The reasons for the appearance of cracks can be very different. From this article you will learn about the causes of their occurrence, classification, degree of danger. We will tell you how to make observations and draw a conclusion about further actions to eliminate or mask cracks.
For completeness, we conditionally divide all deformations into technogenic and natural.
Man-made – they have a sign of interference by foreign bodies – from the hit of shells, the fall of cranes or power transmission towers, trees or ramming by a moving vehicle. Natural disasters can also be referred to here in our conventional classification. Destruction and deformation in this case are of a combined chaotic nature, which is not subject to investigation of the causes, but to ascertain the fact and assess the scale of damage. The presence of individual cracks in this case is rare, mainly their appearance is due to other damage.
Natural, including man-made (with human participation). These are deformations due to soil movement; temperature fluctuations and erosion; dynamic loads; incorrect design, construction and operation, overloading of the structure. In general, everything that accompanies the building throughout its “life”.
The first and foremost thing to know about cracks: this is an irreparable defect. It is impossible to glue the dried material and thereby stop the spread, if we are talking about the material of stone walls – brick, concrete, etc. However, you can take a set of measures that will return a decent appearance to the walls and ceiling or completely stop the course of destructive deformation using special means.
Structural cracks are deformations when excessive loads are applied to structural elements. Simply put – cracks in the material of walls, ceilings, foundations, arising from overloads or mobility of the base.
They appear as a result of the impact on the material of the foundation, walls and floors of loads that exceed the bearing capacity of an element in the structure. Often the cause of deformation lies not in the material itself, but in the element that rests on the structure (with a crack) or the support of this structure (most often the foundation). Let’s consider the popular reasons for the appearance of these unpleasant phenomena. We will divide this list into natural and anthropogenic (with human participation) causes..
Natural mother-in-law appear in materials and structures created in compliance with the technology, without violating the operating rules for the following reasons:
- Material wear. Everything has its own lifespan. For solid red brick – 100-300 years, concrete – 80-150 years, natural stone – 100-300 years and more.
- Erosion, weathering. Materials that are in contact with the natural environment, the atmosphere, are subject to gradual destruction.
- Impact of soil organic matter and groundwater. The underground parts of the building are subject to this factor. Also dangerous is the undermining of the foundation cushion by groundwater and cyclic freezing of the soil..
- Temperature and humidity fluctuations. The most harmful factor. Usually acts in combination with erosion in unprotected areas of loaded structures. Multiple freeze-thaw cycles of an element have a detrimental effect on the binder – the bond between the stone and the mortar weakens. The service life of buildings in the Far North is 30% less (according to the project) than in the Central zone. The most reliable in this regard are monolithic structures that do not have seams..
Deformations of building elements arising from human errors in the design, construction and operation of a building (structure) *:
- Soil research and preparatory work. Neglecting the study of soil settlement leads to the selection of an inappropriate option for the preparation of the base and the structure of the foundation. Most often from the desire to save money, time, materials and habits of relying “at random”.
- Note. The main argument in such cases is the examples of several existing houses that have been standing for a long time without any calculations. The opposite argument – dozens of neighboring houses, built within 20 years and already having visible deformations of the walls and foundations from the outside.
- Incorrect calculation of the loads on the base. In private construction, the mass of all elements is far from always being calculated and the specific load on the base is calculated. Most often this is done “by eye” or by experience. This option is quite acceptable only if the foundation is made with a significant margin of safety (it has impressive dimensions).
- Earthworks next to the building. Digging a pit close up is a bad idea for any foundation..
- Interaction of two or more closely spaced foundations. Several buildings (with foundations), standing closer than 5 meters from each other, create an unnatural, excessive stress on the ground.
- Violation of the technology of using materials during construction and repair. It can manifest itself at all stages of operation. Poorly prepared solution (with altered proportions or organic impurities), carrying out work in winter without heating, overdrying (solutions), lack of reinforcement of finishing layers.
- Violation of the structural properties of elements. Savings on armopoyas, wall thickness, reinforcement of reinforced concrete and masonry, openings without lintels, no intermediate supports on large spans, changes to the original design.
- Violation (change) of the building structure. Creation of additional openings in load-bearing walls, extensions, superstructures. Increased load.
- Dynamic loads from a nearby busy highway or railway.
* – for the greater benefit of the article, we give examples of errors and solutions only for private construction. Structural cracks in multi-apartment and high-rise buildings are the task of large organizations (housing department, SMU, etc.).
All of the above points lead to the appearance of cracks, which, in turn, can be divided into:
- Closed. Formed inside the material, without leaving it.
- Open. Exit to the surface of the material from one or both sides.
Over time, if you do not take action, a closed crack grows and becomes open. This process takes place especially quickly if the closed crack is filled with water and is exposed to air (prone to freezing). A crack, opened on both sides, eventually leads to a shift in the parts separated by it..
According to the dynamics of the state, natural cracks should be divided into:
- Developing. The crack continues to grow in length or width during the observation period.
- Stable. Do not develop. As a rule, these cracks appear in the first years of the building’s service and stop after the final shrinkage of the soil..
We will use all the described terms in the future, describing methods for eliminating these unpleasant defects..
There are about ten more fracture classification factors, but they are more important for expert theorists. In this article we will look at another, last, and most important factor – danger..
In this case, the risk of deformation is determined taking into account the general appearance and condition of the building (structure, element). Surface (non-through) cracks are considered non-hazardous with an opening width of up to 4 mm and a penetration depth of up to 10% of the element thickness. All through deformations are dangerous. You should also pay attention to the appearance of cracks in the supporting elements – walls, beams, ceilings, foundations..
The first thing to do when a structural crack is found is to start observing. This is done with a paper marker glued in the place of minimum disclosure. The date of installation should be marked on the marker and checked daily for 5-7 days. If the crack is stable and does not grow, then the marker will remain intact throughout the observation period. If the crack develops, the marker will rupture, which means that urgent action is needed to prevent further trouble. The depth can be determined using a thin steel plate. How to prevent the appearance of structural cracks and eliminate them, we will tell in one of the following articles.
They appear naturally when “wet” finishing materials dry. This mainly applies to the reinforcing and starting layers of facade and tile adhesives and some types of putties and waterproofing. To avoid cracking during drying, glass mesh is included in such layers. It is also used to secure the joints of drywall sheets (GKL).
Often such defects arise as a result of improper selection of the composition (a lot of cement) of mortar or concrete, as well as as a result of freezing of the raw material. Another susceptible area is the pairing of old material with new, for example, masonry and “wet” cladding.
Without resorting to radical measures (such as screeding with steel clips), such places can be repaired and defects can be masked. To do this, you first need to make sure that they are stable by doing research.
Attention! Masking of developing cracks can give a lasting visual effect of the absence of defects, but will not stop the processes that caused their appearance..
To seal stable technological cracks, fine-grained cement-based repair mixtures are used:
Index Unit rev. Product Master Beton-X Ceresit CN 83 Siltek C-70 Manufacturer – Ukraine Germany Poland Curing time 10 mm hour Up to 24 3 6 Layer thickness (max.) mm 300 35 70 Note – For dry rooms For dry and wet rooms, outdoor use For interior and exterior use Price RUB / kg 6.5 8.3 7.5
Read about the most effective ways to mask stable cracks in the next article..