Often times, cracks in the foundation of a house are inevitable. But don't panic. You should carefully understand what triggered this process and quickly fix the problem. How to repair a crack in the foundation will be discussed in this article.
The causes of cracks and their main types
The most common causes of cracks are:
- poor quality soil preparation for the foundation;
- savings on the purchase of materials for construction;
- natural soil shifts;
- non-compliance with the technology of building a house;
- construction of a new facility nearby.
There are two main types of cracks on the surface of a foundation:
- horizontal;
- vertical.
Horizontal cracks do not pose such a hazard. They can arise for various reasons. The main ones are:
- exposure to low temperatures (concrete dries out);
- increased pressure from wet soil.
Long cracks and horizontal faults with bulges present on the outer wall of the house indicate possible displacement of the foundation or pressure exerted on load-bearing walls... To determine the specifics of faults, you should use a level. If there is a bulge of more than 1 cm or the formation of a ridge at the edge of the wall, it is necessary to carry out a major repair of the base.
What to do when the crack in the foundation is vertical? Such breaks in the walls do not bode well. If there is only one crack in the base of the building, you need to determine its parameters. If there is a crack with even edges and a small thickness (about a hair), it will not be difficult to repair the crack in the foundation.
More difficult work lies ahead when the vertical edges of the fault are uneven and the gap widens in any direction. It should also be noted that the crack can be located underground. In this case, you need to excavate the entire site near it.
Fault sealing technology in the foundation
Depending on the complexity of the work, various materials will be required to seal cracks in the foundation. When the faults are small, they are repaired with conventional repair mortar or sealant. More complex areas are processed with special materials. These include epoxy resin and quick hardening cement.
In most cases, repairing faults in the foundation involves choosing one of two options:
- pouring into it concrete mortar;
- treatment of cracks with epoxy resin.
Using concrete to eliminate cracks
Elimination of a crack in the foundation begins with its preparation. Using a chisel, old concrete chips are removed from the fracture. If there is a small crack, it should be widened at the bottom. Using a construction trowel, the gap is filled with mortar. After that, the entire processed surface is smoothed and leveled.
This method is also used in the case when we have too much damage in concrete structures. The work begins with a chisel cleaning the surface of the crack in the foundation. Having cleared the fault, it is thoroughly washed with water under pressure. While the gap dries, you should start preparing the solution.
The cement material is sold ready-made. It just needs to be diluted with water and mixed to form a paste. Do not prepare a large amount of mortar as it hardens quickly. The preparation of the mortar can also occur from ordinary Portland cement with the addition of sand and water.
Filling of faults in the foundation is carried out in such a way that the concrete mixture protrudes above the surface. When the concrete begins to set, it is thoroughly smoothed with a trowel. After filling the cracks in the foundation, the entire surface is covered with a dense cloth and left for several days. Moreover, it is necessary to maintain a moist state of the finished area. For this, a light wetting of the fabric is carried out.
Elimination of defects with epoxy resin
The second way to seal cracks in the foundation of a house involves the use of epoxy. Its maximum efficiency is achieved for filling small gaps (up to 5 mm) in monolithic concrete.
The embedding process itself consists of the following main stages:
- removal of old concrete chips;
- drying the surface;
- epoxy resin application.
Using a metal brush, the entire area with defects and the surface near it are cleaned. For complete cleaning of concrete chips, the crack is blown. The inner part of the fault is dried with a construction hairdryer.
The constituent elements of the epoxy resin structure are the nozzle and the liquid resin, which is placed in the tube. The insertion of the nozzles into the fault occurs at intervals of 30 cm. The first nozzle is inserted 30 cm from the ground surface. The epoxy resin is mixed with a hardener. The prepared solution is applied to the bottom of all attachments. They are glued to the base of the gap. The resin should harden.
After that, the entire damaged area is sealed with epoxy resin. The mixture is rubbed around the rift. After the mortar has set, liquid resin is injected into all nozzles, starting from the bottom. If there is a crack with a width of more than 3 mm, each nozzle is equipped with several tubes. After 5 days, when the epoxy resin has completely set, the nozzles can be cut off.
You can reduce the likelihood of cracks in the foundation by taking preventive measures. As known, the main problem for the foundation is excess moisture. Therefore, it is necessary to constantly monitor that water does not accumulate near the house.
Video on filling cracks in the foundation:
depth, removing all the crumbs from it before embedding.
Epoxy is most effective for small cracks (3 to 5 mm) in cast concrete. The crack surface must be dry. If the surface is wet or water is oozing through the crack, dry it first, which can be done with a hair dryer. When the surface feels dry to you, wait another 30 minutes to see if it becomes wet again. If it remains dry, repair the cracks.
Epoxy for this purpose can be purchased at the hardware store as a kit containing a two-piece epoxy paste, a nozzle, and a liquid resin packaged in a tube that can be used with a standard joint filler. Wear gloves and goggles.
Clean the crack and the area around it with a wire brush. Make sure there are no crumbs left in it. Blow out the crack with compressed air. Dry the crack surface with a hair dryer.
2. Glue the attachments by inserting them into the crack, starting at 30 cm above the floor and then every 30 cm.
3. Using a spatula, mix the epoxy and hardener onto a piece of cardboard, apply this resin to the underside of each accessory and glue it over the crack. Wear rubber gloves. Let the resin harden.
4. Mix another portion of the two-component paste and cover the crack surface with it. Press the paste into the crack, create a 3mm coating by rubbing the paste around the crack. Leave this coating overnight for the paste to harden.
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5. Now inject liquid epoxy into the cracks according to the manufacturer's instructions. Start injecting resin from the lowest nozzle. When you have finished injecting through the nozzle, close the hole with the cap and start injecting into the next nozzle above. Continue until the crack is completely filled. If you are filling a crack that is more than 3 mm wide with liquid resin, you will need several tubes for each tip.
Let the liquid resin harden for five days, then chop off the nozzles if desired.
Cracks in concrete can also be repaired with other materials. One of them is presented in the form of tubes, from which the cleaned crack is filled. Then the surface is cleaned with a trowel. The excess of this substance can be wiped off the surface with a wet cloth before the filler sets.
Concrete is the most popular building material, characterized by high durability and strength, wide application, absolute nonflammability and low cost. However, violations of the technology of its preparation and stacking lead to rapid wear of products and structures. Accelerated destruction of concrete is also facilitated by operation in aggressive environments and increased mechanical loads. As a result, the material loses its design strength and becomes covered with cracks and cavities.
For restoration, no traditional mortar is used, but a specially formulated concrete repair mixture with suitable technical characteristics... Such formulations are produced and packaged as a dry powder, which is diluted with water in a certain proportion. To give them special properties (frost resistance, moisture resistance, curing rate), various ingredients are added (plasticizers, modifying additives, fractional fillers).
Ready-made compositions for concrete repair are conventionally divided into groups.
By field of application:
- For restoration of structures and products experiencing increased mechanical loads (beams, columns, floor slabs, load-bearing walls).
- For strengthening reinforced concrete elements subject to corrosion.
- For the repair of road surfaces and floors.
By the complexity of the composition:
- One-component (cement with large and small fractions).
- Two-component (epoxy with varying degrees of fluidity).
- Multi-component (liquid polyurethane).
There are also repair mortars for concrete with special conditions of use:
- Thixotropic - for vertical surfaces.
- Casting - for horizontal planes.
- Fast hardening - for urgent repair and liquidation of leaks.
- Frost resistant - for use at low temperatures.
- For industrial and domestic purposes.
Bulk mixtures are used with a working layer thickness of no more than 100 mm, and fast-setting mixtures, which gain the necessary strength after 6 hours, up to 40 mm.
Selection method
Correctly selected repair dry mix for concrete and strict adherence to the technology of its use will ensure the strength and durability of the product or structure. When buying a composition, one should take into account the nature of the damage, the size of the affected area and the operating conditions of the concrete. After hardening, the repair mortar should not shrink and delaminate. Its compatibility with the restored surface and the required level of adhesion to it are extremely important. Almost every manufacturer of repair mortars additionally offers proprietary deep penetration primers that bind concrete and ensure high adhesion to the mortar.
When choosing the type of mixture, the extent of surface damage must be taken into account. Significant potholes, cracks and differences in floor levels are eliminated with solutions with large fractions. To close up small cavities and cracks, it is enough to buy a fine-grained mixture for repairing concrete with increased ductility. If a product or structure is operated under extreme conditions, then the restoring composition must contain additional ingredients that give it special qualities, such as frost and water resistance.
Technology of use
Floor repair
To eliminate large damage on horizontal surfaces and drops in the concrete floor, inexpensive dry cement-sand mixtures are usually used. Before applying the ready-made solution, the work area should be cleaned of debris, dust, degreased, and then treated with a deep penetration primer recommended by the manufacturer. After assessing the extent of damage, it is determined required amount repair mix for concrete. Recommended thickness cement-sand screed does not exceed 40 mm. Control beacons are set up and a solution is drawn out, which will gain strength within 2 weeks. All this time, the surface of the screed, covered with plastic wrap, should be periodically moistened with water so that it does not crack. To eliminate small defects in the floor, it is advisable to use self-leveling finely dispersed bulk compositions with increased plasticity.
Crack repair
Before using the solution, slit on concrete surface usually expand. To do this, grooves are cut around them with a diamond wheel or grinder, up to 50 mm deep, and then the destroyed material is selected with a perforator or chisel. Working area cleaned with compressed air from debris and dust, treated with impregnation, after which a repair solution is applied. Cracks on horizontal and inclined surfaces are eliminated by saturation without excessive pressure. To fill vertical gaps, inexpensive and practical repair mixtures MBR 300 and MBR 500 for concrete are often used, which differ in strength characteristics and speed of hardening. In some cases, to fill internal voids and deep cracks, they resort to the injection method using a special device - a packer. The repair compound that has appeared on the surface under pressure is removed with a strip, and after hardening it is sanded.
Concrete is one of the most durable building materials, but, unfortunately, it is also subject to destruction. The cracks and damages that have appeared must be repaired, but this must be done correctly, otherwise there will be no sense in the repair.
The preparation of a concrete solution is not a difficult operation, but, nevertheless, builders often make mistakes in the recipe, and also violate the technology of placing concrete, as a result of which, after a while, cracks appear on its surface. If they are not eliminated, then the concrete structure will collapse without serving its due date.
There are three types of concrete corrosion:
physical - when, as a result of violation of the concreting technology, water enters the concrete structure, and, freezing, breaks it;
biological - caused by the vital activity of fungi and bacteria;
chemical - it is caused by aggressive chemical elements in the air or in the concrete mixture itself.
Poor quality concrete
Different types of structures require an appropriate concrete mix. If the proportions of all components are not maintained, then the concrete element will subsequently collapse. The cause of destruction can also be unrefined gravel or crushed stone introduced into the concrete mixture as an aggregate. Often it happens in old expired cement, water with inappropriate chemical composition or a violation of the mixing rules, namely, cooking too quickly, not providing a homogeneous mixture. If the mixture, on the contrary, is overexposed in a concrete mixer, then its components may separate, which will also affect the performance of the concrete product.
During installation, it is necessary to carefully monitor the compaction of the concrete, otherwise the remaining voids (shells) will cause fractures load-bearing structures... Compliance with concreting technology is not only a properly prepared mixture and high-quality laying, but also care for hardened concrete. During hardening, it must be watered with water, to prevent overdrying, overheating, and freezing.
Cause of destruction iron concrete structures fittings may become rusty or poorly degreased. To provide her reliable protection from corrosion, it is necessary to lay it to a depth where moisture does not penetrate through concrete of a given density.
Damage to high-grade concrete
Even the highest quality concrete can collapse from strong impacts, or when the load on it exceeds the design. The integrity of the concrete can be affected by acid rain, sea water, gases and corrosive substances from the environment (for example, anti-icing agents). The cause of the destruction of initially high-quality concrete can be the substances formed in it as a result of the entry of some components into a reaction with carbon dioxide and air. Corrosive substances are also produced by bacteria that lodge in the concrete. Basically it is sulfuric acid, hydrogen sulfide and carbon dioxide. The roots of trees that pass under monolithic structures are often destroyed mechanically.
Signs of concrete failure
If mistakes were made in the process of concrete removal, then its surface may delaminate. As a rule, this happens when hardening concrete overheats, when bright sunlight falls on it for a long time. Acid rain can also have a similar effect.
Strongly noticeable efflorescence on the surface of concrete structures indicates that water penetrates into its thickness and gradually flushes out salts that crystallize. The crystals themselves are not as dangerous as the demineralisation of concrete, which can cause it to crack.
When the load on the concrete structure is higher than the calculated one, then the concrete will certainly crack. Often, violations of its integrity are caused by the shrinkage of the building at the initial stage of operation. The main danger of cracks is that moisture entering deep through them, freezing, breaks the concrete until it is completely destroyed.
Rusty streaks and streaks on the surface of concrete structures are also unhealthy signs. If they are not caused by external factors, then they are most likely the result of corrosion of the reinforcement. This means that there are cracks in this location, which will progress, causing gravel to fall out and even spalling of entire concrete fragments.
Elimination of defects
The modern materials market offers many means for repairing cracks, delamination and other damage to concrete. The simplest and most affordable are repair mixtures based on the same cement, which for preparation it is enough to seal with water. A solution with similar characteristics can be prepared independently. For this you need to sand-cement mixture introduce special polymer additives that give the solidified mass elastic properties, as well as making it more durable. If the amount of polymer is more or less than required, then the repair mixture will be ineffective, therefore, in the absence of experience, it is better to use ready-made mixtures, among which there are two main modifications:
Dry mixtures that are mixed only with water (they already contain a powder polymer);
dry mixtures that must be diluted with both water and polymer in a strictly defined amount.
There is also a third modification that requires the addition of a mixture of polymer and hardener, which is prepared immediately before use.
When performing minor repairs, preference should be given to quick-hardening mixtures and leveling putties. The elimination of deposits and efflorescence is carried out with special cleaning agents. Manufacturers of concrete repair materials also produce anti-corrosion agents for protecting reinforcement and special primers for screeds.
Selection of repair mortar
An important factor influencing the choice of the mixture is the location of the problem area. If these are horizontal cracks or potholes that will be repaired from above, then any mixtures will do, and for vertical and sheer places, special mixtures with enhanced adhesion are needed. When choosing a mixture, it is also necessary to take into account its strength, since what is suitable for repairing a crack in a wall will not be suitable for repairing a crack in a garage floor screed, since the hardened mixture will have to withstand the weight of the car. The properties and purpose of the mixture are indicated on the packaging, and before purchasing this or that repair compound, it is necessary to study the manufacturer's recommendations for its use.
Some solutions are designed for application up to 10 mm, others up to 100 mm, and this must be taken into account in each case. Dry repair mortars are mainly sold in 25 kg bags. The mixture that will not be worked up should be stored in a dry place. Some of its types are afraid of low temperatures, which the manufacturer informs about on the package.
Preparing damaged concrete surfaces for restoration
First, it is necessary to chop off all the exfoliated elements, after which the surface is thoroughly cleaned until stable cracks in the base concrete are filled. It is better to do this by hand so as not to damage the whole concrete and not create additional work for yourself. The prepared surface must retain some roughness in order for its adhesion to be higher. Small cracks must be expanded to 5 mm so that the repair mortar can penetrate them to a sufficient depth.
Immediately before applying the repair mortar, the base must be moistened so that it does not pull on the water from the fresh mixture. For the same purpose, the base can be primed, and its adhesion will also improve.
Wide cracks need additional reinforcement. To do this, along the gap, every 20-25 cm, a cross cut is made with a grinder, into which reinforcement with a diameter of 3-4 mm is inserted. If concrete chips expose rusty reinforcement, it must be cleaned to undamaged metal and treated with an anti-corrosion agent. In cases of severe damage to the reinforcement, welding may be necessary.
Since the repair mortar cannot become a monolith with the base, the place of its application should have the best possible adhesion. Where there is a high likelihood of the repair layer leaving, it is necessary to create a contact layer on the surface to be repaired before applying it. For this, there are special primers based on cement and polymers in a 1: 1 ratio or based on liquid resins mixed with fine-grained sand.
After creating the contact layer, you must immediately proceed to applying the repair mortar, otherwise the connecting effect will not be achieved. The tackle mortar is not intended to function as a repair mortar.
In conclusion, it should be noted that before undertaking the repair of cracks in concrete, it is necessary to find out the true cause of their appearance. Wide cracks are usually caused by improper distribution of loads on the concrete element. And just sealing the gap cannot be done here - after some time it will appear again. In order to relieve the stress in the cracked concrete, it may be necessary to reconstruct some of the structural elements of the building.
