Footing: simplest and capital. Purpose and methods of the device

Quality base guarantees the durability and strength of a residential building. Proper preparation foundation will provide long service structure, will prevent leakage of cement during pouring. The work is carried out in accordance with regulatory documents and in strict sequence.

The need for concrete footing

Area prepared for pouring cement mortar, provides a reinforced and leveled base. The concrete layer plays the role of a barrier that can protect the underground monolith from shrinkage and seepage of materials into the ground. A footing laid under any foundation will contribute to:

eliminating leaks of cement mixture;
rapid expansion of the fundamental structure and improvement of its performance indicators;
leveling the impact of moving soils by uniformly dispersing the mass over the area of the product;
weakening the influence of swelling soils;
creating conditions for the installation of a reinforcing frame.

Thanks to concrete preparation, a level surface of the soil is achieved, conditions are created for comfortable and quick work.

Standards for organizing footings

The installation of concrete preparation for the foundation is regulated by regulatory documents. Builders are guided by SNiP 52-01-2003, which indicates the type of base material - crushed stone, profile membrane or lean concrete. The document also contains instructions for the calculation, production and operation of cement paste bases. Content regulatory rules comes down to a few key points:

use of M50 grade composition for the production of lean concrete;
construction of a sand-crushed stone cushion before pouring the mixture;
arrangement of the footing with a layer of 10 cm;
keeping the poured mass for 28 days;
design and construction of the foundation, taking into account the type of soil, nearby architectural objects, load, seismicity and environmental friendliness of materials;
use of reinforcement for the frame (hot-rolled with a diameter of 3-80 mm, strengthened with a diameter of 6-40 mm, cold-deformed with a diameter of 3-12 mm).

It is necessary to calculate the load of the structure if the soil compresses during the cold season, the building will be located on a slope or in a hilly area, and the base of the foundation is located on a surface with an unstable composition. In addition to the main collection of standards, SP 50-101-2004 and SP 52-101-2003 are used.

Digging a pit - preparatory activities

The main goal of the work is to prepare the construction site for the future foundation. At this stage, the soil is treated so that it can withstand the construction and fit tightly to the base of the structure. The tasks are carried out sequentially:

A pit is dug across the width of the building.
The bottom is cleared of debris, stones and plant roots.
The bottom surface is compacted by compaction.
The soil is moistened or drained according to the type of subsequent activities.

The pit must be equipped before the construction of the concrete base begins. In private housing construction, it is advisable to do digging manually.
Depending on the load of the building and the mobility of the soil, there are two traditional methods - laying crushed stone and pouring concrete mixture. Modern manufacturers offer special membranes that are convenient for concrete preparation.

Application of crushed stone

Crushed stone preparation for the foundation will reduce the cost of construction activities and reduce cement consumption. Gravel and crushed stone are laid when the construction of a base from monolithic slab or on pile grillages. When organizing a pillow, it is worth considering some nuances:

The crushed stone layer is laid to a thickness of 10-20 cm.
Bulk medium-fraction material is compacted and then filled with bitumen.
The crushed stone type of structures is relevant for the purpose of maximum saturation and compaction of the earth.

Laying crushed stone will not provide the required rigidity for the substrate of a private house. In a similar way, the concrete base is prepared for the foundation of ancillary buildings and technical structures.

Making a pillow from lean concrete

Concrete preparation under the foundation - a standard type of work that creates the most durable product. In this case, the ground will not sag, and the building will be securely fixed. Before the start of the event, cement paste is prepared.

What is skinny concrete?

A solution containing 6% cement with strength B15, gravel or crushed stone fillers is called lean concrete. The composition is mixed from cement grade M100. Due to the minimum number of components, the mixture is quickly hydrated, prepared and hardened. The recipe for lean concrete provides:

using 275 kg of cement, 590 kg of sand, 1377 kg of gravel and 165 liters of water per 1 m2 of mixture;
filling a 200 liter concrete mixer with 44 kg of cement, 94 kg of sand, 220 kg of gravel and 26 liters of water;
consumption per bag of cement weighing 25 kg is 54 kg of sand, 125 kg of gravel and 15 liters of water.

All components are carefully measured. If the developer has a concrete mixer, water is poured into it and cement is poured. Sand and gravel are introduced gradually, with water added in small quantities. Liquid plasticizers are also mixed with water and added at the end of mixing. The mixing time of the composition should not exceed 5 minutes.

Construction of a footing from lean concrete dough

Preparation for the foundation using lean concrete is carried out according to the following algorithm:

Calculations are being carried out bearing capacity buildings taking into account soil type, groundwater level.
The territory is marked and formwork is installed at 30 cm.
A solution is being prepared. The ingredients are selected based on the height of the pillow - 4-10 cm.
A pit is dug and filled 10 cm with crushed stone. The material must be compacted.
Concrete dough made from thin material is poured under the upper edge of the formwork.
The concrete footing is reinforced with reinforcement with a cross-section of at least 8 mm and compacted with a vibrating plate. The rods should protrude by 20-30 cm.

When carrying out construction, keep in mind that you need to protrude 10-15 cm beyond the base - this increases the size of the preparation and strengthens the structure. The thickness of the concrete preparation will be determined by the characteristics of the soil, the load on the foundation and the area of the house. The parameter specified in SNiP is 4-10 cm.

Construction from profile membranes

Profile membranes are polyethylene plates reinforced with stiffeners. In addition to preparing the foundation, the products can waterproof basement rooms, holding the pressure of soil water on the walls. The construction of the footing is carried out sequentially:

The surface of the pit is cleared of debris.
They build a cushion of crushed stone up to 13 mm in size, raising it by 10 cm. This neutralizes the capillary action of water.
The substrate is poured with concrete dough, which, after drying, is treated with a primer or primer.
Bituminous mastic is applied to the surface of the slab.
Roll out the profile membrane, placing it with protrusions down. When laying the geotextile, the protrusions are brought out.
The membrane tapes are laid overlapping, and then each seam is taped with butyl rubber tape, which eliminates excess consumption of the cement mixture.

On last stage Laying the material seals the joints with self-adhesive tape or liquid sealant.

Footing for various types of foundation

In private housing construction, monolithic and prefabricated strip bases. Concrete preparation – necessary condition construction of each of the foundations.

Footing for the base-tape

The work is carried out sequentially, adhering to the requirements of building regulations:

They mark the area for the strip monolith and level the soil.
Fill with crushed stone to a height of 10 cm and compact. The laid material is filled with liquid bitumen.
The formwork is installed and reinforced. A mesh of rods with a diameter of 8 mm is placed according to the design.
Poured concrete mixture along the height of the formwork and compacted with a vibrating plate.

After the composition has hardened, the formwork frame is dismantled and the side surfaces are waterproofed using mastic.

Preparation for prefabricated strip base

The concrete base is poured intermittently, and special blocks are purchased to make the foundation. The workflow can be followed step by step:

Make a base of sand, pouring and tamping each layer. The layer of material is no more than 10 cm.
Formwork is installed on top of the sand embankment.
Concrete dough is poured according to the level of the sections.

The sand cushion is only relevant for outbuildings.
Concrete preparation of the construction site for necessary foundation, made according to regulatory documents, provides savings in materials. The quality of roughing and marking activities is maintained. No footing is made during formation self-leveling screed floor on flat slab. In other cases, preparation is needed to increase the service life of the building.

In fact, it is very simple to understand what a footing is. Here even the name speaks for itself - this is a layer of thin concrete, which is prepared for comfortable and economical pouring of the main volume of the mixture. Essentially, this layer is placed under the main layer of concrete when installing slab foundations, For example.

But why exactly this needs to be done (and whether it is necessary at all) is worth understanding in detail. In addition, it will be useful to consider what the installation instructions for such a base are.

Photo of the simplest concrete substrate

Let's start with the most important thing.

Purpose of the footing

Pouring the solution onto a pre-prepared base

It is worth noting that the preparatory layer can be made different ways and different materials can be used. However, the meaning and purpose of this work remains the same (read also the article “Methods of gluing materials such as polystyrene foam and concrete in order to create high-quality insulation”).

Purpose of the work What does this give in practice Leveling the rough foundation. This allows you to reduce the amount of the main mixture when pouring, that is, save a little. This happens due to the fact that the concrete layer will be laid evenly and there will be no leakage of the solution into unknown holes. Preparing the surface for easy installation various elements designs. The convenience lies in the fact that on a flat area you can make markings much faster, assemble a frame from reinforcement and install beacons, for example. Agree that this is not so easy to do on loose soil with holes and bumps. Creation of a waterproofing layer. This means that due to the presence of the concrete base, when pouring the bulk of the mixture with your own hands, moisture will not disappear from the solution. Accordingly on finished slab or the screed will not develop cracks, which usually form due to uneven distribution of moisture within the structure of the working area. Creation of protection against groundwater. That is, if this layer is made under a slab-type foundation and at the bottom of the pit often appear groundwater, then in this case the footing is required to take the moisture “on itself” and prevent it from passing further into the main load-bearing layer of concrete.

Example of a slab foundation

In addition, the presence of such a shock-absorbing layer improves the strength characteristics of the entire structure as a whole. At a minimum, due to the fact that the base layer dries and gains strength better and of better quality.

Please note that the installation of concrete footings involves the use of inexpensive concrete mixture. As a rule, “skinny” concrete B3.5-B7.5 is used. That is, it turns out that thanks to the preparation of such a layer, the overall cost of the project is reduced, since a significant amount of the total cubic capacity is filled with a composition with a lower cost.

So, why this kind of work is needed is probably clear. Now let's figure out how this is all done.

Methods for constructing a footing

Before we begin, it is worth noting that concrete footing is, first of all, a very desirable measure, but not always mandatory (see also the article “ Expansion joint in concrete: the need for application and implementation features").

That is, simply put, if you have a small-scale project and the rough foundation consists of an old screed and there is no trace of loose soil or uneven terrain, then it is simply impractical to carry out such work.

So, objectively assess the situation - you shouldn’t waste your money where such additional work will not affect the final quality in any way.

Let's return to the options for constructing such a layer. As clear example Let's take preparations for pouring a slab foundation.

Installation of the simplest concrete footing

For work we need this:

Crushed stone.
Tamping device. It is easiest to make from wood or metal.

Compacting crushed stone

Liquid bitumen.
Good and durable shovels.

We can begin.

It spills onto the work area required amount crushed granite. Typically, the material is dumped from a dump truck and the end result is a large pile of rubble.
Using shovels, the stones are evenly distributed over the entire surface.
A tamping device is taken and the crushed stone is compacted over the entire area.
A layer of bitumen is applied to the resulting surface.

Advice: you can save money and use not bitumen, but more or less durable roofing felt or even film. In any case, this will not provide particularly good waterproofing in the future, but at least these materials will allow the concrete to harden efficiently (without loss of moisture).

In general, the simplest version of the concrete footing has been implemented.

Now let's look at how to do this as correctly as possible.

Installation of capital footing

An example of a completed concrete base

So, we have a working area with loose soil and the risk of groundwater.

We determine the highest point of groundwater - the footing will have to be made just up to this level (well, in any case, it is advisable to do it this way).
Using shovels, we try to level and level the soil.
We pour sand into the bottom of the pit and distribute it evenly over the surface, and then tamp it.
Lay a film or roofing material on top of the sand.
From thin reinforcement we make a kind of “cage” with a cell size of approximately 60 by 60 cm.

Photo of a frame made of reinforcement

If desired, we install guide lines - beacons. It is convenient to stretch the mixture over them to get the most even surface in the end.
Mix cement, sand, crushed stone and water - you should get a homogeneous thick mass.
We pour the solution and, using the rule, distribute it over the entire area.
After the solution has dried, it needs to be treated with bitumen and, in fact, the construction of the footing is completed.

Advice: in almost every similar design then holes are made for communications. As a rule, this involves cutting reinforced concrete with diamond wheels using a grinder or simply drilling using a standard hammer drill. But you can make the work much easier and faster if you “lay” such holes in advance - in the concrete that is still wet.

But even if you simply simply forgot about such moments, and not only the lining layer, but also the main slab has already been poured, then you should not despair, because you can always use such a service as diamond drilling of holes in concrete with powerful industrial equipment.

In principle, that's all. The technology review is complete. Let's summarize.

Conclusion

We have figured out in detail what this is - concrete footing and how it is made. We also learned in which cases it is worth doing and in which it is not. We hope that all the information provided will be useful to you in practice (find out here how to pour concrete steps yourself).

Well, if you want to know more, be sure to check it out. additional video in this article - there is a lot of interesting and useful information in this video!

In fact, it is very simple to understand what a footing is. Here even the name speaks for itself - this is a layer of thin concrete, which is prepared for comfortable and economical pouring of the main volume of the mixture. In fact, this layer is placed under the main layer of concrete when constructing slab foundations, for example.

Let's start with the most important thing.

Purpose of the footing

It is worth noting that the preparatory layer can be made in different ways and different materials can be used. However, the meaning and purpose of this work remains the same ().

Goal of the work	What does this give in practice?
Leveling the rough base.	This allows you to reduce the amount of the main mixture when pouring, that is, save a little. This happens due to the fact that the concrete layer will be laid evenly and there will be no leakage of the solution into unknown holes.
Preparation of the plane for convenient installation of various structural elements.	The convenience lies in the fact that on a flat area you can make markings much faster, assemble a frame from reinforcement and install beacons, for example. Agree that this is not so easy to do on loose soil with holes and bumps.
Creation of a waterproofing layer.	This means that due to the presence of the concrete base, when pouring the bulk of the mixture with your own hands, moisture will not disappear from the solution. Accordingly, cracks will not appear on the finished slab or screed, which usually form due to uneven distribution of moisture within the structure of the working area.
Creation of protection against groundwater.	That is, if this layer is made under a slab-type foundation and groundwater often appears at the bottom of the pit, then in this case the footing is required to take the moisture “on itself” and prevent it from passing further into the main load-bearing layer of concrete.

Please note that the installation of concrete footings involves the use of inexpensive concrete mixture. As a rule, “skinny” concrete B3.5-B7.5 is used. That is, it turns out that thanks to the preparation of such a layer, the overall cost of the project is reduced, since a significant amount of the total cubic capacity is filled with a composition with a lower cost.

So, why this kind of work is needed is probably clear. Now let's figure out how this is all done.

Methods for constructing a footing

Before we begin, it is worth noting that concrete footing is, first of all, a very desirable measure, but not always mandatory ().

So, objectively assess the situation - you shouldn’t waste your money where such additional work will not affect the final quality in any way.

Let's return to the options for constructing such a layer. As an illustrative example, let’s take the preparation for pouring a slab foundation.

Installation of the simplest concrete footing

For work we need this:

Crushed stone.
Tamping device. It is easiest to make from wood or metal.

Liquid bitumen.
Good and durable shovels.

We can begin.

The required amount of granite crushed stone is poured onto the working area. Typically, the material is dumped from a dump truck and the end result is a large pile of rubble.
Using shovels, the stones are evenly distributed over the entire surface.
A tamping device is taken and the crushed stone is compacted over the entire area.
A layer of bitumen is applied to the resulting surface.

Advice: you can save money and use not bitumen, but more or less durable roofing felt or even film. In any case, this will not provide particularly good waterproofing in the future, but at least these materials will allow the concrete to harden efficiently (without loss of moisture).

In general, the simplest version of the concrete footing has been implemented.

Now let's look at how to do this as correctly as possible.

Installation of capital footing

So, we have a working area with loose soil and the risk of groundwater.

We determine the highest point of groundwater - the footing will have to be made just up to this level (well, in any case, it is advisable to do it this way).
Using shovels, we try to level and level the soil.
We pour sand into the bottom of the pit and distribute it evenly over the surface, and then tamp it.
Lay a film or roofing material on top of the sand.
From thin reinforcement we make a kind of “cage” with a cell size of approximately 60 by 60 cm.

If desired, we install guide lines - beacons. It is convenient to stretch the mixture over them to get the most even surface in the end.
Mix cement, sand, crushed stone and water - you should get a homogeneous thick mass.
We pour the solution and, using the rule, distribute it over the entire area.
After the solution has dried, it needs to be treated with bitumen and, in fact, the construction of the footing is completed.

Advice: in almost every similar structure, holes for communications are then made. As a rule, this involves cutting reinforced concrete with diamond wheels using a grinder or simply drilling using a standard hammer drill. But you can make the work much easier and faster if you “lay” such holes in advance - in the concrete that is still wet.

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 times” 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 in your area, 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
What if, by and large, 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 for more comfortable work on site, to ensure more reliable waterproofing and for reliable fixation of 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 result 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: making a “concrete base” for the convenience of applying waterproofing to the foundation slab 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 has not yet had a single case of receiving falsified concrete (underloading is a sin) Although the main brands we use are 100-200. And rarely 250 if in a short time we need to obtain the necessary minimum strength for 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 it changes protective layer fittings. And waterproofing using concrete preparation is done when groundwater is high, 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, in 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. He should be with high coefficient filtration 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 open field without snow cover, at maximum negative temperatures for a given area, which last as long as possible. That is, in reality, forty centimeters of drained sand base Most likely they won't 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 in a liquid state, concrete is afraid of water that will freeze in it, and, moreover, 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 fill a slab of almost any thickness, but you need to understand that what thinner slab the more reinforcement. It won't be possible to tailor it here. No way. We poured different slabs, and 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, has been on the topic for 13 years, including since 2008 suburban construction, before major renovation hydraulic structures.

The difference in the quality of the foundation of houses depends not only on the materials used for construction, but also on how the site was prepared before construction began. When building a house, it is worth deciding whether the concrete preparation for the foundation is suitable as the highest quality and most stable, or whether it is better to choose another one for this soil. Sand or crushed stone preparation is less reliable, more difficult to create, but cheaper in building materials and installation time.

What is preparation used for?

Most often, concrete preparation is used for a poured foundation or to increase the strength and stability of the foundation of a house.

Reasons to make a concrete footing:

Additional waterproofing, which slows down the rise of moisture from the soil into the foundation.
A level construction site, removes any unevenness left when digging a pit by equipment or builders, allows you to level out differences of up to 10 cm.
Prevents the absorption of “concrete milk” into the soil, due to the fact that concrete pouring not produced at open ground, and on a solid base, the base, when hardened, has the same density, which increases its performance.
Facilitates the installation of reinforcement, makes it possible to use clamps, protecting the base reinforcement from corrosion.
Eliminates bending of reinforcement due to pressing into the ground under the weight of uncured concrete.

What types of preparations are there?

Preparing the site for a monolithic or strip foundation, can choose different materials depending on the required characteristics, budget and difficulties in installing on your own. The main reasons to choose one or another option are the endurance of the soil, its moisture content, and whether a basement or a basement is planned. It is also important what type of support will be used, not recessed, shallowly recessed or recessed. From what materials and in what way will it be built, poured or from ready-made blocks, strip or slab.

Unfortunately, SNiP 52-01-2003 and SP 50-101-2004 do not give clear recommendations in which case and what kind of preparation to carry out, so the reason for the choice is the type of foundation and the materials used for it.

Sand preparation

The simplest and cheap way level the ground for construction, this is sand preparation for the base, for light wooden houses used quite often, but not suitable for houses with a design life of more than 10 years. It is unreliable; gradual mixing with the soil and germination of plant roots causes subsidence under the weight of the building, and distortions and cracks of floors and walls are possible. Low moisture resistance requires additional waterproofing to prevent dampness in the premises.

Concrete preparation

“Lean” concrete is used with a maximum of 6% cement content, the main filler of which is sand, sometimes crushed stone or gravel. Poured thin layer over the entire area of the future foundation, the thickness of the concrete preparation depends on the type of soil, the weight of the house and the level of groundwater. Depending on these three factors, the thickness can be from 4 to 10 cm.

Preparation with profile membranes

A new way to prepare a foundation, easy to install and less expensive than concrete or crushed stone. Despite manufacturers' assurances of strength and similar durability, it is in less demand.

If possible, proven concrete footings are often chosen. Because of additional expenses for thermal insulation, the cost can reach the price of standard preparation.

Crushed stone preparation

Crushed stone preparation for the foundation is used if reinforcement or uneven weight distribution is not provided. Crushed stone is poured with a thickness of 15 to 20 cm, filling it with bitumen until a film forms or the layer is completely saturated. For heavy houses it is unreliable due to the heterogeneity of the crushed stone and can lead to warping and cracks in the foundation and walls.

In the cold season, crushed stone preparation is almost not used due to the difficulty of creating desired temperature for bitumen filling.

Preliminary work before pouring the concrete base

The construction of the foundation and preparation for it begin with geotechnical work to find out how deep the groundwater lies and what pressure the earth can withstand at the site of the future house. A construction plan is drawn up and the type of foundation is selected, monolithic or strip, poured or prefabricated.

Before creating a concrete pad, it is necessary to mark the territory in order to dig a pit. It should make it possible to make formwork for pouring, so an indent of at least 30 cm is made on each side of the future support.

The fertile layer of soil is removed and transferred to another place where it can be used. The depth of the foundation pit should be at least 20 cm greater than the planned height of the support.

If thermal insulation is installed, the depth of the pit is increased by the width of the additional layers.

Method for preparing lean concrete

Skinny concrete is called because it is very little content cement, which, due to its fragility, makes it useless for full-scale construction, but ideal for concrete preparations for the foundation. Depending on durability, the choice is provided by 2 classes of concrete mixtures, these are B7.5 and B15, the latter is more difficult to use due to the high content of expanded clay.

To obtain a cubic meter of ready-made solution from B7.5 you need:

160 kg of cement is 6.4 bags of cement weighing 25 kg each;
2.2 tons of sand;
75 liters of water.

All ingredients must be mixed well and poured onto the prepared area.

When making B15, special equipment is needed to obtain a uniform consistency of the finished mixture.

Footing for a monolithic slab

10 cm of crushed stone or sand is poured onto the cleaned space and compacted using a vibrating plate. This is done to remove excess moisture from the base, making it last longer.

Formwork is mounted on the crushed stone cushion, into which a concrete mass of B7.5 cement will be poured. The formwork is made at such a height that the poured concrete forms a level top on which the foundation of the house will be laid. It must be a minimum of 10 cm and a maximum of 30 cm in height.

Often, when installing formwork, it is recommended to install concrete preparation for the foundation with an area reserve of 10–30 cm relative to the foundation. This is done in order to reduce pressure on the ground and leave space for thermal insulation and Finishing work, which prevent the destruction of the foundation from the walls.

Concrete is poured flush with the top of the formwork, leveled and sometimes compacted using a vibrating plate. For better adhesion to the poured foundation slab, rods 0.8 cm in diameter are installed in the footing, protruding 10 cm from the preparation; if the base is planned to be large, then the footing will have to be poured in parts in order to insert the connecting reinforcement.

If a ready-made concrete slab is purchased and not poured, then the rods are not installed.

The layer of thin concrete is then left to dry for 7–21 days depending on the weather. Sometimes for heavy buildings the substrate is reinforced with a mesh with reinforcement 0.8 cm in cross section. In addition, the size of such a substrate must be at least 15 cm.

If the connecting rods were not installed in the substrate, then it is recommended to lay layers of waterproofing, thermal insulation made of EPS, and then waterproofing again on the finished flooring. After this, you can install the formwork to fill the monolithic base slab.

How concrete preparation is poured and insulated can be seen in the video:

Footing for strip base

Concrete preparation for a strip foundation differs from preparation for a slab. They dig a trench that is 40 cm wider on each side of the foundation strip. Level the bottom of the trench and lay waterproofing. Formwork with a height of 20–30 cm is installed and the concrete mixture is poured.

The width of the concrete strip should be 15 cm greater than the base on each side. If you plan to use a poured strip foundation, the concrete footing is reinforced with rods for better adhesion.

When a buried strip base is built from ready-made blocks, it is advisable to use a preparation made of crushed stone impregnated with bitumen, compacted with a vibration plate. Sometimes waterproofing is placed on top and a second layer of concrete is poured for better resistance to damage.

With a shallow or shallow foundation on stable soils, leveling with sand or compacted crushed stone without bitumen is possible. Due to the lightness of the building, such a foundation does not require serious strengthening.

Preparation for a columnar foundation

For pile foundations they are more often used sand preparation due to the functions of the foundation itself. It is installed for light houses and on stable soils. Most often, it does not require additional amplification. If the house under construction is heavy enough, then crushed stone filled with bitumen is used. Concrete substrate is used extremely rarely, due to the ability to buy small concrete plates, which are more reliable than poured ones.

Whatever the foundation and the house, in most cases concrete preparation will extend the service life and, spending money during the construction phase, will prevent spending on more expensive foundation repairs.