The critical stage is to study cracks, identify the causes of their occurrence and the dynamics of their development.
According to the degree of danger for load-bearing and enclosing structures, cracks are divided into three groups:

• cracks are not dangerous, worsening only the quality of the front surface;
• dangerous cracks that cause significant weakening of sections, the development of which continues with unabated intensity;
• cracks of the intermediate group, which worsen the operational properties, reduce the reliability and durability of structures, but do not contribute to their complete destruction.

If there are cracks in load-bearing structures buildings and structures, it is necessary to organize systematic monitoring of their condition and possible development in order to find out the nature of deformations in the structure and the degree of their danger for further operation.

Cracks are identified by inspection of surfaces, as well as selective removal of protective or finishing coatings from structures. It is necessary to determine the position, shape, direction, distribution along the length, width of the opening, depth, and also determine whether their development continues or has stopped.

A beacon is installed on the crack, which breaks when the crack develops. The beacon is installed in the place of greatest development of the crack. When observing the development of a crack along its length, the ends of the crack are fixed with transverse strokes during each inspection. The date of inspection is indicated next to each stroke. The location of the cracks is schematically plotted on the drawing of the walls of the building or structure, noting the numbers and date of installation of the beacons. For each crack, a schedule of its development and opening is drawn up.

Based on the results of systematic inspections, a report is drawn up, which indicates the date of inspection, a drawing with the location of cracks and beacons, information about the absence or appearance of new cracks.
The lighthouse is a plate 200-250 mm long, 40-50 mm wide, 6-10 mm high, placed across the crack. The lighthouse is made from plaster or cement-sand mortar. Two glass or metal plates, each fixed at one end on different sides of the crack, or a lever system, are also used as a beacon. The rupture of the beacon or the displacement of the plates relative to each other indicates the development of deformations.
The lighthouse is installed on the main material of the wall, having first removed the plaster from its surface. It is recommended to place beacons also in pre-cut grooves. In this case, the grooves are filled with gypsum or cement-sand mortar.
Beacons are inspected a week after their installation, then at least once a month. In case of intense cracking, daily monitoring is required.

The opening width of cracks during observations is measured using crack gauges or crack gauges. The observation log records the number and date of installation of the beacon, the location and layout, the initial width of the crack, and changes in the length and depth of the crack over time. If the beacon is deformed, a new one is installed next to it, which is assigned the same number, but with an index. Lighthouses on which cracks have appeared are not removed until the end of observations.
If no change in the size of the cracks is detected within 30 days, their development can be considered complete, the beacons can be removed and the cracks can be repaired.

We have already written earlier on the website in the article “” how cracks in load-bearing structures can be dangerous and what are the main reasons for their formation. Some idea of ​​monitoring can also be obtained from the article "", published earlier. And today's publication is dedicated to specific ways monitoring and devices used for these purposes, the so-called “beacons”. At the end of the article you can watch a presentation with photographs and diagrams of the lighthouse structures described.

In what cases is it usually necessary to monitor cracks in a building?

1. As part of comprehensive monitoring of building deformations
2. In the presence of load-bearing structures that have limited operability and emergency conditions
3. If the building falls into the zone of influence of new construction or reconstruction

The main task when monitoring cracks is to record changes in their parameters for objective control technical condition designs.

The goals of monitoring may be different, but their essence is the same - timely receipt of information about ongoing changes for decision-making. Based on the monitoring results, decisions can be made on the possibility of further operation, the need and type of repair measures, prompt elimination of factors affecting the development of cracks (for example, dynamic influence from a nearby construction site), prevention emergency situations and so on.

Monitoring objectives, technical condition and design features influence how crack development is monitored. When choosing the method and methods of observation, the following main factors must be taken into account:

1. The need to take into account temperature and humidity influence
2. The need to quickly obtain information
3. Required measurement accuracy
4. Cost, reliability and durability of the monitoring system and its components
5. The complexity of taking readings and servicing the system

What beacon designs are used for observing (monitoring) cracks and what are the features of their use?

Electronic sensors and monitoring systems

To take into account temperature and humidity influences on structures, it is necessary to make appropriate measurements. Moreover, for an objective assessment of such influences, indicators of temperature/humidity of air and structures both outside and inside the premises may be required. A sufficient amount of such data can only be provided by an electronic continuous monitoring system with sensors appropriate for the tasks. It is also possible to obtain the necessary data in fragments using manual measurements with instruments at the time of taking readings from beacons installed on cracks. But this approach should still be considered uninformative, since it does not provide enough data to assess the influence of temperature and humidity on changes in the parameters of cracks in structures.

Electronic devices also have the greatest efficiency in obtaining measurement results. measuring systems with the possibility of remote information transfer. They also generally have the greatest measurement accuracy - they record the width of the crack opening to hundredths of a millimeter. The disadvantages include the impossibility of measuring with one sensor the movement of parts of a structure relative to each other in the vertical and horizontal directions simultaneously.

Accurate electronic measuring monitoring systems allow short-term (2-15 days) observation cycles to be carried out, providing information on current trends in the development of deformations and allowing prompt decisions to be made. Such systems are becoming increasingly widespread, but the main obstacle to their wide application remains high cost with low resistance to vandalism. Nevertheless, this is certainly a promising direction in the development of deformation monitoring tools, with the help of which it is already possible to solve a wide range of monitoring tasks.

Gypsum beacons

Of all the methods, the traditional design of a gypsum beacon for observing cracks has the least cost. However, it has a number of disadvantages:

1. Ineffective for use in outdoor structures and places where significant temperature fluctuations are possible. In such conditions, the gypsum beacon is “triggered” by temperature deformations, which does not make it possible to unambiguously determine the presence of other factors influencing the crack.
2. Low durability and intensive destruction under unfavorable external conditions, high damageability.
3. Labor-intensive installation, impossibility of installation at subzero temperatures.
4. Dependence of the beacon's performance on the quality of the installation. Failure to comply with the recommended requirements for surface preparation, dimensions and design of the beacon leads to its inoperability.
5. Due to the low reliability of the received data, installation is required large quantity lighthouses. Typically at least two per crack and at least one per 3 meter crack.
6. The accuracy of crack width measurements is very low due to unevenness at the measurement site. For the same reason, there is no possibility of using high-precision measuring instruments.
7. The main thing is that the gypsum beacon is disposable. In most cases, when it is triggered (a crack appears in the body of the beacon), it is necessary to install a new beacon nearby.

Plate beacons

Plate beacons do not have many of the disadvantages of their gypsum counterparts. One of their main advantages is the ease of installation - this is done with quick-curing epoxy glue, or on dowels, or by combining these two methods. Depending on the design, these beacons can implement additional features that are not available in beacons of other designs:

A signal measuring scale that allows you to visually assess changes in the crack opening width without additional tools.

1. The ability to measure the movement of structures along two axes (when using a special design, three) relative to each other - in the vertical and horizontal directions.
2. Possibility of using high-precision measuring instruments to measure hundredths of a millimeter change in crack opening width.
3. Ease of use, including the ability to add additional information to the beacon.

Currently, this is perhaps the most effective design in terms of the ratio of installation cost, labor intensity of observations and the quality of the results obtained.

Point beacons

Another type of beacons for monitoring cracks are point devices that allow observations to be made at two, three or four points fixed on the structure. Design Such devices can be extremely varied from simple dowel-nails to special installation devices. Such devices can be made inconspicuously in the color of the wall finish or transparent (made of plexiglass). The advantage of some of them is that there is no need to prepare the surface and clear the finishing layers. The use of special calculation methods makes it possible to track movements in both vertical and horizontal directions. The accuracy of measurements is limited only by the accuracy of the instruments used. The undoubted advantage of most representatives of this type lighthouse structures are extremely high resistance to vandalism, achieved by rigid fastening to the structure, with small dimensions of the device.

Sentinel beacons

In addition to those mentioned above, sentry-type beacons (messuras) are common, having a measuring scale and relatively high accuracy measurements without the use of additional tools. These are the most intuitive devices to use, allowing you to easily navigate the changes taking place and take readings. For some reason, it is this type of beacon that most attracts vandals; sometimes even special protective structures do not help. In addition, their cost is significantly higher than plate, point, and even more so gypsum, which significantly reduces the scope of their application. Greater efficiency can be achieved by fixing two points on the structure and using the measurements only as a measuring tool to perform control measurements of the distance between the fixed points.

There are other types of beacon designs, but in conclusion I would like to once again warn against the use of paper and glass beacons, since their designs do not meet the requirements and can be misleading when making observations.
.

First, let's quote from regulatory documents, where definitions of beacons and gap gauges are given. The first document is an updated GOST, the requirements of which apply to monitoring deformations of the foundations of buildings and structures.

GOST 24846-2012 Soils. Methods for measuring deformations of the foundations of buildings and structures:

3 Terms and definitions

3.34 beacon, crack gauge: A device for monitoring the development of cracks: gypsum or alabaster tiles attached to both edges of the crack on the wall; two glass or plexiglass plates with marks for measuring the size of the crack opening, etc.

10 Observation of cracks

10.1 Systematic observation of the development of cracks should be carried out when they appear in the load-bearing structures of buildings and structures in order to determine the nature of the deformations and the degree of their danger for the further operation of the facility.

10.2 When observing the development of a crack along its length, its ends should be periodically recorded with transverse strokes applied with paint, next to which the date of inspection should be indicated.

10.3 When observing the opening of cracks along the width, you should use measuring or fixing devices attached to both sides of the crack: beacons, crack gauges, next to which their numbers and installation date are indicated.

10.4 If the crack width is more than 1 mm, its depth must be measured.

Appendix A

(required)

A.1 The program for monitoring deformation of the foundations of buildings and structures should cover:

- for buildings (structures) in use - period of operation, results of inspection of the facility, presence of cracks and places to lay beacons (crack gauges);

The second document is the new STO used at Rosatom facilities.

SRO NP "SOYUZATOMSTROY"

STO SRO-S 60542960 00043-2015 “Geodetic monitoring of buildings and structures during construction and operation”

3 Terms and definitions

…
3.21 lighthouse: A signaling device installed on a crack/seam/joint so that changes in crack parameters (opening, closing, shear, elongation, etc.) can be determined visually - without the use of additional tools and devices.
3.22 crack beacon: A device for observing (monitoring) cracks/seams/joints, combining a signal function for visually identifying the fact of changes in the parameters of cracks/seams/joints with the function of measuring the magnitude of these changes.
…
3.50 gap gauge: A device used to perform, when monitoring the condition of structures, measurements of changes in the parameters of cracks/seams/joints.

Beacon ZI-2.2 according to the classification of STO SRO-S 60542960 00043-2015 is a gap-measuring beacon

An observation beacon or gap gauge is special devices or instruments designed to monitor changes in the state of defects and damage in building structures of buildings and structures. When observing cracks, they are used either to identify the fact of a change in the crack opening width, or to determine the magnitude and direction (crack opening/closing) of a change in the crack opening width. Also, in some beacon models, it may be possible to observe the shift along a crack or from the plane of the observed building structures.

Beacon for measurements on two axes

To monitor cracks, beacons are installed directly at the location of the crack for the period necessary to carry out observations. To monitor structural deformations, readings from installed beacons must be periodically taken and recorded in an observation log. The process of constant observation of structures is called monitoring. Specific monitoring periods are established depending on design features building, observation purposes, location and other parameters of the crack. In the vast majority of cases, the beacon should remain on the crack until the causes of the crack have been completely eliminated and the crack has been completed. repair work to restore/strengthen structures damaged by cracks. Sometimes, beacons can remain on structures after completion of work, to monitor the effectiveness of the repair work carried out. Also, with the help of beacons, changes in the position of building structures of buildings and structures can be observed throughout the entire period of their operation in order to monitor the technical condition.

Types and designs of lighthouses

The simplest beacons are a strip of plaster applied to the structure at the location of the crack. Such a beacon serves to identify the fact of changes in the width of the crack opening and cannot help in determining the quantitative values ​​of these changes. Gypsum and cement beacons have a number of requirements and restrictions on use. what you need to know when installing them. Glass beacons can be made similarly to plaster ones - a strip of glass across the crack, or provide for the possibility of taking measurements in the case where two glass plates are installed on both sides of the crack. Such beacons are the most common due to their low price and ease of installation. However, their use is ineffective due to low accuracy and other problems associated with the design of these beacons. Additional information about glass and other types of lighthouses can be found in the article describing methods for monitoring deformations in building structures. It should be noted that paper and other similar materials cannot be used to observe cracks for a number of objective reasons, which can be read about in the corresponding article “The myth about the existence of “paper beacons”.

Mechanical beacon

Electronic monitoring device

There are also so-called “mechanical” beacons. These are devices of various designs, the task of which is to measure the magnitude of changes in crack opening. There are a lot of lighthouse designs of this type. Basically, these are some elements installed on both sides of the crack, with a scale and pointer that allow you to see the change in the crack opening value without additional accessories. The most accurate of mechanical devices is a beacon made on the basis of a dial indicator. Expanding the functionality and accuracy of “mechanical” type beacons is possible when using modern high-precision measuring instruments, such as electronic calipers, for measurements. The design of professional observation beacons always includes special reference points, which are used for high-precision measurements.

Monitoring system

The most modern beacons are based on electronic components, such as strain gauges or using optical technologies. They also have different design and opportunities. In addition to directly measuring the crack opening, they can collect information about temperature and humidity conditions and other parameters. It is possible to equip them with modules for remote information transfer for monitoring the condition of structures in real time. The problems with their use are mainly related to the high price and the difficulty of preventing unauthorized access to them by unauthorized persons. Some

In the process of monitoring cracks in load-bearing structures of buildings, the question arises of how best to record the observation results. After all, to control the development of deformations in structures, it is not enough to simply install beacons to monitor cracks. It is also necessary to periodically take readings from these beacons, i.e. measure the width of the crack opening and its other characteristics. These readings must be recorded in documents so that you can always view the history of changes and analyze the monitoring results.

Mandatory forms of documents currently do not exist, but there are recommended ones, which were developed in the development of norms and rules for the operation of buildings, and are also given in recommendations for the inspection of buildings. Let us dwell on the two main forms of documents filled out when monitoring load-bearing structures using beacons.

Crack Surveillance Log

The form of the log for monitoring cracks in building structures is proposed in the Manual for Assessing the Physical Wear of Residential Buildings, developed as a follow-up to VSN 57-88 ( Regulations on technical inspection of residential buildings). In this form of the log, the results of installation and monitoring of cracks using beacons are continuously recorded. The journal form can be downloaded from our website.

Crack Observation Graphic Template

Graphical template for monitoring cracks in load-bearing walls buildings using beacons is intended to record the results of observations in the form of a visual diagram showing the nature of the measurements taking place. This template is developed based on building inspection guidelines and provides a convenient visual representation of building deformation processes. This form of observation can be used in addition to the log to analyze monitoring results. After downloading, you need to print one template for each observation location (beacon installation). You can download the graphic template form on our website.

The proposed forms for documenting the results of monitoring the development of cracks in buildings can be used both in the process technical operation, and when inspecting buildings. Typically, building maintenance specialists install beacons during spring and fall building inspections when new cracks are identified. Further monitoring of the installed beacons and filling out documents is carried out depending on the accepted frequency, the nature of the deformations and the characteristics of the object.

Gypsum crack monitoring beacons have previously been the most popular inspection tool. Due to the spread of more effective means for monitoring damage and deformation of building structures, gypsum beacons have lost their former importance and are used less and less. However, there are many adherents to their use, and the cracks on which they are present are still sufficient quantity, so that those who wish could familiarize themselves with this device in person. Today we will analyze the basic requirements and conditions for the use of gypsum beacons when observing cracks in the building structures of buildings and structures and will try to find the answer to the question: “Is it time to ban the use of gypsum beacons?”

Beacons made of cement-sand mortar are usually installed on the street side

Beacons of the type discussed today can be made from building gypsum(alabaster), from cement-sand, or any other mortar, from various dry construction mixtures, or from ready-made gypsum plates. Despite the variety of materials, they are united by the main thing - the mechanism of use for observing cracks in building structures. The signal for a specialist is the so-called “triggering” of the beacon - the appearance of a crack in the beacon itself. It is for this reason that we have united under the common most common name “ gypsum beacons» any structures for observing cracks that work on the above principle (with the exception of glass, which work on the same principle, but differ significantly in the material of manufacture). The vast majority of experts have seen gypsum beacons installed on structures. Many people have experience in “making” them. But when it comes to their shortcomings, limitations and principles of use, not everyone understands the features of this type of observation and the reasons for its displacement by more advanced instruments. Let's start studying the issue with methodological literature and recommendations for the use of gypsum beacons.

Methodological literature

The literature describing the requirements and methods for using gypsum (alabaster / cement) beacons relates to different areas. The corresponding descriptions are in the documents intended for:

• services for the operation of buildings and structures for various purposes
• specialists in technical supervision and control of construction processes
• experts and technical survey specialists
• specialists performing geotechnical monitoring and observation of deformations of foundations of buildings and structures
• and etc.

We have made a selection from the texts of these sources and below we post quotes only from some of the documents that best reveal the features of lighthouses of this type. It so happened that the selected documents are mainly intended for specialists in technical inspection and monitoring of buildings and structures.

Guidelines for monitoring deformations of foundations of buildings and structures

NIIOSP Gosstroy USSR 1975

This manual is the oldest of the sources provided. It should be noted that already in the 60-70s of the last century, gypsum beacons were not the only means of crack control, and the manual contains descriptions of other devices. Regarding gypsum beacons it contains the following information:

8. OBSERVATIONS OF CRACKS

8.1. When cracks appear in the load-bearing structures of buildings or structures, systematic monitoring of their development should be organized in order to determine the nature of the deformation of the structures and the degree of its danger for further normal operation.
…
8.3. A beacon is installed on each crack, which breaks when the crack develops. The beacon is installed in the place of greatest development of the crack.
…
Lighthouses of the simplest type are shown in Fig. 68. The lighthouse is a gypsum or alabaster tile about 10 mm thick and 50 - 80 mm wide. The tile is attached to both edges of the crack on the wall, which has been cleared of plaster. The rupture of the beacon indicates the development of a crack.

A guide to assessing the physical deterioration of residential and public buildings

TsMPIKS at MGSU V.V. Meshechek, E.P. Matveev, M. 1999

The manual covers the issues of crack control quite fully, gives practical instructions, and contains forms and requirements for documentation drawn up during the observation process. But there is quite a bit of space allocated for plaster beacons:

Lighthouses are made of plaster, cement and glass. Beacons are installed on stone wall, cleared of the facing layer, at least two on each crack...

Beacons are placed on the cleaned surface of the structure perpendicular to the crack: cement and alabaster - at least two per crack and one beacon for every meter, the rest - one beacon for every 3 meters, but not less than one beacon per crack.
The number and date of installation of the lighthouse is noted on the structure and in a special journal; In addition, the journal records the width of the crack opening and provides a diagram of the installation of beacons (Fig. 3).
When a cement or alabaster beacon breaks, which indicates the development of a crack, new beacons are installed...

A manual for the inspection of building structures

JSC "TsNIIPromzdaniy" M. 2004

This guide offers even more wide choose methods for dealing with cracks in buildings and clear instructions regarding the size of gypsum beacons:

5.3.10. The lighthouse is a plate 200-250 mm long, 40-50 mm wide, 6-10 m high, made of gypsum or cement-sand mortar, placed across a crack, or two glass or metal plates, each with one end fixed on opposite sides of the crack , or lever system. The rupture of the beacon or the displacement of the plates relative to each other indicate the development of deformations.
The lighthouse is installed on the main material of the wall, having first removed the plaster from its surface. It is also recommended to place beacons in pre-cut grooves (especially when installing them on a horizontal or inclined surface). In this case, the grooves are filled with gypsum or cement-sand mortar.

Recommendations for inspection and assessment of the technical condition of large-panel and stone buildings

TsNIISK them. V.A. Kucherenko M. 1988

We have previously reviewed these recommendations and provided excerpts regarding monitoring cracks, seams and joints. The document does not set out in too much detail the methods of working with beacons, but contains diagrams, including those for gypsum beacons:

2.14. Observations of the development of cracks in walls over time are carried out using gypsum, glass or plate beacons. Recommended dimensions and installation diagrams for the indicated beacons on cracks are shown in Fig. 8.

Technical inspection of building structures of buildings and structures

All-Russian Public Foundation “CENTER FOR CONSTRUCTION QUALITY” St. Petersburg branch V.T. Grozdov St. Petersburg. 1998

This is the source that covers the topic of crack control in the most detail. It contains not only a description of working methods, but also some information about the features of using beacons:

An initial inspection of cracks caused by uneven settlement of the foundation and temperature changes makes it possible to determine their origin and opening, but does not make it possible to determine whether deformation has stabilized or not. To get an idea of ​​the dynamics of crack development and their stabilization, beacons are installed on the walls. At least two beacons are placed on each crack; one is at the place of maximum development of the crack, the other is at the place where its development begins. Lighthouses are most often made of plaster (alabaster). Cement beacons are sometimes made on the outer surfaces of walls. Lighthouses can also be glass or metal.

Gypsum (cement) beacons are installed on the wall surface cleared of plaster. Beacons must have widening at the ends (figure eight type) (Fig. 1.3, a). The thickness of the gypsum beacon near the crack should be minimal (6...8 mm).

With the help of gypsum (cement) beacons it is possible to establish only the fact of continued development of deformations (formation of a crack in the beacon) and measure the opening of the crack.

Metal beacons with marks make it possible to identify the values ​​of both opening and closing cracks.
…
When analyzing the behavior of lighthouses, it should be kept in mind that a crack in the masonry becomes a natural expansion joint. The beacon installed on it will record not only deformations from uneven settlement of the foundation, but also temperature. Therefore, with temperature changes, even in the absence of uneven settlement of the foundations, hairline cracks will almost always appear in the lighthouse.

It is necessary to constantly check whether the beacon has separated from the wall surface. In case of detachment, a new beacon is installed.

The above quotes contain a lot of information we need on the use of gypsum beacons, but still the picture will be incomplete if we do not take into account the practice of using gypsum beacons. Accordingly, we will analyze these and other documents taking into account the existing practice of using gypsum beacons and, based on such analysis, we will formulate the basic requirements for these devices.

Basic requirements for gypsum beacons

Dimensions of gypsum beacons

The shape of a gypsum beacon can be very different - from a rectangular plate to a figure eight

Summarizing information from sources, we can say that the following sizes are acceptable:

• length - 150-250 mm
• width - 40-70 mm
• thickness - 6-15 mm

In this case, the plan configuration can be in the form of a rectangular plate, a figure eight, or intermediate figures between these two. Overall dimensions should have an aspect ratio of approximately 1:3 to 1:5. The thickness can range from 6 to 15 mm, but it is indicated that the thickness where the crack passes under the lighthouse should be the smallest.

Why do the sources give such a variation in the sizes of gypsum beacons and can their sizes differ from those indicated in practice? To answer this question, you should refer to the conditions for using beacons and the features of the structures on which they are installed. Firstly, the size of the crack opening is important - the wider the crack, the longer the beacon. But with a large crack opening, the cross-section of the beacon should also be large enough, because in the place where the beacon passes over the crack, as we remember, its thickness is assumed to be minimal. Respectively, largest dimensions beacons are used when the crack opening is large. Typically, this picture can be observed in brick buildings that have damage in the form of extended single cracks from uneven settlement of foundations and foundation soils. On the contrary, in reinforced concrete structures, cracks most often have slight openings and beacons for them are made of smaller sizes. Although, for reinforced concrete structures the use of gypsum beacons is not recommended. In any case, the area of ​​connection between the lighthouse and the surface of the structure depends on the width and length of the beacon. To assess the necessary geometric parameters gypsum beacon in each specific case, you should remember the main rule:

The design of the gypsum / alabaster / cement (mortar) beacon should ensure its reliable adhesion to the surface of structures and the integrity of the beacon in the absence of changes in the width of the crack opening. In this case, in the case of an increase in the opening width of the crack, the following condition must be met: the magnitude of the tensile force required to break the beacon must be less than the magnitude of the force acting on tearing or shear, and capable of tearing the beacon away from the surface of the structure on which it is installed.

Such beacons are more likely to come off the surface of the structure than to crack

Gypsum lighthouse peeling off from the base

Those. when a crack opens, the beacon should rupture above the crack, and not tear off from the surface of the structure. And at the same time, if the crack is stable, the lighthouse should remain intact. Too large a cross-section of a gypsum beacon (this usually happens when its thickness exceeds 15 mm) leads to separation of the beacon from the structure on one side of the crack, while the beacon itself remains intact. The same picture can be observed in cases where, when installing the beacon, it was not ensured high-quality fastening to the design. This may occur due to the small size of the contact area between the beacon and the structure, or poor preparation surface of the structure before installing the beacon. Those. when determining required sizes For a lighthouse, the surface of the structure is also important - how smooth, dusty, absorbent, etc. it is. The worse the adhesion to the surface, the larger the area of ​​contact between the beacon and the structure should be.

Speaking about the geometry of gypsum beacons, one cannot help but say that the small thickness of the beacon is unacceptable. When the beacon thickness is less than 5 mm, even minor temperature and vibration influences lead to the formation of a crack. Those. in fact, the beacon “triggers” without significant changes in the crack opening width.

Material for gypsum beacons

Lighthouse in the form of a glued plaster plate

Most often, lighthouses are made of building plaster (alabaster). This material is susceptible to moisture, and therefore its use for the manufacture of beacons in damp rooms and outdoors (especially in the basement area of ​​buildings) is not recommended. Mortar beacons are more stable in such places - they are made from cement-sand mortar. Their disadvantages include poor adhesion to the surface of structures. Currently, more than suitable materials- dry building mixtures. It is preferable to use gypsum and cement plaster, as well as adhesive mixtures. In addition, there are beacons in the form of gypsum plates mounted on glue, prepared in advance. Such blanks can be made from gypsum in molds, or cut from sheet gypsum materials. When using ready-made gypsum beacons, it is important to ensure their reliable adhesive fastening to the surface of structures. The advantages of gypsum blanks for beacons include the ability to make beacons of any shape and dimensional stability.

Features of using gypsum beacons

Temperature influences

It’s hard to call such a “plaster blot” a beacon

If it is of significant length, a crack located, for example, in a boundary wall, acts as expansion joint, changing the opening width depending on temperature changes. If a gypsum beacon is installed on such a crack, then it always “triggers”, regardless of whether or not there are other reasons other than temperature effects. The ability to judge the trends in deformation development using such a beacon is almost completely absent. In addition, most surveillance methods require that a new one must be installed next to the “triggered” beacon. For the situation described above, this means installing a new beacon at each inspection, i.e. in general, once a month. Based on these facts, the use of gypsum beacons should be excluded in situations where the crack has a significant extent and significant temperature changes in the structures are possible. It also makes no sense to install beacons on cracks, the nature of which is related to thermal deformations of structures - so-called temperature cracks. The length of the crack on which the beacon can be installed under the specified conditions is determined based on the design features of the building and the location of the crack. Based on practical experience, we can say that, taking into account the described features, the scope of application of gypsum beacons in building envelopes is extremely limited and their use outside heated premises should be completely abandoned.

Possibility of measurements

The gypsum beacon does not help in measuring the width of the crack opening

As mentioned above, the purpose of the gypsum beacon is to signal that an increase in the width of the crack is occurring. Is it possible to measure the change in crack opening width using a gypsum beacon? If the crack closes, then the gypsum beacon does not work at all - in most cases it will come off or receive damage exceeding the amount of change in the width of the crack opening. In any case, it is not possible to measure the amount of crack closure using a gypsum beacon. It seems that it remains possible, using a gypsum beacon, to measure the magnitude of the change in the width of the crack opening as it increases. But in fact, this is also completely unjustified. When observing cracks in buildings and structures, it is recommended to measure the crack opening width with an accuracy close to 0.1 mm. Try measuring the crack with a caliper with such precision in one place, and then step back a few centimeters from it and repeat the measurement. In most cases you will get results that differ by more than 0.1mm. It is for this reason that in most methods it is recommended to mark the places where crack widths are measured with a stroke drawn across the crack. This mark allows you to take measurements in the same place every time, but even this method is not accurate enough. Remember the geodetic observations of building settlements and the design of the settlement marks used there. They are designed in such a way as to make it possible to install the geodetic rod in only one correct way. For this purpose, rounded surfaces are used, which gives point support for the slats, i.e. the rail can only be installed at one specific point. This is exactly how it is necessary to organize observations of cracks - to ensure the possibility of measuring the opening width in only one single right place- between two points. In the most simple version- these can be two dowels driven in to different parties from a crack. In the advanced version, these are reference points provided in the design of the plate beacon. The gypsum beacon provides absolutely nothing for the ability to measure the magnitude of the change in crack opening width. Those. its design does not carry any useful functions, except for the one for which it is intended - signaling.

Practical errors

They missed the mark here with the installation of the beacon

Such plaster strokes do not at all correspond to the danger of a crack

The most common critical mistake when installing gypsum beacons on cracks is failure to comply with the recommended dimensions. Most often, they deviate from the thickness requirements - either it’s just a stroke with a spatula/brush soaked in a liquid gypsum solution, or, on the contrary, a blotch whose thickness is close to the width. In the case of a thin lighthouse, a hairline crack forms in it in the very first days or weeks, and if it is very thin, then the crack in it continues to grow, subsequently taking on the shape and size of a crack in the structure itself. And in the case of a thick beacon, the beacon usually separates from the base. We see the same effect in cases when dimensions the beacon is too small and the area of ​​attachment to the surface of the structure is insufficient. The situation develops similarly when committing the second main mistake— improperly prepared surface of the structure for installation of the beacon. If the paint or plaster layers are not removed and the beacon is installed directly on them, then it will not stay there. The separation of the beacon from the surface of the structure is the most common reason its failure.

The next common mistake is pressing the beacon material into the crack during manufacturing. This happens when the crack is not small, and the beacon is made without closing the crack under the beacon with a temporary barrier. In this case, gypsum or mortar gets into the crack, partially filling it at the place where the beacon is installed. The possibility of normal operation of the beacon in this case is extremely problematic, since above the crack the beacon must have the smallest cross-sectional value in order for a signal crack to form in it exactly in this place. Otherwise, it can be extremely difficult to identify and analyze a chaotically cracked piece of plaster mixed with remnants of plaster and pieces of wall around the crack.

A plaster beacon on a crack in the corner of a building usually looks good only in pictures in technical literature. In practice, making a gypsum beacon in a corner is extremely problematic and always impractical. However, adherents of gypsum try to use it in such places, which in the vast majority of cases does not bring good results.

Another mistake is the fact that often after a beacon is broken (triggered) a new one is not installed next to it. Yet gypsum beacons should be treated as disposable signaling devices - after a crack appears in them, it is difficult to obtain any reliable additional information from them.

Advantages and disadvantages of gypsum beacons

Advantages

The main advantage of a gypsum beacon is the low cost of materials for its manufacture and their high availability. A couple of handfuls of construction plaster (alabaster), gypsum plaster or cement mortar no problem to find. If necessary, all this can be bought for little money in construction stores, and in convenient small packaging. True, when determining the price of the beacon, you should add to the price of materials the amount of the specialist’s salary, in proportion to the time spent on installing the gypsum beacon. And it takes a lot of time to fashion this “miracle”, although the speed of installation increases with experience.

It is unlikely that the plaster beacon adds beauty to this wall, however, neither does the crack

Some people attribute their aesthetics to the advantages of gypsum beacons. And indeed, if a real sculptor has a hand in the process of installing a plaster lighthouse, you can enjoy the sight of this creation for a long time. However, in most cases, gypsum beacons are made ordinary people and they don't look very presentable. So this feature can only be called an advantage conditionally.

The low cost of materials and their availability seem to remain the main and only advantages of gypsum beacons.

Flaws

When comparing gypsum beacons with plate ones, the conclusions are completely obvious

It is rightly said that everything is known through comparison. Any beacon on a crack is better than none (with the exception of “paper” and similar “beacons”, the use of which can only cause harm). However, if you compare gypsum beacons with alternative options, the list can be quite long. For example, it makes no sense to compare gypsum beacons with electronic systems monitoring, because in most cases, electronics will lose out to plaster due to the high cost, which is not justified for the purposes pursued in these cases. Although “electronic beacons” give a lot useful information, their use in everyday work is quite limited. Based on most of the most common tasks in practice, the main disadvantages of gypsum beacons should be highlighted. This problem can be easily solved by comparing the properties of gypsum beacons with their closest competitors in terms of cost and tasks solved - plate beacons. Firstly, in addition to the function of sending a signal, most models of plate beacons have the ability to determine the direction of changes taking place, not only “left-right”, but also “up-down”, and some models allow you to track movement “out of the plane”. Professional models of plate beacons have fixed points for precise measurements the magnitude of the change in the crack opening width. The time spent on installing a plate beacon is several times, or even an order of magnitude, less than in the case of its gypsum counterpart. Plate beacons are ready for installation in any weather, at any time of the year and under different conditions. negative impacts, either aggressive environment or high humidity. With gypsum beacons you need to be more scrupulous and understand exactly what operating conditions they can withstand.

Mortar lighthouses preserved from the beginning of the last century

If we collect all the shortcomings of gypsum beacons and take into account the actual absence of any serious advantages, then a reasonable question arises: “Why are gypsum beacons still used?” It is unlikely that there is room in today's legislation for an official ban on the use of plaster beacons. And as they say: “Everything that is not prohibited is permitted.” But it is possible to increase the efficiency of monitoring cracks without resorting to prohibitions. This can be achieved by setting out in more detail in the methodological literature the features and conditions for using certain control tools. In addition, organizations can independently develop enterprise standards, the so-called. STOs, in which to determine the procedure and methods for monitoring and observing cracks, including beacon structures that are acceptable for use. Eat whole line such regulations that require minor adjustments that can significantly increase the level of efficiency of specialists through their use modern means observations. Each specialist and each organization has the right to establish their own ban on the use of gypsum beacons at objects under their control, eliminating this anachronism from the professional environment.