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One of the most popular threads on FORUMHOUSE is the section on foundations, because our experts are always ready to answer any question. Many novice developers are interested in why a sand cushion is needed for the foundation and whether it is needed at all. In this article, we will seek the answer to this question.

Sand bedding is done all the time during most work with the base of the house. But some builders believe that it is obligatory in all cases, others - that only under certain conditions, and in other cases it is simply harmful.

To find out why a sand cushion is needed and whether sand is needed to be added over the entire area, we turn to practical experience experts of our site.

The main purpose of the foundation is to redistribute the load from the weight of the house to the underlying soil layers. Any negligence in the preparation of the foundation

under the house

It can lead to unpleasant consequences - the appearance of cracks in the walls due to subsidence of the base.

Do I need a pillow under the strip foundation

A sand cushion under the tape base of the house is made by almost everyone, since it seems to be a guarantee of its strength and durability. However, many people can pour sand into a dug trench, guided by the principle: "the more the better, because everyone does it." Neither the geology of the site, nor the features of the soil and its bearing capacity, nor the level of groundwater are taken into account.

DenisminkoA FORUMHOUSE User

I have read that a strip foundation must rest on an undisturbed (untouched) layer of soil, and does not require a sand cushion. But many of my friends did it before pouring. To the question "why" they answer - "they saw it with their neighbors."

To clarify, you need to clearly define for yourself: what type of tape base of the house are we talking about. Namely:

• shallow - MZFL;
• laid below the freezing depth;
• monolithic;
• assembled from FBS blocks.

Each of these four types requires an individual approach in preparing the base.

Why do you need a sand pillow under a monolithic foundation

RNikonov:FORUMHOUSE user

A pillow for a strip foundation may not be done if we are talking about a monolithic foundation. But only under the following conditions:

• The soil is non-porous;
• The soil under the base is sandy;
• The tape is poured below the freezing depth, with concrete preparation under the sole;

For prefabricated base, from FBS blocks a sand cushion is simply necessary, because. only sand can level out all the irregularities that remain after sampling (i.e. removing the loosened layer) of the soil. Only sand can be compacted almost to its natural density.

If this is not done, then the foundation block will lie unevenly on the ground (not the entire surface of the sole), and there may be voids under it. This will lead to uneven pressure of the base of the house on the ground. Accordingly, the probability of its uneven drawdown increases.

RNikonovFORUMHOUSE User

When constructing a prefabricated foundation, sand preparation is performed with a thickness of 10-15 cm.

Why do you need a pillow under the tape base

putnik 777User FORUMHOUSE

I once asked the chief engineer of a construction company why there was a sand cushion in the foundation. He said: in order to level the foundation under “0” and to save concrete.

If it suits monolithic tape base, then it is no longer necessary to achieve a “mirror” foundation, because due to plasticity, the poured concrete fills all the irregularities. Accordingly, the sole of the base will rest on the soil with its entire surface and redistribute the load on the ground.

When it comes to MZFL, then a sand cushion is necessary, because. with its help, heaving soil is replaced by non-heaving. Moreover, MZFL requires a drainage system, an insulated blind area and insulation of the foundation itself. These measures minimize the frost heave forces acting on it.

When constructing a sand cushion, it is important to understand what kind of soil is under the future base. If the soil has low water permeability (this primarily applies to loams and clays), then the sand, being less dense, will become a place where water will constantly accumulate. As a result, over time, the bearing capacity of constantly waterlogged soil will decrease, which can lead to subsidence of the foundation.

Conclusion - a drainage and stormwater device is needed to drain surface and groundwater from the base of the house.

You can read articles about the correct warm blind area cake and the features of the drainage system of the foundation and site by clicking on the links.

The issue of using a sand cushion should be considered based on the specific characteristics of the soil, the level of GWL, the weight and structure of the building, and the depth of freezing. It is impossible to consider a sand cushion as a universal tool suitable for the construction of any foundation, without reference to the specific operating conditions of the building.

Podsypka under the foundation: sand or gravel

• 20-30 cm is the minimum thickness of the sand cushion;
• To level the base, a thickness of 5-10 cm is sufficient;
• Coarse-grained sand is best suited for backfilling.

• Sand must be compacted in layers, no more than 15-20 cm per filling - in the case of using a mechanical tamper, and add 10-15 cm if a manual tamper is used.

• Before tamping, the sand must be moistened. Because water, due to surface tension, “sticks together” sand particles and prevents them from “running away” when compacting;
• It is best to moisten the sand before it is laid in the trench, and not in it. This will avoid waterlogging and "limp" soil under the base;
• To compact the sand and obtain a better base, you can use crushed stone of a large fraction (40-60). In this case, after tamping the sand, crushed stone is poured over the entire area with a layer of 5-10 cm, and the tamper is already passed over it again. Due to the point load (impact), the crushed stone is driven into the sand and, due to the wedging effect, the compaction depth increases from 15-20 to 30-40 cm.

• To avoid silting up the sand cushion and mixing sand with the surrounding soil, material such as geotextiles can be pre-laid in a dug trench over the entire area.

Sand foundation and waterproofing.

The algorithm for designing a strip foundation for "dummies" is available here. This topic is about the Finnish version of a shallow strip foundation. Why insulate the foundation with foam, you will learn from this topic. Reinforcing the foundation in the corners - we do it right by reading this topic. And this video shows how to arrange a foundation on swampy soil.

The foundation for any house performs a very important function, it is on its reliability and strength that the duration of the operation of the structure depends, as well as the quality of life in the house. In order to make the foundation easier to fill and give it special reliability, you need to make a sand cushion before installing it. Its main function is to create a flat and stable surface for the foundation, even on marshy soil.

Definition and Functions of a Sand Pad

The sand cushion under the strip foundation is the filling of a certain layer under the future foundation. In order to understand why it is equipped, you need to look at its functions:

• Smoothing out uneven ground, thereby creating a flat surface favorable for the installation of a reinforced concrete base.
• Uniform distribution of loads from the structure to the underlying soil and foundation.
• Fencing off concrete from wet ground, which helps to avoid the adverse effects of heaving forces in frost.

Advice! If the site is distinguished by high groundwater or even represents a swamp on the surface, then before the sand cushion is installed, geotextiles must be laid on the bottom of the trench, which will prevent the sand layer from silting.

Pillow Mounting Materials

For a pillow under the foundation are used:

• River sand without any impurities.
• Pebble.
• Crushed stone with sand.

If a pillow for a strip foundation is erected on swampy soil, then a mixture of sand with crushed stone or gravel is used for its construction in a ratio of 40% coarse sand and 60% crushed stone or gravel. Such pillows are suitable for the base for a light one-story house. They usually require additional moisture and tamping. Such a mixture shrinks less than just a sand layer.

Important! For heavy buildings, tamping a sand cushion is required.

The pillow for the foundation should not be made of sand mixed with clay. This is due to the fact that water lingers under such a pillow and as a result of low temperatures, heaving begins, which adversely affects the construction of the base and the whole house.

Cases where a pillow is optional

There are cases during construction in which the arrangement of a sand cushion is either completely useless, or can even harm. It is impossible not to mention them:

• Backfilling into hard soils such as loams and clays can be a challenge. This is due to the fact that the sand will not be as dense in structure as the soil and will begin to absorb all the water. There it will accumulate and make the base of the foundation less durable. To exclude such a turn of events, it is necessary to additionally equip the drainage system in loamy soils, which will remove excess moisture from the base.
• Due to the presence of steam in the soil, it can pass through the sand cushion and settle on the foundation. To prevent the formation of condensate, moisture-resistant concrete is used and waterproofing is done.

It is obligatory to backfill under those foundations that are made of prefabricated blocks in order to eliminate soil irregularities that can provoke the presence of voids under the foundation. The result of the uneven surface under the foundation can be deformation or destruction.

Important! During the pouring of a monolithic slab, a sand cushion is not necessary, since the concrete fills all the voids and preliminary leveling is not necessary.

Arrangement of a sand cushion for a strip foundation

A strip foundation is a foundation that can withstand any load, which is why its arrangement is so common. It is possible to make a strip foundation on a sand cushion with your own hands, for this you only need to know the technology and choose the right material.

Pillow device

First you need to mix sand and crushed stone or gravel in the proportions described above, and then you can proceed to the main work:

1. Digging a trench or pit, depending on the dimensions specified in the project.
2. Leveling the bottom of the trench.
3. Backfilling of sand and gravel to the bottom of the trench with a layer of no more than 20 cm.
4. Gradual wetting and tamping of the sand cushion using a vibrating plate.

   Advice! If there are no traces left on the sand cushion after a person, then the tamping is done with high quality.

5. The layer of sand must be strictly horizontal, without distortions and slopes.

A vibratory plate or roller can be used to compact sand, but this is suitable for large volumes of work. For several trenches under the strip foundation, it is quite possible to use a home-made unit.

It is possible to water the sand with water only when the surrounding soil is not so moistened, but if the strip foundation is settled in a swampy area, then the sand must be moistened before being laid in a trench. Also, if you moisten the sand in advance, you can wash out those clay particles that are in it.

Mounting the strip base

After arranging the sand cushion in the trench, you can proceed to the direct installation of the strip base. A waterproofing material is laid on top of the sand layer, which can be used as roofing material or more modern materials that do not allow moisture to pass through.

During the installation of the reinforcing cage, a small layer of concrete base is made, equal in thickness to 6–7 mm.

Before pouring the cement mortar, it is necessary to provide holes in the foundation for utilities and ventilation, so that in the future they do not have to be hollowed out already in the finished base.

Be sure to install formwork for the foundation, which can be metal or wooden. A reinforcing mesh is laid in it and concrete is poured. For uniform filling without voids and bubbles, the poured concrete solution is treated with a deep vibrator. Concrete must be poured at a time, so it will not be superfluous to order a concrete mixer of the required volume in advance.

After the entire volume of concrete is poured, you need to cover the finished foundation with a film so that debris and precipitation do not get into it. Every day, the surface of the base is moistened with plain water. These actions are carried out until the concrete becomes half strong. It usually takes about 5 days in warm weather and up to 10 days in cool weather. Only after the base is fully strengthened, it is possible to carry out further work, or rather, the removal of formwork, waterproofing and erection of the walls of the structure.

It is very important when building a house to take into account to prevent moisture from entering the sand cushion under the foundation. To do this, measures are taken such as installing gutters on the roof to divert water to the side, as well as installing a blind area around the perimeter of the house so that melt water in the spring cannot get under the base of the foundation through the ground.

Features of the strip foundation

In this topic, one cannot fail to mention the advantages of a strip foundation on sand. By itself, it is a construction in the form of a tape that fits under the load-bearing and internal walls of the house. Thanks to this placement, the foundation distributes the load from the structure evenly throughout its structure.

The strip foundation can be of three types:

• Prefabricated is a structure of concrete blocks connected by cement mortar, installed inside the trench.
• Monolithic is created by pouring the solution into a pre-prepared formwork with reinforcement inside.
• Combined is a combination of these two types of foundation in one design.

So, about the advantages of the tape type of base:

• Affordable cost of work with high quality of the end result.
• Subject to the construction technology, such a foundation will serve its owners for a very long time.
• The ability to do all the work yourself, which gives significant savings.
• The ability to withstand both a light frame house and a heavy multi-storey one.
• Under the house, you can equip a basement or basement floor without wasting time and money on installing walls there, since the foundation itself serves as walls.
• In addition to all of the above positive aspects, the tape base has its drawbacks:
• The need for a long wait for the concrete to set.
• The need to carry out accurate calculations, which include the depth of the foundation, the thickness of the sand cushion and other characteristics.

Be sure to check the strength of the reinforcing belt and its equivalence on all sides before installing the strip base, since in the case of weak reinforcement, the foundation can be divided into several parts.

If there is dense soil on the site, then the trench under the tape must be expanded by an indicator that will allow mounting the formwork. But if a strip foundation is mounted on clay soil, then it will be necessary to leave room for further filling it with sand. Such a comprehensive cushion will become a shock absorber during ground movements.

Conclusion

The strip foundation is very popular in private housing construction, and this is not surprising, because the foundation has a lot of advantages over other types. But to be sure of long-term operation, you need to properly arrange it. In most cases, a sand cushion is laid under this base, the device of which also has a lot of nuances and subtleties that are fully reflected in the article.

• Bored foundation for the house
• Foundation for a brick bath
• Depth of strip foundation
• Strip foundation for a two-story brick house

Many people know that there is a sand cushion for the foundation, but not everyone can say for sure why it is needed and how it is created. As a result, beginners in the construction business often pour sand into the trench without any understanding and, as a result, only harm the entire structure.

The cushion under the sole of the foundation can perform three functions:

• Leveling. If the soil is not heaving and not mobile, then the only task of the sand is to level the bottom of the trench or pit for even placement of the solution or the correct distribution of the load from the FBS.

Compensatory. Heaving soils under the support of the house in winter can greatly affect the distribution of loads, leading in difficult cases to the destruction of the concrete tape or slab.

In this case, the task of sand is to compensate for deformations, to reduce them to an acceptable level for a given foundation.

Substitute If there is organo-mineral or organic soil under the house (for example, peat), then you have to put up with continuing decomposition processes.

In this case, the soil will necessarily be mobile, heaving and characterized by low bearing capacity. It has to be taken out to a great depth, until the end of the organic layer, and the trench is covered with sand.

How thick a pillow is needed under the foundation depends on what function it performs in this particular case.

Pillow device

The easiest way is to create a backfill that performs a leveling role. As a rule, its thickness in this case does not exceed 15-20 cm. It is enough to fill in the sand once, carefully level it, spill it with a small amount of water - moisten it and then compact it.

But such a minimum can be dispensed with either on non-rocky soils, or in the case of a deep foundation, below the level of freezing and relying on non-deformable soil layers. In other cases, you have to lay a compensating pillow. Its dimensions depend on the width of the base of the foundation. Exact data can be calculated from the table.

For example, if a foundation is laid with a base width of 60 cm, then the width of the pillow will be 60 * 2.4 = 144 cm, and the height will be 60 * 1.2 = 72 cm. A strip foundation with a tape width of more than 120 cm does not need a compensating pillow .

A compensating sand cushion is laid as follows:

1. The dug trench is freed from loose materials and leveled.
2. If the site is characterized by a high level of groundwater, measures are taken to prevent sand silting - geotextiles are laid or other methods are used.
3. Sand is laid in the trench - in layers, no more than 20 cm per layer. After each layer, the material must be carefully compacted.
4. After reaching the required height, a material should be laid on top, which will prevent the penetration of cement laitance from the solution into the pillow. If FBS is supposed to be laid, then a protective film is not needed, you can lay the blocks directly on the pillow.

Sand is considered a non-heaving material; also, due to its structure, it prevents the capillary rise of moisture from the underlying layers to concrete. But all this is typical only for sand that is not filled with water.

If a lot of moisture gets under the foundation, then it can radically change the properties of the pillow.

Therefore, in areas with a high level of groundwater or where there is a possibility of sedimentary water getting under the concrete, it is imperative to provide a system for removing moisture - drainage.

The process of laying a replacement cushion under the foundation does not fundamentally differ from a compensating one. The role of geotextiles and systems for water drainage is only increasing. Anyway important point is the correct rammer. It is worth considering in more detail.

Watch our video compilation

The architecture and beaches of Croatia are the two main attractions of this country. And if the first "good" in Europe is enough, then there are often problems with rest by the sea. While it's expensive in France, and far away in Spain, the blue sea of ​​Croatia annually falls in love with everything more tourists. Croatia is becoming more and more popular destination for beach holiday, both among European tourists and travelers from the CIS.

The best time to rest on Adriatic coast Croatia - the period from mid-June to September. At this time, the sea heats up to +24°C, there is practically no rain, the water is calm and clear. Is there in Croatia sandy beaches and where are they located? Where to go on vacation with children and what do experienced tourists advise? Find out the answers in our top the best beaches Croatia.

Sandy beaches

It should be noted right away that there are not so many sandy beaches in Croatia and they are located mainly on the islands. But it is still possible to find them.

Find out the RATES or book any accommodation using this form

The beaches of Croatia are places where tourists who like to combine sightseeing with historical sights and seascapes. Get inspired by photos Adriatic Sea, choose the beach that suits you and go towards the warm waves. Have a good trip!

More details about the beaches of Croatia - in this video.

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The snake, which will be discussed in this article, belongs to the family of vipers, and they, in turn, are considered the crown of the evolution of reptiles and are recognized as the most poisonous snakes in the world. The sand efa, despite its beautiful appearance and quite friendly character, is capable of poisoning its opponent with a very strong poison in a matter of seconds, which, even after the introduction of the serum, will remind the bitten person of health problems for the rest of his life.

What does a sandy efa look like?

These cold-blooded ones are no different large sizes, their average body length is 70–75 cm, and individuals over one meter long are very rare. Males are slightly larger than females. Their body is decorated with white spots, and two zigzag lines run along the sides, giving the snake an elegant and unusual look.

On the head there is a pattern that looks like a cross or a bird soaring in the sky. The eyes are large, round in shape, the color of the iris depends on the overall color of the scales, the pupil is vertical. The ventral side is light yellow, and the color of the scales can be either golden or brown - the exact color depends on the habitat of the snakes.

The body of the efa is covered with small and rough scales, some of which grow in the opposite direction and are used by the snake to notify others of their appearance - they make a special sound similar to rustling or a kind of rustling.

Did you know? The sand efa is able to jump to a height of more than one meter and about three meters in length. An angry female guarding her nest will rush at her opponent with lightning speed without warning of an attack. That is why snakes are especially dangerous during the mating season.

Is a bite dangerous for a person

It is not for nothing that the sandy efa is among the ten most poisonous snakes on Earth. Every fifth person bitten by a sand epha dies. The toxins contained in its venom have a special effect on the hematopoietic process - they dramatically reduce the level of fibrinogen - a special protein responsible for blood clotting.
Without providing the necessary assistance, the bitten person will soon begin to bleed severely - from the wound at the site of the bite, nose, ears, and even throat. A particular danger is the long wait for the body's reaction to the poison - death can occur even 40 days after the bite of the efa.

It should be noted that these snakes prefer to lead a reclusive life and avoid meeting people. As practice shows, most efa bites were due to a person - the victims either stepped on a reptile or stirred up its nest, even if this happened unintentionally.

Where does it live

Efa prefers to hide in thickets of branched shrubs that grow in sandy areas, on the banks of shallow rivers, as well as in areas where loess and clay soils predominate.
This type of poisonous snake is widespread in the deserts of India, northeast Africa and in the arid territories of countries East Asia and the Arabian Peninsula.

What does it eat

Sand efas differ from their relatives in increased activity - they are in constant motion, even after a hearty lunch. The main part of the diet of the sand efa is made up of various insects - locusts, beetles and centipedes. Adults are not averse to pampering themselves with small rodents, chicks and even small lizards.

Important! One of the main rules for providing first aid for a bite of poisonous snakes is to suck out the poison from the wound at the site of the bite. This technique significantly reduces the amount of toxins that enter the human blood. But this is effective only in the first ten minutes after the bite.

The snake goes hunting with the onset of darkness, however, meeting with it during the day is not uncommon.
True, on especially hot days, she does not leave her hole, preferring to move in the cool of the night. With a slight decrease in temperature in winter, they can easily overwinter without falling into hibernation.