The expansion joint is an integral part and the most important event in the construction of concrete floors.
There are three main types of expansion joints:
- Insulation seams;
- Shrink seams;
- Construction seams.
Types of expansion joints
Insulation seams are arranged along walls, around columns and around foundations for equipment in order to prevent the transfer of deformations from the building structures to the floor screed.
The insulating seam is created by laying insulating material along the building structures immediately before pouring concrete mixture.
Shrink seams necessary in order to prevent random cracking of the screed during the hardening process. They allow you to create straight slack planes in concrete. As a result, the screed cracks in a given direction.
Shrinkage seams must be cut along the axes of the columns and connected to the corners of the seams running along the perimeter of the columns.
Floor maps formed by shrinkage joints should be as square as possible. Elongated or L-shaped cards should be avoided. The length of the card should not exceed 1.5 times the width. Shrinkage joints should be straight and, if possible, without branches.
In aisles and driveways, shrinkage joints should be located at a distance equal to the width of the screed. Paths wider than 300-360cm must have a longitudinal seam in the center. When concreting in open areas, the distance between joints should not exceed 3 m in all directions. General rule- the smaller the card, the less likely it is to randomly crack.
The cutting of shrinkage joints is carried out after the finishing of the concrete surface is completed.
Typically, the seams are cut with 6x6 m cards in the same sequence in which the concrete was laid. The seams should be cut to a depth of 1/3 of the thickness of the screed. This creates a zone of weakness in the screed, and when the concrete shrinks, it cracks in this zone, i.e. cracks directionally, not randomly. In this case, the edges of the resulting crack have a certain roughness, which eliminates their vertical displacement until the crack becomes too wide.
Construction seams set up where the day's work of laying concrete has been completed.
The shape of the edge of the tie for a structural seam is usually done according to the tongue-in-groove principle; sleepers (slats) laid across the seam can be used. The slats should be installed in the middle of the depth of the screed under right angles to the seam. One end of the lath must be lubricated with bitumen in order to move freely in the screed.
Construction joints act as shrinkage joints - they allow small horizontal movements, but not vertical ones. It is desirable that the construction seam coincides with the shrinkage seam.
The construction of the expansion joint should be carried out in strict accordance with the developed project. If any changes occur (for example, the size of the seam or replacement of material), the design of the expansion joint must be agreed upon with representatives of the design organization.
Sealing seams
If available on premises wet processes special meaning acquires tightness of seams, since the lack of tightness leads to peeling of organic coatings from the floor slab. This process is especially active at elevated temperatures in the premises.
When carrying out work, the number and location of seams are determined based not only on the coefficient thermal expansion materials, but also taking into account the shrinkage of concrete and possible deformations, which most often occur in areas where the floor interfaces with foundations for equipment, walls and columns.
Sealing seams allows you to protect the seam from the penetration of water and aggressive media, as well as from clogging.
The type of sealant depends on the loads and operating conditions. For example, in many industrial and food processing plants, floors must be easy to clean and withstand high traffic loads.
Sealants for such floors must be hard enough to support joint edges and prevent chipping, and flexible enough to withstand easy opening and closing of the joint.
Crack problem
The formation of cracks in concrete can be reduced by reducing the volume of water used for mixing. But concrete, even with a low water content, shrinks, and, in addition, concrete made with some fillers can shrink more than concrete with other fillers.
Due to the fact that it is impossible to eliminate shrinkage of concrete made from traditional cements, best solution- give the crack the opportunity to appear in the place where its appearance is desired and, moreover, in the form of a straight line. This is an expansion joint.
Joints can be made in freshly laid concrete using a special cutter. In dry concrete, the seams are sawn through. But even in ties with slotted or sawn expansion joints cracks sometimes appear in other places. The likelihood of such cracks occurring can be reduced by doing the following:
Cut seams on time
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If the joints are cut in freshly laid concrete, then time does not matter. But if they are cut later, random cracks are likely to appear. Cutting joints in freshly laid concrete is carried out immediately after grinding the surface. On dry concrete, cutting joints should be done as quickly as possible so that the edges of the joints do not begin to crumble. It is usually recommended to do this after 12 hours at normal temperature, at reduced - 24 hours after laying concrete.
Cut seams to the required depth
Seams cut with regular seam cutters should be 1/4 to 1/3 the thickness of the screed. Joints made by special cutters on freshly laid concrete may have a shallower depth.
Cut seams at required intervals
Typically, the cutting interval for seams is chosen within the range (24-36) x (thickness of the screed). On a 10cm screed, the seams are cut at a distance of 240cm to 360cm from each other. For concrete with greater cone slump and shrinkage, it is preferable to have a cutting interval closer to 240cm.
Exclude internal corners
Cracks are most likely to appear on the inside corners. The seam grid should be such as to prevent the formation of internal corners.
Avoid T-shaped intersection of seams
T-shaped intersection of seams leads to the formation of a crack passing through the crossed seam. When planning the seam grid, T-shaped intersections should be avoided.
Areas bounded by seams should have a shape close to a square
If the length of the section is 1.5 times greater than the width, then the crack will most likely appear in the middle of the long side. The seam pattern should be such as to prevent the formation of long and narrow sections.
Avoid the formation of triangular areas with sharp corners
Plots triangular shape with sharp corners usually crack at the end of the sharp corner. In general, triangles should be avoided, but if this must be done, the seams should form an equilateral triangle.
Sometimes cracks form in concrete that has not gained strength. These shrinkage cracks usually occur in dry, hot and windy weather. If such conditions are expected during concrete laying weather, then you should use concrete with synthetic fibers, and during the process of laying and grouting the concrete, wet its surface with water.
How to use drywall finishing material for walls allows you to achieve flat surface. However, in some cases there is no need to level the wall itself. It is impossible to make a smooth wall using drywall alone; it is also necessary to use auxiliary materials. One of them is reinforcing tape for drywall. It helps create invisible joints between sheets, as well as strong and even corners. This will be discussed further.
Application of tape
Reinforced drywall tape is an ideal material for reinforcing and sealing seams and corners. The purpose of its use, as a rule, is to prevent the appearance of cracks in the putty between the gypsum boards. By choosing quality material and proper installation, you can achieve good results. This material is universal, as it is used quite widely.
There are several types:
- Serpyanka - a five-centimeter tape consisting of synthetic fiber. Its main role is to prevent cracks at the joint of gypsum board sheets and create a durable layer of putty;
- Bandage. The basis for its production is fiberglass. Its width is also five centimeters. The high strength of the mesh allows you to create a reinforced corner that is not susceptible to minor mechanical damage. Its advantage is that it is not thick, and this makes it possible to make a seam between sheets with almost no difference.
- Perforated paper - promotes good penetration of putty into the joints of the finishing material. This type is excellent for drywall, as it has a high moisture absorption rate and the same linear expansion as drywall;
- Reinforcing fiberglass mesh with adhesive side. Its width ranges from 10 to 23 centimeters. Its width allows you to create high adhesion between it and drywall. It is often used to reinforce slopes on windows or doors.
It is possible to achieve a smooth surface and ideal joints regardless of the type of reinforcing tape.
Any of them is designed for these purposes.
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How to seal seams
Before applying the reinforcing layer to the joint, it must be prepared. The fact is that drywall can have straight edges and rounded ones. If the edges are rounded, then no preliminary work is necessary. In this case, the putty perfectly seals the gap. And in the case of even corners, they need to be modified. To do this, you need to cut them at an angle of 45 degrees with a stationery knife so that a 90-degree angle is formed between the sheets.
Next, you need to prepare putty or use a ready-made one. It fills the joint between the sheets and a few centimeters of the edge of the sheet. The putty should be applied slightly wider than the reinforcing tape. To do quality work you need to have necessary tool- spatulas (one narrow and two wide, one of them should be wider than 300 millimeters).
So, the application process begins with the joints needing to be filled with putty. To do this, take a narrow spatula and apply the mixture inside. We rub all excess onto the adjacent surface of the sheets. Reinforcing tape is applied to this layer; its width should cover the surface near the seam by at least one hundred millimeters. Next, the tape should be pressed well into the layer of putty that has not yet hardened, only leaving the joint as is. You need to try to prevent waves from appearing, but to make sure that the film fits tightly to the wall in all places. After all requirements are met, it is necessary to allow the joint to dry. You'll have to wait about twenty hours, or better yet, a day.
The presence of a reinforcing film at the joint is noticeable. To get rid of the protrusion and make the joint flush with the rest of the surface, you need to take a wide spatula and clean the surface of excess putty (lumps, drips, etc.). The second stage of leveling is applying a fresh layer. To do this, you need to use the spatula even wider than the first time in order to cover more surface. This layer should be very thin. At this stage, you need to try to make the bump invisible. If necessary, you can use the spatula even wider, and apply another layer of putty. You just need to understand that the thinner it is, the smoother the surface will be. After this, the layer should dry. If it doesn’t work out the first time, you need to repeat this action several times until the surface meets the desired requirements.
How successfully you cope with such a task as sealing drywall joints depends on the stability of the future structure and its appearance. If you process the seam incorrectly, then over time: And if the sealing of drywall seams is carried out using technology and using high-quality materials, then you will never have to spend your family budget on a complete renovation of the apartment. Drywall joints can be treated using many methods. We will tell you the most popular and correct ones. Those that are carried out according to approved technological processes, in accordance with GOSTs, methods and construction regulations. Their list is given at the end of the article. It doesn’t matter whether you need to seal the joints of drywall that is mounted on a metal frame, or glued to a flat wall. It is important to follow the process. Conditions for carrying out work on sealing butt joints In order to save your earned money, effort and time, several requirements should be met before starting work: Fiberglass mesh, professionally called serpyanka, is produced with an adhesive layer. It is intended for sealing butt joints of plasterboard sheets, gluing seams, and cracks on repaired surfaces. Serpyanka absorbs moisture well. After interaction with the putty and final drying, it gives a single, strong, reinforced plane. The mesh characteristics are given in this table. Let's look at how to seal the seams on a plasterboard structure with your own hands using fiberglass mesh. It is not worth mentioning once again that the surface must be cleaned not only of dirt, but also of dust. The indoor microclimate should not be disturbed. The process itself will consist of the following stages: The end joints for any type of seam sealing must necessarily have a chamfer. For this purpose, a special device is used - an edge plane. This tool will chamfer at an angle of 22.5° by 2/3 of the sheet thickness, which is quite enough for this type of work. Using a plane is much more convenient, and the process is much faster. It is also permissible to use a knife in this procedure. True, he chamfers at an angle of 45 degrees. But this is quite enough for high-quality performance, you just need to work more carefully and take your time. It doesn’t matter what you use to make the cut - whatever tool you have, use it. It is imperative to chamfer the cut of drywall. This will be needed so that putty can be placed in the resulting recess. This procedure will significantly strengthen the structure of the partition or wall. If you do not do this, then when puttying, you will get a bump on the cut, which will have to be leveled with a thicker layer of finishing putty. And this will lead to greater consumption of building materials and higher costs of work. If the layer is thin, then during operation the seam will crack, since the technology for sealing plasterboard seams was initially violated. The slightest deviation from the technology leads to the formation of cracks on the finishing surface and entails unforeseen expenses in impressive amounts. Experienced specialists in such circumstances say that the stingy pays twice. And, unfortunately, in practice this is a very common case of technology violation. Now you should start priming the joints. To do this, we need a special composition bearing the same name. It can be bought in specialized stores. The primer composition is well absorbed into the material, an invisible film is formed, which has excellent connecting properties and adheres to surfaces. This water-soluble mixture only saturates the top layer of drywall and does not penetrate inside. During subsequent surface treatment, the cardboard itself will draw water from the solution or glue, thereby worsening the adhesion quality of the material. And the primer layer will prevent this process, since the film does not allow moisture to pass through, does not allow dust to get onto the surface being treated, and even has antifungal components. The layer thickness must be at least 0.03 mm, and it can be applied: For ease of use, the solution can be poured into a cuvette. And if the volume of the primer container you are using is small, use it by dipping the brush directly into it. Manufacturers offer us three types of primer composition: When choosing a primer mixture, pay attention to one of the parameters - it must be for interior work. The facade mixture contains harmful substances that are prohibited for use in residential premises. GCR treated with a special primer mixture lasts longer and does not lose its aesthetic appearance and properties. In addition, the putty lays more evenly on the primed surface. This type of work is required to level the surface. According to our method, we will do this twice, then the joint between the sheets will become even, smooth and with good adhesive properties. To work, we need dry or powder putty. It is diluted strictly according to the instructions just before application to the surface. You cannot prepare the composition for future use in large volumes - it dries quickly and you will have to throw away the unclaimed material, as it will become unsuitable for work. There are some subtleties here. If you are diluting the mixture in large quantities, say, you will be processing a large volume of surface and you have a lot of workers, then when using a construction mixer for mixing, do not use high speeds. This method involves a lot of additional air in the composition, and its excessive amount has a bad effect on the strength of the final product. If you are diluting a small volume, then pour the dry powder into the water until islands form on the surface of the water and stir gently. The color of the putty can be beige or gray. This indicator does not affect the strength of the material in any way. Two spatulas are required for work: A layer of putty is applied to the joint with a narrow spatula in such a way that the composition can penetrate deep into it, you can drown it a little - press it into the seam. In this case, you should not spare the solution, but you also do not need to show fanaticism. You don’t have to remove the remains for now, because the mesh will then be glued onto them. The excess will be removed at another stage of the work. Don't forget about the places on the drywall where the screw heads are screwed in - they also need to be puttied. After applying the putty solution to the joint, you need to apply tape to the seam. It’s better to measure it in length in advance, but you can do it while you’re working, but this is when you have an assistant nearby. Serpyanka cuts well with scissors. Using a spatula, press it firmly along the entire length to the joint. The tape must be applied strictly in the center of the seam. If one piece is finished, overlap the next one and continue working. Using a wide spatula, go over the surface you are working on again and at the same time remove excess putty. Now it takes time for the joints to dry. The covering layer can be applied to the joints when the surface is dry. To do this you will need to wait from 8 to 12 hours. The second pass will remove all the imperfections that were missed earlier and make the seam stronger. It is necessary to achieve a minimum covering layer - so that the joint cannot be determined by eye. But if this does not work out, there is a next stage in the technology of work. Sanding the areas we need is done with regular sandpaper, an abrasive mesh, which is fixed to a special block, or a special abrasive grater. What to choose - decide for yourself. Sandpaper is not very convenient to use, but you can stuff it onto a block - and then the work will become much more convenient. The sandpaper constantly becomes clogged with dust during operation, so you have to constantly clean it. You can buy the material in the store in rolls or cut into pieces. An important indicator for purchasing this product is grain size. You can start work with P100-P180, this is a larger option, and finish with P 220-P280. The abrasive mesh has a perforated structure and most of the dust passes through the holes. It is mounted on special holders; the meshes can be changed at your discretion. Stores sell it already cut into pieces. This tool is convenient to work with, although it costs a little more than sandpaper. Think not only about the material, but also about yourself. The work you want to do with your hands now is very dusty. Therefore you will need: The room must have good lighting, otherwise you will not be able to see defects that require correction. If you do not have practical skills in this process, first try sanding the joint in a small area. This is done in a circular motion. Cover a small area at the same time and control the pressure. If scratches appear on the surface, change the material number to a smaller one or reduce the pressure. After the work is completed, all dust and dirt will need to be removed. When working using this technology, you will end up with alternating layers: putty, serpyanka, putty. This combination is made using approved technology and gives a good effect. The joint is flush with the surface of the sheet and is difficult to determine by touch. Now let's look at how to seal butt joints on gypsum boards using perforated paper tape. In principle, the technology is the same as described above. Having a clean surface and observing the acceptable microclimate in the room, you have to complete the following steps: The first, second and third points are carried out using the same technology as described in the “” section, so the information indicated there will be useful for this type of joint processing. But let’s stop at point four and talk about this material in more detail. This material is a strip of paper on which there are: Perforated paper tape for drywall prevents the appearance of cracks at the joints of the sheets. Its physical and chemical properties are identical to drywall; it reacts to any changes in temperature and humidity in the same way as it does. This means that deformation in seams treated with this material is excluded. Paper tape is presented to the consumer in rolls, width 52 mm, sold in lengths of 50, 76 and 153 m. An environmentally friendly material, which is produced on the basis of cellulose. It is made of especially strong paper reinforced with fiberglass in the longitudinal and transverse directions. Its surface is slightly rough to the touch. This helps with better adhesion to the putty. The internal structure with microscopic holes prevents the formation of air inclusions during operation. If you tear off a small piece of paper tape, you can see how long the fibers are. This means that it can withstand a high tensile load. However, it is worth considering that the tape should fit fairly tightly on the layer of putty to the seam, without bends or bubbles. Therefore, the putty solution should not be thick at all. You can also avoid the appearance of bubbles using micro-perforated tape. According to the technology, tape should be applied to the joints with cut edges, which has been previously moistened in water. The process is more labor-intensive than with serpyanka; the installation method differs from the mentioned technology and has some nuances. The tape itself is not self-adhesive, which means it is applied to a layer of putty. First soak the measured pieces in boiling water for about five minutes. Take one out and squeeze out excess water. To do this, the material must be passed between the thumb and forefinger of either hand, thereby removing excess moisture from it. Adjust the tape to the center of the joint and, in a taut position, lightly press it into the putty. Adjacent ends should overlap. Carefully use a spatula to go along the tape - from the center to both ends alternately. Apply some force to ensure proper adhesion, but be careful not to overdo it as you might squeeze the putty layer out from under the tape. A layer of 1.5-2 mm should remain under its middle part, and 0.8 mm under the edges. Now you can use a spatula to remove excess mortar along the longitudinal edges. Then you need to wait until the joints dry, putty them a second time and leave them again for 8-12 hours. Do not forget - the necessary microclimate must be maintained in the room. After the seams have dried, you need to sand their surface. How to do this and with what is described in the “” section, in the “” subsection. The work described above is, of course, labor-intensive, and a certain amount of the family budget has to be spent on it. But nothing can be done. After all, puttying drywall joints is just as necessary as a metal profile and its high-quality installation. Having forgotten to putty the seam or decided to save money at this preparatory stage, one day you will find a small crack in your apartment that will increase in size. No matter how rigidly the frame is installed and the sheets are securely fastened, under the influence of vibrations and unexpected shocks, the gypsum board joints will “play.” Which will certainly lead to their cracking and loss of dried putty, since the owner did not use reinforcing tape. Violation of any of the existing technologies leads to poor quality work, and subsequently to a shorter service life of all materials involved. Which is fraught with additional costs of money and time. When installing masonry with thin mortar joints, mesh reinforcement made of corrosion-resistant or corrosion-protected steels, as well as composite materials, is used. Regulatory requirements for metal mesh reinforcement are determined by SP 15.13330.2010 (updated edition of SNiP II-22-11) and Eurocode 6. The purpose of reinforcing masonry is to absorb the tensile stresses that arise in it, “unload” the latter and “smooth out” deformations in areas of stress concentration. The role of reinforcement especially increases when switching to masonry with thin mortar joints. This became possible thanks to the technology of manufacturing ceramic, silicate and foam concrete blocks with high precision sizes and shapes. Such masonry is less labor-intensive to construct, requires significantly less mortar consumption, and is more heat-resistant due to the absence of cold bridges in the form of vertical and horizontal mortar joints. In terms of their homogeneity, they are close to monolithic unreinforced concrete walls and, therefore, have reduced crack resistance. Experience in the operation of buildings shows that masonry with thin-layer joints is very sensitive to temperature and shrinkage deformations, local loads, uneven settlements of foundations, as well as dynamic impacts of a technological nature or from driving vehicles and seismic impacts. Recently, the issue of increasing the crack resistance of non-load-bearing stone partitions erected on reinforced concrete floors has become relevant. Due to the deflections of the latter from the action of the payload and the creep of concrete, the partitions operate under their own weight as transversely bent beam-walls supported at the end sections. In this case, vertical cracks appear in the middle lower sections of the partitions, and oblique cracks appear in the end sections. To absorb the tensile stresses arising in the lower zone of the partitions, they are reinforced with meshes, which are laid in horizontal joints of the masonry. Due to the tightening of regulatory requirements for heat transfer resistance since the mid-1990s. In the CIS countries, layered walls with a facing brick layer are widely used. The operation of layered walls, especially in multi-storey frame-monolithic housing construction, revealed a number of serious shortcomings, which in many cases led to the emergency condition of the wall fence due to cracking in the facing layer. One of the main reasons for the occurrence of cracks, as noted in the work of M.K. Ishchuk, is temperature effects, which cause significant horizontal tensile stresses in the masonry of the facing layer. SP 15.13330.2010 (updated edition of SNiP II-22-11 “Stone and reinforced masonry structures”) introduces requirements for mesh reinforcement of masonry floor-supported walls with flexible connections, including the facing layer. It is indicated that meshes should be designed from corrosion-resistant steels or steels protected from corrosion; It is possible to use meshes made of composite polymer materials. The thickness of the anti-corrosion coating of metal mesh must comply with the requirements of SNiP 2.03.11-85 “Protection of building structures from corrosion”. There are no requirements for meshes made of composite polymer materials in SP 15.13330.2010. Eurocode 6 (EC 6) establishes requirements only for metal reinforcement made of ordinary or stainless steel, and does not apply to the recently widely used reinforcement of masonry structures with composite materials. The steel used for masonry reinforcement is assigned depending on the class of environment in which the structure is operated, on the material in which the reinforcement product is laid (mortar, concrete), and on the minimum thickness of the protective layer of concrete. Reinforcement of horizontal mortar joints in masonry is used to solve the following problems: Unlike SP 15.13330.2010, Eurocode 6 does not contain instructions for the calculation of compressed elements of masonry structures reinforced in horizontal masonry joints. According to the principles of Eurocode 6, reinforcing mesh is used to reinforce horizontal joints in masonry, the requirements for which are established in EN 845-3: Rice. 1. Examples of reinforcing products used for reinforcing horizontal joints in masonry: Unlike reinforcing bars, the requirements for which are set out in Eurocode 2, the reinforcing products shown in Fig. 1, are characterized by certain parameters set in accordance with the requirements of the EN 846 standard block. These parameters include: Standard EN 845-3:2002 prohibits the use of the products shown in Fig. 1, as flexible anchors connecting masonry layers through an air gap. If the reinforcement product is used for structural reinforcement, then it can correspond to any type of mesh shown in Figure 1. In this case, the diameter of the longitudinal rods of welded or woven steel mesh must be at least 1.25 mm, and the number of turns of transverse wire around the longitudinal rods in steel woven mesh - at least 1.5. According to SP 15.13330.2010, the minimum value of reinforcement with mesh reinforcement for compressed pillars and piers is 0.1%, and for non-load-bearing multilayer walls with flexible connections and facing layers of masonry ≈ 0.05%. The protective layer of the solution should not only protect the reinforcement from corrosion, but also ensure its sufficient adhesion. Eurocode 6 states that the thickness of the protective layer of mortar, i.e. the distance between the reinforcement and the surface of the masonry, must be at least 15 mm. In this case, the thickness of the protective layer above and below the reinforcement is taken such that the thickness of the seam exceeds the diameter of the reinforcement by at least 5 mm (Fig. 2). Rice. 2. Protective layer of mortar according to the principles of Eurocode 6. Rice. 3. Protective layer of mortar for thin-layer joints According to EN 845-3, materials for the manufacture of reinforcing mesh (Fig. 1 a, b, c) and their protective coatings should be taken in accordance with Table 1. At the same time, combining stainless steel elements with elements from other types of steel in one product is not allowed . Table 1. Materials and corrosion protection system for reinforcement products for horizontal masonry joints To manufacture expanded metal mesh (Fig. 1d), it is necessary to use one of the sheet steel materials indicated in Table 2. Table 2. Characteristics of steel sheet material for the manufacture of expanded metal mesh Unlike SP 15.13330.2010, Eurocode 6 contains detailed requirements regarding anti-corrosion protection of reinforcement products. In accordance with these requirements, when designing masonry structures, the conditions in which the structure will be located during operation must be taken into account. These conditions are divided into classes (Table 3). Table 3. Classification of microconditions affecting the completed masonry structure according to environmental classes Table 3 shows the protection systems for reinforcement products depending on environmental classes. As follows from the table, reinforcement of the masonry of external walls exposed to dampness or humidity should preferably be made of stainless steel mesh or zinc-coated (60 g/m2) steel wire with an organic coating applied to all external surfaces of the finished product. Note that in Eurocode 6, as well as in SP 15.13330.2010, there are no instructions on the reinforcement of thin-layer masonry joints. Such instructions can be found from manufacturers of reinforcement products intended for thin-layer masonry joints. Figure 3 shows an example of placing reinforcement mesh in thin-layer joints according to BEKAERT recommendations. If we sum up the parameters of the protective layers shown in the figure and the diameter of the reinforcement, then the thickness of the thin-layer seam will be 3.5 mm. Table 4. Corrosion protection systems for reinforcement of horizontal joints, complying with EN 845-3, relative to the environmental class according to operating conditions In Eurocode 6, the maximum thickness of thin-layer joints is 3 mm, which is 0.5 mm less than the recommended one. Therefore, in many CEN member countries, reinforced masonry with thin-layer joints is not used. At the same time, studies show that reinforcement of thin-layer joints increases not only crack resistance, but also the strength of masonry. Therefore, issues related to the requirements for reinforcement of thin-layer joints are currently under consideration by the CIB W23 Wall structures CEN/TC250/SC6 commission (their introduction is expected in the next version of Eurocode 6). Literature Paper tape is sold in rolls 52 mm wide, 50.76 m or 153 m long. Among the brands that are well-known are Sheetrock, Knauf, NextBuild. Serpyanka is self-adhesive. Now let’s look at how to work with each type of tape. Method of sealing joints using serpyanka.
It is recommended to reinforce longitudinal joints of plasterboard with a thinned edge with self-adhesive serpyanka (mesh). It is easier to use and requires less working time. Plus, you don't have to worry about air bubbles or peeling (which can sometimes happen when using paper tape).
Method of sealing joints using paper tape.
As mentioned earlier, fiberglass mesh works well at the longitudinal joints of gypsum board sheets with a thinned edge. But it is not strong enough to reinforce transverse joints. Such places require special strength and only paper tape can reduce the risk of cracking here (the main problem of joints). Unlike fiberglass mesh, paper tape creates an extremely strong seam when used with any type of joint compound. However, the installation procedure for paper tape differs from the technology for installing fiberglass mesh and has some subtleties. Further work is the same for both options. And finally, a quote: «
Multiple strength tests of reinforced joints showed that joints finished with conventional fiberglass mesh (serpyanka) and conventional joint putty are more prone to cracking than joints finished with paper tape and a similar putty. This happens because fiberglass mesh (serpyanka) tends to stretch under load, even when covered with putty. Major renovation such cracks are difficult to form. Therefore, it is not recommended to use regular fiberglass mesh to finish drywall joints in most cases.” Paper tape is the most “ancient” and traditional material for reinforcing plasterboard joints, recommended by gypsum board manufacturers and at the same time the most reliable and still unsurpassed in strength. Sealing seams with serpyanka
Primer of joints
Seam putty
Processing the joint with fiberglass mesh
Second layer of putty
Sanding drywall joints
Sealing drywall seams with perforated paper tape
Processing the joint with perforated paper tape
The need to perform these works
a) increasing the load-bearing capacity of stone structures:
- elements that bend in their plane (lintels, beams-walls),
- elements bent out of plane (external walls, retaining walls),
- elements subject to shear forces (stiffening diaphragms);
b) anchoring layers of masonry or connecting transverse and longitudinal walls;
c) increasing the crack resistance of masonry under impacts caused by temperature, shrinkage or swelling of masonry materials;
d) preventing the formation of cracks or limiting the width of their opening in areas of stress concentration (corners of window or door openings, walls or partitions supported by flexible floor discs, areas of concentrated load transmission, etc.).
- welded mesh made of steel wire, consisting of longitudinal rods welded to transverse rods (lattice type mesh, Fig. 1 a) or with continuously angled rods (zigzag mesh, Fig. 1 b);
- woven steel mesh, made by alternately wrapping transverse wire rods around longitudinal rods (Fig. 1c);
- expanded metal mesh, obtained by drawing sheet steel, in which slots are previously made in a certain order (Fig. 1d).
a), b) welded mesh, c) woven mesh, d) expanded metal mesh
- adhesion strength of mesh to masonry mortar (EN 846-2),
- shear strength of welded joints (EN 846-2).
If the horizontal seams of masonry are reinforced in order to increase the load-bearing capacity of the structure, then in this case reinforcement products are used, which are welded meshes of steel rods (Fig. 1 a or Fig. 1 b). The diameter of the longitudinal rods in the meshes must be at least 3 mm.
Eurocode 6 establishes the following values for the minimum percentages of reinforcement in horizontal masonry joints:
- = 0.0005 effective cross-sectional area of the masonry, if the purpose of the reinforcement is to increase its load-bearing capacity;
- = 0.0003 of the total cross-sectional area of the wall (i.e. 0.00015 along the stretched and compressed edges), if the purpose of the reinforcement is to increase the load-bearing capacity of the wall under horizontal loads;
- = 0.0003 total wall area, if reinforcement is installed to prevent the formation of cracks or limit their width, as well as increase the distance between expansion joints;
- = 0.0005 cross-sectional area of a two-layer wall with the intermediate space between the layers filled (mortar or concrete), if the reinforcement is structural, installed perpendicular to the main reinforcement; the cross-sectional area of the wall is determined as the product of the total width of the wall and the effective height;
- = 0.0005 cross-sectional area of the wall, defined as the product of the width of the wall section and the effective height, if the reinforcement is located in structural elements in which the installation of shear reinforcement is required.
SP 15.13330.2010 states that the width of masonry joints in reinforced masonry structures should be no more than 15 mm, but exceed the diameter of the reinforcement by at least 4 mm.
1. Derkach V. N. “On the morphology of cracks that occur in the internal partitions of modern buildings.” — Bulletin of Brest State Technical University: “Construction and Architecture”, No. 1, 2010.
2. Orlovich R. B., Derkach V. N. “Foreign experience in the reinforcement of stone structures.” // “Housing Construction”, No. 11, 2011
3. Ishchuk M.K. “Domestic experience in the construction of buildings with external walls made of lightweight masonry.” - M.: RIF "Building Materials". 2009
4. Derkach V. N. “Reinforcing products for reinforcing horizontal joints of masonry.” // “Technical regulation, standardization and certification in construction”, No. 3, 2012.
5. BEKAERT Design manual.
6. Kubica J. Murowe konsrukcje zbrojone - podstawy projekto-wania. XXVI Ogolnopolskie warsztaty Pracy proektanta konstrukcji. — Szczyrk, 2011.
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Topic of the article: What can be used to reinforce the joints of sheet materials
(reinforcing tape plus putty for finishing joints) should ensure the strength of the joint is the same as the plasterboard panel itself. Otherwise, normal deformations in the structure of walls or ceilings can cause cracks to appear at the joints of plasterboard panels. Thus, the quality of work on sealing gypsum board joints largely depends on the choice of reinforcing tape and putty.
In this review, we will not consider various putty options, but will focus on tape. In the practice of dry construction in recent years, two main types of tape have been used for sealing flat joints: self-adhesive construction serpyanka (
mesh) and perforated paper tape. Accordingly, the question arises: what is the difference and what to prefer? First, let's look at each one separately.
The paper tape is made of special high-strength paper reinforced with fiberglass in the longitudinal and transverse directions. Its surface is slightly rough for better adhesion to the putty. The tape has a small depressed fold in the center, which makes it easy to use for finishing interior corners. The paper tape effectively resists stretching and creasing.
The disadvantages of paper tape include a slightly more labor-intensive installation process compared to serpyanka and (if the worker is insufficiently qualified) a tendency to form air bubbles with a small amount of putty under the tape (more on this below). To avoid bubbles, it is better to use a tape with micro-perforation, which reduces the likelihood of bubbles and at the same time does not affect the strength characteristics of the tape.
Serpyanka is sold in rolls 45 and 50 mm wide, 20, 45 and 90 m long. Usually used for finishing joints plasterboard sheets with a thinned edge, and also for sealing cracks and small holes. There are a lot brands, which are characterized by tensile strength. Meshes are also divided into two types: self-adhesive and non-self-adhesive. The latter is less expensive, but more labor-intensive (requires fastening with paper clips).
One important detail: When using self-adhesive tape, the started roll must always be stored in plastic packaging to prevent the adhesive layer from drying out.
For obvious reasons, fiberglass tape, unlike paper tape, is not recommended for reinforcing internal corners.
The disadvantages of this method are (attention !) lower strength of serpyanka compared to paper tape, as well as the need to select suitable type putty for application.
When using serpyanka, it is recommended to first mount it on all joints of the room, pressing the mesh tightly to the previously dust-free surface to avoid the formation of wrinkles. Then you need to apply putty over and deep into the mesh with a spatula along the entire length of the mesh, preferably in a thin and uniform layer
Since paper tape is not self-adhesive, first you need to apply a thin and relatively uniform layer of putty to the joint to adhere the tape. At the same time, there is no need to try to cover all the joints of the room with putty at once, since it may begin to dry out before you reach the last joint with the tape. And this, in turn, will lead to complications in the work process and the formation of air bubbles under the tape. 
It is recommended to finish the joints one by one, especially in the absence of sufficient skills and, accordingly, low speed of work. Then you need to adjust the tape in the center of the joint and, holding it taut, lightly press it into the putty, while the ends of the tape should overlap. After this, use a spatula to “stretch” the glued tape.
This is usually done from the center of the joint and alternately to both ends. It is important to apply enough pressure to ensure proper adhesion of the tape, but it should be such that only excess putty is squeezed out and leaves a layer of 1.5-2.0 mm thick under the middle part of the tape and approximately 0.8 mm under the edges. There is no need to try to squeeze out as much putty as possible - the tape will have nothing to stick to. After the tape is glued evenly, tightly and without wrinkles, you need to remove excess putty along the longitudinal edges of the tape with a spatula.
So ,
summary
Choosing the most reliable reinforcing system is especially important for climates with large seasonal differences in temperature and humidity. preventive measure against cracking.
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