Rules for the installation of the floor of the house from the plates. Supporting the floor slab on the wall: permissible limits, SNiP Is it possible to install supports under the floor slabs

Comments:

During the construction of a building, such an important issue as the support of floor slabs must be taken into account without fail.

Building codes have specific guidelines for this.

An important structural element

Ceilings - load-bearing elements of the building, made of reinforced concrete structures. They receive and distribute the loads from their weight and the people and equipment in the building to the walls and supports. With their help, the internal space of the structure is divided into floors, and the attic and basement are also separated.

Ceilings in a building must meet many requirements. They must be strong, rigid, have good soundproofing characteristics, do not burn and do not let water through.

The material used for the production of floor slabs is reinforced concrete. Basically, these are multi-hollow structures with voids of various shapes: polygonal, oval, round. Most often in construction, elements with round voids are used. They are high-strength, technologically advanced and completely ready for installation. Their bearing capacity is 800 kg / m². They are laid on load-bearing walls located at a distance of about 9 m from each other. Rely on two sides. They are distinguished by fire resistance, rigidity, long service life. Brick, aerated concrete, foam blocks and reinforced concrete panels are used as the material for the walls on which such overlapping elements will be laid.

Back to index

Some calculations

To find the support value of the floor slab, the base on which it is planned to be laid is of great importance. Without fail, it is necessary to take into account the length and weight of the structure, the thickness of the supporting wall, the seismological stability of the building. In addition, the load and its nature, whether it be temporary or permanent, must be taken into account. Such calculations should be carried out by specialists. For an individual developer, when drafting a project and installing, the marking of the manufacturer becomes the main reference point.

When using flat overlapping elements, the span can be calculated as follows: you need to sum the thickness of this element and the distance between the two supports. As for the depth of support of the floor slab on the brick base, this value should be equal to the thickness of the structure itself, but not less than 70 mm. To calculate the minimum thickness of the outer wall, which will become the basis for floor slabs, it is necessary to take into account the heat-insulating layer and facing material on the end parts of the latter. So, a structure with a thickness of 140 mm should be supported by a base whose thickness is not less than 300 mm.

Installation of often ribbed structures that have liners involves a minimum deepening of the floor slabs on the base - 150 mm. During installation, do not allow hollow inserts to enter the wall. If the ribs are reinforced with two rods, then it is necessary to bend them on the support after one. If the rib has one rod, then the stirrups will take shear stress.

Reinforced stone structures are analogues of flat ones. Therefore, the minimum value of the support depth of these elements can be determined in the same way. They must be at least 90 mm thick, supported on two sides.

Back to index

Individual construction

In the specialized literature on construction work, the definition of the necessary standards regarding the depth of support of floor slabs is given. This indicator is in the range of 90-120 mm. To determine this value more accurately, certain calculations must be made, which take into account the length and weight of the structure, the thickness of the supporting wall and the material from which it is made. The expected load must also be determined.

For example, the use of a slab with a length of 6 m implies a support depth of at least 100 mm on a brick base. When using structures made of reinforced concrete or steel, a depth of at least 70-75 mm is permissible, on walls made of foam blocks and aerated concrete - at least 120 mm.

Reinforced concrete slabs are one of the most common types of floors. They provide high strength and allow you to mount a rigid structure in the shortest possible time. Installation of floor slabs is a responsible task that requires certain knowledge in the field of construction. About everything in order.

Types of floor slabs

Before you start mounting a horizontal structure, you must select the type. Reinforced concrete prefabricated structures are produced in the form of:

multi-hollow;
flat (PT);
tent panels with ribs located around the perimeter;
with longitudinal ribs.

Most often, the use of reinforced concrete multi-hollow. They are produced in two types, depending on the method of manufacture:

round-hollow (PC);
continuous molding (PB).

Diagram of a hollow core slab with holes

Hollow-core slabs are time-tested products that have been used in construction for several decades. Under them, a lot of regulatory documents and installation rules have been developed. Thickness - 220 mm. Products are installed according to serial sizes, which creates inconvenience during individual construction.

The manufacturing technology of these plates involves the use of reusable molds for pouring, and before manufacturing non-standard products, you first need to prepare the formwork. Therefore, the cost of the desired size can increase significantly.. Typical PC boards have a length of 2.7 to 9 meters in 0.3 m increments.

Scheme of reinforced concrete products with dimensions

The width of reinforced concrete products can be:

1.0 m;
1.2 m;
1.5 m;
1.8 m

Structures with a width of 1.8 m are purchased extremely rarely, because due to the large weight, the process of installation in the design position is greatly complicated.

PBs are used in much the same way as the previous type. But the technology of their manufacture allows you to give the product any length. Thickness - 220 mm. Width same as PC series. The disadvantage is the little experience of use and the rawness of regulatory documentation.

As additional elements for multi-hollow slabs, flat PTs are often purchased. They are available with a thickness of 80 or 120 mm and are smaller in size, allowing you to block narrow corridors, closets, bathrooms.

Slab support

The laying of floor slabs is carried out after the preparation of the project or scheme on which the products are laid out. The floor elements must be selected so that they are sufficiently supported by a brick wall or expanded clay concrete blocks and laid without gaps in width.

The minimum support for PB and PK series depends on their length:

products up to 4 m long - 70 mm;
products longer than 4 m - 90 mm.

A visual diagram of how to properly and incorrectly support floor slabs

Most often, designers and constructors take the optimal value of leaning on the wall of 120 mm. This value guarantees reliability with small installation deviations.

It will be correct to pre-arrange the load-bearing walls of the house at such a distance that it is easy to lay the slabs. The distance between the walls is calculated as follows: the length of standard plates minus 240 mm. PK and PB series must be laid with support on two short sides without intermediate supports. For example, PK 45.15 has a size of 4.48 m, 24 cm is subtracted from it. It turns out that the distance between the walls should be 4.24 m. In this case, the products will lie down with an optimal support value.

The minimum support of products of the PT series on the wall is 80 cm. Installation of such reinforced concrete slabs is possible with the location of support points on all sides.

The support must not interfere with the passage of the ventilation ducts. The optimal thickness of the bearing internal brick wall is 380 mm. 120 mm on each side goes under reinforced concrete floors, and 140 mm remains in the middle - the standard width of the ventilation duct. In this case, it is necessary to lay as correctly as possible. Displacement of the product towards the ventilation opening will lead to a decrease in its cross section and insufficient ventilation of the premises.

A summary of what has been said:

PK and PB series up to 4 m are supported on two sides by at least 7 cm;
PK and PB series more than 4 m - not less than 9 cm;
PT series - on two, three or four sides at least 8 cm.

Slab storage

Storage schemes for products of different types

After the scheme has been developed and the products have been purchased, they must be placed on the building site for easy installation in the design position. There are rules for warehousing materials:

you need to lay the elements under a canopy;
the place of storage should be located in the access zone of the crane;
linings are provided under the support points.

Failure to follow the last rule will result in a split in half. PC, PB and PT products work in such a way that the appearance of intermediate supports or a solid base leads to cracks. Laying is performed in the following order:

wooden bars or boards are laid on the ground under the edges of the slab;
I shift the floor element onto the boards with a crane from the machine;
boards or bars are again placed on the laid slab;
unload the second plate from the machine;
repeat points 3 and 4, the maximum storage height is 2.5 m.

masonry requirements

Floor slab calculation scheme

In order to properly install floor slabs, it is necessary to ensure that special requirements for a brick wall are met:

evenness of masonry at the place of laying floors;
laying in three rows until the overlap of reinforcing mesh with a cell of 5 by 5 cm from wire with a diameter of 3-4 mm;
the top row to the lining on the inside should be bonded.

If the slabs are mounted on expanded clay concrete blocks, a monolithic belt is additionally arranged under the floors. This design will help to evenly distribute the load from heavy floors on expanded clay concrete blocks with less strength. The construction technology provides for pouring a monolithic concrete tape 15-20 cm thick onto the blocks.

Floor laying

To carry out the work, at least three people will be required: one performs the slinging, and two install them in the design position. If the installers and the crane operator cannot see each other, another worker will be needed to install the slab to give commands to the crane.

Scheme of laying reinforced concrete products

Fastening to the crane hook is carried out with a four-branch sling, the branches of which are fixed at the corners of the slab. Two people stand on both sides of the support and control its evenness.

When installing a PC, pinching into the wall is carried out in a rigid way, that is, bricks or blocks are laid on top and bottom of the slab. When using ceilings according to the PB series, it is recommended to perform hinged fastening. For this, the plates are not pinched from above. Many builders mount the PB series in the same way as PCs and buildings stand, but it’s not worth the risk, because human life and health depend on the quality of installation of load-bearing structures.

Another important feature of the use of products from the PB series is that it is forbidden to make technological holes in them.

These punches are needed for heating, water supply and sewerage pipes. Again, many builders, even when building multi-storey buildings, neglect this. The difficulty is that the behavior of this type of floors under load over time has not been fully studied, since there are no objects built a long time ago yet. The ban on punching holes is justified, but it is rather preventive.

Slab cutting

Sometimes, in order to install the slab, it is necessary to cut it. The technology provides for the work of a grinder with a disk on concrete. It is impossible to cut the PC and PT slabs along the length, since they have reinforced reinforcement in the support zones. If you support such a cut slab, then one edge will be weakened, serious cracks will go along it. It is possible to cut PB plates along the length, this is due to the peculiarities of the manufacturing method. A bar or board is placed under the cut site, which will facilitate the work.

Separation along the length is performed along the weakened part of the section - the hole. this method is suitable for PC, but not recommended for PB, since the width of the walls between the holes is too small.

After installation, the holes in the areas of support on the walls are poured with lightweight concrete or clogged with mineral wool. This is necessary to provide additional strength in places pinched into the walls.

What to do if it was not possible to evenly spread the products across the width

Sometimes the dimensions of the room do not correspond to the width of the products, in which case all the gaps are driven into one. This space is covered with a monolithic section. Reinforcement occurs with curved meshes. In length, they rest on the top of the ceiling and seem to sag in the middle of a monolithic section. for floors, concrete not lower than B 25 is used.

The technology of prefabricated floors on bricks or blocks is quite simple, but requires attention to detail.

Currently, in our country, the most popular are three methods of building floors in the house. This is the installation of floor slabs, the device of a monolithic reinforced concrete floor and the device of flooring on wooden (rarely metal) beams. We will definitely talk about all these methods and not only. And the first technology that we will consider is the installation of finished floor slabs.

First, a little about the floor slabs themselves. Depending on their shape, all plates can be divided into flat and ribbed. Flat, in turn, are divided into solid and hollow. We are now interested in void ones, because it is this type of slabs that is used mainly in low-rise construction.

Hollow-core slabs, in turn, are also classified according to various parameters, such as the shape and size of the voids, the thickness of the slabs, the manufacturing technology of the slabs, and the method of reinforcement.

I will not delve into the topic of classification. It is better to look for this information on the websites of enterprises producing reinforced concrete products (reinforced concrete products). We'd better talk directly about the installation.

The very first point that you need to pay attention to even at the design stage of your future home is the opportunity to purchase in your area exactly the slabs of the sizes that are laid down in the project. Each manufacturer has its own specific range of manufactured products and it is always limited. This is really important and it surprises me that very often developers forget about this recommendation and then they have to either cut one or more slabs or make a monolithic section on the floor. We'll talk more about this below.

Storage of floor slabs at the construction site.

Of course, it's great if you have the opportunity to lay floor slabs immediately upon delivery, directly from the machine that brought them. But most of the time this doesn't happen. Or the driver insists that you unload the plates as quickly as possible, because. he is in a hurry for the next order, or the plates are not laid on the machine in the order you need, or you just bought them in advance and are not going to lay them yet. In all these cases, the plates will need to be stored on your site.

Try to choose a flat surface for this. Never lay tiles directly on the ground. Be sure to put something under the edges of the slab, for example, trimming a wooden beam. There should be only two linings, at a distance of about 25-40 cm from the edges. Linings cannot be placed under the middle of the plate.

Boards can be stacked up to 2.5 meters high. Make the linings under the first slab higher so that in the event of their possible indentation into the ground when laying subsequent slabs, the first one in no case touches the ground, otherwise it can easily break. It is enough to make all subsequent linings even from an inch (2.5 cm). They must be stacked strictly on top of each other.

Preparation for installation of floor slabs.

Preparation begins even at the moment when the masons kick out the last rows of masonry. The slabs will lie flat and without drops if the upper rows of load-bearing walls are even and lie in the same horizontal plane.

To achieve this, there must be horizontal level marks in all corners of the overlapped room. They are put in the process of building walls using a level, either a laser level, or a hydro level. And when the last row of masonry is done, the distance from the marks to the top of the walls is controlled with a tape measure. It should be the same in all corners. From my own experience, I can tell you for sure that some masons neglect this, especially when they make backing masonry at the same time as the front one, performed “under the bar”.

The top row of load-bearing walls should be bonded. That is, if you look from inside the overlapped room, then only poking should be visible on the load-bearing walls (on which the floor slabs rest) in the uppermost row of masonry.

If the slabs are placed on a load-bearing partition 1.5 bricks thick (i.e., the slabs rest on it on both sides), then the top row of such a partition is laid out in one of two ways:

Before laying floor slabs on walls from various blocks (foam concrete, gas silicate, slag, etc.), it is necessary to make a reinforced concrete belt (usually about 15-20 cm thick). Such a belt is made either by pouring concrete into the formwork, or using special U-shaped blocks around the entire perimeter of the house box, i.e. not only on load-bearing walls, but also on non-bearing ones.

When installing hollow core slabs, the holes in them must be sealed. It is much more convenient to do this in advance, while the plates are still on the ground. In general, SNiP prescribes to fill voids without fail on the side of the slab that rests on the outer wall (to reduce the likelihood of freezing of the slab), and on the side that rests on the internal partition, only starting from the third floor from the top of the house and below (to increase strength). That is, if, for example, the house has a basement floor, a floor between the 1st and 2nd floor and an attic floor over the 2nd floor, then it is mandatory to close the voids from the side of the load-bearing partitions only in the basement floor.

I will say that when laying the slabs, we always close up the holes. Moreover, in recent years, more and more hollow-core slabs come from factories with holes already sealed. It's comfortable. If the holes are not sealed, we insert a one-and-a-half brick (maybe even a half) into them and pass the remaining gaps with mortar.

Also, before installing the plates, it is necessary to prepare a site for the crane in advance. Well, if in the place where the crane will stand, the soil is, as they say, native, caked. Worse, when the ground is bulk. If you have a basement, you can not put the tap too close to the house, in order to avoid what is shown in the figure below:

In such cases, it is better to order a truck crane with a longer boom. Also, sometimes in the place where the crane will stand, you first have to put several road slabs (usually there are used ones somewhere). Often this has to be done in the fall in rainy and slushy weather, when the site is so “broken” that the crane simply gets stuck on it.

Floor slab laying.

Three people are enough for the installation of floor slabs. One clings to the slabs, two lay. If desired, you can cope with two, although not always. It happens that when overlapping, for example, the second floor, the installers and the crane operator do not see each other. Then at the top, in addition to 2 people directly laying the slab, there should be another person who will give commands to the crane operator.

Laying starts from the wall on a mortar layer of no more than 2 cm. The mortar must be thick enough so that the slab does not squeeze it completely out of the seam. After the crane operator places the slab on the walls, he first leaves the lines taut. At the same time, with the help of a crowbar, the plate, if necessary, is not difficult to move a little. If the upper surfaces of the load-bearing walls were made even, then the slabs will lie flat, without drops, as they say "from the first approach."

Regarding the size of the support of the plates on the walls, I will give an extract from the document “Manual for the design of residential buildings. Issue. 3 (to SNiP 2.08.01-85) 6. FLOORS ":

Paragraph 6.16.: The depth of support of prefabricated slabs on the walls, depending on the nature of their support, is recommended to be taken at least, mm: when supported along the contour, as well as on two long and one short sides - 40; when supporting on two sides and a span of slabs of 4.2 m or less, as well as on two short and one long sides - 50; when supported on two sides and the span of plates is more than 4.2 m - 70.

When assigning the depth of support for floor slabs, the requirements of SNiP 2.03.01-84 for anchoring reinforcement on supports should also be taken into account.

In our practice, we try to make the support at least 12 cm, since now it is possible to purchase exactly those plates that are needed. The step of their lengths is 10 cm.

I often hear disputes about whether hollow core slabs can be supported on three sides (two short and one long) and how long it is possible to put the slab on the wall with the long side. From what is written above, it follows that it is possible to support the plates in this way. But it is not so. If you read the indicated SNiP, then it says that slabs that rely on three sides have a different reinforcement scheme than those that rely on only two sides.

The vast majority of hollow core slabs, which are now produced by reinforced concrete factories, are designed specifically to be supported on two short sides, so it is not recommended to start them with the long side on the wall. Under a certain load, this can lead to cracking of the plate. The reinforcement scheme and, therefore, the possibility of supporting the slab on a third side must be clarified with the manufacturer.

Also, an error associated with improper loading of the slab is the overlapping of two spans at once (see the figure below):

Under certain unfavorable conditions, the slab can crack, and the place where the crack appears is absolutely unpredictable. If you still use such a scheme, make a cut with a grinder (to the depth of the disk) on the upper surface of the plate strictly above the middle partition. Thus, in which case the crack will pass exactly along this section, which, in principle, is no longer scary.

Of course, it’s good if we manage to overlap only with whole slabs. But the circumstances are different, and yet sometimes some plate (or even more than one) has to be cut along or across. To do this, you will need a grinder with a diamond blade for concrete, a sledgehammer, a crowbar and not the most frail man at a construction site.

To facilitate the work, it is better to lay the stove on a lining. Moreover, this lining is placed exactly under the cut line. At some point, the plate will simply break along this line from its own weight.

First of all, we make a cut on the upper surface of the plate with a grinder along the cut line. Then, striking with a sledgehammer from above, we cut a strip along the top of the slab. It is quite easy to break through concrete in the void area. Next, we break through the lower part of the plate with a crowbar (also along the voids). When cutting the slab along (we always chop along the hole in the slab), it breaks rather quickly. When cutting across, if the slab did not break after the destruction of the lower part with a crowbar, a sledgehammer strikes from the side on the vertical partitions of the slab until the victorious one.

In the process of cutting, we cut the falling reinforcement. It is possible with a grinder, but it is safer by welding or a gas cutter, especially when the reinforcement in the slab is pre-stressed. A disk from a grinder can bite. To prevent this from happening, do not cut the reinforcement to the end, leave a couple of millimeters and then break it with a blow from the same sledgehammer.

Several times in our practice, we had to cut the slabs along. But we have never used, let's say, "stumps" with a width of less than 60 cm (less than 3 holes remain), and I do not advise you. In general, when making a decision to cut a slab, you take full responsibility for the possible consequences, because not a single manufacturer will officially tell you that it is possible to cut a slab.

Let's now see what can be done if, nevertheless, a whole number of plates is not enough for you to completely cover the room:

Method 1- we put the first or last (maybe both) plates without bringing the long side to the wall. We lay the remaining gap with bricks or blocks, hanging them no more than half from the wall (see Fig.):

Method 2- we make the so-called "monolithic section". From below, plywood formwork is placed under the slabs, a reinforcing cage is made (see the figure below) and the area between the slabs is poured with concrete.

Anchoring of floor slabs.

After all the plates are laid, they are anchored. In general, if the construction of a house is carried out according to the project, then an anchoring scheme must be present in it. When there is no project, we usually use the circuit shown in the figure:

The anchor is made by bending the end into a loop that clings to the mounting loop of the plate. Before welding the anchors to each other and to the mounting loops, they must be pulled as far as possible.

After anchoring, we immediately seal with mortar all the mounting eyes in the slabs and rustication (seams between the slabs). Try not to delay this so that construction debris does not get into the rusts, and water does not pour into the eyes during rain and snow. If you suspect that water did get into the slabs (for example, you bought slabs with voids already sealed, and rainwater could get in even during storage at the factory), it is better to let it out. To do this, after laying, simply drill a small hole in the slabs from below with a perforator, into those voids where the mounting eyes are located.

It is especially dangerous to find water in voids in winter, when the house is not yet heated (or not completed at all) and the slabs freeze below zero. Water saturates the bottom layer of concrete, and with repeated freeze-thaw cycles, the slab simply begins to collapse.

Another way of fixing the plates is the construction of the so-called concrete ring anchor. This is a kind of the same monolithic reinforced belt, only it is not made under the slabs, but in the same plane with them, also around the entire perimeter of the house. More often, this method is used on foam concrete and other blocks.

I must say right away that we have never used it because of the much greater laboriousness. I think the ring anchor is justified in more seismic regions than our Nizhny Novgorod region.

At the end of the article, I propose to watch a short video in which we are talking about the choice of floor slabs:

In houses made of brick, concrete or concrete blocks, floors are usually made of reinforced concrete. They provide exceptional strength and seismic resistance of the structure, and are also very durable and do not burn, which is important. There are several ways to arrange reinforced concrete floors. The most common and versatile is laying prefabricated floor slabs. Such slabs are ordered at reinforced concrete factories, and then mounted with a crane and a team of workers. In those cases where the use of a crane on a construction site is difficult, or when the house has a non-standard layout and it is difficult to lay out finished slabs, a monolithic floor slab is equipped. In fact, you can pour a monolithic slab not only when there are indications for this, but also simply because you consider it more appropriate. In this article we will tell you how to lay floor slabs and how to pour a monolithic slab. Not all work can be done independently, but it is still worth familiarizing yourself with the technology, if only in order to control the process at the construction site.

Do-it-yourself monolithic floor slab

A monolithic floor has a number of advantages compared to a floor made of prefabricated reinforced concrete slabs. Firstly, the construction is solid and monolithic without a single seam, which provides a uniform load on the walls and foundation. Secondly, a monolithic fill allows you to make the layout of the house more free, as it can be based on columns. Also, the layout can imply as many corners and nooks as you like, for which it would be difficult to pick up floor slabs of standard sizes. Thirdly, it is possible to safely equip a balcony without an additional support plate, since the structure is monolithic.

You can equip a monolithic floor slab yourself; this does not require a crane or a large team of workers. The main thing is to follow the technology and not save on materials.

Like everything related to construction, a monolithic ceiling begins with a project. It is advisable to order the calculation of a monolithic floor slab in the design office and not save on it. It usually includes the calculation of the cross section of the plate for the action of the bending moment at maximum load. As a result, you will receive the optimal dimensions for the floor slab specifically in your house, instructions on which reinforcement to use and what class of concrete. If you want to try to perform the calculations yourself, then an example of calculating a monolithic floor slab can be found on the Internet. We will not focus on this. Consider the option when an ordinary country house is being built with a span of no more than 7 m, so we will make a monolithic floor slab of the most popular recommended size: from 180 to 200 mm thick.

Materials for the manufacture of a monolithic floor slab:

Formwork.
Supports for supporting the formwork at the rate of 1 support per 1 m2.
Steel fittings with a diameter of 10 mm or 12 mm.
Concrete brand M 350 or separately cement, sand and crushed stone.
Bending fixture for fittings.
Plastic coasters for fittings (clamps).

Technology of pouring a monolithic floor slab includes the following steps:

Calculation of the floor slab, if the span is more than 7 m, or the project involves the support of the slab on the column / columns.
Installation of formwork type "deck".
Reinforcement of the slab with steel bars.
Pouring concrete.
Compaction of concrete.

So, after the walls are driven to the required height, and their level is almost perfectly aligned, you can proceed to the arrangement of a monolithic floor slab.

The device of a monolithic floor slab assumes that the concrete will be poured into a horizontal formwork. Sometimes horizontal formwork is also called a "deck". There are several options for its arrangement. First - rental of ready-made removable formwork from metal or plastic. Second - making formwork on site using wooden boards or sheets of moisture-resistant plywood. Of course, the first option is simpler and preferable. Firstly, the formwork is collapsible. Secondly, it offers telescopic supports, which are needed to support the formwork on the same level.

If you prefer to make the formwork yourself, then please note that the thickness of the plywood sheets should be 20 mm, and the thickness of the edged boards 25 - 35 mm. If you knock down shields from edged boards, then they need to be tightly fitted to each other. If gaps are visible between the boards, then the surface of the formwork should be covered with a waterproofing film.

Formwork is installed in this way:

Vertical poles are installed. These can be telescopic metal racks, the height of which can be adjusted. But you can also use wooden logs with a diameter of 8 - 15 cm. The step between the posts should be 1 m. The posts closest to the wall should be located at a distance of at least 20 cm from the wall.
Crossbars are laid on top of the racks (a longitudinal beam that will hold the formwork, an I-beam, a channel).
Horizontal formwork is laid on the crossbars. If not ready-made formwork is used, but self-made, then transverse beams are laid on top of the longitudinal bars, on which sheets of moisture-resistant plywood are placed on top. The dimensions of the horizontal formwork must be perfectly adjusted so that its edges rest against the wall without leaving gaps.
The height of the support-racks is adjusted so that the upper edge of the horizontal formwork coincides with the upper edge of the wall masonry.
Vertical formwork elements are installed. Taking into account the fact that the dimensions of a monolithic floor slab should be such that its edges go onto the walls by 150 mm, it is necessary to make a vertical fence at exactly this distance from the inner edge of the wall.
For the last time, the horizontal and even arrangement of the formwork is checked using a level.

Sometimes, for the convenience of further work, the surface of the formwork is covered with a waterproofing film or, if it is made of metal, lubricated with machine oil. In this case, the formwork can be easily removed, and the surface of the concrete slab will be perfectly flat. The use of telescopic racks for formwork is preferable to wooden supports, as they are reliable, each of them can withstand a weight of up to 2 tons, microcracks do not form on their surface, as can happen with a wooden log or beam. Renting such racks will cost about 2.5 - 3 USD. per 1 m2 of area.

After the arrangement of the formwork, a reinforcing cage of two meshes is installed in it. For the manufacture of the reinforcing cage, steel reinforcement A-500C with a diameter of 10 - 12 mm is used. From these rods, a mesh with a mesh size of 200 mm is connected. To connect the longitudinal and transverse rods, a knitting wire of 1.2 - 1.5 mm is used. Most often, the length of one reinforcing bar is not enough to cover the entire span, so the bars will have to be connected along each other. To make the structure strong, the rods must be connected with an overlap of 40 cm.

The reinforcing mesh should go onto the walls at least 150 mm if the walls are made of brick, and 250 mm if the walls are made of aerated concrete. The ends of the rods should not reach the vertical formwork along the perimeter by 25 mm.

Reinforcement of a monolithic floor slab is carried out using two reinforcing meshes. One of them - the bottom one - should be located at a height of 20 - 25 mm from the bottom edge of the plate. The second - top - should be located 20 - 25 mm below the top edge of the plate.

In order for the lower grid to be located at the desired distance, special plastic clips. They are installed in increments of 1 - 1.2 m at the intersection of the rods.

The thickness of a monolithic floor slab is taken at the rate of 1:30, where 1 is the thickness of the slab, and 30 is the span length. For example, if the span is 6 m, then the thickness of the slab will be 200 mm. Considering that the grids should be located at a distance from the edges of the slab, the distance between the grids should be 120 - 125 mm (from the thickness of the slab of 200 mm we subtract two gaps of 20 mm and subtract 4 thicknesses of reinforcing bars).

In order to separate the grids at a certain distance from each other, 10 mm reinforcing bars are made using a special bending tool. special clamps - stands as in the photo. The upper and lower shelves of the latch are 350 mm. The vertical size of the latch is 120 mm. The installation step of the vertical clamps is 1 m, the rows should be staggered.

Next step - end stop. It is installed with a step of 400 mm at the ends of the reinforcing cage. Serves to strengthen the support of the plate on the wall.

Another important element is upper and lower mesh connector. How it looks, you can see in the photo. It is necessary so that the spaced grids perceive the load as a whole. The installation step of this connector is 400 mm, and in the zone of support on the wall, within 700 mm from it, with a step of 200 mm.

pouring concrete

Concrete is best ordered directly from the factory. This greatly simplifies the task. In addition, pouring the mortar from the mixer in an even layer will ensure exceptional strength of the slab. What can not be said about the stove, which was poured by hand with breaks to prepare a new portion of the solution. So it is better to pour concrete immediately with a layer of 200 mm, without interruptions. Before pouring concrete into the formwork, it is necessary to install a frame or boxes for technological openings, for example, a chimney or a ventilation duct. After pouring, it must be vibrated with a deep vibrator. Then leave to dry and gain strength for 28 days. The first week the surface must be moistened with water, only moistened, and not filled with water. After a month, the formwork can be removed. The monolithic floor slab is ready. For the installation of floor slabs, the price includes the cost of reinforcement, concrete, formwork rental and the order of a mixer machine, as well as a concrete pump. In fact, it comes out to about 50 - 55 USD. per m2 of flooring. How the floor slab is poured with concrete can be seen in the video demonstrating the installation of floor slabs.

How to properly lay floor slabs

The use of factory-made monolithic reinforced concrete floor slabs is considered more traditional. PC slabs are more popular - slabs with round voids. The weight of such slabs starts from 1.5 tons, so laying floor slabs with your own hands is impossible. A crane is required. Despite the seeming simplicity of the task, there are a number of nuances and rules that must be observed when working with floor slabs.

Rules for laying floor slabs

The factory-made floor slab is already reinforced at the factory and does not require additional reinforcement or formwork. They are simply laid in the span with leaning on the walls, following some rules:

The span should not be more than 9 m. It is this length of the slab that is the largest.
Unloading and lifting of plates is carried out with the help of special equipment provided by the project. To do this, there are mounting loops in the plates, for which the mounting slings are hooked.
Before laying floor slabs, the surface of the walls on which they will be laid must be leveled. Large height differences and distortions are not allowed.
The slabs should rest on the walls by 90 - 150 mm.
It is impossible to lay the slabs dry, all cracks and technological seams must be sealed with mortar.
The location of the plates must be constantly monitored relative to the walls and supporting surfaces.
Plates are laid only on load-bearing walls, all piers are equipped only after the installation of ceilings.
If you want to cut a hatch in the ceiling, then it must be cut at the junction of two plates, and not in one plate.
The slabs should be placed as close as possible to each other, but with a gap of 2 - 3 cm. This will ensure seismic resistance.

If there are not enough floor slabs to cover the entire span, and, for example, 500 mm remains, then there are different ways of laying floor slabs in this case. The first is to lay the slabs back to back, and leave the gaps along the edges of the room, then close the gaps with concrete or cinder blocks. The second is the laying of slabs with uniform gaps, which are then sealed with concrete mortar. To prevent the solution from falling down, a formwork is installed under the gap (a board is tied up).

Floor slab laying technology

In the process of laying floor slabs, there should be clear coordination between the crane operator and the team receiving the slab. To avoid injuries at the construction site, as well as to comply with the entire technological process and the rules described in SNiPs, the foreman at the construction site must have a flow chart for the installation of floor slabs. It indicates the sequence of work, the number and location of equipment, special equipment and tools.

It is necessary to start laying the floor slabs from the flight of stairs. After laying the plates, their location is checked. Tiles are well laid if:

The difference between the lower surfaces of the plates does not exceed 2 mm.
The height difference between the upper surfaces of the plates does not exceed 4 mm.
The height difference within the site should not exceed 10 mm.

As the installation diagram of the floor slabs shows, after laying the slabs, they must be connected to each other and to the walls using metal connecting parts. Work on the connection of embedded and connecting parts is carried out by welding.

Do not forget that safety precautions must be observed. It is not allowed to work with a crane in an open area with a wind of 15 m / s, as well as in ice, thunderstorms and fog. During the movement of the slab with a crane, the assembly team should be away from the path along which the slab will be moved, from the side opposite to the feed. Despite the fact that using the services of a professional foreman and a team of installers significantly increase the cost of installing floor slabs, this is not the case when you can save. The foreman must provide a project.

Before ordering plates from the factory, it is necessary to carry out preparatory work. It is better to coordinate the delivery time of the machine with plates and the crane at the same time so as not to overpay for simple special equipment. In this case, the installation of plates can be performed without unloading, directly from the vehicle.

Preparatory work before laying floor slabs

First - flat support surface. The horizon should be almost perfect, a height difference of 4 - 5 cm is unacceptable. First of all, we check the surface of the walls, then, if necessary, level it with a concrete mortar. Subsequent work can be done only after the concrete has gained maximum strength.

Second - ensure the strength of the support zone. If the walls are built of brick, concrete or concrete blocks, then no additional measures need to be taken. If the walls are built from foam blocks or gas blocks, then before laying the plates, it is necessary to fill in the armored belt. Proper laying of floor slabs implies that the bearing surface must be strong enough to support the weight of the slab and not deform along the abutment line. Neither aerated concrete nor foam concrete have the necessary strength. Therefore, a formwork is installed around the entire perimeter of the building, a reinforcing cage made of a rod of 8–12 mm is inserted into it, and then everything is poured with concrete with a layer of 15–20 mm. Further work can be continued only after the concrete has dried.

Third - install mounting towers. Telescopic supports, as described in the section on the installation of a monolithic floor slab, are installed in increments of 1.5 m. They are designed to take on the weight of the slab if it suddenly slips from its place. After installation, these towers are removed.

Installation of hollow core slabs with a crane

After the freshly poured concrete has taken on sufficient strength and dried, the installation of floor slabs can begin directly. For this, a crane is used, the lifting capacity of which depends on the size and weight of the slab, cranes of 3-7 tons are most often useful.

Stages of work:

A concrete solution is applied to the bearing surface with a layer of 2 - 3 cm. 150 mm. If the slab rests on two opposite walls, then the mortar is applied to only two walls. If the slab rests on three walls, then on the surface of three walls. Directly laying the plates can begin when the solution gains 50% of its strength.

While the mortar dries, the crane operator can hook the slings onto the slab fasteners.
When the signal is given to the crane operator that it is possible to feed the slab, the team of workers must move away from the place where the slab is moving. When the slab is already very close, the workers hook it with hooks and unfold it, while damping the oscillatory movements.

The stove is directed to the right place, one person should stand on one wall, and the other on the opposite. The slab is laid so that its edges rest on the wall at least 120 mm, preferably 150 mm. After installation, the plate will squeeze out the excess solution and evenly distribute the load.

If there is a need to move the plate, you can use a crowbar. It is possible to align its location only along the laying zone, it is impossible to move the plate across the walls, otherwise the walls may collapse. Then the slings are removed, and a signal is given to the crane operator to pick them up.
The procedure is repeated for all plates without exception. The rules for installing floor slabs suggest that the alignment of the slabs should be carried out along the bottom edge, since it is the bottom surface that will be the ceiling in the room. Therefore, the slab is laid with the wider side down, and the narrower side up.

You may come across a recommendation that it is necessary to lay reinforcement in the support area of \u200b\u200bthe slab. Proponents of this method say that it is more convenient and easier to move the stove. In fact, putting anything other than concrete mortar under the slab is prohibited by the technical card. Otherwise, the slab can easily move out of the support zone, as it will slide over the reinforcement. In addition, the load will be distributed unevenly.

Laying floor slabs on the foundation is practically no different from laying interfloor floors. The technology is exactly the same. Only the foundation surface must be carefully waterproofed before laying the slabs. If the project provides for non-standard support of floor slabs, then special steel elements are used for this. Such work should not be done without a specialist.

Anchoring - tying plates together - can be done in two ways, depending on the project.

First - tying slabs with reinforcement. Reinforcing bars with a diameter of 12 mm are welded to the fastening embedded elements on the slab. For plates from different manufacturers, the location of these elements may be different: in the longitudinal end of the plate or on its surface. The most durable connection is considered to be diagonal, when the plates are connected to each other with an offset.

Also, the plate must be connected to the wall. Why is reinforcement embedded in the wall.

The second way - ring anchor. In fact, it looks like an armored belt. A formwork is arranged along the perimeter of the slab, reinforcement is installed in it and concrete is poured. This method slightly increases the cost of laying floor slabs. But it's worth it - the plates are clamped from all sides.

After anchoring, you can start sealing the cracks. The gaps between the floor slabs are called rusts. They are filled with concrete grade M150. If the gaps are large, then a board is tied from below, which serves as a formwork. If the gaps are small, then the floor slab will be able to withstand the maximum load the very next day. Otherwise, you must wait a week.

All modern slabs with round voids are produced with the ends already filled. If you purchased plates with open holes, then they must be filled with something 25 - 30 cm deep. Otherwise, the plate will freeze. You can fill the voids with mineral wool, concrete plugs or simply fill with concrete mortar. A similar procedure must be performed not only on those ends that face the street, but also on those that rely on internal walls.

The price for laying floor slabs depends on the amount of work, the area of \u200b\u200bthe house and the cost of materials. For example, the cost of only PC floor slabs is approximately 27 - 30 USD. per m2. The rest is related materials, crane rental and hiring workers, as well as the cost of shipping plates. Professional teams for the installation of floor slabs have a variety of prices from 10 to 25 USD. per m2, maybe more depending on the region. As a result, the cost will be the same as for pouring a monolithic floor slab.