Why do you need a footing for the foundation? Preparation for concreting. What is a foundation footing and why is it needed? What is skinny concrete

Laying the foundation is one of the most important components construction work. Not least important in this process is the construction of a special concrete footing, which should be located under a solid foundation. The quality of its execution determines the stability and durability of the structure. Before carrying out work, it is necessary to determine what density of concrete or crushed stone layer is needed for the construction of a particular building.

Definition

The footing is a layer of concrete mortar that must be prepared for the economical, convenient laying of the main foundation. This thin layer is poured to the main mass (for example, during the installation of the base using concrete slabs).

Purpose and thickness

A preparatory concrete or crushed stone base is made using different methods, funds and building materials. But with any device, its purpose will remain the same - it consists in preparing and leveling the surface. Due to this, the main concrete pouring it is consumed more economically due to uniform laying, which does not require additional mixture consumption for unevenness and depressions in the ground. Concrete and crushed stone footing, which is required for construction work, is used in the following cases:

Surface preparation for easy installation of structural parts. On a leveled site it is much easier to do markings, reinforcement cages, etc. Obviously, this work is more difficult to carry out on loose soil.
Waterproofing. Thin concrete bases are also necessary in order to retain moisture from the poured solution. Cracks appear on the frozen slab. They often appear due to the fact that the liquid is unevenly distributed in the cement structure.
Protection of the foundation from groundwater. If the layer is laid under a slab base, groundwater may enter the pit. In these cases, the footing absorbs part of the liquid, thereby preserving the load-bearing layer on which the building rests.

In addition, the presence of shock absorption increases the strength of the structure due to the fact that the base is better preserved. As for the thickness of the foundation monolith, it will depend directly on the dimensions and weight of the structure. On average, this figure is in the range of 0.15-1 meter.

Preparation can be made of concrete, bulk or film materials.

Types of training

Before starting the main work, it is necessary to carry out preparations. The work package includes the following three stages:

performing calculations;
leveling the site;
preparing the surface before laying the foundation.

First preparatory stage involves careful calculations and work with documentation. Then you need to clear the site. You will need to remove debris from the area, cut down and uproot trees, dig up bushes and other plants. The next step involves creating a “cushion” on the surface, which will be located under the foundation of the future building. The following building materials are used for this:

Preparation device (work stages)

First you need to clear the soil surface and make a pit. Proper preparation deepening involves carrying out a series of works that are aimed at bringing the soil to the desired state. In other words, the soil must withstand the heavy loads specified in the project. It is necessary that after the foundation is laid, the soil tightly grips the foundation from below. First, you should form a pit, clean its bottom with a bulldozer, and then thoroughly compact the base. In addition, during compaction of the pit, the soil should be moistened or dried. Most often, trenches are dug by hand. In addition, builders visualize the surface of the base itself and set the corners of the walls using pegs. After the pit is dug, specialists begin the following stages of construction:

marking the construction site for the foundation;
leveling the area;
Preparation required quantity crushed stones (layer - ten centimeters);
compacting the pillow using a vibration device;
installation of formwork (its height depends on the layer concrete mixture layer;
pouring mortar to the top of the formwork;
reinforcement of the pillow (cross-section of the rods - at least eight millimeters);
compaction cement mixture vibrating plate;
installation of a reinforcement cage that allows you to fasten the crushed stone cushion to the base (they should protrude above the poured concrete by about twenty to thirty centimeters).

Can be installed in concrete reinforced frame, but you can do without this material. In practice, the two options have almost no differences. The only difference is that a pillow created without reinforcement is limited in size. will strengthen the bottom of the cushion, which absorbs the pressure arising from the load of the structure and transmitted through the base.

The foundation is one of the most important components of every building. The durability and reliability of the entire building will depend on the quality of its execution. The concrete under the foundation also plays an important role. In this article we will tell you more about this element and everything that is connected with it.

Preparatory activities during the construction process

First, it is necessary to carry out a set of preparatory work. This includes three main stages, including the following:

first you need to perform the necessary preliminary calculations;
the second stage consists of preparing the site for the foundation;
the third step includes preparatory work immediately before laying the base.

Everything is clear with the first stage - documentation work is being carried out. As for the second step, within its framework the area under the foundation must be thoroughly cleared. There should be no debris left behind, and shrubs, trees and other plants should also be removed. The third stage involves arranging a special pillow for the foundation. For this purpose, crushed stone is used, which must be constantly compacted. To provide such a cushion, lean concrete can also be used. In any case, all the steps are not that complicated, so it is quite possible to do it on your own.

More details about the features of such a pillow are described below. In any case, with regard to the technological requirements regulating the thickness of layers and others important points, then they are set out in the relevant SNiP. Regarding the main goal, the achievement of which is the main task of this type of work, it consists in direct preparation for the construction of the foundation. There are several varieties preliminary work, which includes the footing.

Functions of the footing

The concrete footing is designed to perform a number of different tasks. These include the following:

Protection of concrete from leakage of cement mixture. Thanks to this function, it becomes possible to accelerate achievement required parameters grounds. At the same time, due to the use of concrete footings, the quality will not only be no worse, but in some respects improved.
Redistribution of forces arising in the soil. The footing is capable of leveling Negative influence forces emanating from the ground.
Providing the greatest convenience in the process of reinforcing the structure being built. The leveled surface facilitates work aimed at accurately aligning the foundation frame.

What are the types of preliminary preparation of the base?

Preparation for the foundation is carried out in two ways. This includes crushed stone and concrete. Thus, crushed stone preparation has an undeniable advantage, which consists in significant savings on the total cost of construction work. This is due not only to the low cost of crushed stone, but also to significant savings in the cement component. As for the crushed stone layer, its thickness should be twenty centimeters. This layer must be compacted and then thoroughly compacted.

It should be remembered that this technology is not the most reliable, since it has serious weak side. It lies in the insufficient rigidity that the substrate will have. As a result, the arrangement of the best convenience in the process of further work on installing the foundation is called into question. It is better not to use this kind of operation in cases where serious buildings are being erected. In the event that, for example, it is necessary to install a utility block or other ancillary structure, then the use this method quite justified. Thus, it will be possible to significantly reduce the costs of construction operations.

As for the concrete preparation for the foundation, its arrangement is especially important in cases where there is a need to build tile and strip type structures. This is due to the fact that when using the above technologies for building a foundation, they usually resort to using a rigid frame made of steel rods. Such a frame is most often used before pouring the structure with concrete mortar. There is also another reason, which is that it is much easier to build a foundation on a hard surface. It is also worth noting that the foundation footing becomes especially relevant in winter period. This is explained by the fact that it is at this time that the soil deteriorates its characteristics.

Here are the most important points contained in the instructions:

Arrangement of sand and crushed stone cushion

The sand cushion under the foundation performs the task of ensuring the best redistribution of the load. It becomes especially relevant in autumn-spring period. This is due to the fact that the soil at this time undergoes changes caused by the change of seasons. Using a sand cushion, the lower part of the foundation is raised above the groundwater level. At the same time, any deformation effects emanating from third-party materials and objects are also smoothed out.

A sand cushion is usually installed in cases where the bottom of the pit is located in an area of problematic soil. IN in this case it is necessary to remove some layer of soil and fill in its place with coarse river sand. Its layer should be at least one and a half centimeters thick. Then, using a level, the resulting pillow must be leveled. After this, all that remains is to compact it thoroughly. For this purpose they use specialized tool- rammer.

A sand cushion can be considered to be of high quality only in cases where the level of groundwater is taken into account. In addition, it is extremely important to take into account possible changes in this indicator that occur with the change of season. If you are dealing with a high level, then there is a need to arrange a drainage system. In principle, its construction will not hurt in other cases. For this purpose, it is necessary to dig a trench along the entire perimeter of the building being erected. She will be the protector of the structure from melt water. In addition, with heavy rainfall, the groundwater level also rises, drainage system will cope with this problem too. It is necessary to properly waterproof the trench. The resulting drainage will also prevent water from entering the basement.

Instead of sand, crushed stone footing can also be used under a strip foundation. Compared to the previous type, it boasts better strength qualities. For its arrangement, crushed stone is used, which is poured into a twenty-centimeter layer. It would not be superfluous to provide a small layer of coarse sand, the thickness of which will be about ten centimeters. Using a vibrating plate, the crushed stone bed must be compacted.

We present an algorithm of actions in the process of concrete pouring

After arranging the cushion, we move on to the stage of erecting the formwork structure.
Next, steel reinforcing bars must be laid. Reinforcement is intended to improve the strength properties of the structure as a result.
Then the structure is filled with concrete.
Using a deep vibrator, it is necessary to complete the final compaction of the concrete pad.

This is exactly how the construction of the concrete under the foundation is carried out. In order to guarantee best quality execution of the structure as a result, all work is required to be carried out in accordance with all norms and rules. Neglecting technology is unacceptable; a lot really depends on it.

A durable one is important for a home, reliable foundation. However, for this you should initially prepare quality foundation, on which he will rely, and open ground not suitable for this at all.

Compacted sand and gravel pads are often used, but they are not without disadvantages associated with high drainage and uneven load distribution. The foundation footing will help solve the problem and prepare the foundation, which will be discussed in this material.

The foundation of a house is often a monolithic reinforced concrete structure belt type or stove. Strength directly depends on the quality of the reinforcement, strict geometry of the reinforcement frame and quality of concrete.

All three parameters directly depend on the quality of preparation of the base on which the foundation will be formed.

A bed of sand or gravel is required element grounds for laying the foundation. However, sand and gravel themselves, even when compacted, can negatively affect the quality of the concrete being poured.

You may encounter the following problems:

On a sandy or gravel bed it is difficult to mark with high accuracy angles and all necessary dimensions;
The reinforcement cage rests on supports, bosses or buried reinforcing bars, but they can be pulled down due to the heavy weight of the structure. Even with careful compaction, a point load will displace some of the sand or gravel;
When pouring high-grade concrete over the formwork, part of the cement laitance and mortar will go into the sand, thereby reducing the strength and grade of concrete, this is especially true when using deep-seated hand vibrators.

The foundation footing helps to get rid of the listed disadvantages of the sand cushion. The entire base area is simply filled with thin concrete up to 10 cm thick.

Due to its high fluidity and plasticity, concrete is easily leveled in one plane. For the footing it is not important that part of the solution goes into the prepared sand cushion.

The main thing is that it remains relatively flat plane, much stronger than compacted sand.

The foundation footing is:

a solid basis for installation and preparation of the reinforcing frame;
protection of the base from deformation during all preparatory work;
a surface laid out in one plane on which it is convenient to mark the corners of the foundation;
the location of the walls of the future house and the correspondingly verified installation of reinforcing frame reinforcements.

In addition to this, the footing is an ideal surface for arranging a waterproofing layer, on which the main foundation will be poured.

The waterproofing layer will ultimately be protected on both sides by concrete and will not be subject to deformation, the negative effects of cold soil heaving and even temperature changes along the foundation plane.

SNiP

Strict requirements for the design and quality of the result apply to the construction of concrete monolithic foundations. Basic regulations – these are SNiP 52-01 and SP 50-101-2004. General rules for preparing the foundation, laying the reinforcing frame, selecting concrete and pouring it are stipulated.

The final document to refer to is finished project house, which indicates all the nuances and requirements for the construction of the house and the foundation in particular.

All work is carried out in strict accordance with the construction project, from the schedule to the requirements for marking, preparation of the base and foundation concrete.

The key information for pouring lean concrete is the brand of solution, the thickness of the required layer and, accordingly, the volume of material that should be ordered to the construction site.

It is advisable to take ready-made concrete from production and deliver it using a concrete mixer. For small volumes and small foundations, manual preparation of concrete mortar is allowed. It is important to maintain, first of all, the uniformity and uniform quality of the solution.

Concrete grade

For the foundation footing, lean concrete is used in accordance with the requirements of GOST 25192-2012, GOST 7473-2010. To prepare such concrete, a minimum amount of binder, cement and more aggregate, usually coarse and medium gravel, are used.

The surface of the mortar after pouring turns out to be non-uniform due to the protrusion of the filler; the cement mortar does not cover the gravel and only adheres the stones to each other.

The concrete class or grade is usually used. In accordance with the GOST classification, lean concrete class must correspond to B7.5 or lower and grade M50(75).

These indicators indicate the strength of concrete in a hardened state and are not related to the density of the material. So the higher the class or grade, the stronger the concrete and the more it can withstand loads.

There is no need to use durable or heavy duty concrete. Lean concrete is enough, because its task is only to bind the base, to provide a flat and relatively strong platform on which you can adequately work and carry out preparatory work on the construction of the foundation, without fear of disturbing the already established plane.

Device

The first step is to prepare the site for building a house. Part of the soil with green spaces is removed and compared to the pit level. Next, trenches are prepared for the strip foundation or a pit is deepened over the entire area for a monolithic slab.

Depending on the type of soil and its properties, a sand or gravel cushion is formed. The thickness of the cushion is determined by the construction project based on the load capacity and characteristics of the base.

It is incorrect to compare the footing with a specific layer of sand or gravel; all three materials are involved in forming the base for the foundation.

Compaction of sand and gravel is carried out layer by layer 40-50 mm each. The sand must be moistened.

There are three options:

The footing is carried out without formwork along the bottom of a pit or trench;
Before pouring lean concrete, formwork is installed to cover a larger area;
Before pouring the base, formwork for the foundation is installed, along the bottom of which thin concrete is poured.

Filling is performed according to general rules concreting. The solution is prepared on site or delivered ready-made and distributed over the entire surface.

Using the rule and pre-installed beacons, the surface is leveled. Using hand-held immersion vibrators, the solution is compacted to remove air and ensure tight contact with the base.

Waterproofing

Waterproofing of the concrete base along the lower border is not carried out, except in cases specified in the construction project. Layer waterproofing material spread or applied over lean concrete after it has dried and before laying the reinforcing frame.

Concrete in the base will slow down the capillary suction of moisture under the foundation and will protect the waterproofing layer from cold heaving or any other deformation of the base soil.

The following can serve as waterproofing:

bitumen, which is applied in a layer of at least 2 mm over the entire surface of the base;
roofing felt and other rolled bitumen-containing materials;
geomembrane or dense polyethylene.

Additional fastening roll materials are not required, but it is important to prevent damage to the waterproofing layer before pouring concrete under the foundation. Strips of waterproofing material are laid with an overlap of at least 15 cm.

The result will be a strong and reliable foundation for installing a reinforcing frame and subsequent pouring of concrete.

Many novice builders ask the question “concrete, what is it and why is it needed?” It is not difficult to understand what this structure is, since from the name it is clear that this is a thin layer of material with which the foundation pit is covered before laying the foundation (often such a layer is also called a pillow). However, it is worth deciding why you need to do this, and whether it is necessary to install concrete when building a house or bathhouse.

Why do you need to install a concrete footing?

The concrete footing performs a number of useful functions, namely:

Creates a layer of waterproofing. Thanks to this, during the process of pouring the foundation, liquid cement mortar will not leak. In addition, the moisture in the screed will be distributed evenly and the base will not crack when drying.
Allows you to create a flat surface for a rough concrete base. Thanks to this, the consumption cement-sand mortar decreases.
Protects the foundation from groundwater.
Redistributes the pressure exerted by the soil and ground parts of the structure.
Allows for higher quality reinforcement.
Eliminates shrinkage of the building.

In addition, such a shock-absorbing layer significantly improves the strength and durability of the entire structure. A foundation laid on a concrete base “survives” the winter more easily.

From all of the above, it becomes obvious why a footing is needed, so let’s move on to the varieties of these slabs.

Types of simple concrete footings

There are several types of foundation slab:

Shchebnevaya

This “preparation” is considered more economical, since crushed stone is cheaper cement composition. The crushed stone layer must be at least 20 cm high. During the process of laying the footing prerequisite is thorough tamping (preferably using vibratory tamping equipment).

If it speaks about the shortcomings of “preparation,” then the technology for laying crushed stone footings under the foundation is considered unreliable. The fact is that such a substrate is not rigid enough, so further work on installing the foundation on such a foundation will not be carried out properly. high level. However, if you don't plan to build multi-storey building, then such a concrete base will be quite sufficient for a utility block or bathhouse.

To install a simple base, follow these steps:

Prepare work surface and lay crushed stone on it.
Level it with shovels.
Compact and compact the pillow over the entire surface.
Apply a layer of bitumen to the resulting footing to obtain good waterproofing. If you want to save money, you can use roofing felt or polyethylene instead of bitumen, however, these materials have lower waterproofing properties.

Sandy

“Preparation” of sand allows for the best redistribution of loads on the foundation. It is recommended to lay such pillows in autumn and spring, when the soil undergoes changes. Due to the underlying layer of sand, the lower part of the foundation will be located above the groundwater level, so the monolith will not suffer from the harmful effects of moisture. That is why sand concrete footings are most often installed in areas with problematic soil.

To install such a layer you need:

Remove the layer of soil.
Fill it with river sand in a fraction of at least 1.5 cm.
Using a building level, level the cushion around the entire perimeter.
Compact the “preparation”.

Healthy! To determine required thickness footings, and also choose desired type layers, it is necessary to take into account: soil type, the presence of surrounding buildings, seismicity and effective loads. Detailed requirements and calculations are set out in SNiP 2.02.01-83, as well as in SP 50-101-2004 and SP 63.13330.2012.

Sand and crushed stone cushions are not suitable for all buildings and are characterized by low strength. If you want to make the most reliable foundation for a residential building, then, of course, you should give preference to a concrete slab.

Concrete pad

The construction of a footing of this type requires large financial investments, however, it is this type of base that is best suited for slab and strip foundation. The fact is that when installing such fundamental foundations, a heavy reinforcing frame made of rigid steel rods is installed, which requires a more durable foundation.

Before you start installing the base, you need to consider a few tips:

To install the concrete base, “thin concrete” of classes from B 3.5 to B 7.5 (M 50, 75, 100) is used. There is no point in using stronger cement; besides, it will cost many times more.
To obtain a durable “preparation”, it is enough to lay a concrete pad 10 cm thick (provided that groundwater does not predominate in the area).
Before laying the concrete mixture, it is necessary to pour a thin layer of sand or crushed stone onto the bottom of the pit or trench.
If a reinforcing frame is not used when installing a concrete pad, then optimal thickness the base will be 15-20 cm.

Thanks to the reinforcement of the concrete base, the ground part of the structure will be located on a reliable foundation. For the armored belt, metal rods with a cross section of 8 mm are used. The rods are installed vertically and should protrude above the surface by approximately 25-30 cm. In this case, the thickness of the “preparation” can be reduced by 6-10 cm.

Installation of footings

Let's say you plan to build a house on a site with fairly loose soil and increased level groundwater. To do this you need to follow these steps:

Define highest point groundwater - it is better to do “preparation” exactly to this level. Some install the “preparation” in such a way that it protrudes beyond the underground structure by 10 cm.
Level and compact the soil.
Pour coarse sand into the bottom of the pit, spread it over the surface and compact it thoroughly. For a better effect, you can also lay a layer of crushed stone.
Lay roofing material or polyethylene on top of the sand.
Lay the reinforced frame with cells 60 x 60 cm.
Install guides; it will be more convenient to level the liquid mixture along them.

Mix cement, crushed stone, sand and water until a homogeneous thick mass is obtained.
Fill in concrete mortar and align it with the beacons using the rule.
After the base has hardened, treat the surface with bitumen.

Healthy! In order not to use expensive drilling equipment after the monolith has hardened, it is recommended to think through openings for communications at the stage of laying raw concrete.

In custody

Depending on the type of construction, sand, crushed stone or concrete “preparation” can be laid. Such a cushion will give the entire structure additional strength and protect the foundation from groundwater.

Post Views: 11

If you are not building on a swamp, just waterproof it with sand and you will be happy. I used regular PE film for waterproofing. I laid it on a sand cushion. Even taking into account the numerous holes in the film (the reinforcement was welded and not knitted), the technical underground is dry.. there is dust. The neighbor next door has a tape - the logs in the underground are getting damp.

usa, 02/09/11

amarak said:

If the waterproofing is laid on a concrete base, then there is no need to cover it with another layer of concrete. Nothing will break if you use conventional protective layer fasteners. This is from experience.
In this case, it is better to use fasteners for loose base. , 09.02.11

Hello!
What to say?
People have a mess in their heads. Why does everyone think that without studying at a specialized institute you can advise something “from experience”?
I’ll start with the small things: footing is the internal name of the construction itself, usually engineers or that specialist who has read SNiP at least once, drawn up estimates (not by anyone), drawn up acts of hidden work, calls it: concrete preparation.
It was needed initially, back in “those days” for some strengthening of the sandy, leveling soil, it was correctly said above, to avoid leakage of cement jelly into the sand, for ease of installation of reinforcement, etc., in “those times” there were no films, insulation -limited, you don’t mind the concrete, and to compensate for small salaries they laid in a lot of other things.
Well, then, decide for yourself (the customer): should you count evaporation, coefficients, or something else? It's time to get things done. Decide on the soil on your site, drill about ten holes with a small diameter drill, in the corners, at the joints of future walls, in places where the axes intersect to a depth of ~ 1.4 m, when excavating the soil, you will see the composition of the soil layer by layer, its moisture content, depth (if God forbid you get caught) groundwater, puff or hire someone, for yourself, your beloved, there are all the descriptions about soils on the Internet, well, lay it down, even polyurethane, even waterproofing, even geotextiles, dance from the soil, and yes, I agree , without further ado, sand cushion or leveling sand layer, concrete preparation, waterproofing, screed, etc., ugh, sorry
, 11.02.11
Here is the correct economic scheme from an ASG engineer, i.e. me:
-removal of the vegetation layer 300mm (usually a shovel bayonet);
-laying geotextiles with an overlap of 10-15cm at the joints
-sandy base made of alluvial sand with 200mm compaction;
- crushed stone base (fr. 5-20 or 20-40mm) 100mm;
-laying roofing felt with an overlap of 10-15cm (coat the overlaps with waterproofing mastic);
-installation of formwork from boards 40mm thick (not 25mm);
-reinforcement of a slab D=12mm 200x200mm in 2 tiers by KNITTING rods while maintaining a protective layer of 30-50mm;
- concreting with READY-MADE (factory-made) concrete of a grade not lower than M300, which corresponds to class B22.5 using a submersible vibrator, the thickness of the slab should be no less than 200 mm, and preferably from 250 mm;
If there is a desire to raise the slab higher, we increase the thickness of the sand base.
I’ve been working on foundations for 5 years now - I consider this “pie” optimal
#10 , 11.02.11
PROrab82 said:

It compacts and declumps well and is easily leveled with normal vibratory ramming.
And then make a cut into the “pie”, can you tell where the sand is and where the crushed stone is?! In this case, the question is, “What the hell is this accordion for?”, what are we achieving using crushed stone?
Viktor Petrovich said:

The footing is needed for further laying of the reinforced frame
If according to by and large that the reinforced frame is prohibited or impossible to lay on the ground? Before you make any body movement, you need to think. The footing is made to make work on site more comfortable, to provide more reliable waterproofing and to securely fix the lower part of the formwork. Anyone who wants to save money can avoid doing it, adding to the hassle. #21 , 13.02.11

Dear colleagues!
I read the topic and understand that many simply do not understand the meaning of waterproofing... which everyone strongly recommends sticking, spreading, etc. Comrades, we are not in the Soviet Union... in our time, the need for gluing and coating of any materials has completely disappeared... unless it is a special object with specific requirements for the deformability of the waterproofing layer!
Now there are a number of measures that make it possible to completely avoid the process of gluing, coating, spraying waterproofing on the surface of concrete to protect it from the effects of an aggressive environment (as a consequence of corrosion and destruction of concrete and reinforcement and a decrease in the service life of the structure), these are additives to concrete that increase its waterproof grade and imparts properties such as resistance to aggressive environments, increased frost resistance, etc.
That is, I think that after carrying out measures to compact the soil, it is possible to lay a PE film (to prevent the leakage of cement laitance into the soil, as a result of a decrease in the performance of concrete) and pour concrete with an additive, at the end we have waterproof concrete, resistant to aggressive environments... this that waterproofing that will not tear or rot.
Conclusion: make a “concrete base” for the convenience of applying waterproofing foundation slab It is not advisable both economically and functionally.
#33 , 21.06.11
In short, I understood one thing. Concrete footing is not needed at all, just like crushed stone. Especially concrete footing. It’s just money thrown away! Here, no one could clearly explain its purpose! It is best to dig a 30 cm pit. Then geotextiles. Then fill 20 cm with sand with a wet tamper and on top 10 cm of fine gravel with a fraction of up to 0.5 (screening). Then the cheapest roofing material and that’s it! Tie the reinforcement and pour the slab itself. Waterproofing (2 rows of glass insulation) is needed between the foundation and the outer wall. Why is it under the slab? And the cheapest roofing felt (only $80 for an 11x11 house) will only serve to prevent the leakage of cement laitance. And regarding the reasoning that it is better to pour the slab on sand than on gravel, I think this is a misconception. First of all, gravel is drainage and it does not attract moisture, unlike sand, which means the slab itself will always stand on dry ground! So it’s better to pour on gravel. Basically on the first page
Regarding TEFOND, as one of the developers here sent a photo, that’s my personal opinion. Of course it’s beautiful. But why is it there? Better if the price of TEFOND is at least 4 dollars square meter and note that this is the cheapest one, put 30mm EPSS instead. The money is the same, but the benefit will be ten times more, if not a hundred. For that kind of money, so that the cement milk does not go into the ground, there is nothing for him to do there. But that's my opinion.
#51 , 31.12.11
Based personal experience receiving concrete from factories in the Moscow region and Moscow, I have not yet had a single case of receiving falsified concrete (they sin underloading) Although we use the main brands 100-200. and rarely 250 if in short time it is necessary to obtain the necessary minimum strength to carry out the work.
The advice is simple: don’t take it from an intermediary, go to the factory. Intermediaries (he also caught foremen by the hand) and are engaged in falsification with the replacement of brands and mobility with individual representatives of the plant with whom they share. Today, competition in the concrete market is high and the factories themselves do not engage in such matters.
#73 , 10.08.12
Ready-mix concrete already contains super C-3 (or an analogue). Self-pouring will only spoil the concrete with an overdose...
And here are the designers (also a mess) with SNIPs
Concrete or crushed stone preparation? - Reinforced concrete structures
SP 50-101-2004 DESIGN AND CONSTRUCTION OF FOUNDATIONS AND FOUNDATIONS OF BUILDINGS AND STRUCTURES
12.8.6. Under monolithic foundations Regardless of the underlying soil (except rocky), it is recommended to provide a concrete preparation device with a thickness of 100 mm. It is allowed to use crushed stone or sand preparation with cement screed. The thickness of the protective layer of concrete for the working reinforcement of the base of the foundations is taken to be at least 35 mm.
When justifying Concreting of foundations without preparation is allowed. In this case, the thickness of the protective layer is taken to be at least 70 mm.
P/e film eliminates all fears, including far-fetched ones - milk leakage, capillary suction, and... what else? #74 al185 , 03.20.13

AlexKuban said:

If you are going to insulate the blind area, then, excuse me, how will the soil under the house freeze? Forgive me for the stupid questions...I'm a fool...But there aren't enough ARGUMENTS here for a self-builder...
The foundation slab is often broken by frost heaving right in the first year of construction if it is not insulated for the winter. During operation, it does not require insulation. #84 baus , 04/27/13

Footing, or how concrete preparation can be done correctly, or not. Depending on this, the protective layer of the reinforcement changes. And waterproofing according to concrete preparation done at high groundwater, above the slab.
#150 , 12.11.13
gatch78 said:

It somehow seems to me that after crawling on the sand for one season, this film will turn into scraps. or not?
The film is not laid under the elosion, but under polystyrene foam or concrete. Film reinforcement, TP pipes, concrete acceptance. Not at any site...
I don’t provide links with reports: you won’t read it until the process of generating and chewing on your own fears allows it...
You will have to overpay for imaginary fears... #164 al185 , 11/19/13

My two cents:
Concrete footing is not needed.
Film is not needed.
Now I'll try to explain. The footing, as a rule, is positioned either as protection for waterproofing or as a base for it. Let us consider the step-by-step construction of a non-buried foundation of the “floating slab” type:
1 – Pit. The depth of the pit is determined by nothing more than the thickness of the plant layer of soil; as a rule, I initially do not consider options for four meters of peat, etc., this is a separate story. The bottom of the pit must be smooth and dry. If there is wet clay at the bottom, it should be removed; if this is not possible, then it should be filled with a coarse fraction of crushed stone, thin layers, tamping it into the clay. Under no circumstances should you start pouring sand if there is liquid clay in the pit.
2 – geotextile, ideally darnite, the role of this material is to prevent mixing of the base soil and the backfill material. Geotextiles are laid on the dry and level bottom of the pit, no matter how you achieved this, and whether you had to come out of the mud with crushed stone.
3 – Pillow. The role of the cushion in uniformly distributing the load from the foundation onto the foundation soil. In addition, drainage is laid in it (and, of course, communication lines). I always make a sand pillow. It doesn’t necessarily have to be alluvial, although that’s not a bad thing. It must have a high filtration coefficient and have a medium or large fraction. Sand is checked quite simply: if in a pile of sand that was brought to you, make a hole and pour a bucket of water into it, then the water should go away, if this is the case, then the sand is good, if slurry has formed at the bottom of the hole, then no. There is one small digression here. Although it is believed that a “floating slab” type foundation is capable of absorbing loads caused by soil heaving, IMHO, it is better to play it safe and make a cushion of at least 40 cm, even if there was less plant soil. Reinsurance is quite justified, given that the depth of soil freezing is taken based on the most unfavorable conditions, i.e. wet clay in an open field without snow cover, at maximum negative temperatures for a given area, which last for the maximum possible time. That is, in reality, forty centimeters of drained sandy base most likely will not freeze at all.
4 – Waterproofing. Since the base is drained and the foundation is not buried, it is not serious to say that it will stand in a puddle. As a rule, when digging a pit, the excavated soil is used to level the area and create a small “hill” on which the house will stand. That is, waterproofing is aimed at preventing capillary suction of moisture from the pillow. Is there a lot of moisture there? Let us also take into account that side surfaces the foundation is subsequently insulated with EPP and EPP is also laid under the blind area, which is not only insulation, but in some way also waterproofing. Actually concrete is not afraid of water liquid state, concrete is afraid of water, which will freeze in it, and for there to be a danger of destruction of concrete, it must not only be wet, it must be saturated with water as much as possible. For example, we can consider reinforced concrete quay walls; they are destroyed in the zone of ice formation. Below and above this level they are generally in excellent condition.
5 – It’s worth considering separately the versions about cement laitance leaving somewhere. Nothing flows from normal concrete in such critical quantities. All these puddles on the surface of the foundation are nothing more than excess water in the concrete, which was either swelled there in a factory with a crappy laboratory, or added by a mixer to make it drain faster, or by the builders themselves to make it easier to lay. There is such a term: Water-cement ratio. That is, in a concrete mixture, a strictly defined amount of water must be added for every kilogram of cement, taking into account the moisture content of the inert materials. Apparently, many concrete plants have not even heard of this. Further, clamps for reinforcement used on a soil base determine the thickness of the protective layer with a huge margin from what is required, i.e., even if some of the milk goes into the sand, it will not affect the strength of the structure in any way. In addition, just for fun, do an experiment, pour a small slab on sand and when it gains strength, turn it over, make sure that the stories about cement milk leaking into the unknown are nothing more than fairy tales.
6 – Slab thickness. This parameter is primarily determined by how high you want the floor to be raised above ground level. You can pour a slab of almost any thickness, but you need to understand that the thinner the slab, the more reinforcement there is. It won't be possible to tailor it here. No way. We poured different slabs, both regular and with stiffening ribs, and “inverted” and double. Practice shows that structurally complex foundations bring very illusory savings on materials, but the work costs significantly more. Today, the most frequently poured slabs are from 400 to 600 mm thick. Ordinary, without ribs and other frills. For those who understand how reinforcement works and don’t stupidly put 12a3 everywhere in increments of 200, it will be clear what I mean.
PySy: “I ate oysters,” if anything, on the topic for 13 years, including since 2008 in suburban construction, before that major renovation hydraulic structures.