Why cement. What is cement made from? Causes of cracks

Process errors

When laying a sand-cement floor screed, we very often encounter the problem of its deformation: it can crack both immediately after drying and crack for several years.

Cracks in the concrete floor appear as a result of making mistakes during the installation

If the crackles can also be corrected, then the swollen areas will have to be dismantled and refilled. Dismantling even a small damaged area of ​​​​the floor brings a lot of problems and costs. After all, even the smallest area during dismantling spoils everything around.

Reinforcement of the cement-sand screed avoids the destruction of the concrete floor.

Creating a screed wet way, always spread the reinforced mesh and make beacons (you can do it in the opposite direction: first the beacons, then the mesh). This work is done in one day. When the beacons are frozen (the next day), you can pour sand-cement mortar between them. The beacons fixed in this way will be the guiding support for the rule. Further, leaning the rule on the beacons, you can remove the excess solution.

Following this technology, it is quite possible to achieve a relatively flat floor surface and ensure that the concrete floor screed does not crack at all. But this action is not enough to lay thin linoleum on such a screed. In this case, you will have to additionally level the screed with self-leveling floors.

When drying, the cement mortar shrinks, and the beacons installed earlier have already shrunk. After laying a fresh screed over the settled beacons, the concrete will settle below the beacons.

The causes of cracks are as follows: when maturing, the cement loses a little in volume and gradually shrinks. If you lay a fresh cement mortar between the beacons and stretch it along the settled beacons, then, of course, there will be shrinkage. In this case, it will turn out much more than in the usual case. The shrinkage will be so lower than the beacons that the peaks will be in their place, and large depressions will form between the beacons. The more water the solution contains, the lower the screed will settle.

If you want to speed up the construction process (place the beacons and pour the floor screed on the same day), then use gypsum building mixtures to fix the beacons. With the help of such mixtures (Rotband), beacons can be installed in 3-4 hours. But there are also disadvantages to this method. Rotband, unlike the sand-cement mixture, practically does not shrink, in connection with this, cavities will certainly appear on the entire surface.

Amount of water

A solution with an excessive water content dries longer, shrinks and deforms more, and also loses strength.

Of course, a solution that is too thin is much easier to level on the floor surface. The rule is a perfectly smooth floor. But the problems will start a little later.

A screed from a too liquid solution will shrink and deform for a long time. The probability of cracking the screed is 80%.

The strength grade drops several times when an excess amount of water is added to the solution. The surface of the flooded floor will be loose. When cleaning, you will regularly wash off or sweep away part of the top coat. Due to constant contamination, you will not be able to use any floor decorative coverings. In order to somehow correct the situation, you will have to work hard, for example, treat the floor with a special deep-penetrating primer.

Reinforcement

And the last mistake that leads to floor cracking is incorrect and poor-quality reinforcement. If you spent money on fittings, it should be useful and somehow work. If the reinforcement lies under the screed (practically by itself), then there is no sense from it. The reinforcing mesh must be in the body of the concrete pavement.

most inexpensive and effective method- fiber reinforcement for mortar. Fiberglass perfectly copes with the task of reinforcing screeds, thanks to which, in many European countries, fiber reinforcement has been adopted by national building standards.

The advantage of a semi-dry screed is the reduced amount of water used to prepare the mortar, and as a result, the drying time and the risk of cracks and shrinkage are reduced.

Use a damper tape to avoid contact between the screed and other structures (columns, walls, partitions).

Do not lay sand-cement mixture on a wooden base. Such a base requires a special approach and the use of elements of adjustable floors.

When screeding using semi-dry technology, try to use a plastic film with which you will cut off the screed from the concrete base. This technique will avoid the adsorption of moisture released from the solution. Therefore, you will ensure that the screed does not crack.

For screed, use only high-quality cement and sifted sand with a small admixture of clay.

So that the floor screed does not crack, approach responsibly to the beginning of work, install a reinforced mesh with high quality, use a first-class self-leveling mortar, and you will definitely succeed!

• Causes of cracks
• Varieties of structural cracks
• Plastic shrinkage damage
• Temperature shrinkage damage

Private developers, who are not professional builders, often do not understand why concrete cracks when it dries.

Often, with improper preparation and pouring, concrete cracks and crumbles after drying.

It seems that high-quality components for concrete were used, and the proportions are maintained correctly, and the pouring technology is observed, but cracks in the concrete monolith still appear. So why does this happen and are there ways to avoid it?

Cracks in concrete can occur for a variety of reasons. Conventionally, these reasons can be divided into several large groups:

• structural;
• structural;
• impact external factors.

Structural cracks occur due to miscalculations by designers or due to unjustified changes in the design calculations of the structure, such as replacing the M100 grade mortar with a lower grade during pouring or erecting an additional floor not taken into account in the project.

Types of cracks in concrete: a) longitudinal cracks; b) transverse cracks; c) corrosion of concrete and reinforcement; d) buckling of compressed reinforcement bars.

Such cracks are a serious threat to bearing capacity structures up to destruction. But to eliminate the causes of their appearance, very little is needed: to trust the design calculations only to reputable firms and not deviate from these calculations either during concrete pouring or during further construction.

Cracks in concrete can also appear under the influence of external factors: fire, flood, soil movements due to an earthquake or nearby explosions. The reason for their appearance is practically beyond the control of human will, so their prediction is impossible.

Structural cracks are the most common and most diverse group of cracks in concrete. Often the danger of such cracks is underestimated and sufficient measures are not taken to eliminate them, which leads to the loss of the strength characteristics of the concrete monolith and its gradual destruction.

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Varieties of structural cracks

Structural cracks in concrete are the most common and diverse group of concrete cracks. In fact, these are shrinkage cracks. The reason for their appearance is the natural physical and chemical processes occurring in concrete. They are especially active at the initial stage of maturation of a concrete monolith, then their speed slows down, but the processes themselves do not stop until the full maturation of concrete.

Causes of cracking in concrete.

In other words, these damages appear in concrete due to the drying and shrinkage of the concrete mixture after pouring. It is well known that the concrete mixture consists of 4 main components: cement (binder), sand and gravel or crushed stone (aggregates) and water. Each of the components plays its strictly defined role in the creation of a concrete monolith.

Freshly prepared concrete mortar has a plastic or even liquid consistency. The mixture poured into the mold begins to solidify. The further this process goes, the more the cement and water that are part of the concrete are reduced in volume. As a result, the poured mixture shrinks, and in the body of the emerging concrete monolith, due to the compaction of the mass, loads arise that the cement mortar, which has not yet gained sufficient strength, which holds together the mixed components of concrete, is simply unable to cope with.

As a result, shrinkage cracks are most often the result of processes occurring inside the hardening concrete monolith. Conventionally, they are divided into:

• damage from plastic shrinkage;
• temperature shrinkage damage;
• shrinkage damage from drying mortar.

It is very important to correctly determine the cause of damage in a concrete monolith, because the method of their repair directly depends on this.

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Plastic shrinkage damage

Scheme of crack formation due to shrinkage.

This type of damage usually occurs due to intense loss of moisture by the exposed surface of the laid concrete, resulting in uneven shrinkage and compaction of the concrete mass.

This process occurs at the very beginning of the setting of the poured concrete mixture. Due to the evaporation of moisture, the surface of the mortar actively loses volume, while the middle and lower layer of the laid concrete remain in their original dimensions. The result of such shrinkage is the appearance on the surface of the concrete mixture of a grid of small (the width of a human hair) and shallow cracks.

Similar to the described phenomena occur with concrete during precipitation. During rain, the surface of the concrete gets wet, and a certain amount of moisture gets inside the monolith. When the rain stops and the sun comes out, the wet surface of the concrete heats up, expanding, and cracks can appear on it.

Also, this type of damage includes cracks that appear in concrete under the influence of gravity. The reason for the appearance of such cracks is insufficient compaction of the laid concrete. In this case, the following happens: the forces of gravity act on the setting concrete monolith, and if insufficiently compacted areas remain in its body, the mixture in these areas will continue to compact, breaking the integrity of the concrete monolith.

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Temperature shrinkage damage

Scheme of processes during concrete hardening, formation of structure and formation of properties.

Such deformations occur because the cement used for the binder, in contact with water, enters into a hydration reaction, the result of which is the release of a large amount of heat and, in accordance with physical laws, an increase in the volume of the solution.

In the mortar being laid, this heating and increase occurs evenly, but in the hardening concrete, in the hardened areas, hydration slows down, and in the non-hardened areas it continues with the same force. This unevenness causes damage to the drying concrete.

The hydration reaction also has the opposite effect, which is no less dangerous for the integrity of the concrete monolith. In the hardening upper layers of the poured concrete mixture, hydration stops, and they decrease in volume, while in its deep layers the process continues, and they, accordingly, increase their volume. The result of such an impact on the monolith of multidirectional forces is often ruptures of the concrete monolith.

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Shrinkage damage from concrete drying out

This kind of damage usually happens because the already set, but not yet fully mature, concrete monolith continues to shrink in volume.

This is a feature not only of concrete, but also of any cement and adhesive compositions, such as cement screed, plaster, etc.

This is the most common type of shrinkage damage, and preventing the formation of such cracks is a very difficult task. In addition, from such temperature damage, small cracks in concrete expand and deepen, which appeared from the first two varieties of shrinkage damage.

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How to prevent and eliminate cracks in concrete

Components for the preparation of concrete mix.

It is clear to any sane person that it is better to prevent a problem from occurring than to eliminate its consequences. All this is completely true for cracks in a concrete monolith. To save yourself from unnecessary work in the future, when preparing a concrete mix, you need to follow a few simple rules.

When mixing the mixture, it is necessary to maintain the recipe and strictly observe the proportions between its components. Keep in mind that cracks can appear not only from an excess of water in the composition of the mixture, but also from an excess of cement in it.

When pouring, the concrete mixture must be compacted as much as possible. This will protect the poured mixture from the appearance of damage in it due to the influence of the forces of gravity. Also, to prevent the appearance of cracks in the laid concrete, reinforced belts are arranged.

Concrete after pouring necessarily needs care. Its main task is to prevent excessively rapid or uneven evaporation of moisture from the body of the poured concrete mixture. To do this, the mixture is covered with a moisture-proof film or burlap, periodically - after 4-8 hours - its surface is moistened with water until it completely sets.

Expansion joints in concrete floors.

With large areas of pouring, in order to avoid the appearance of cracks from temperature shifts, it is imperative to arrange expansion joints. If necessary, formwork can be insulated.

If cracks nevertheless appear, then it is necessary to carry out work to eliminate them as quickly as possible. Cracks must be sealed with Portland cement mortar. Moreover, it is desirable to prepare the cement mixture of the same brand as the poured concrete, then the uniformity of the concrete structure will not be disturbed.

After sealing cracks with cement mortar, the treated surface must be carefully smoothed with a brush. Then the surface is covered for 2-3 days with a plastic film, fixed along the edges with planks or bars. The film should be periodically removed to moisten the treated surface with water.

Even the most highly professional builder will not be able to completely avoid the appearance of cracks in concrete, sooner or later they will appear. But their appearance can be delayed for a long time, and the cracks that have appeared can be repaired quickly and efficiently, preventing the destruction of the concrete monolith. Good luck!

Cracking in concrete structures is a fairly common occurrence. The causes of this harmful phenomenon are identified and systematized. However, regardless of the source of cracks, when this defect occurs, immediate repair work is required.

Why do cracks occur in concrete?

There are two main reasons for the appearance of cracks in concrete structures - this is the influence of external factors and uneven internal stresses within the concrete thickness.

Cracks that appear in concrete under the influence of external factors are divided into types:

• Cracks on bends located perpendicular to the axis of reinforcement, working in tension during bending;
• Shear cracks resulting from bending cracks. They are located in the zones of transverse stresses diagonally to the reinforcement axis;
• Fistula cracks (through). Occur under the influence of central tensile forces;
• Cracks at the points of contact of concrete with anchor bolts and reinforcing elements. Cause stratification of reinforced concrete products.

Causes of occurrence: incorrect anchoring and reinforcement in the corners of strip foundations, subsidence or heaving of the soil, “flimsy” or poorly fixed formwork, loading of reinforced concrete products to the point of acceptable strength development, incorrect selection of the section and location of reinforcement, insufficient compaction of concrete during pouring, exposure to chemically active liquids.

As practice shows, as a rule, the causes of concrete cracks are several of the listed factors.

Causes of internal stresses that literally "tear" concrete structure is a significant temperature difference on the surface and in the thickness of the concrete. The temperature difference may be due to the following reasons:

• Rapid cooling of the concrete surface by wind, water or snow;
• Fast surface drying high temperature air and direct sunlight;
• Intensive release of heat during hydration of large volumes of cement located inside massive reinforced concrete products.

Such cracks caused by a temperature difference go deep into several tens of millimeters and, as a rule, completely close after the temperature of the concrete thickness and the temperature of the surface layer equalize. Only the so-called "hairy" cracks remain on the surface, which are acceptable and can be easily eliminated by grouting or ironing.

Methods for eliminating cracking in freshly poured concrete

• Reinforced concrete cracks that appeared before the material began to set can be eliminated by repeated vibration treatment;
• Cracks that have arisen in the process of setting and hardening are eliminated by rubbing cement (iron) or repair mortar into the crack;
• The network of cracks that appeared 8 hours after pouring is eliminated in the following way. The surface is cleaned with a metal brush. The resulting cement dust is removed. The surface is treated with a repair compound and, after drying, it is re-cleaned with a brush or foam glass.

Cracks that appear in concrete after complete hardening are eliminated by injection with polyurethane compounds. The injection technology consists in applying special compounds into the crack, which seal the crack and form an elastic "seam".

The latter effectively restrains further crack propagation under the influence of static and dynamic loads.

Having said in this article why concrete cracks, it is impossible not to mention how to prevent this very harmful process, which ultimately leads to the complete destruction of concrete structures.

• Very often, when mixing the material on their own, inexperienced builders add a large amount of water. This leads to strong evaporation and very fast setting and curing. The result is the formation of shrinkage cracks. In this regard, water must be added in small portions and the recommended consistency of the solution should be observed, even if it seems that it is too thick;
• Concrete structures cast in conditions of high air temperature and bright sunlight are necessary in without fail protect with polyethylene film, wet cloth or special mats. If this is not possible, the surface of the concrete (at least four times during the day) is abundantly sprayed with water;
• In order to avoid the appearance of cracks due to soil shrinkage, one should strictly adhere to the accepted concrete work technologies: soil compaction, cushion filling, laying of reinforcing belts, etc.

In any case, before starting concrete works, should be carefully studied and strictly followed the theoretical and practical recommendations GOST and specialists in: the choice of the brand and type of cement, the type and type of reinforcement, the composition of concrete and other features of concrete work.

Why is the floor screed cracking?

Many builders claim that a narrow crack is acceptable and does not require repair, but this is not always the case. It is important why the floor screed is cracking, because if the cause is improper installation or an unreliable foundation, then destruction will continue. In this case, the solution will crumble, the defects will increase, and as a result, the finishing layer and, in general, the entire repair will be broken. Thus, you need to know what to do if the floor screed is cracked.

Causes of screed cracking

Gypsum plaster almost does not shrink when ripe, but the cement-sand mixture does. Therefore, despite the small gap in time between the installation of beacons and the laying of the screed, depressions and peaks on the surface of the screed will still be obtained. In its structure, any gypsum-containing mixture differs from cement mortar. They differ in plasticity, coefficient of linear expansion, adhesion. The probability that at the junction of gypsum and cement mortar along the lighthouses cracks form to the entire depth is almost 100%.

The second common mistake is to prepare the solution with excess water. The purpose of adding more water than necessary is to make it easier for yourself, because the solution becomes more convenient to work with and very plastic. Of course, this is very convenient in the process of pouring the solution, but after a while you will have problems with such a screed:

• Excess water in the solution exposes it to large shrinkage and deformation. Therefore, most likely the screed will crack and swell.
• An increased ratio of water and cement during the preparation of any cement slurry greatly reduces the strength grade. That is, the screed will not acquire the strength it needs and its surface will turn out to be loose. Accordingly, it will dust and sweep out, which will adversely affect the laying of any floor covering. To add strength to the screed, you will have to cover it with a special deep penetration primer.

Another mistake that the masters make when laying the screed is the wrong reinforcement. The reinforcement must be in the body of the concrete, but not under the screed. By and large, the use of reinforced mesh is pointless. Fiber reinforcement will be much cheaper and more effective.

To prevent cracking of the screed, you must:

• Use a damper tape that cuts off the screed from walls, columns, partitions. The screed must not come into contact with them.
• Do not pour cement-sand mortar on wooden base. In this case, other flooring technologies are used (adjustable floors, Knauf prefabricated floors).
• Use a plastic film in the process of laying a semi-dry screed, which will isolate it from concrete base. This is necessary to prevent the absorption of moisture from the mixture being laid into the concrete.
• Purchase high-quality cement and river or quarry coarse sand with a minimum amount of clay.

How to fix cracks?

Sealing cracks in the screed will only help if we are talking about an old coating or cracks have formed in problem areas: the border of different communications, pipes or base materials, cracks above beacons.

In this case, for repair, it is necessary to prepare a mixture of 1 part of cement and 6 parts of cement, knead it on PVA glue. Cracks need to be embroidered to the base and choose all of them, but what can be crumbled. The surface should be puttied and primed with a repair mixture. It is very important to align it before solidification. It should also be noted that the repair of cracks in the screed is only an opportunity to obtain a more even surface, and it does not at all guarantee the strength and integrity of the screed in the future.

How to strengthen the screed from cracking?

If you want to avoid problems and not resort to further repair work with a screed, you just need to follow the technology of its installation. Quality primarily depends on the proportions of the composition. With an excess of water or cement, you are guaranteed to form cracks. The quality of the base is also important. If its surface is unreliable or strongly absorbs moisture, the screed must be reinforced.

Another important point is the drying of the solution. Most try to speed up this process and start drafting or heating the room. Because of this, uneven and too rapid evaporation of moisture occurs, which also leads to cracking. Sand-cement mortar should dry gradually at normal temperature and humidity, in addition, in windy and hot weather, they should be moistened and protected from drying out too quickly. For this, as a rule, wet burlap is used.

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Cracked screed can be easily repaired

Most craftsmen say that a narrow, small crack is allowed in the floor screed in new apartment and you don't have to do anything about it. In most cases, this is not the case. The question arises, what is the reason that it cracked? Such a defect may occur due to improper pouring or a weak base, and if, without eliminating these defects, a new screed is poured or cracks are repaired on the old one, the base will continue to collapse. The next step will begin to crumble concrete along the edges of the crack, then the final finishing layer will begin to warp, then the plinth. And you will have to do all the repairs again. Therefore, it is necessary first of all to find out why the floor screed cracked in the new building and what to do so that the cracks do not go further?

Like it or not, the floor screed is the best, and sometimes almost the only way leveling the base for finishing. She makes a smooth and even coating for the flooring of the finishing layer, hiding communications or any defects in the base under her thickness. But when pouring it, some people face such minor difficulties as preparing the right mixture or putting the wrong beacons for the floor screed. Just the same, these little things lead to unwanted cracks when the screed dries. But don't despair! Sometimes sealing cracks in the floor screed is not the same difficult task. Let's take a look at the reasons why the screed can burst and how to avoid it. And if it was not possible to avoid this, we will analyze a specific example of how to repair cracks in the floor screed.

Causes of cracks

• Broken manufacturing technology
• Incorrect mixing ratio of ingredients
• Poor quality or low amount of cement in the mixture
• No expansion joint
• Wrong reinforcement

Mixing proportion not correct

This is the most common cause of cracks in the floor screed. This is usually found in ready-made mixtures. First of all, those who decide to do this for the first time, go to the store and purchase a ready-made dry mix, fall into the risk group. Manufacturers of dry mixes in production calculate the exact amount of necessary additives, which, dissolving in water, are uniformly distributed among themselves.

You probably know that the liquid solution is better applied to the floor, and beginners will probably be tempted to add a little water. Such a move in the end result will only make the quality of the mixture worse. What the manufacturer writes on the pack of the mixture must be strictly observed according to the instructions.

Mixing the solution by hand is not recommended, a construction mixer is most suitable for this purpose, and if you don’t want to fork out for this expensive miracle of technology, you can buy a simple nozzle for an electric drill and make a uniform batch at low speeds.

For a high-quality screed, it is recommended to take medium-grained sand mined in a quarry and not river sand, which is more affordable. The optimal brand of cement will be M-400. First of all, the sand is sifted from lumps of clay and pebbles. Water is added by eye until the mixture has sufficient viscosity and plasticity.

If this minimum condition is not met, cracks are more likely to appear.

Lots of water in solution

Lots of water in concrete subject it to shrinkage or deformation. In this case, the screed is also likely to crack. The flooding of the concrete mixture also reduces the strength of the finished product (screed). In simple words the screed will not be strong enough and the surface will be loose.

In this case, the screed will need to be covered with a deep penetration primer in order to avoid dusting and sweeping after the topcoat is laid. And this is again an extra cost.

Material difference

The second common mistake is the different material of the beacons and the screed itself. Gypsum-based plaster will rarely shrink after drying, which cannot be said about the cement-sand mixture. And since not much time passes between the installation of the beacons and the pouring of the screed, either depressions or bumps will be obtained on the surface of the screed.

They arise not only because of the different compositions of the gypsum mixture of beacons and cement-sand screed. but also differences in plasticity, coefficient of linear expansion and adhesion. And in those places where the cement mortar adjoins the gypsum beacons, cracks may occur in the floor screed, so what to do. We'll have to fix everything.

No expansion joint

Another rough cause of a crack in the screed is the incorrect location of the expansion joints or their complete absence. Namely wall seam and intermediate seams on the floor.

The wall expansion joint must be filled with an elastic material (polypropylene, polystyrene), pass through the entire thickness of the screed, thereby separating it from the influence of the deformation loads of the walls. Some craftsmen also recommend laying an expansion joint around columns, built-in interior items and stairs.

Intermediate expansion joints, per turn, do not pass through the entire thickness of the screed, but only half. They divide the screed into equal shares, preventing it from cracking after shrinkage. The width of such seams is selected depending on the thickness, and the presence of a warm floor. Do not forget to make special marks in the area of ​​\u200b\u200bthe reinforcing mesh if your screed is reinforced.

Expansion joints are provided in all types of screeds in rooms with an area of ​​​​more than 30 m. Accordingly, the maximum area of ​​\u200b\u200bthe fields into which the screed must be divided is the same 30 m. The sides of the area should not be more than 6 m. At one time, intermediate expansion joints must be cut out in the corridors , and the distance between these types of seams should be less than six meters.

If ceramic tiles or porcelain stoneware are chosen as the finishing coating, then the notches from the expansion joints should be comparable to those between the tile joints.

Indoors, we leave the seams unfilled, but it is recommended to seal the seams on the street site with silicone or waterproof glue in order to avoid water getting into them and not to break your screed at sub-zero temperatures.

Wall joints can usually be left empty. In the event that you decide to repair them, it is recommended to use only soft materials.

Reinforcement

Another of the common mistakes in which the screed cracks is incorrect, poor-quality reinforcement. If you decide to purchase reinforcement and make a high-quality foundation, then it should be in the body of concrete and not lie under the thickness of the screed. It is not recommended to use a reinforcing mesh here, and there is simply no need to transfer so much money for nothing, but fiber reinforcement will be very effective. The reinforcement must be in the body of the concrete, but not under the screed. By and large, the use of reinforced mesh is pointless. Fiber reinforcement will be much cheaper and more effective.

Before renovation

It does not matter if the screed is cracked, but the beginning of resuscitation work should carry out a number of procedures to simplify and speed up work to eliminate the crack.

1. First of all, determine for what reason they were formed. If the screed was not performed, you will determine the presence of expansion joints and how the floor was poured.
2. If cracks in the floor screed look like segments scattered over the entire base, they are repaired with epoxy adhesives using the “forced closing” technology.
3. If cracks in the underfloor screed appeared due to the lack of expansion joint between rooms or along the walls, you should not close them up without making this very seam.

Before starting repair work, you must first identify the cause of the cracks. Otherwise, after a few months, they will again make themselves felt, and not only in old, but also in new places.

Before repairing cracks in the floor screed, you will need to see what the degree of damage is and highlight the areas that need to be repaired.

You can easily find visible cracks. But you will have to look for hidden voids by tapping the whole base with a wooden mallet.

If during this procedure you hear ringing sound, then you have found one of these voids. Found hidden flaws should be marked and at the end of the work, calculate the area that needs repair.

If, as a result, it turned out that 30% of the area of ​​​​the room or more is needed to be repaired, it is recommended to dismantle the old base and fill in a new coating.

Repairing small cracks

Minor cracks in the floor screed are recommended to be cut with a grinder up to 20 mm. Remove debris after processing with a conventional vacuum cleaner and wipe the remaining dust with a damp cloth and allow the surface to dry before repairing. After drying, the surface is ready for repair.

Cunning! If the premises are non-residential, it is recommended to check the cracks for possible subsequent deformation. To do this, cracks in the floor screed are sealed over with sheets of paper and left for a while. If the sheet is torn, the resulting crack continues to expand and repairs require a more difficult approach.

Repairing large cracks

It is not for nothing that a crack is one of the most severe damage to a screed, so repairing cracks in a floor screed must be done here and now. If you do not pay attention to this in time, then most likely it will grow, which will lead to the impossibility of repair and you will have to make a new screed.

In order to eliminate cracks in the floor screed, it is necessary to make quite a few costs, both financial and physical. Therefore, we recommend that you follow all the technologies described above and strictly follow them, then the repaired floor will serve you for a long time and you will not have to undertake its repair again.

To avoid repair work after drying, it is enough just to follow the technology of laying the screed. To summarize: First of all, we observe the proportions of the mixture. Excess water 100% will give us cracks on the dried floor. Ground preparation also plays a big role. If it absorbs moisture, the screed will need to be reinforced anyway.

And the most important thing! No need to speed up the drying of the solution by artificial drafts or warming up the room. With such actions, moisture evaporates unevenly and quickly, cracks will also appear from this.

The screed on the floor should dry itself, gradually and at an equal temperature. If the weather outside is hot or, on the contrary, windy, it will need to be moistened, thereby protecting it from rapid drying. To carry out this process, wet burlap is mainly used.

By following these simple rules when pouring screed cracks on your floor will never be

Video instruction

Why does the screed crack?

Cracks in the floor screed - a defect or an acceptable error. Many builders argue that if the crack is not wide, and a coating is laid on top, then no repair is needed. Unfortunately, this is not always the case. It all depends on why the screed is cracking. If the reason is an incorrect filling or an unreliable foundation, then the destruction will continue, the solution will crumble, defects will increase, and subsequently the finishing layer will be broken, and the entire repair as a whole. To avoid troubles and unnecessary expenses in the future, consider the cases when and how to repair the floor screed.

Reasons and solution

‘’yandex’’ is not found

• improperly prepared cement mortar;
• too fast or uneven drying;
• too thin or uneven layer;
• installation of beacons on gypsum-containing mixtures.

All the above cases can be ignored if the cracks are few and very thin. Usually such defects appear immediately after drying and do not change over time. For most decorative coatings they are not critical.

Deep cracks that diverge over time can form when mounted on an unreliable or soft base without additional reinforcement. Cracking is also very likely if the base is porous. It "pulls" moisture out of the solution. In this case, echoing areas may also appear (determined by tapping) - this means that the screed has peeled off in some places. Ragged and deep cracks can also appear when using a "greasy" solution - with a large amount of cement. Unfortunately, such damage is very serious, and a simple repair of cracks will not solve anything. In this case, you will have to do everything again.

It will help to seal cracks in the screed if we are talking about an old coating, or if cracks appeared in problem areas: this is the border different materials bases, pipes or communications, cracks over lighthouses.

For repair, a mixture of 6 parts of pure sand and one part of cement is prepared, and kneaded with PVA glue. Cracks are embroidered to the base, and everything that can be crumbled is selected. The surface is primed and puttied with a repair mixture. It is very important to level it before solidification. It is worth noting that the repair of cracks in the screed is just an opportunity to get a more even surface, and it does not guarantee its integrity and strength in the future.

To avoid problems

‘’yandex’’ is not found

Another important point is the drying of the solution. Many try to speed it up by creating drafts or heating the room. Because of this, moisture evaporates unevenly and too quickly, which also leads to cracking. Cement-sand mortars should dry gradually at normal humidity and temperature, moreover, in hot and windy weather, they must be moistened and protected from rapid drying (for example, covered with damp burlap).

In accordance with generally accepted technology, if the mortar or concrete is made in accordance with the rules and proportions, immediately after pouring into a mold, formwork or on the surface, it begins to harden. However, his strength characteristics increase not immediately, but over a period of time.

During this period, even if visually the mortar or concrete looks solid, a significant load cannot be applied to them - the material may crack and collapse.

In this regard, novice builders are interested in the question of how much cement (concrete or mortar) dries, as well as what factors affect the slowdown or acceleration of this process.

Stages of hardening of the cement mixture

IN general case, to continue construction works a 30-day exposure of a freshly poured structure will be enough. In some cases, when pouring powerful foundations for buildings, structures or industrial equipment, this period is extended to 90 days.

With a small "domestic" construction - pouring floor screed, laying ceramic tiles, arranging a concrete blind area or path and other similar work, you can walk and move objects on the surface after 72 hours from the moment the mortar or concrete is laid.

In this case, the material goes through two stages of hardening: setting and actual hardening.

• grasping. This is a fairly fast process - no more than 24 hours from the moment the mixture was prepared. Temperature is the main factor influencing setting speed. environment.

In the warm season, when the air temperature is in the range of 20-22 degrees Celsius, the mortar (concrete) begins to “set” approximately 2 hours after mixing. If the air temperature fluctuates around 0 degrees, this process can drag on for 20 hours.

At the same time, the material retains “mobility” all this time, and if at this time you start to perform any actions with it, the “setting” stage can be significantly delayed in time.

• hardening. According to building codes and instructions, the mortar (concrete) hardens within 30 days after the structure is poured.

However, in this case, not complete curing is implied, but curing to such a value at which the next stage of construction work can begin. Full hardening occurs within one or even several years.

It should be noted that the indicated periods are valid while maintaining optimum temperature environment and humidity according to the instructions. Also, in order for the set mortar or concrete to gain its strength evenly and not crack, its surface must be protected from direct sunlight (usually with plastic wrap), on very hot days, fill in the morning or evening hours, and during the day sprinkle the surface with water in within 72 hours.

builder

Good day Now, as it were, the construction season has ended ... and cement has fallen in price. We sell even at 90 rubles per bag (50 kg) is it worth it now to buy cement for not expensive, with the expectation that it loses 5 per month % of your strength? Is it even possible to buy cement without a production date? How to check the quality of cement upon delivery? (quick way)

Registration: 06/28/09 Messages: 243 Acknowledgments: 67

Such what is!

Registration: 06/28/09 Messages: 243 Acknowledgments: 67 Address: Krasnoyarsk

Registration: 28.11.10 Messages: 133 Acknowledgments: 48

builder

Registration: 28.11.10 Messages: 133 Acknowledgments: 48 Address: Ufa

Registration: 21.09.09 Messages: 34 Acknowledgments: 7

alagg

Participant

Registration: 21.09.09 Messages: 34 Acknowledgments: 7 Address: Town

Don't take if you won't consume. Designated Cement is not gravel or sand. They store the current in purged columns and then not for long, it seems up to 6 months. and then the brand falls. If the cement is of high quality, he gets kirdyk faster.

Registration: 03.08.10 Messages: 101 Acknowledgments: 70

I want to give!!!

Registration: 03.08.10 Messages: 101 Acknowledgments: 70 Address: Samara

Participant

I just signed up, welcome.
11 years worked at a cement plant. was a process engineer, was a shift foreman in shipping and packaging (source of information - experience and specialized education).
Strictly speaking, you can't test it without a lab. As always, there is one BUT.
if we talk about the use of such cement in low-rise construction - with the appropriate REASONABLE tolerances for strength and setting time, then there is a small arsenal of methods for express analysis of cement quality.
A. Is it cement? our dealers manage to "suck in" under the guise of cement any mineral powders of a more or less gray color, insoluble in water. these are trivial mineral powders for the production of asphalt concrete and for filling powder fire extinguishers (dolomite dust), this is the dust of electrostatic precipitators of cement plants, this is cement "activated" in artisanal mills of various kinds, ground together with "additives", such as sand (sand cement), slag, concrete waste and so on. the common property is NOT astringent. it can catch on. but it is better to keep silent about strength, about predictability.
B. cement. quality? you can talk for a long time about manufacturers, about standards, about the country of origin, about alites, belites and aluminoferrites. sending those interested, for example, to Duda's book "Chemistry of Cement" and to any textbooks on the topic "building materials", I will say that we are interested in 3-4 parameters:
1. it is not, not a brand. this is the rate of strength development, which is expressed in terms of the setting start time (so that the cement begins to set not 3 minutes after mixing with water and not 3 hours), but in the range of 40-60 minutes. this indicator indirectly reflects the entire chemistry of cement.
2nd indicator, this is not, not a brand. this is the uniformity of hardening - it manifests itself in the absence of cracks and deformations in the cement cake (thick dough is made from cement and water, cow cake D 10 and 1.5 cm thick is made from dough, it hardens in a humid environment for 3 days. Warping and cracks (hello, Chinese cement!) should not be.
3. yes. it's a brand. why not important? yes, because at home it is not possible to prepare a CB mixture with the desired WCO (water-cement ratio) and compact it for the full use of the declared brand. when preparing concrete from what is in what is, we will inevitably pour out 2-5 times more cement than it should be, based on the required strength of this structure. therefore, the requirements for the actual brand of cement can be omitted, respectively, by 2-3 times. from this place in more detail: cement mainly comes with grades 400 and 500 (we are not talking about the British standard (BS) and ISO). brand of cement is an average (arithmetic average of samples in a batch) indicator of activity (such a term) of cement. from a self-respecting plant, cement is released by ... hm ... 5-10% higher than the declared grade. just in case. cement activity is determined by the surface properties of each grain of cement and its chemical and mineralogical properties, but - through the surface of this very tiny grain. accordingly, the activity can be "stretched" in 2 ways: by the chemistry of the starting materials (through the overestimation of aluminoferrites) and by mechanics - through the surface area, i.e. by increasing the fineness of the grind. the result will be approximately the same - the required activity (the strength of the cube at the age of 28 days).
3 1/2 - additives. oooh, ShPTs, D0, D20 - how many feathers are broken ... in short: ShPTs (aka D40 and above) is distinguished by a long time for the onset of setting. slow increase in strength - these are minuses. pluses - excellent corrosion resistance (to sulfate and other aggressive groundwater, cowshed drains, filling septic tanks, etc.), the almost complete absence of warping and deformation, high winter hardiness, above average fire resistance, low heat generation in the array is of no interest. D0 - high rate of curing, close to the minimum setting time, NOT high corrosion resistance, winter hardiness and fire resistance. D20 - average between extremes. "innovative" types of cements, sand cement, activated cements (in which the input of additives sometimes exceeds 80%) - maybe. see checks.
4 and the last - not the GOST term "stability". it has the most direct relation to the brand, setting speed and warping, since it determines the most important parameter for the operator (not for the builder, for the operator!) - the preservation of the declared properties over time.

Registration: 23.12.10 Messages: 21 Acknowledgments: 130

Participant

Registration: 23.12.10 Messages: 21 Acknowledgments: 130 Address: Cherkessk

Now, on to the test method itself.
lice check. alas, this is Russia (Ukraine, Kazakhstan, etc.) - the risk of running into a one-day company selling with a good discount 100 (1000, you need to enter) tons of powder for fire extinguishers taken FOR DISPOSAL is a common thing for us. Accordingly, potential suppliers should be left either with those retail outlets that have not changed signs for decades (they are not in one place, namely, they do not change signs while sitting in one place), or structures affiliated with cement manufacturers (although ...).
quality check.
physical properties. cement should be a fine powder from light to dark gray, very heavy (much heavier than gypsum). shades of green indicate sufficient iron content, which is GOOD. fresh after pneumatic transport or after grinding, its properties are similar to water - it flows, waves over the surface, if such cement is in big bags, but is declared as imported from afar - I would NOT take it. or a dry powder stuck together in plasticine, leaving a sticky feeling on the fingers, sticking together into a "snowball" - this is normal. adhesion occurs due to the fact that each particle of cement loses its electrostatic charge (during storage, pouring, vibration) and, accordingly, its personal air jacket, after which the particles begin to stick together with each other. grains: if the grains are (when kneading in the fingers, this is not dangerous, usually) pebbles with sharp edges or grains of sand, into the furnace. if the grains are rounded and covered with caked cement pebbles in the center of which round balls are felt - this is normal. oldish cement, you can go further. smell: yes. often "grave" is heavy, this is normal.
chemistry. the most delicious of all my opus.
based on the high reactivity of the cement grain surface.
for analysis, you will need a mineral water like Essentuki-17 (the most salty or similar) and rubber gloves, or knead something. a disposable plate, the same spoon, a plastic bag for a humid atmosphere and a rag or newspaper for the same. I haven’t really tried other types of mineral water, so I can’t recommend them.
to gain experience, a sample of known good cement is highly desirable.
actual check: pour half a glass of the cement to be tested into a plate, with a spoon (do not climb with your hands without gloves! chemical burns are almost guaranteed!) -7 cm and from 1 to 0 to the edges, it’s good if you make a sharp transition from the thick part to the thin one in one part, it’s sharp. take a close look at:
high-quality cement begins a false setting almost immediately, which is overcome with a spoon, becomes plastic again. sets within 5-10 minutes, heats up noticeably in the thick part, can change color to blue-green (D0). take.
mineral powders, powders for fire extinguishers, etc. - practically do not seize within 30-60 minutes, do not heat up. cement - in the furnace. the seller - in the snout.
mixed badly mixed and body cements: they seize in pieces, with the formation of subsidence and cracks, they can warm up or not. into the furnace. the seller - on the kidneys.
many Chinese cements, ours are highly active in chemistry: they seize almost instantly, heat up strongly, to vaporization, and often burst from thermal deformations. into the furnace, although ... if a masonry or plaster mortar with lime - you can, in principle, take it. if concrete is on fine and contaminated with silt, clay, dust, sands - you can take it (with caution, do not use hardening accelerators, moderately plasticizers, plasticizers and vibration - carefully. activity buffer - clay, silt, dust, but this is a separate issue). decide individually.
electrostatic precipitator dust and other waste: KhZ. who how. pure dust from filters - does not react in any way, does not harden. into the furnace. dust from bag filters (aka ultra-high grade cement) - like good cement, a little more energetic, due to the developed surface. take.
Everything about everything takes 10-15 minutes.
the sample, together with a plate and a wet rag (even with water from a puddle, it doesn’t matter), we shove it into a bag and wrap it tightly. preferably for a day or three, in the warmest place (only so that the package does not burn out). if there is no time, then for several hours. Well, at least for an hour.
normal cement: hard, without cracks (almost without), rings when tapped, breaks when dropped. when dried in air - may be covered with salt. verification passed, you can take.
mineral powders, bad cements, and other mura: it will most likely seize, with cracks up to a split into several parts or crumbling into crumbs. into the furnace.
yes, still: if the cement is in bags or in big bags, it may be important to check for setting. hammer. tapping run, you can bags. from the grasped hammer bounces with a ringing. we look at small bags during loading - even the most compacted cement in the bag will allow the bag to bend and deform in the hands of the worker. tap on pallets selectively, from above and from the corners. when receiving cement from a cement truck - we listen. stones, cylpebs and other rubbish make a cheerful "ding-ding" sound.
I hope the information is helpful:

Registration: 26.09.10 Messages: 23 Acknowledgments: 13

Participant

Registration: 26.09.10 Messages: 23 Acknowledgments: 13

Here is an interesting article I found.

Feri detergent, and cement masonry mortar

For a long time I worked as a bricklayer at various construction sites and covens, and therefore I have first-hand knowledge of everything related to this difficult craft.

To begin with, the work itself at a construction site is a very time-consuming process that requires enormous physical costs. And it doesn't matter if you're a plasterer, a painter or a bricklayer. The important thing is that it is really very hard. I still know the feeling of fatigue to such an extent that even hands do not rise after a long day at work, not to mention something else. And it happens day after day, year after year!

No, no, I'm not going to complain at all! In the end - who studied what, especially since in addition to difficulties, there is also a lot of positive: For example, do you often feel satisfaction with the results of your work at the end of the working day? And for me, if I build a house, this feeling is always present, because every evening I personally observe what I have done with my own hands. And it's worth it. This is what makes a person feel needed and useful! A kind of driving force!

But this is all a saying, and I want to talk about masonry mortar, and about the difficulties that a hardworking bricklayer has to face while working with him. If you have ever worked with a cement masonry mortar, then you know perfectly well what happens to the prepared mortar during the day: it simply gradually shrinks, losing its softness and the necessary elasticity. In the end, after a while, this solution becomes simply impossible to work with. It is good if the solution was brought from the solution unit, where the necessary plasticizers were added. But there are also moments when plasticizers are not added, and the solution itself has been riding in the back of ZILka for another hour before getting to the construction site, where masons are looking forward to it. Naturally, such a solution must be rejuvenated within a couple of hours after unloading. There were moments in my practice when the helpers put on tarpaulin boots and stirred the solution with their feet, trampling it, and cursing strongly at the same time, since it became impossible to break the formed lumps with a shovel. If the solution was kneaded by hand, then it was also necessary to thoroughly think about the substances that give it softness and elasticity. In private construction, clay was often used for these purposes, but, as you know: the more clay in the cement mortar, the weaker it becomes after setting. So, this is also not an option.

Building materials appeared at the moment when, at the dawn of our civilization, the first people began building houses and fortifications. Over time, mankind has been looking for materials that have great strength and availability in any place of residence. After long searches and experiments, it was found that finely crushed limestone and gypsum, when mixed with water and minerals, acquires special astringent properties.

After hardening, it forms a monolithic joint having the characteristics of a hard stone. From that moment, cement began to be produced in large quantities and used in the construction of large and small structures. Passing once again past a building made of stone and metal, we often ask ourselves the question: “So how is cement made?”

Interesting fact: during the construction of the Egyptian pyramids, the pharaohs used a technology similar to the production of concrete. A mixture of crushed limestone and stone chips was poured with water and turned into monolithic stone blocks.

What is cement made from?

The first stage of production begins in a limestone quarry, when the components of the future cement are removed from the soil with the help of mining machines. To construction material had the required strength, limestone is chosen for production, which lies close to the surface. In its composition, in large numbers, silicon, iron and aluminum oxide are present. If you dig deeper, the rock will be cleaner, but with a high content of calcium carbonate. The mined stone, if necessary, is sorted and sent to production, where the proportions are changed to obtain cement of different grades.

Related materials:

How do bees make honey?

limestone processing

At the plant for the production of cement, the rock is unloaded into the apparatus for the primary crushing of stones. Large boulders, under the influence of a pressing force of several tons, are gradually crushed to the size of a tennis ball and fed to the conveyor. Small and large stones are sent to secondary crushing, where they are reduced to the size of a golf ball and into a fine powder. Limestone, with different percentages of calcium carbonate, is processed separately.

Scheme of the line for crushing and drying limestone: 1 - belt feeder PL-650; 2 – magnetic separator; 3 – drying complex; 4 - elevator; 5 - supply hopper with a sliding head; 6 – belt feeder PL‑500; 7 – mill МЦВ-3; 8 – rotary jet mill MRS-2/770; 9 - cyclone-bunker TsB-4.5; 10 – dust collector II ПЦ-2.0 with a bunker; 11 – bag filter FRI-60; 12 – sector feeder PS-1V; 13 – VVD fan; 14 – medium pressure fan; 15 - slide gates; 16 - compressor.

This is necessary for their further mixing in different proportions and according to a certain technology in order to produce cement of different grades.

Sorting and grinding

Fine limestone, with the help of a sorting loader, is placed in dry warehouses, protected from moisture and temperature changes. Heaps are formed from the raw mix, of different composition, ready for the grinding stage. On the conveyor, the crushed stone enters the grinding machine - roller mill, in which limestone dust is formed.