk on them, the boards are removed and you can fill the places from which the boards were removed. If for some reason you forgot to leave expansion joints, you can still have time to do them as soon as the screed allows you to walk on it. In this case, only the top layer of the screed becomes strong, while the inside is still soft. Using a jointer, an old file or another similar tool, you need to cut the top layer of the screed to the depth of the old screed. Essentially, create artificial cracks in the screed and relieve internal stress in it. If this is not done or if you do not have time to create expansion joints, then the screed will make them itself, that is, it will crack. Needless to say, the cracks will be completely different from where we would have made them ourselves. After the inner layer of the screed has set and hardened, the internal stresses in it subside and the scratched cracks can be filled with putty.

After the leveling mixture has hardened, the screed is ready for all types of floor coverings, both with and without a backing. The strength of self-leveling mixtures is usually at least 20–25 MPa (200–250 kg/cm²), which corresponds to international standards.

For leveling concrete or wood flooring, and also to create it on the ground in private houses, a concrete screed is used. Often, after some time from the start of use or immediately after drying, cracks form on the coating; in most cases, this defect can be corrected.

To know what to do if cracks occur in the floor screed, you must first understand the reasons for their formation.

There are several reasons for the formation of such defects. Depending on the nature of the crack in concrete, different methods for removing it are used.

Problems with the base

If the base has not been properly prepared, the screed will crack immediately after drying. This occurs in cases where the soil, sand or crushed stone has not been compacted well. Rotten and split flooring boards on which concrete has been applied also lead to its rapid cracking. The presence of large potholes, different materials, improperly carried out waterproofing - all this also provokes the appearance of cracks in the floor screed.

Gross violations of base preparation technology lead to radical defects

Incorrectly arranged expansion joints and lack of damper tape

As the concrete flooring dries, the entire structure experiences various mechanical loads. The screed is made in order to level the floor, which means that its thickness will be different in different places, as a result of which the material shrinks unevenly. The duration of this process is influenced by the following factors:

Thickness of the solution layer. It usually takes about 4 weeks to dry and gain strength, but with a layer of 5–7 cm it may take more than a month.
Temperature difference at opposite ends of the room. Near heating devices or on the sunny side, drying occurs much faster.
Mechanical impact of other elements of the structure. Especially in the area doorways, where cracks in the screed most often form. In this area, the solution dries faster because it is in a ventilated place, but at the same time it experiences mechanical impact from neighboring rooms.

The damper tape compensates for the expansion of the monolith during temperature changes, and its absence leads to the appearance of cracks, even delamination

As a result, the screed does not hold up and cracks, but these problems do not pose any danger; they can simply be repaired with finishing putty. At correct design expansion joints would not have caused cracks to appear at the time the floor was poured.

Note! To avoid the appearance of defects in places that are subject to increased loads, seams are made; they separate the screeds of different rooms and do not affect each other.

If the room is large, then expansion joints are made every 5–6 meters along the entire perimeter of the screed. They look like cuts with a depth of no more than a third of the thickness of the concrete layer. You can make them with a grinder or hand tools.

Incorrectly prepared solution

If the question arises as to why the screed cracks, the answer most often lies in a violation of the solution manufacturing technology, usually by adding an excessive amount of water. Home craftsmen unknowingly make the solution very liquid to make it easier to apply and level. The result is a mixture that, after drying, does not have a sufficient level of strength, which is why cracks appear in the concrete.

Excess water in the solution leads to shrinkage and, as a result, the appearance of defects

Also, the strength of concrete may decrease due to the presence large quantity air in the solution, so you cannot mix concrete by hand, you should use a special mixer.

Wrong layer thickness

The thickness of the concrete layer must be at least 7 mm; a thinner screed will crack from mechanical influences. If the layer is too thick, the screed will dry unevenly: it will remain wet on the inside and dry on the outside, the structure will experience strong internal pressure and the screed will begin to crack.

Due to the large thickness and uneven evaporation of moisture, the screed is destroyed even from a small load

Violation of the solidification process

In order not to wonder why concrete cracks, it is important to properly organize the drying process. There is one rule for all concrete surfaces: the longer it remains wet, the better it will gain strength. Attempts to speed up drying with heating or any other devices result in the concrete cracking after pouring.

For the same reason, it is necessary to protect the room from drafts and direct sun rays. To increase the drying time, the surface can be watered or covered with plastic film with wet sand on top.

According to the rules, the concrete screed must be kept damp for about 7 days after pouring; for this purpose, the monolith is covered with polyethylene

Main types of defects

To properly seal cracks in concrete floor, you need to know what they are.

The size of the cracks directly determines the choice of method to eliminate the problem.

Microcracks. These are defects less than 1.5 cm in size. Most often they occur due to improper drying of the coating. If there are few such defects on the screed, then you can simply cover them with tile adhesive.
Large cracks. The size of such defects is from 2 cm. They usually appear due to incorrectly made expansion joints and the absence of a damper tape. To seal such cracks in the floor screed, use a cement-sand mortar or a special sealant.
"Movable" concrete. When walking on such a surface, you feel like it is “walking.” This is due to the presence of air cavities inside. In this case, you need to remove the exfoliated fragments and fill the potholes with mortar.
Bulges and potholes no larger than 5 mm. In this case, cracks in concrete are eliminated using cement mortar, and bulges are cleaned off with a grinding machine.
Irregularities more than 1.5 cm. Correcting each such defect is time-consuming and labor-intensive, so it is easier to pour a new screed about 4 cm thick on top.

When found large number defects, it is cheaper to fill in a continuous layer of self-leveling mortar

Screed repair

Now about how to repair a floor screed with your own hands. To do this you will need: a puncher, a hammer, grinder(grinder), construction syringe, hacksaw for metal processing, 12 mm metal staples. Materials you will need: epoxy grout, quartz sand, primer, as well as the composition from which the screed solution was made. Depending on the nature of the damage, repairing cracks in concrete occurs in different ways.

Microcracks

The first step is to clean the area that will be processed, remove everything from the floor and carefully inspect it. It is recommended to circle places with cracks with a marker so that you don’t have to look for them again later. Using a hammer and chisel, you need to widen and deepen the crack, the result should be a gap that narrows downwards. Remove dust and small stones from the crack with a vacuum cleaner. Next, you need to mix epoxy resin with solvent in proportions of 1:10, apply the composition to the surface of the groove and let it dry. All that remains is to cover the crack with cement-sand mortar and, after drying, sand the area.

Relatively shallow cracks can be repaired quite simply and quickly

Large cracks

To repair a floor with such defects, it is necessary to prepare the surface and make the crack deeper to the full thickness of the layer using a grinder. With the same tool you need to make two cuts on both sides, and then remove all the concrete with a chisel. Next, remove dust and debris and apply grooves to the surface epoxy composition. In some cases, metal staples are used to increase the strength of the treated area. To do this, you need to make cuts across the crack to a depth of 2 cm, place a metal bracket in the resulting gap, pour in a cement-sand mortar, wait for it to dry, and then grind it.

Steel staples are used to repair cracks up to 5 – 7 cm deep

Potholes

If the surface is cracked so badly that a pothole has formed, you will have to use a hammer drill. With its help, you need to expand the pothole to a depth of 2 cm. Further actions are the same as in previous cases: dust and debris are removed, the walls of the crack are treated with epoxy, and the defect is covered with a solution.

Before applying epoxy compounds, the base is primed, and only after the primer has dried, the mixture is poured

Movable sections

In this case, it will require more than just sealing with epoxy resin and then sealing with mortar. The first step is to outline the boundaries of the moving surface with a marker and make cuts using a grinder according to the markings; sometimes at this stage you can remove concrete fragments. If it sits firmly, you need to remove it with a hammer drill, removing the entire screed to the base. After this, remove the dust and check the base for defects. If they are not there, then the surface is primed and filled with concrete again, level with the floor. If there are potholes in the base, you first need to seal them, wait until they dry, and only then fill the pothole.

Deep defects expand several centimeters on both sides

Repair of moving concrete by injection

Injection of building composition is one of the newest methods of repairing surfaces after concreting. For this process, it is necessary to locate the moving area, outline its boundaries with a marker and drill holes to a depth of about 1 cm over the entire area every 2.5 cm. After this, you need to pour the epoxy composition into a construction syringe, fill all the holes with it, wait for the material to dry and repeat procedure.

The composition will gradually penetrate into all internal cavities and simultaneously impregnate the concrete, which will significantly increase the strength of the coating. After the operation is completed, you should not walk on the floor for 24 hours so that the epoxy resin has time to harden. After this time, you need to check the result: if the mobility cannot be eliminated, you will have to completely remove the concrete layer.

The injection method of repairing a concrete monolith is available only with special equipment and professional knowledge

Important! If the defect occupies more than 30% of the surface, it is necessary to completely remove the coating and refill it.

Thus, there are a variety of methods for sealing cracks depending on their type and size.

To summarize, we can say that defects are easier to prevent than to eliminate. Therefore, it is strongly recommended to mix the solution correctly, carefully prepare the surface and never speed up the concrete drying process. If you follow all these recommendations, there will be no cracks in the concrete screed.

What to do if the screed is cracked and there is movement (movement) of the screed along these cracks?

There are at least two options - completely dismantle the screed and make a new one, or repair and bind these cracks, stopping their further growth.

Repairing cracks is a less labor-intensive and expensive process than dismantling and installing the screed all over again. Therefore, if you do it correctly, you can save a lot of time and money.

It is highly advisable to tie up the cracks before leveling the floor, because... all of which can show up over time on a new finished floor.

Like most people do.

Basically, everyone does this in one way - they open (expand) the cracks and fill these cavities with mortar or repair mixtures.

It's not effective.

When there is tension in the screed or the slightest movement along these embroidered cracks, additional cracks may appear and their number will only increase.
Those. the likelihood of delamination at the junction of the screed and fresh mortar is very high.

How to do this much more efficiently.

It will be much more effective if you tie this crack across its direction with a strong “patch”.
In this way, the cracks are better bonded and immobilized, and movement of the screed is prevented.

Naturally, not always and not the entire screed can be saved. If it has crumbled into many unrelated fragments, then nothing will help. Only dismantling.

Procedure for repairing cracks:

First, we mark with a pencil the locations of future repair seams.

The width of the groove should be about 2-3cm, length 15-25cm. Grooves are made every 30-50cm, depending on the number of cracks.

Then cut with a wall chaser or an ordinary grinder with a vacuum cleaner, make grooves along the intended lines.

Then we use a puncher or a hammer and a chisel to knock out the grooves between the cut lines.

Then we remove dust using a vacuum cleaner and prime the grooves.

This is a very important point; it determines how well our “patch” will adhere to the screed.

We put reinforcement or a couple of rods of metal wire (no thinner than 3mm) into the repair seams.

Fill the grooves with the repair mixture.

In my opinion the most suitable composition for these purposes, self-leveling floor/leveling compound is used (it hardens quite quickly, and after hardening it becomes very durable) or good repair mixtures (such as Mapei, etc.).

Cement-sand mortars or tile adhesives are much weaker. Their use is not advisable.

One of the main tasks of renovating an apartment is getting a flat floor. Whatever the external coating, it is impossible to solve this problem unless it is carried out. Only with a high-quality screed will the floors look perfect.

Floor screed, like any covering, requires repairs, which must be done in a timely manner so that they do not need to be done complete replacement.

DIY repair floor screeds are not very challenging task, but will require certain physical efforts and material costs. These inconveniences should not stop the owner. Any coatings age over time and become covered with obvious and hidden defects, but it is much more profitable to carry out timely partial renovation than a complete replacement of the screed when its destruction intensifies.

What is the role of coating?

In any room, there is a floor screed between the finishing floor covering and the floor slabs. It is usually performed from concrete mortar of various thicknesses. IN modern designs a special mixture for self-leveling floor is used. The floor screed itself is hidden under the floor covering and therefore it may seem that it is not subject to destruction. However, in fact, the main task of the concrete coating is to absorb the main mechanical load acting on the floor. It is a damper layer for the ceiling. Constant mechanical load naturally leads to the gradual destruction of the floor screed material.

An important role of the screed is that it levels the surface and thereby ensures the horizontalness and evenness of the outer floor covering and increases its durability. In addition, the concrete coating is designed to hide various communications: electrical wiring, pipes, floor heating, etc. Finally, the screed is an additional layer that provides thermal and sound insulation. The role that the coating plays in ensuring the quality and reliability of the floor is enormous, which is why it is so necessary to independently monitor its condition and ensure its performance.

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Types of damage to floor screed

Under the influence of various loads or due to poor-quality manufacturing, the floor screed is subject to destruction. When removing the top floor covering, all defects that have arisen become visible and can be assessed for the possibility of repairing the floor yourself. The main types of damage to the screed include: the occurrence of noticeable cracks or potholes, peeling of concrete from the floor slabs in certain areas with the appearance of air gaps, small cracking, peeling or the appearance of small shells and holes on the surface of the screed.

Cracks, and sometimes large gaps, are formed due to uneven or impact loads, as well as due to violations during construction: lack of shrinkage joints, insufficient reinforcement or poor quality concrete pouring. Such damage is very dangerous due to its tendency to increase in size and number of cracks. When removing the floor covering, these defects are visible to the naked eye.

Potholes and large sinkholes appear in areas of local powerful loads (for example, vibration of household equipment) or in places where a void appeared in the concrete when it was poured. Detachment of concrete from the ceiling can occur due to uneven loads or poor surface preparation before pouring concrete. Such damage is invisible from the outside and can be determined by a dull sound when tapped with a hammer. Poor-quality concrete or violations of pouring conditions cause multiple surface damage, which manifests itself in the form of peeling of the screed surface, heavy dusting, or small cobweb-like cracks.

All types of damage considered can be repaired with your own hands on the floor screed in certain areas. The only condition for the feasibility of its implementation is that it is unprofitable if more than 35% of the surface of the screed is damaged. In this case, it is recommended to completely replace the screed.

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Small cracks and their repair

Small cracks in the screed can be covered with ordinary concrete mortar.

Repair of small visible cracks is carried out in next order. Using a chisel, the crack expands and deepens by 10-15 mm. Use a vacuum cleaner to thoroughly clean the crack and the area around it from dust. A solution of epoxy primer in solvent (proportion 1:10) is applied to the surface of the crack and dried. This surface treatment improves the adhesion of the grout to the crack surface. After this, a solution is poured into the crack or crevice, which is special mixture for self-leveling floor screed. The dried area is sanded.

Repair of small cracks in the screed can usually be done using cheaper conventional primers and plaster mixtures on cement based. However, such repairs are likely to be short-lived, since the cause of the previous damage remains. The use of mixtures based on epoxy or other synthetic adhesive significantly strengthens the dangerous area and makes it possible to neutralize the source of crack formation.

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Repair of large cracks

Large and deep cracks in the floor screed can also be repaired. To do this, using a grinder, cracks are widened and deepened to the floor slab or to a depth of at least 50 mm. Grooves are formed on the side surfaces of the cracks. The widened crack is thoroughly cleaned of dirt and dust. Along the crack, grooves 15-20 cm long and 20 mm deep are made perpendicular to it. The distance between the grooves is set to 20-30 mm. The crack and surrounding area are thoroughly cleaned with a vacuum cleaner. Just as in the case of small cracks, the entire area of a large crack is treated with a primer solution.

Large cracks are sealed with a mixture for screeding a self-leveling floor or a special epoxy mortar for concrete (for example, brand Rizopox-3500) filled with quartz sand. The crack is filled in two stages. First, the crack is filled to the depth of the beginning of the grooves. Metal brackets are installed in the transverse grooves in vertical position. The final pouring of the solution into the crack is done after the first layer has dried and the metal brackets have been secured in it. When repairing particularly deep cracks, grout can be poured in three stages. After drying the screed repair area, all irregularities are eliminated by cleaning and grinding. Doing this yourself allows you to ensure that the dangerous area is reinforced with metal elements, which eliminates the risk of re-formation of cracks or cracks.

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Repairing potholes and surface sinks

A pothole in a screed can be repaired using a special resin-based sealant.

Potholes on the surface of the coating can occupy a significant area. Do-it-yourself screed repair in this case is carried out in several stages. First, using a grinder, cuts are made around the perimeter of the pothole with a depth of 2 cm greater than the depth of the pothole. If the pothole is deep, cuts are made to the base. Then, using a hammer drill, the screed concrete is removed inside the marked perimeter to the depth of the slot. The formed recess is thoroughly cleaned of concrete residues and dust using a vacuum cleaner.

At the next stage, the bottom and walls of the recess are covered with a primer. After it has hardened, the repair mortar is poured in several layers. The thickness of each layer is usually selected within 20 mm. Each layer is poured after the previous one has hardened. At large areas repair, it is advisable to reinforce the repaired area with metal rods, mesh or synthetic threads. After the top layer of the mortar has completely hardened, the entire repair area is cleaned and sanded so that its surface is strictly level with the surface of the floor screed.

Repair concrete floors with your own hands - this is by no means a simple “greasing” with cement mortar. Such a “blame” will not stop the destruction of concrete, will not level the floor and will not block the access of vapors through it.

The thing is that concrete, even if it has gained structural strength, lives its complex physical and chemical life for decades: it changes its structure, gains strength, and then weakens a little until it stabilizes. Fresh concrete has a number of indicators, including shrinkage rate and coefficient of thermal expansion, that differ significantly from cured concrete. For the repair of an old floor to be successful, you need to somehow coordinate the properties of the old and new concrete. One of the optimal methods for minor DIY repairs is giving a fresh cement mortar thixotropic and rheological properties.

Thixotropy and rheology

Thixotropy is the ability of a medium to yield, to reduce its viscosity under even small but constant influence. Good example thixotropic substance - ordinary construction bitumen. If you move your finger along it with pressure, you will first feel roughness, and then the movement becomes easier and a hollow remains behind your finger. By the way, continental plates move across the face of the Earth due to the fact that the material in the upper mantle is thixotropic.

Rheology is nothing more than superfluidity. The phenomenon is not at all a privilege of ultra-low temperature physics. Any housewife who forgot to tightly close a container with sunflower oil has encountered rheology. However, if liquid helium-II is 100% superfluid, then vegetable oils- by units and fractions of percent. But this is enough for the vessel to end up all sticky after a while, and the kitchen furniture to be damaged.

Under normal conditions, thixotropy and rheology are inextricably linked. When builders say “thixotropy,” they immediately mean rheology. When repairing a concrete floor, rheology ensures that the smallest irregularities are filled with the repair composition, and thanks to thixotropy, the new concrete mass, figuratively speaking, does not rest against the old one, but plays along with it.

IN construction stores There is a wide range of thixotropic-rheological mixtures for repairing concrete floors based on epoxy resin and polyurethane. However, to repair an apartment floor that is in relatively stable conditions and lightly loaded, a cheap thixotropic composition can be prepared independently:

To do this, PVA glue or bustylate is diluted three to five times with water, and a cement-sand mortar is mixed on the resulting suspension in a ratio of 1:3. If the amount of work is large enough, you can immediately buy PVA putty. This is the same highly diluted glue, but the minimum packaging is 5 liters.

PVA suspension is not suitable for sealing deep deformation cracks; here you will have to buy a branded thixotropic primer for concrete and a repair compound. In this case, you should focus solely on price: an apartment floor is a lightweight object, and exclusive quality compounds are not required.

Mixer and rule

All repair compounds for concrete must be mixed: ready-made with water; homemade - with PVA suspension. It is impossible to knead manually: the finished solution must be as “dry” as possible, i.e. water or suspension is added to minimum quantity. A very viscous mixture will have to be “pounded” for too long to achieve the desired homogeneity, and irreversible changes will begin in it, deteriorating the quality of work.

To mix small volumes of repair building compounds, I use an electric drill or hammer drill at low speeds with a special attachment - a mixer. The principle of its operation is no different from a cocktail mixer.

In tool stores you can find a wide selection of different mixers, sometimes in completely bizarre configurations. But a mixer, in no way inferior to them, is made from an even rod 8-10 mm in diameter and half a meter long, the end of which is bent into a ring or simply folded in half.

The kneading lasts 3-5 minutes. When kneading in a bucket, move the tool in a circular motion; in the trough - transverse zigzag. You should have a bucket of water at hand - after kneading, the mixer should be rinsed immediately by immersing it in water and turning it up to high speed. When kneading with a hammer drill, under no circumstances should you turn on impact mechanism: the whole room and you will immediately find yourself covered in a thin layer of concrete.

In addition to the mixer, to repair a concrete floor you will need a rule - a wide, one meter, spatula. A plaster float will not work: it will not smooth out the concrete properly, and will wear off on it. The rule, on the contrary, is to purchase a factory one, and you should not skimp on it, especially since it is inexpensive. Concrete is a good abrasive, and if the middle of the rule turns out to be “eaten away,” then the floor will turn out humpbacked.

Types of concrete floor repairs

There are four different types of concrete floor repairs:

Elimination of defects - bulges, potholes, seams from markers and formwork, cracks in the screed.
Sealing gaping cracks.
Major repairs of the floor screed for polishing concrete, laying a finishing coating or underfloor heating with insulation and waterproofing.
Dust removal.

Each type of repair is carried out using a special technology. Repairing the screed under a clean floor is the most labor-intensive and expensive. To overhaul it, you will additionally need a metal rolling roller with a width of at least 0.5 m and a weight of at least 10 kg with a carrier handle.

After all types of repairs, except for dust removal, the floor must be left for at least 20 days before continuing work, sprayed with water every day or wiped with a generously dampened rag. It is impossible to pour or wet the floor more often: set concrete absorbs a certain amount of water and slowly. "Binge drinking" will harm him.

Recommendations about mandatory curing for 40 days or more, covering concrete with wet burlap, etc. are intended for concreting outdoors. In relatively stable conditions of a residential or commercial premises, 20 days of exposure is more than enough.

Preparing the premises

Preparing to repair a concrete floor comes down to emptying the room and thoroughly cleaning it. Large debris is raked with a shovel, then the floor is thoroughly swept two or three times with a wet broom and spraying. After each sweep, potholes and cracks are blown out with a household vacuum cleaner after the floor has dried.

If it is possible to use an industrial vacuum cleaner, preparing the floor can be done in an hour: they suck the floor, blow out potholes with cracks, suck it again - and that’s it, the preparation is complete.

Procedure for repairing a concrete floor

Repairing the floor in an apartment begins with its inspection and assessment of its condition. Before dismantling the old finished flooring and cleaning it is impossible to correctly assess the required degree of repair. The following cases are possible:

The floor is generally level, but dusty, and in places there are potholes, clearly defined small ledges or thin, snaking cracks. Do-it-yourself repairs are possible and inexpensive.
There are gaping cracks no longer than half the short side of the floor, gravitating towards the perimeter or longitudinally and transversely. Self-repair is possible using proprietary thixotropic compounds.
The floor is “all humped”: small bulges and depressions alternate relatively regularly. Self-repair “on concrete” is possible in a private house or outbuildings.
In a single-apartment building, there are long gaping cracks on the floor of the floor screed, generally located diagonally or crosswise. Only possible major renovation screeds with a preliminary professional assessment of the condition of the ceiling.

Note to point 3: Leveling a carelessly poured screed is possible either with a milling machine or with a liquid leveler after sealing the cracks. Leveling the floor with a hardening compound is a subject for a separate discussion, and a milling machine in apartment building cannot be used: it generates a lot of dust, and the presence of cement dust in the air of residential premises is strictly prohibited by sanitary standards. In addition to the “gratitude” of your neighbors, you can also fall under serious legislative sanctions, including imprisonment. For example, if during or after your work one of the residents is hospitalized with an exacerbation of asthma or a pulmonary disease, this is a moderate or severe harm to health. Deadlines - see the Criminal Code.

Minor pothole repair

The potholes are sawed off with a grinder and a diamond wheel along a rectangle with at least 20 mm of sticking to the sides. The cutting depth is to the depth of the pothole plus 10-20 mm. Less - if the floor is dense; more - if dusty. The protrusions are knocked down with a hammer drill or manually to the depression.
Using a hammer drill with a concrete chisel, select a rectangular depression at the site of the pothole. Small potholes can be picked out by hand using a 200g hammer and chisel with carbide brazing. You can’t hit a dull chisel with all your might: it could cause a crack.
The recess is blown out with a vacuum cleaner, then the remaining dust is sucked out with it.
Coat the recess with one layer of any concrete primer. Choice - by price; the case is not responsible.
After the primer has dried, fill the recess with a thixotropic compound, homemade or purchased, level it using a rule and leave it to cure - sealed.

Notes:

Branded repair compounds are mixed only with sifted quartz sand. It can be purchased at the same store. Proportion - according to the instructions on the package. Thixotropic mixtures in small packaging are sometimes sold as a set with a package of sand in the required quantity.

Sawing work must be done in a respirator, safety glasses, ear muffs, gloves and tightly buttoned clothing, with the windows wide open, the door tightly closed, and as quickly as possible. Unlike your hypothetical asthmatic neighbor, you will certainly find yourself in the very center of a cloud of cement dust. In this case, headphones protect more from it than from noise.

Repair of small cracks

Small cracks are first sawed through with a grinder along the length to a depth of 20-50 mm and a width of 10-20 mm. As in the previous case, the minimum/maximum depth and width of the cut are determined based on the condition of the floor. The cut is also blown and sucked.

How to repair cracks in the floor? If the floor itself is not dusty, but the circle is a little tight, then a homemade repair mixture will do just fine. If sawing is easy, and the grinder even slips at times, you definitely need a good branded primer and thixotrope. But if the dust during sawing is so thick that the tool is hard to see in your hands, and/or streams of sand are thrown out from under the wheel, you need to seal it in full, like gaping cracks.

Repairing small cracks comes down to coating with a primer and filling with thixotrope, just like the recesses.

Advice: If possible, two to six months before repair, stick paper strips on the cracks every half meter. If the paper is not torn before repair, the crack is a shrinkage one, it will not go any further, and can be repaired at a quick fix as described. If at least one piece of paper is torn, the crack is deformation and must be repaired according to the complete scheme.

Repairing gaping cracks

A crack with a width of more than 2 mm is considered gaping, but this criterion is very relative. Greater value has the dynamics of the process: whether the crack will continue or not. You can independently evaluate the dynamics, without having construction experience, using the “paper” method described above or turning on a laser level for several days with a sensor or reflector on the opposite wall. If, for example, the light spot has decreased by 0.01 mm on average per day, then in a year it will be 3.65 mm - the situation is emergency, and you need to think about overhauling the entire building.

If the condition of the building as a whole does not cause concern, then repair of gaping cracks is carried out as follows (see figure):

The crack is sawed 50-60 mm deep and 20-30 mm wide.
The edges of the cut are knocked together to form a triangular hollow.
The cut is thoroughly blown and sucked out.
The hollow is treated with a primer.
Once the primer has dried, markers are inserted into the cut one by one. Holding the next marker vertically with your hand, cover the hollow with a thixotropic compound, leveling it with the rule. Homemade thixotrope cannot be used in this case!
Once the thixotrope has set, the markers are removed, and using the holes from them, the seam is cut to the previous width.
A damper cord of the Viloterm type or similar is placed in the seam. Clotheslines, synthetic ropes, etc. no good.
The seam is finally sealed with silicone or polyurethane sealant; in no case with polyurethane foam, epoxy or other completely hardening compounds.

Note: markers are thin, smooth metal rods. Excellent markers are made from bicycle spokes. To make it easier to remove later, the markers can be lubricated with grease before installation.

Overhaul of screed

Overhauling a screed means actually replacing it. This is a last resort, costly and time consuming. They go for it if it is intended to be finished, but the moisture test gave an unfavorable result.

More information about the formation various types Floor screeds from scratch can be read using the links below:

Calculation of screed thickness

If the renovation is carried out in a room adjacent to others, then the floors should be on the same level. And in any case, the finished floor should not be higher than the door threshold. Therefore, the calculation of the thickness of the screed is carried out from the bottom up with a margin to the larger side. In this case, the level of the base floor will be lower, but this can be compensated by increasing the thickness of the plywood underlay or the height of the joists. The thickness of the mortar layer above the reinforcing mesh must be at least 8 mm.

Calculation example: from the bare floor to the door threshold 80 mm. Initial data:

Waterproofing – 1 mm.
Expanded clay bedding in one layer - 25 mm.
Reinforcing mesh – 6 mm.
The concrete layer above the mesh is 8 mm.
Mastic layer – 1 mm.
Plywood – 8 mm.
Adhesive layer – 1 mm.
Laminate – 16 mm.

The total is 66 mm. You can improve thermal insulation by adding one and a half layers of expanded clay or taking thicker plywood. However, laying the floor on joists will not work, unless you abandon expanded clay insulation, but such a floor will be colder and more sensitive to dampness.

Markers for screeds

The screed is leveled using pin or plaster rack markers. Both of them are sealed with a small amount of cement-sand mortar (see figure below):

Pins - in the corners and along the walls every half meter or less.
Plaster markers - parallel to the short wall. The first is 25-30 cm from it; further - half the width of the rule from each other.

The pins can be made from scrap materials, but you will have to buy plaster markers, and you will need to roll out the expanded clay very carefully. But it’s unlikely that even the pins will be able to maintain a horizontal surface better than 3 mm/m. to an experienced master, since as a rule you will have to work without additional support.

The height marks on the pins are made with a tightly stretched cord and a bubble level, starting from the corner closest to the door diagonally. Then a second diagonal is beaten along the primary cord, the cords are pulled along the perimeter and marks are made on wall markers. To speed up the tapping of heights, you can use laser level, but this will not improve the accuracy and smoothness of the floor, see above.

The procedure for overhauling the screed

Lay waterproofing ( plastic film) with an overlap of 0.5 m and an overlap of 10-15 cm on the walls. The joints along the entire length are taped.
Expanded clay is poured in and leveled with a rolling roller. It is permissible to use a manual tamper, wooden or metal, under the subfloor.
Lay the reinforcing mesh with an overlap of 1-2 cells and a distance of 30-40 mm from the walls.
The markers are lined up.
If pin markers are used, the heights are marked after the underlining has hardened.
Mix viscous cement-sand mortar (1:3) in 10-20 liter portions; thixotropic additives are not necessary. At the end of kneading, the next portion is dumped between the markers next to the previous one.
Each portion of the solution is leveled using a rule, starting from the far wall: along a cord or with the rule resting on two adjacent markers. The rule is held obliquely so that excess solution falls into the empty cell.
Kneading the next portion begins after leveling the previous one.
Once the solution has hardened, the markers are removed and the grooves are sealed with the solution.
Excess waterproofing is not touched; they are cut after installing the baseboard.

Note: under the subfloor, instead of plaster markers, you can use wooden beams, even and of the same height.

Video: example of pouring screed

Dust removal

A concrete floor that is in good working order, but dusty due to surface wear, can be quickly repaired with special compounds:

Subfloor and floors in outbuildings - domestic Neomer-LP, Elakor-PU or imported Ashford-formula, etc. They give a layer of 150 microns.
Finish concrete floor in residential premises, garage, workshop - GruntElast-PU, Elakor-ED, Retroplate. Layer – 250 microns.

In terms of quality and cost, these compositions are approximately equivalent.

Bottom line

Repairing concrete floors yourself can be simple, quick and cheap, or complex, difficult and expensive. The need for some degree of repair, other than the presence of gaping cracks, can be determined independently. In any case, it is definitely beneficial for self-execution only removing dust from the worn-out floor surface.