Calculations and recalculations on the vapor permeability of windproof membranes. Vapor permeability of walls - getting rid of fiction Estimated vapor permeability coefficient

The concept of "breathing walls" is considered a positive characteristic of the materials from which they are made. But few people think about the reasons that allow this breathing. Materials capable of passing both air and steam are vapor-permeable.

A good example of building materials with high vapor permeability:

• wood;
• expanded clay slabs;
• foam concrete.

Concrete or brick walls are less permeable to steam than wood or expanded clay.

Sources of steam indoors

Human breathing, cooking, water vapor from the bathroom and many other sources of steam in the absence of an exhaust device create a high level of humidity indoors. You can often observe the formation of perspiration on window panes in winter, or on cold water pipes. These are examples of the formation of water vapor inside the house.

What is vapor permeability

The design and construction rules give the following definition of the term: the vapor permeability of materials is the ability to pass through moisture droplets contained in the air due to different partial vapor pressures from opposite sides at the same air pressure values. It is also defined as the density of the steam flow passing through a certain thickness of the material.

The table, which has a vapor permeability coefficient, compiled for building materials, is conditional, since the specified calculated values ​​\u200b\u200bof humidity and atmospheric conditions do not always correspond to real conditions. The dew point can be calculated based on approximate data.

Wall construction taking into account vapor permeability

Even if the walls are built from a material with high vapor permeability, this cannot be a guarantee that it will not turn into water in the thickness of the wall. To prevent this from happening, it is necessary to protect the material from the difference in partial vapor pressure from inside and outside. Protection against the formation of steam condensate is carried out using OSB boards, insulating materials such as foam and vapor-tight films or membranes that prevent steam from penetrating into the insulation.

The walls are insulated in such a way that a layer of insulation is located closer to the outer edge, incapable of forming moisture condensation, pushing the dew point (water formation) away. In parallel with the protective layers in the roofing cake, it is necessary to ensure the correct ventilation gap.

The destructive action of steam

If the wall cake has a weak ability to absorb steam, it is not in danger of destruction due to the expansion of moisture from frost. The main condition is to prevent the accumulation of moisture in the thickness of the wall, but to ensure its free passage and weathering. It is equally important to arrange a forced extraction of excess moisture and steam from the room, to connect a powerful ventilation system. By observing the above conditions, you can protect the walls from cracking, and increase the life of the whole house. The constant passage of moisture through building materials accelerates their destruction.

Use of conductive qualities

Taking into account the peculiarities of the operation of buildings, the following principle of insulation is applied: the most steam-conducting insulation materials are located outside. Due to this arrangement of layers, the likelihood of water accumulation when the temperature drops outside is reduced. To prevent the walls from getting wet from the inside, the inner layer is insulated with a material having low vapor permeability, for example, a thick layer of extruded polystyrene foam.

The opposite method of using the steam-conducting effects of building materials is successfully applied. It consists in the fact that a brick wall is covered with a vapor barrier layer of foam glass, which interrupts the moving flow of steam from the house to the street during low temperatures. The brick begins to accumulate humidity in the rooms, creating a pleasant indoor climate thanks to a reliable vapor barrier.

Compliance with the basic principle when building walls

Walls should be characterized by a minimum ability to conduct steam and heat, but at the same time be heat-retaining and heat-resistant. When using one type of material, the desired effects cannot be achieved. The outer wall part is obliged to retain cold masses and prevent their impact on internal heat-intensive materials that maintain a comfortable thermal regime inside the room.

Reinforced concrete is ideal for the inner layer, its heat capacity, density and strength have maximum performance. Concrete successfully smooths out the difference between night and day temperature changes.

When carrying out construction work, wall cakes are made taking into account the basic principle: the vapor permeability of each layer should increase in the direction from the inner layers to the outer ones.

Rules for the location of vapor barrier layers

To ensure the best performance of multilayer structures of buildings, the rule is applied: on the side with a higher temperature, materials with increased resistance to steam penetration with increased thermal conductivity are placed. The layers located outside must have a high vapor conductivity. For the normal functioning of the building envelope, it is necessary that the coefficient of the outer layer is five times higher than the indicator of the layer located inside.

When this rule is followed, it will not be difficult for water vapor that has entered the warm layer of the wall to quickly escape through more porous materials.

If this condition is not observed, the inner layers of building materials lock up and become more heat-conducting.

Familiarity with the table of vapor permeability of materials

When designing a house, the characteristics of building materials are taken into account. The Code of Practice contains a table with information on what vapor permeability coefficient building materials have under conditions of normal atmospheric pressure and average air temperature.

Material	Vapor permeability coefficient mg/(m h Pa)
extruded polystyrene foam
polyurethane foam
mineral wool
reinforced concrete, concrete
pine or spruce
expanded clay
foam concrete, aerated concrete
granite, marble
drywall
chipboard, OSB, fiberboard
foam glass
ruberoid
polyethylene
linoleum

The table refutes erroneous ideas about breathing walls. The amount of steam escaping through the walls is negligible. The main steam is removed with air currents during ventilation or with the help of ventilation.

The importance of the material vapor permeability table

The vapor permeability coefficient is an important parameter that is used to calculate the thickness of the layer of insulation materials. The quality of the insulation of the entire structure depends on the correctness of the results obtained.

Sergey Novozhilov is an expert in roofing materials with 9 years of practical experience in the field of engineering solutions in construction.

1. Only a heater with the lowest coefficient of thermal conductivity can minimize the selection of internal space

2. Unfortunately, we lose the storage heat capacity of the outer wall array forever. But there is a win here:

A) there is no need to spend energy on heating these walls

B) when you turn on even the smallest heater in the room, it will almost immediately become warm.

3. At the junction of the wall and the ceiling, "cold bridges" can be removed if the insulation is applied partially on the floor slabs with subsequent decoration of these junctions.

4. If you still believe in the "breathing of the walls", then please read THIS article. If not, then there is an obvious conclusion: the heat-insulating material must be pressed very tightly against the wall. It is even better if the insulation becomes one with the wall. Those. there will be no gaps and cracks between the insulation and the wall. Thus, the moisture from the room will not be able to get into the dew point zone. The wall will always remain dry. Seasonal temperature fluctuations without moisture access will not adversely affect the walls, which will increase their durability.

All these tasks can be solved only by sprayed polyurethane foam.

Possessing the lowest coefficient of thermal conductivity of all existing thermal insulation materials, polyurethane foam will take up a minimum of internal space.

The ability of polyurethane foam to adhere reliably to any surface makes it easy to apply it to the ceiling to reduce "cold bridges".

When applied to walls, polyurethane foam, being in a liquid state for some time, fills all the cracks and microcavities. Foaming and polymerizing directly at the point of application, polyurethane foam becomes one with the wall, blocking access to destructive moisture.

VAPOR PERMEABILITY OF WALLS
Supporters of the false concept of “healthy breathing of the walls”, in addition to sinning against the truth of physical laws and deliberately misleading designers, builders and consumers, based on a mercantile urge to sell their goods by any means, slander and slander thermal insulation materials with low vapor permeability (polyurethane foam) or heat-insulating material and completely vapor-tight (foam glass).

The essence of this malicious insinuation boils down to the following. It seems like if there is no notorious “healthy breathing of the walls”, then in this case the interior will definitely become damp, and the walls will ooze moisture. In order to debunk this fiction, let's take a closer look at the physical processes that will occur in the case of lining under the plaster layer or using inside the masonry, for example, a material such as foam glass, the vapor permeability of which is zero.

So, due to the heat-insulating and sealing properties inherent in foam glass, the outer layer of plaster or masonry will come into an equilibrium temperature and humidity state with the outside atmosphere. Also, the inner layer of masonry will enter into a certain balance with the microclimate of the interior. Water diffusion processes, both in the outer layer of the wall and in the inner one; will have the character of a harmonic function. This function will be determined, for the outer layer, by diurnal changes in temperature and humidity, as well as seasonal changes.

Particularly interesting in this respect is the behavior of the inner layer of the wall. In fact, the inside of the wall will act as an inertial buffer, the role of which is to smooth out sudden changes in humidity in the room. In the event of a sharp humidification of the room, the inner part of the wall will adsorb the excess moisture contained in the air, preventing the air humidity from reaching the limit value. At the same time, in the absence of moisture release into the air in the room, the inner part of the wall begins to dry out, preventing the air from “drying out” and becoming like a desert one.

As a favorable result of such an insulation system using polyurethane foam, the harmonics of fluctuations in air humidity in the room are smoothed out and thus guarantee a stable value (with minor fluctuations) of humidity acceptable for a healthy microclimate. The physics of this process has been studied quite well by the developed construction and architectural schools of the world, and in order to achieve a similar effect when using fiber inorganic materials as a heater in closed insulation systems, it is highly recommended to have a reliable vapor-permeable layer on the inside of the insulation system. So much for "healthy breathing walls"!

There is a legend about the "breathing wall", and legends about the "healthy breathing of the cinder block, which creates a unique atmosphere in the house." In fact, the vapor permeability of the wall is not large, the amount of steam passing through it is insignificant, and much less than the amount of steam carried by air when it is exchanged in the room.

Vapor permeability is one of the most important parameters used in the calculation of insulation. We can say that the vapor permeability of materials determines the entire design of insulation.

What is vapor permeability

The movement of steam through the wall occurs with a difference in partial pressure on the sides of the wall (different humidity). In this case, there may not be a difference in atmospheric pressure.

Vapor permeability - the ability of a material to pass steam through itself. According to the domestic classification, it is determined by the vapor permeability coefficient m, mg / (m * h * Pa).

The resistance of a layer of material will depend on its thickness.
It is determined by dividing the thickness by the vapor permeability coefficient. It is measured in (m sq. * hour * Pa) / mg.

For example, the vapor permeability coefficient of brickwork is taken as 0.11 mg / (m * h * Pa). With a brick wall thickness of 0.36 m, its resistance to steam movement will be 0.36 / 0.11 = 3.3 (m sq. * h * Pa) / mg.

What is the vapor permeability of building materials

Below are the values ​​​​of the coefficient of vapor permeability for several building materials (according to the regulatory document), which are most widely used, mg / (m * h * Pa).
Bitumen 0.008
Heavy concrete 0.03
Autoclaved aerated concrete 0.12
Expanded clay concrete 0.075 - 0.09
Slag concrete 0.075 - 0.14
Burnt clay (brick) 0.11 - 0.15 (in the form of masonry on cement mortar)
Lime mortar 0.12
Drywall, gypsum 0.075
Cement-sand plaster 0.09
Limestone (depending on density) 0.06 - 0.11
Metals 0
Chipboard 0.12 0.24
Linoleum 0.002
Polyfoam 0.05-0.23
Polyurethane hard, polyurethane foam
0,05
Mineral wool 0.3-0.6
Foam glass 0.02 -0.03
Vermiculite 0.23 - 0.3
Expanded clay 0.21-0.26
Wood across the fibers 0.06
Wood along the fibers 0.32
Brickwork from silicate bricks on cement mortar 0.11

Data on the vapor permeability of the layers must be taken into account when designing any insulation.

How to design insulation - according to vapor barrier qualities

The basic rule of insulation is that the vapor transparency of the layers should increase outward. Then in the cold season, with a greater probability, there will be no accumulation of water in the layers, when condensation occurs at the dew point.

The basic principle helps to decide in any cases. Even when everything is "turned upside down" - they insulate from the inside, despite the insistent recommendations to make insulation only from the outside.

In order to avoid a catastrophe with wetting the walls, it is enough to remember that the inner layer should most stubbornly resist steam, and based on this, for internal insulation, use extruded polystyrene foam with a thick layer - a material with very low vapor permeability.

Or do not forget to use even more “airy” mineral wool for a very “breathing” aerated concrete from the outside.

Separation of layers with a vapor barrier

Another option for applying the principle of vapor transparency of materials in a multilayer structure is the separation of the most significant layers by a vapor barrier. Or the use of a significant layer, which is an absolute vapor barrier.

For example, - insulation of a brick wall with foam glass. It would seem that this contradicts the above principle, because it is possible to accumulate moisture in a brick?

But this does not happen, due to the fact that the directional movement of steam is completely interrupted (at sub-zero temperatures from the room to the outside). After all, foam glass is a complete vapor barrier or close to it.

Therefore, in this case, the brick will enter into an equilibrium state with the internal atmosphere of the house, and will serve as an accumulator of humidity during its sharp jumps inside the room, making the internal climate more pleasant.

The principle of separation of layers is also used when using mineral wool - a heater that is especially dangerous for moisture accumulation. For example, in a three-layer construction, when mineral wool is inside a wall without ventilation, it is recommended to put a vapor barrier under the wool, and thus leave it in the outside atmosphere.

International classification of vapor barrier qualities of materials

The international classification of materials for vapor barrier properties differs from the domestic one.

According to the international standard ISO/FDIS 10456:2007(E), materials are characterized by a coefficient of resistance to steam movement. This coefficient indicates how many times more the material resists the movement of steam compared to air. Those. for air, the coefficient of resistance to steam movement is 1, and for extruded polystyrene foam it is already 150, i.e. Styrofoam is 150 times less vapor permeable than air.

Also in international standards it is customary to determine the vapor permeability for dry and moist materials. The boundary between the concepts of “dry” and “moistened” is the internal moisture content of the material of 70%.
Below are the values ​​of the coefficient of resistance to steam movement for various materials according to international standards.

Steam resistance coefficient

First, data are given for dry material, and separated by commas for moist (more than 70% moisture).
Air 1, 1
Bitumen 50,000, 50,000
Plastics, rubber, silicone — >5,000, >5,000
Heavy concrete 130, 80
Medium density concrete 100, 60
Polystyrene concrete 120, 60
Autoclaved aerated concrete 10, 6
Lightweight concrete 15, 10
Artificial stone 150, 120
Expanded clay concrete 6-8, 4
Slag concrete 30, 20
Burnt clay (brick) 16, 10
Lime mortar 20, 10
Drywall, plaster 10, 4
Gypsum plaster 10, 6
Cement-sand plaster 10, 6
Clay, sand, gravel 50, 50
Sandstone 40, 30
Limestone (depending on density) 30-250, 20-200
Ceramic tile?, ?
Metals?
OSB-2 (DIN 52612) 50, 30
OSB-3 (DIN 52612) 107, 64
OSB-4 (DIN 52612) 300, 135
Chipboard 50, 10-20
Linoleum 1000, 800
Substrate for plastic laminate 10 000, 10 000
Substrate for laminate cork 20, 10
Polyfoam 60, 60
EPPS 150, 150
Polyurethane hard, polyurethane foam 50, 50
Mineral wool 1, 1
Foam glass?, ?
Perlite panels 5, 5
Perlite 2, 2
Vermiculite 3, 2
Ecowool 2, 2
Expanded clay 2, 2
Wood across grain 50-200, 20-50

It should be noted that the data on the resistance to the movement of steam here and "there" are very different. For example, foam glass is standardized in our country, and the international standard says that it is an absolute vapor barrier.

Where did the legend of the breathing wall come from?

A lot of companies produce mineral wool. This is the most vapor-permeable insulation. According to international standards, its vapor permeability resistance coefficient (not to be confused with the domestic vapor permeability coefficient) is 1.0. Those. in fact, mineral wool does not differ in this respect from air.

Indeed, it is a "breathing" insulation. To sell mineral wool as much as possible, you need a beautiful fairy tale. For example, that if you insulate a brick wall from the outside with mineral wool, then it will not lose anything in terms of vapor permeability. And this is absolutely true!

The insidious lie is hidden in the fact that through brick walls 36 centimeters thick, with a humidity difference of 20% (outside 50%, in the house - 70%), about a liter of water will come out of the house per day. While with air exchange, about 10 times more should come out so that the humidity in the house does not increase.

And if the wall is insulated from the outside or from the inside, for example, with a layer of paint, vinyl wallpaper, dense cement plaster (which, in general, is “the most common thing”), then the vapor permeability of the wall will decrease several times, and with complete insulation - tens and hundreds of times .

Therefore, it will always be absolutely the same for a brick wall and for households - whether the house is covered with mineral wool with “raging breath”, or “dull-sniffing” foam plastic.

When making decisions on the insulation of houses and apartments, it is worth proceeding from the basic principle - the outer layer should be more vapor-permeable, preferably at times.

If for some reason it is not possible to withstand this, then it is possible to separate the layers with a continuous vapor barrier (use a completely vapor-tight layer) and stop the movement of steam in the structure, which will lead to a state of dynamic equilibrium of the layers with the environment in which they will be located.

The concept of "breathing walls" is considered a positive characteristic of the materials from which they are made. But few people think about the reasons that allow this breathing. Materials capable of passing both air and steam are vapor-permeable.

A good example of building materials with high vapor permeability:

• wood;
• expanded clay slabs;
• foam concrete.

Concrete or brick walls are less permeable to steam than wood or expanded clay.

Sources of steam indoors

Human breathing, cooking, water vapor from the bathroom and many other sources of steam in the absence of an exhaust device create a high level of humidity indoors. You can often observe the formation of perspiration on window panes in winter, or on cold water pipes. These are examples of the formation of water vapor inside the house.

What is vapor permeability

The design and construction rules give the following definition of the term: the vapor permeability of materials is the ability to pass through moisture droplets contained in the air due to different partial vapor pressures from opposite sides at the same air pressure values. It is also defined as the density of the steam flow passing through a certain thickness of the material.

The table, which has a vapor permeability coefficient, compiled for building materials, is conditional, since the specified calculated values ​​\u200b\u200bof humidity and atmospheric conditions do not always correspond to real conditions. The dew point can be calculated based on approximate data.

Wall construction taking into account vapor permeability

Even if the walls are built from a material with high vapor permeability, this cannot be a guarantee that it will not turn into water in the thickness of the wall. To prevent this from happening, it is necessary to protect the material from the difference in partial vapor pressure from inside and outside. Protection against the formation of steam condensate is carried out using OSB boards, insulating materials such as foam and vapor-tight films or membranes that prevent steam from penetrating into the insulation.

The walls are insulated in such a way that a layer of insulation is located closer to the outer edge, incapable of forming moisture condensation, pushing the dew point (water formation) away. In parallel with the protective layers in the roofing cake, it is necessary to ensure the correct ventilation gap.

The destructive action of steam

If the wall cake has a weak ability to absorb steam, it is not in danger of destruction due to the expansion of moisture from frost. The main condition is to prevent the accumulation of moisture in the thickness of the wall, but to ensure its free passage and weathering. It is equally important to arrange a forced extraction of excess moisture and steam from the room, to connect a powerful ventilation system. By observing the above conditions, you can protect the walls from cracking, and increase the life of the whole house. The constant passage of moisture through building materials accelerates their destruction.

Use of conductive qualities

Taking into account the peculiarities of the operation of buildings, the following principle of insulation is applied: the most steam-conducting insulation materials are located outside. Due to this arrangement of layers, the likelihood of water accumulation when the temperature drops outside is reduced. To prevent the walls from getting wet from the inside, the inner layer is insulated with a material having low vapor permeability, for example, a thick layer of extruded polystyrene foam.

The opposite method of using the steam-conducting effects of building materials is successfully applied. It consists in the fact that a brick wall is covered with a vapor barrier layer of foam glass, which interrupts the moving flow of steam from the house to the street during low temperatures. The brick begins to accumulate humidity in the rooms, creating a pleasant indoor climate thanks to a reliable vapor barrier.

Compliance with the basic principle when building walls

Walls should be characterized by a minimum ability to conduct steam and heat, but at the same time be heat-retaining and heat-resistant. When using one type of material, the desired effects cannot be achieved. The outer wall part is obliged to retain cold masses and prevent their impact on internal heat-intensive materials that maintain a comfortable thermal regime inside the room.

Reinforced concrete is ideal for the inner layer, its heat capacity, density and strength have maximum performance. Concrete successfully smooths out the difference between night and day temperature changes.

When carrying out construction work, wall cakes are made taking into account the basic principle: the vapor permeability of each layer should increase in the direction from the inner layers to the outer ones.

Rules for the location of vapor barrier layers

To ensure the best performance of multilayer structures of buildings, the rule is applied: on the side with a higher temperature, materials with increased resistance to steam penetration with increased thermal conductivity are placed. The layers located outside must have a high vapor conductivity. For the normal functioning of the enclosing structure, it is necessary that the coefficient of the outer layer is five times higher than the indicator of the layer located inside.

When this rule is followed, it will not be difficult for water vapor that has entered the warm layer of the wall to quickly escape through more porous materials.

If this condition is not observed, the inner layers of building materials lock up and become more heat-conducting.

Familiarity with the table of vapor permeability of materials

When designing a house, the characteristics of building materials are taken into account. The Code of Practice contains a table with information on what vapor permeability coefficient building materials have under conditions of normal atmospheric pressure and average air temperature.

Material	Vapor permeability coefficient mg/(m h Pa)
extruded polystyrene foam
polyurethane foam
mineral wool
reinforced concrete, concrete
pine or spruce
expanded clay
foam concrete, aerated concrete
granite, marble
drywall
chipboard, OSB, fiberboard
foam glass
ruberoid
polyethylene
linoleum

The table refutes erroneous ideas about breathing walls. The amount of steam escaping through the walls is negligible. The main steam is removed with air currents during ventilation or with the help of ventilation.

The importance of the material vapor permeability table

The vapor permeability coefficient is an important parameter that is used to calculate the thickness of the layer of insulation materials. The quality of the insulation of the entire structure depends on the correctness of the results obtained.

Sergey Novozhilov is an expert in roofing materials with 9 years of practical experience in the field of engineering solutions in construction.

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General information

Movement of water vapor

• foam concrete;
• aerated concrete;
• perlite concrete;
• expanded clay concrete.

aerated concrete

The right finish

Expanded clay concrete

The structure of expanded clay concrete

Polystyrene concrete

rusbetonplus.ru

Vapor permeability of concrete: features of the properties of aerated concrete, expanded clay concrete, polystyrene concrete

Often in construction articles there is an expression - the vapor permeability of concrete walls. It means the ability of the material to pass water vapor, in a popular way - "breathe". This parameter is of great importance, since waste products are constantly formed in the living room, which must be constantly brought out.

In the photo - moisture condensation on building materials

General information

If you do not create normal ventilation in the room, dampness will be created in it, which will lead to the appearance of fungus and mold. Their secretions can be harmful to our health.

Movement of water vapor

On the other hand, vapor permeability affects the ability of the material to accumulate moisture in itself. This is also a bad indicator, since the more it can hold in itself, the higher the likelihood of fungus, putrefactive manifestations, and destruction during freezing.

Improper removal of moisture from the room

Vapor permeability is denoted by the Latin letter μ and is measured in mg / (m * h * Pa). The value shows the amount of water vapor that can pass through the wall material on an area of ​​1 m2 and with a thickness of 1 m in 1 hour, as well as a difference in external and internal pressure of 1 Pa.

High capacity for conducting water vapor in:

• foam concrete;
• aerated concrete;
• perlite concrete;
• expanded clay concrete.

Closes the table - heavy concrete.

Tip: if you need to make a technological channel in the foundation, diamond drilling in concrete will help you.

aerated concrete

1. The use of the material as a building envelope makes it possible to avoid the accumulation of unnecessary moisture inside the walls and preserve its heat-saving properties, which will prevent possible destruction.
2. Any aerated concrete and foam concrete block contains ≈ 60% of air, due to which the vapor permeability of aerated concrete is recognized as good, the walls in this case can "breathe".
3. Water vapor freely seeps through the material, but does not condense in it.

The vapor permeability of aerated concrete, as well as foam concrete, significantly exceeds heavy concrete - for the first 0.18-0.23, for the second - (0.11-0.26), for the third - 0.03 mg / m * h * Pa.

The right finish

I would especially like to emphasize that the structure of the material provides it with effective removal of moisture into the environment, so that even when the material freezes, it does not collapse - it is forced out through open pores. Therefore, when preparing the finishing of aerated concrete walls, this feature should be taken into account and appropriate plasters, putties and paints should be selected.

The instruction strictly regulates that their vapor permeability parameters are not lower than aerated concrete blocks used for construction.

Textured facade vapor-permeable paint for aerated concrete

Tip: do not forget that the vapor permeability parameters depend on the density of aerated concrete and may differ by half.

For example, if you use concrete blocks with a density of D400, their coefficient is 0.23 mg / m h Pa, while for D500 it is already lower - 0.20 mg / m h Pa. In the first case, the numbers indicate that the walls will have a higher "breathing" ability. So when choosing finishing materials for D400 aerated concrete walls, make sure that their vapor permeability coefficient is the same or higher.

Otherwise, this will lead to a deterioration in the removal of moisture from the walls, which will affect the decrease in the comfort level of living in the house. It should also be noted that if you used vapor-permeable paint for aerated concrete for the exterior, and non-vapor-permeable materials for the interior, the steam will simply accumulate inside the room, making it wet.

Expanded clay concrete

The vapor permeability of expanded clay concrete blocks depends on the amount of filler in its composition, namely expanded clay - foamed baked clay. In Europe, such products are called eco- or bioblocks.

Tip: if you can’t cut the expanded clay block with a regular circle and a grinder, use a diamond one. For example, cutting reinforced concrete with diamond wheels makes it possible to quickly solve the problem.

The structure of expanded clay concrete

Polystyrene concrete

The material is another representative of cellular concrete. The vapor permeability of polystyrene concrete is usually equal to that of wood. You can make it with your own hands.

What does the structure of polystyrene concrete look like?

Today, more attention is being paid not only to the thermal properties of wall structures, but also to the comfort of living in the building. In terms of thermal inertness and vapor permeability, polystyrene concrete resembles wooden materials, and heat transfer resistance can be achieved by changing its thickness. Therefore, poured monolithic polystyrene concrete is usually used, which is cheaper than finished slabs.

Conclusion

From the article you learned that building materials have such a parameter as vapor permeability. It makes it possible to remove moisture outside the walls of the building, improving their strength and characteristics. The vapor permeability of foam concrete and aerated concrete, as well as heavy concrete, differs in its performance, which must be taken into account when choosing finishing materials. The video in this article will help you find more information on this topic.

Page 2

During operation, a variety of defects in reinforced concrete structures can occur. At the same time, it is very important to identify problem areas in time, localize and eliminate damage, since a significant part of them tend to expand and aggravate the situation.

Below we will consider the classification of the main defects in the concrete pavement, as well as give a number of tips for its repair.

During the operation of reinforced concrete products, various damages appear on them.

Factors that affect strength

Before analyzing common defects in concrete structures, it is necessary to understand what can be their cause.

Here, the key factor will be the strength of the hardened concrete solution, which is determined by the following parameters:

The closer the composition of the solution to the optimal, the less problems there will be in the operation of the structure.

• Composition of concrete. The higher the brand of cement included in the solution, and the stronger the gravel that was used as a filler, the more resistant the coating or monolithic structure will be. Naturally, when using high-quality concrete, the price of the material increases, therefore, in any case, we need to find a compromise between economy and reliability.

Note! Excessively strong compositions are very difficult to process: for example, to perform the simplest operations, expensive cutting of reinforced concrete with diamond wheels may be required.

That is why you should not overdo it with the selection of materials!

• reinforcement quality. Along with high mechanical strength, concrete is characterized by low elasticity, therefore, when exposed to certain loads (bending, compression), it can crack. To avoid this, steel reinforcement is placed inside the structure. It depends on its configuration and diameter how stable the entire system will be.

For sufficiently strong compositions, diamond drilling of holes in concrete is necessarily used: an ordinary drill “will not take”!

• surface permeability. If the material is characterized by a large number of pores, then sooner or later moisture will penetrate into them, which is one of the most destructive factors. Particularly detrimental to the state of the concrete pavement are temperature drops, at which the liquid freezes, destroying the pores due to an increase in volume.

In principle, it is these factors that are decisive for ensuring the strength of cement. However, even in an ideal situation, sooner or later the coating is damaged, and we have to restore it. What can happen in this case, and how we need to act - we will tell below.

Mechanical damage

Chips and cracks

Identification of deep damages with a flaw detector

The most common defects are mechanical damage. They can arise due to various factors, and are conventionally divided into external and internal. And if a special device is used to determine the internal ones - a concrete flaw detector, then problems on the surface can be seen independently.

The main thing here is to determine the cause of the malfunction and eliminate it promptly. For the convenience of analysis, we structured examples of the most common damage in the form of a table:

Defect
Bumps on the surface	Most often they occur due to shock loads. It is also possible to form potholes in places of prolonged exposure to a significant mass.
chipped	They are formed under mechanical influence on the areas under which there are zones of low density. The configuration is almost identical to potholes, but usually have a shallower depth.
Delamination	Represents the separation of the surface layer of the material from the main mass. Most often it occurs due to poor-quality drying of the material and finishing until the solution is completely hydrated.
mechanical cracks	Occur with prolonged and intense exposure to a large area. Over time, they expand and connect with each other, which can lead to the formation of large potholes.
Bloating	They are formed if the surface layer is compacted until air is completely removed from the mass of the solution. Also, the surface swells when treated with paint or impregnations (silings) of uncured cement.

Photo of a deep crack

As can be seen from the analysis of the causes, the appearance of some of the listed defects could have been avoided. But mechanical cracks, chips and potholes are formed due to the operation of the coating, so they just need to be repaired periodically. Instructions for prevention and repair are given in the next section.

Prevention and repair of defects

To minimize the risk of mechanical damage, first of all, it is necessary to follow the technology for arranging concrete structures.

Of course, this question has many nuances, so we will give only the most important rules:

• Firstly, the class of concrete must correspond to the design loads. Otherwise, saving on materials will lead to the fact that the service life will be reduced significantly, and you will have to spend more effort and money on repairs.
• Secondly, you need to follow the technology of pouring and drying. The solution requires high-quality concrete compaction, and when hydrated, the cement should not lack moisture.
• It is also worth paying attention to the timing: without the use of special modifiers, it is impossible to finish surfaces earlier than 28-30 days after pouring.
• Thirdly, the coating should be protected from excessively intense impacts. Of course, the loads will affect the condition of the concrete, but it is in our power to reduce the harm from them.

Vibrocompaction significantly increases strength

Note! Even a simple restriction of the speed of traffic in problem areas leads to the fact that defects in the asphalt concrete pavement occur much less frequently.

Another important factor is the timeliness of the repair and compliance with its methodology.

Here you need to act according to a single algorithm:

• We clean the damaged area from fragments of the solution that have broken off from the main mass. For small defects, brushes can be used, but large-scale chips and cracks are usually cleaned with compressed air or a sandblaster.
• Using a concrete saw or a perforator, we embroider the damage, deepening it to a durable layer. If we are talking about a crack, then it must not only be deepened, but also expanded in order to facilitate filling with a repair compound.
• We prepare a mixture for restoration using either a polyurethane-based polymer complex or non-shrink cement. When eliminating large defects, so-called thixotropic compounds are used, and small cracks are best sealed with a casting agent.

Filling embroidered cracks with thixotropic sealants

• We apply the repair mixture to the damage, after which we level the surface and protect it from loads until the agent is completely polymerized.

In principle, these works are easily done by hand, so we can save on the involvement of craftsmen.

Operational damage

Drawdowns, dusting and other malfunctions

Cracks in the sagging screed

In a separate group, experts distinguish the so-called operational defects. These include the following:

Defect	Characteristics and possible cause
Screed deformation	It is expressed in a change in the level of the poured concrete floor (most often the coating sags in the center and rises at the edges). Can be caused by several factors: · Uneven density of the base due to insufficient tamping · Defects in the compaction of the mortar. · Difference in humidity of the top and bottom layer of cement. Insufficient reinforcement thickness.
Cracking	In most cases, cracks do not occur due to mechanical action, but due to deformation of the structure as a whole. It can be provoked both by excessive loads exceeding the calculated ones and by thermal expansion.
Peeling	Peeling of small scales on the surface usually begins with the appearance of a network of microscopic cracks. In this case, the cause of peeling is most often the accelerated evaporation of moisture from the outer layer of the solution, which leads to insufficient hydration of the cement.
Surface dusting	It is expressed in the constant formation of fine cement dust on the concrete. May be caused by: Lack of cement in the mortar. Excess moisture during pouring. · Ingress of water to the surface during grouting. · Insufficient quality cleaning of gravel from dust fraction. Excessive abrasive effect on concrete.

Surface peeling

All of the above disadvantages arise either due to a violation of technology, or due to improper operation of the concrete structure. However, they are somewhat more difficult to eliminate than mechanical defects.

• Firstly, the solution must be poured and processed in accordance with all the rules, preventing it from delamination and peeling during drying.
• Secondly, the base must be prepared no less qualitatively. The denser we compact the soil under the concrete structure, the less likely it will be to subside, deform and crack.
• So that the poured concrete does not crack, a damper tape is usually mounted around the perimeter of the room, which compensates for deformations. For the same purpose, polymer-filled seams are arranged on large-area screeds.
• It is also possible to avoid the appearance of surface damage by applying polymer-based reinforcing impregnations to the surface of the material or by “ironizing” the concrete with a fluid solution.

Protective treated surface

Chemical and climate impact

A separate group of damages is made up of defects that have arisen as a result of climatic effects or reactions to chemicals.

This may include:

• The appearance on the surface of stains and light spots - the so-called efflorescence. Usually the reason for the formation of salt deposits is a violation of the humidity regime, as well as the ingress of alkalis and calcium chlorides into the composition of the solution.

Efflorescence formed due to excess moisture and calcium

Note! It is for this reason that in areas with highly carbonate soils, experts recommend using imported water to prepare the solution.

Otherwise, a whitish coating will appear within a few months after pouring.

• Destruction of the surface under the influence of low temperatures. When moisture enters porous concrete, microscopic channels in the immediate vicinity of the surface gradually expand, since when freezing, water increases in volume by about 10-15%. The more often the freeze / thaw occurs, the more intensively the solution will break down.
• To combat this, special anti-frost impregnations are used, and the surface is also coated with compounds that reduce porosity.

Before repair, the fittings must be cleaned and processed

• Finally, reinforcement corrosion can also be attributed to this group of defects. Metal mortgages begin to rust in places where they are exposed, which leads to a decrease in the strength of the material. To stop this process, before filling the damage with a repair compound, we must clean the reinforcing bars from oxides, and then treat them with an anti-corrosion compound.

Conclusion

The defects of concrete and reinforced concrete structures described above can manifest themselves in a variety of forms. Despite the fact that many of them look quite harmless, when the first signs of damage are found, it is worth taking appropriate measures, otherwise the situation may worsen over time.

Well, the best way to avoid such situations is to strictly adhere to the technology of arranging concrete structures. The information presented in the video in this article is another confirmation of this thesis.

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Vapor permeability of materials table

To create a favorable microclimate in the room, it is necessary to take into account the properties of building materials. Today we will analyze one property - the vapor permeability of materials.

Vapor permeability is the ability of a material to pass vapors contained in the air. Water vapor penetrates the material due to pressure.

They will help to understand the issue of the table, which cover almost all the materials used for construction. After studying this material, you will know how to build a warm and reliable home.

Equipment

When it comes to Prof. construction, then it uses specially equipped equipment to determine vapor permeability. Thus, the table that is in this article appeared.

Today the following equipment is used:

• Scales with a minimum error - an analytical type model.
• Vessels or bowls for experiments.
• Instruments with a high level of accuracy for determining the thickness of layers of building materials.

Dealing with property

There is an opinion that "breathing walls" are useful for the house and its inhabitants. But all builders think about this concept. “Breathable” is the material that, in addition to air, also allows steam to pass through - this is the water permeability of building materials. Foam concrete, expanded clay wood have a high rate of vapor permeability. Walls made of brick or concrete also have this property, but the indicator is much less than that of expanded clay or wood materials.

This graph shows the permeability resistance. The brick wall practically does not let in and does not let in moisture.

Steam is released when taking a hot shower or cooking. Because of this, increased humidity is created in the house - an extractor hood can correct the situation. You can find out that the vapors do not go anywhere by the condensate on the pipes, and sometimes on the windows. Some builders believe that if the house is built of brick or concrete, then the house is "hard" to breathe.

In fact, the situation is better - in a modern home, about 95% of the steam leaves through the window and the hood. And if the walls are made of breathable building materials, then 5% of the steam escapes through them. So residents of houses made of concrete or brick do not particularly suffer from this parameter. Also, the walls, regardless of the material, will not let moisture through due to vinyl wallpaper. The "breathing" walls also have a significant drawback - in windy weather, heat leaves the dwelling.

The table will help you compare materials and find out their vapor permeability index:

The higher the vapor permeability index, the more moisture the wall can contain, which means that the material has low frost resistance. If you are going to build walls from foam concrete or aerated concrete, then you should know that manufacturers are often cunning in the description where vapor permeability is indicated. The property is indicated for dry material - in this state it really has a high thermal conductivity, but if the gas block gets wet, the indicator will increase by 5 times. But we are interested in another parameter: the liquid tends to expand when it freezes, as a result, the walls collapse.

Vapor permeability in a multi-layer construction

The sequence of layers and the type of insulation - this is what primarily affects the vapor permeability. In the diagram below, you can see that if the insulation material is located on the front side, then the pressure on moisture saturation is lower.

The figure shows in detail the action of pressure and the penetration of steam into the material.

If the insulation is located on the inside of the house, then condensation will appear between the supporting structure and this building. It negatively affects the entire microclimate in the house, while the destruction of building materials occurs much faster.

Dealing with the ratio

The table becomes clear if you understand the coefficient.

The coefficient in this indicator determines the amount of vapor, measured in grams, that pass through materials with a thickness of 1 meter and a layer of 1 m² within one hour. The ability to pass or retain moisture characterizes the resistance to vapor permeability, which is indicated in the table by the symbol "µ".

In simple words, the coefficient is the resistance of building materials, comparable to the permeability of air. Let's analyze a simple example, mineral wool has the following vapor permeability coefficient: µ=1. This means that the material passes moisture as well as air. And if we take aerated concrete, then its µ will be equal to 10, that is, its vapor conductivity is ten times worse than that of air.

Peculiarities

On the one hand, vapor permeability has a good effect on the microclimate, and on the other hand, it destroys the materials from which houses are built. For example, “cotton wool” perfectly passes moisture, but in the end, due to excess steam, condensation can form on windows and pipes with cold water, as the table also says. Because of this, the insulation loses its qualities. Professionals recommend installing a vapor barrier layer on the outside of the house. After that, the insulation will not let steam through.

Vapor resistance

If the material has a low vapor permeability, then this is only a plus, because the owners do not have to spend money on insulating layers. And to get rid of the steam generated from cooking and hot water, the hood and the window will help - this is enough to maintain a normal microclimate in the house. In the case when the house is built of wood, it is impossible to do without additional insulation, while wood materials require a special varnish.

The table, graph and diagram will help you understand the principle of this property, after which you can already decide on the choice of a suitable material. Also, do not forget about the climatic conditions outside the window, because if you live in a zone with high humidity, then you should forget about materials with a high vapor permeability.

Recently, various systems of external insulation have been increasingly used in construction: "wet" type; ventilated facades; modified well masonry, etc. All of them are united by the fact that these are multilayer enclosing structures. And for multilayer structures questions vapor permeability layers, moisture transport, and quantification of the resulting condensate are issues of paramount importance.

As practice shows, unfortunately, both designers and architects do not pay due attention to these issues.

We have already noted that the Russian construction market is oversaturated with imported materials. Yes, of course, the laws of building physics are the same, and they operate in the same way, for example, both in Russia and in Germany, but the approach methods and the regulatory framework are very often very different.

Let us explain this with the example of vapor permeability. DIN 52615 introduces the concept of vapor permeability through the coefficient of vapor permeability μ and air equivalent gap s d .

If we compare the vapor permeability of an air layer 1 m thick with the vapor permeability of a material layer of the same thickness, we obtain the vapor permeability coefficient

μ DIN (dimensionless) = air vapor permeability / material vapor permeability

Compare, the concept of vapor permeability coefficient μ SNiP in Russia it is entered through SNiP II-3-79* "Construction heating engineering", has the dimension mg / (m * h * Pa) and characterizes the amount of water vapor in mg that passes through one meter of the thickness of a particular material in one hour at a pressure difference of 1 Pa.

Each layer of material in a structure has its own final thickness. d, m. It is obvious that the amount of water vapor that has passed through this layer will be the smaller, the greater its thickness. If we multiply µ DIN and d, then we get the so-called air equivalent gap or diffuse-equivalent thickness of the air layer s d

s d = μ DIN * d[m]

Thus, according to DIN 52615, s d characterizes the thickness of the air layer [m], which has equal vapor permeability with a layer of a specific material with a thickness d[m] and vapor permeability coefficient µ DIN. Vapor resistance 1/Δ defined as

1/Δ= μ DIN * d / δ in[(m² * h * Pa) / mg],

where δ in- coefficient of air vapor permeability.

SNiP II-3-79* "Construction heat engineering" determines the resistance to vapor permeation R P as

R P \u003d δ / μ SNiP[(m² * h * Pa) / mg],

where δ - layer thickness, m.

Compare, according to DIN and SNiP, vapor permeability resistance, respectively, 1/Δ and R P have the same dimension.

We have no doubt that our reader already understands that the issue of linking the quantitative indicators of the vapor permeability coefficient according to DIN and SNiP lies in determining the air vapor permeability δ in.

According to DIN 52615, the vapor permeability of air is defined as

δ in \u003d 0.083 / (R 0 * T) * (p 0 / P) * (T / 273) 1.81,

where R0- gas constant of water vapor, equal to 462 N*m/(kg*K);

T- indoor temperature, K;

p0- average air pressure inside the room, hPa;

P- atmospheric pressure in the normal state, equal to 1013.25 hPa.

Without going deep into the theory, we note that the quantity δ in depends to a small extent on temperature and can be considered with sufficient accuracy in practical calculations as a constant equal to 0.625 mg/(m*h*Pa).

Then, if the vapor permeability is known µ DIN easy to go to μ SNiP, i.e. μ SNiP = 0,625/ µ DIN

Above, we have already noted the importance of the issue of vapor permeability for multilayer structures. No less important, from the point of view of building physics, is the question of the sequence of layers, in particular, the position of the insulation.

If we consider the probability of temperature distribution t, saturated vapor pressure pH and pressure of unsaturated (real) steam pp through the thickness of the enclosing structure, then from the point of view of the process of diffusion of water vapor, the most preferable sequence of layers is in which the resistance to heat transfer decreases, and the resistance to vapor penetration increases from outside to inside.

Violation of this condition, even without calculation, indicates the possibility of condensation in the section of the building envelope (Fig. P1).

Rice. P1

Note that the arrangement of layers of different materials does not affect the value of the total thermal resistance, however, the diffusion of water vapor, the possibility and place of condensation predetermine the location of the insulation on the outer surface of the bearing wall.

Calculation of resistance to vapor permeability and checking the possibility of condensation should be carried out according to SNiP II-3-79 * "Construction heating engineering".

Recently, we had to face the fact that our designers are provided with calculations made according to foreign computer methods. Let's express our point of view.

· Such calculations obviously have no legal force.

· Techniques are designed for higher winter temperatures. Thus, the German method "Bautherm" no longer works at temperatures below -20 °C.

· Many important characteristics as initial conditions are not linked to our regulatory framework. So, the thermal conductivity coefficient for heaters is given in a dry state, and according to SNiP II-3-79 * "Construction heating engineering" it should be taken under conditions of sorption humidity for operating zones A and B.

· The balance of moisture intake and return is calculated for completely different climatic conditions.

Obviously, the number of winter months with negative temperatures for Germany and, say, for Siberia, does not coincide at all.