Novice builders often ask themselves a question - do you really need a pillow under the foundation. We recommend a small experiment. Put a regular pillow on a pile of rubble or gravel and sit on it. Conveniently? Now remove the pillow and sit right on the gravel. Do you feel the difference? That's the house. He also wants to feel comfortable and confident - not to sag, not to heel, not to crack, and so that his inhabitants would feel the same comfort and confidence.
Its primary task is to provide the highest strength and reliability of the foundation, and therefore the entire structure as a whole. The pillow is soil (a layer of compacted soil within the zone of deformation of the foundation), sand, gravel or sand and gravel, gravel, concrete.
Which variety to choose depends entirely on the soil and the level of its freezing, the location of deep waters, the type of foundation, the number of storeys of the building being built, the complexity of its structural elements and other factors.
Soil pillows are not made in flooded areas with a high level of groundwater and in sandy lands.
The main task of the foundation pillow is to protect the foundation of the house from the forces of frost heaving and ensure its strength and reliability
The foundation has a huge load, it provides support and support to the building for the entire period of operation. The strength of the structure depends on it, therefore, the requirements for the foundation are the most stringent. But in order to fully fulfill his mission, he needs help, which is the pillow (substrate).
It is a smooth and stable base, which helps to evenly distribute the load from the building located above. In addition, if there is a substrate, then the foundation itself has no contact points with objects capable of deforming it, that is, in addition to the distribution function, the pillow also has a protective function.
As for the thickness of the substrate, the opinions of our builders were divided with their foreign colleagues. In the West, they believe that under any building it is necessary to make a pillow of at least 80 cm.
Domestic craftsmen start with 20 cm and calculate the thickness depending on the design features of the building, on its purpose and on the area where this building will be built.
There is probably a reason for this. It makes no sense to fill the base with a layer of the same thickness for the construction of a skyscraper and a small one-story building, this will only create unnecessary costs for a private developer.
In our country, it is customary to make a substrate with a thickness of 20 cm
Nevertheless, there are general requirements - when falling asleep a substrate of any thickness, the height of the foundation should not decrease. To do this, before digging a pit, you must first calculate the thickness of the substrate layer and the height of the foundation itself.
In addition, the pillow can not be equipped nearby groundwater. If they are located very high, and this does not allow laying the foundation below the freezing of the soil, then it is better to abandon the construction on such a site, as if you did not like it. Or apply effective technologies for the removal of groundwater.
Sand foundation under the foundation
A sand cushion is an artificial formation. A small layer of sand at the bottom of the excavated pit is not yet a pillow, but just a preparation. The pillow should be much thicker (by construction standards from 20 cm).
It is used in the construction of low-rise buildings on weak, subsidence-prone soils (to improve them), peat bogs or for replacing directly under the foundation of heaving soil with non-heaving soil. The shape, dimensions and thickness are calculated individually for each building according to the parameters of the foundation.
Is she always needed? No, in some cases it is quite possible to do without it (for example, when pouring the base with reinforced concrete, which itself will fill all the cracks). However, most often it is necessary because it performs important functions:
- leveling the bottom of the pit after excavation using heavy equipment (you can, of course, level it with concrete, but it’s cheaper to sand);
- drainage - with a considerable thickness of sand, the capillary deep connection in the soil is broken, which does not allow the raising of soil moisture and its entry into the foundation with active underground waters;
- load distribution. Here we will clarify - the load with or without a sandy substrate will be the same, but such a layer reduces the increased pressure on the foundation and protects it from possible ground movement (replacing heaving and weak earths with sand, we strengthen the bearing capacity of the soil, providing a reliable foundation for building);
- protection against erosion - the sand discharges water well (however, it is still advisable to equip the drain so that the moisture in the sand itself does not further aggravate the situation).
As the main raw material when creating a sand cushion, medium and coarse sand are used. The sandy foundation substrate must be protected from siltation with groundwater using geotextiles (you can use ruberoid), otherwise it will turn into a heaving soil with all the negative consequences.
The sand pillow is divided from large and medium fractions of sand
The sand backfill sequence is simple and easy to do on your own.
- At the bottom of the pit (or trench) we put geotextiles so that it covers the pillow on the sides and top.
- Pour sand slightly moistened with water to the required thickness, periodically tamping well.
- We close with geotextiles.
The construction of a sand substrate is mandatory for slab and prefabricated foundations.
Photo gallery: sand foundation foundation and its laying
- The scheme of the correct filling of the sand cushion under the foundation
- To protect against siltation, a geotextile is placed under the sand cushion
- Sand surface must be tamped
Crushed stone under the foundation
The crushed stone pillow differs from the sand one in greater strength, it is indispensable when pouring the foundation on complex soils. It is used in the construction of solid cottages from any building materials.
The purpose and functions are the same as that of a sand cushion. The most frequently used rubble is the first category with low radioactivity, which is harmless to health, with a fraction of 20–40 mm and the strength of M1200 for adding residential buildings.
A cheaper option is secondary crushed stone (obtained by grinding old concrete) or broken brick.
Well, if a building is being built for centuries, then the best option is granite rubble.
Granite crushed stone - the most durable and frost-resistant material for pillows under the foundation
It will withstand any buildings and the most adverse weather conditions. It is usually combined with sand.
The order of the work.
- The surface of the base is leveled with a sand embankment (10–15 cm thick), applied and compacted uniformly over the entire area.
- Crushed stone is poured to the zero mark of the foundation. It, as well as the preparatory layer, must be carefully tamped. This is best done using a rammer.
- The crushed stone layer is covered with a solution with a height of 15–25 cm from the ground level (use a cement-clay, lime or sand-cement mixture). The foundation masonry is reinforced to strengthen its strength, while the masonry itself can be any (brick or stone).
A compacted layer of crushed stone is poured from above with a solution with preliminary reinforcement
These works are often done on their own, because they are not particularly difficult.
In order to avoid unnecessary costs, the preparatory sand layer can not be built if the soil allocated to the building site has sand impurities. Crushed stone itself is a good leveling device, so it fits perfectly with the base of the foundation, providing it with durability and a long service life.
Sand and gravel layer under the foundation
This is a refined and fairly high-quality mixture of sand and gravel. It happens natural, extracted from reservoirs or quarries, or enriched. The enriched layer contains more gravel, which means it is harder.
Sand and gravel substrate is used in the construction of country houses with a monolithic foundation on weakly bearing soils.
The arrangement works themselves are carried out in the following order.
- The bottom of the pit is laid with cobblestones (diameter from 15 cm). Depending on the severity of the building, there may be several cobblestones.
- A layer of gravel is poured on top (optimally 20 cm).
First, the bottom of the pit is strengthened with cobblestones, and then a layer of gravel is poured
- The next layer is sand. It is made in such a way as to completely cover the gravel. Sand is watered from above.
- If necessary, sand is poured again and watered with water. This is done until a sandy crust forms on the surface after irrigation.
- The formed surface is rammed with a vibrating plate or other mechanical devices.
- Then put waterproofing material and fill it with a small concrete layer. It turns out a solid plate, which will serve as the floor of the basement.
A layer of waterproofing is put on the sand and a concrete slab is poured on it - the floor of the basement
Video: do-it-yourself sand and gravel pillow under the foundation
The technology of manufacturing pillows for the foundation
Different types of pillows imply different technologies for their manufacture. When choosing one or another type, many factors are taken into account: soil features, terrain, house construction, building materials, etc.
It should be borne in mind that:
- the higher the building, the stronger the foundation it needs, and therefore the substrate must be more thorough (for tall and heavy buildings it is better to make a concrete pillow);
- when using foam blocks, a sandy foundation is enough;
- if you plan to equip the basement with various household, game or sports facilities, then you can not do without the use of fittings to connect the base and the foundation itself (it is installed vertically during concrete pouring);
- the substrate must have a waterproofing layer, especially for a sand cushion (for small buildings, you can use a plastic film);
- no need to save on laying the foundation - whatever it is, underneath it is necessary to make a pillow.
It is necessary to follow the instructions for laying any type of foundation pillow, then the house will serve faithfully for many years.
Video: creating the base of the foundation for a house with a basement
Concrete foundation pillow
This pillow is the most durable, reliable and high quality. Its only drawback is the higher cost compared to other types of substrates. But its operational properties are much higher. In addition, the concrete pillow serves as much as the building itself, which means that no repairs will be required if, of course, it is laid out according to all the rules.
How to make a concrete substrate
For work you will need: wooden boards, concrete and crushed stone, a deep vibrator and a vibrating plate, as well as metal rods (with a diameter of at least 8 mm).
- The soil at the bottom of the dug trench is leveled and compacted.
- A 10-centimeter layer of crushed stone is poured and densely packed. A vibrating plate is used for this (you can replace it with a similar one that is at hand).
It is more convenient to compact crushed stone with the help of a vibrating plate
- Formwork is created from wooden boards (optimum height 30 cm).
Before pouring concrete, formwork is built and a reinforcing cage is laid
- If desired, the pillow is reinforced with metal bars for greater strength.
- Concrete is poured into the finished formwork and rammed with a deep vibrator.
- The surface of the pillow is carefully leveled and, after the concrete has dried, it is rubbed so that when removing the formwork, the foundation substrate can be easily cleaned of debris.
The surface of the concrete cushion must be carefully leveled.
Some nuances you should know:
- the concrete substrate should be wider than the foundation. It should protrude at the edges of at least 15 cm;
- the reinforcing cage should extend 20-30 cm upward to ensure good adhesion to the foundation.
Typical dimensions of a concrete substrate for a strip foundation are 30 cm in height and 60 cm in width. Such a foundation is usually enough to build a private house or cottage.
So to do or not to do the foundation substrate? We hope that in this article we have relieved you of doubts - to do. In any case, it will strengthen the building, give it stability and protect it from deformation. Good luck with your construction.