Do-it-yourself columnar foundation made of blocks: calculation of materials and design

When the idea of building your own real Russian bathhouse is born, everyone wants to implement it as soon as possible. And in reality, there is no point in necessarily going the most difficult routes - there are special construction technologies and methods that can save not only time, but also money. And among these is a high-quality and inexpensive prefabricated foundation made of FBS - it is built with your own hands much faster than any other foundation.

FBS blocks are often used to build a basement - which, of course, is not very traditional for a Russian bathhouse, but is still popular due to the possibility of building a garage on the ground floor.

Advantages and disadvantages of this design

This is what a block foundation is: a reinforced concrete pad and vertical walls made of the blocks themselves.

But such a foundation has its drawbacks - only a crane can lift concrete blocks for the foundation. And these, of course, are costs. But this is perhaps its only serious disadvantage. But in all other respects, even an amateur can do all the work. But it is worth noting that the FBS foundation itself, of course, is always inferior in terms of rigidity and reliability to a monolithic one, but pleases with a more affordable price and ease of working with it.

A modern foundation made of FBS blocks is simply ideal for soils that have too much sand. But it is not suitable for soft and crumbly soils - it will simply sag. An interesting observation: due to serious heaving forces, a foundation made of blocks can bend - but a rigid strip foundation could even break. After all, trying to reduce soil heaving by tightening the zero level is irrational; in this case, it only makes sense to insulate the soil and the foundation itself. This is what else a strip foundation made of blocks is good for - due to the lack of solidity, i.e. Thanks to the presence of masonry joints, it has valuable flexibility and mobility.

Another plus: the construction of a foundation from FBS blocks can be carried out in the rain and in the snow - nothing is scary for it.

What blocks can a foundation be built from?

When choosing a building material, it should be taken into account that all the blocks inside the prefabricated foundation strip are hinged beams with at least two degrees of freedom. Therefore, the larger the format of concrete products, the stronger the foundation made of blocks , the more stable its spatial geometry. The industry produces several modifications of products:

FBS - large format, laid on FL slabs with a crane, there are blocks with FBP voids and with cutouts for laying FBV communications

wall block/concrete stone – small format, laid manually, only solid modifications are used for underground structures

Attention: Some manufacturers sell blocks without voids, like FBS 2-2-4, citing their own technical specifications. Such products are not specified in GOST, so the quality is certified according to the standards of blocks for plinths and wall masonry.

The dimensions of the FBS correspond to – length 24, 12 or 9 dm, width 3 – 6 dm, height 3 dm or 6 dm. The wall blocks have dimensions of 2 x 2 x 4 dm and replace seven standard bricks. Unlike brickwork, concrete has a greater service life in underground structures and can reduce the construction budget.

Therefore, if there is an entrance for special equipment, it is recommended to choose FBS; in dense buildings, when it is impossible to drive the crane into the building area, the option of a prefabricated foundation made of small-format blocks remains.

Foundation block

The strength of FBS made from sand concrete corresponds to B12.5 - B15, from light/heavy concrete B3.5 - B15. The industrial manufacturing method ensures unified dimensions, the same location of mounting loops, stable geometry, and the absence of internal pores.

Attention: FBS blocks do not have reinforcement, so they are placed inside reinforced foundation elements - FL slabs at the bottom + monolithic reinforced belt at the top of the last row.

In any case, the developer will not be able to completely get rid of monolithic works. Construction of walls is possible after the reinforced belt has gained strength, that is, the gain in time is ensured only by reducing formwork, reinforcement, concrete, and stripping work. LF from FBS blocks is in demand in the following cases:

reduction of construction time
reduction of labor costs in deep belts
provision of dismantling for mobile buildings

For laying FBS blocks, there are TTK maps that describe the sequence of work.

Wall block

According to SP 22.13330, the width of the prefabricated foundation must exceed 0.4 m, therefore, when using wall blocks, the masonry is carried out in at least one block. Concrete with moisture-permeable fillers (sawdust, expanded clay, shell rock) is not recommended for underground structures. Laying foundations from hollow/slotted blocks is prohibited, as this disrupts the distribution of prefabricated loads from the building to the soil.

Compared to brickwork, a prefabricated strip foundation receives an increased service life. However, the default reliability is significantly lower than monolithic structures. Therefore, this technology is used in the following cases:

easy construction from SIP panels, foam concrete, aerated concrete blocks, using log house and frame technology
dry soils with high design resistance

Compliance with technologies that reduce/eliminate frost heaving is a prerequisite for prefabricated foundations.

Step-by-step construction - quick and easy!

Initially, at least basic geological exploration is needed, on the basis of which the foundation walls are calculated for each section separately.

Stage I. Selection of blocks for the foundation

The building foundation block, or FBS, is produced in factories by vibrocompression and is used specifically for the construction of the foundation. Most often it is a strip foundation. So, what should be the dimensions of concrete blocks for the foundation and how to choose them correctly?

To begin with, in a regular computer program, it is advisable to make a layout of the blocks in advance - in order to know exactly how they will need to be mounted and knitted together. So, the first row is often made 40 cm wide, and the next two are 30 cm wide. And only when the required block sizes and their quantity are known, does it make sense to go to the store and order them. There you can also agree on delivery and installation, and for this both the machine and the crane should be free on the same day if possible.

When choosing such blocks from the warehouse, it is initially important to determine where and in what places the communication will take place and how to build a foundation from the blocks, taking these points into account - for this they will be needed with special holes. If you forget about this, then in the future you will have to drill them, and this will additionally cost money and time.

Stage II. Pit preparation and marking

Experienced builders advise, first of all, to draw a diagram of the site before installation - think about where exactly the crane will be located, what difficulties may arise.

Next, as usual, the top fertile layer is removed. For these purposes, it is better to hire an excavator. Part of the soil is specially left for backfilling. And along the edges of the pit, the axes of the bathhouse walls are carried out using pegs with fishing line.

But internal drainage of such a foundation is not necessary - only when serious repairs are needed or leaks cannot be eliminated. Otherwise, it is recommended to simply carefully waterproof the walls and floor of the bathhouse - that’s all.

Stage III. Making the sole

If during construction you do not make a concrete cushion belt, but place the blocks directly on the sand, then it is advisable to use a masonry mesh. It is this that will prevent the formation of unwanted holes between the blocks in the future.

Therefore, it is necessary to get reinforcement and bring a car of sand and a car of crushed stone. It is advisable to take 20-40 fractions of the latter.

In the prepared pit, markings are now made for the future sole. Using an ordinary shovel, the place for it needs to be leveled strictly according to the levels, covered with sand, generously moistened and compacted. Next, everything is covered with crushed stone and compacted again. And after that, the formwork is built and the reinforcement is tied.

Stage IV. Construction of formwork

To do this, you will need to purchase at least half a cube of 25th edged board in advance. In order for the formwork to be level, you need to level it in advance using a hydraulic level and tighten the cord inside the formwork itself.

It is better to take the reinforcement for such a foundation F12 and tie it together. After pouring, the reinforced belt needs to settle - and this is a forced break in work for at least two weeks. In total, this will require about a hundred rods of 60 cm each and about 4 rods of one meter each. They can be laid either in four rows, two below and two on top, or in three - in a triangle. It is better to take D4 wire for forming the frame - it will take up to 10 kg. It will take about two days to make the reinforcement alone - and after that you can start making the formwork. The standard thickness of the armored belt is 20 cm, and the width is 30 cm.

Stage V. Filling the pillow

At this stage, you will need a mixer - it is he who will pour concrete into the prepared cushion for the FBS blocks. Next, it is covered with film or sawdust and dries for a whole week, with periodic wetting.

The pillows themselves, of course, can be prefabricated - but more often they use monolithic ones, such as for strip foundations.

Stage VI. Installation of FBS blocks

Now you need to order a crane - it will lift heavy FBS blocks, and workers or help will straighten them.

During construction, it is best to use M100 masonry mortar - it will have to be used from 10% to 20% of the volume of all blocks, and much here will depend on the quality of the blocks, the planned gaps and the masonry itself.

Stage VII. Foundation waterproofing

The most proven option in this regard is good mastic. In total, it will take about 4 cans of mastic, and you need to coat one row on the inside of the future bathhouse and two on the outside. Convenient - no need to wrap or heat anything.

By the way, some builders also lay Bikrost waterproofing under the bottom of the blocks in areas that are especially generous with rainfall.

Stage VIII. Manufacturing of reinforced belt

As for the monolithic belt, which is placed on FBS blocks, and the floor slabs are placed on it, not all builders see any sense in this. After all, it turns out that the blocks, and the belt, and the slabs are no longer a monolithic structure, but parts that seem to be on their own. It is believed that the belt for floor slabs is just an invention of non-professionals. After all, the slabs themselves distribute the entire load quite well and evenly - you just need to place them on a high-quality solution of a few centimeters, or even throw a net for reliability. But, if beams rest on the walls, which in itself is an additional load, a belt is really needed.

The belt itself can be made monolithic or brick, but under the first one you will also have to make formwork, and, most likely, use a concrete mixer. According to reviews, the brick version of the belt is still more convenient.

That's the whole technology for making a foundation from FBS - labor-intensive, but not difficult, reliable and safe.

Some advantages of this type of foundation

Simplicity of design.
High construction speed.
High professionalism in the construction field is not required.
There is no need to involve construction equipment and various machines.
Even one person can cope.

There are several types of them, which differ in cost, reliability, durability and other parameters. The cheapest option for this type of foundation is the foundation for a wooden house.

A columnar foundation is the required number of pillars, which are located under the walls and supporting structures, as well as in the corners of the future building.

What are FBS blocks made of?

To make a mold for the fundamental blocks, you need to take multilayer OSB plywood. Its width must correspond to the height of the blocks, and its length must be more than 20 cm than the length of the blocks. When making molds for foundation blocks, plywood must be cleaned and painted with waterproof paint. The production of foundation blocks involves the use of moisture-resistant plywood, which does not deform when water gets on it.

The plywood is painted on both sides and, after it has dried, transverse slits about 5 mm deep are made from the edges using a hacksaw. Next, between the edges of the plywood and the slot, you need to drill a hole for bolts and ties with a diameter of 14 mm.

From the prepared steel sheet we cut out two rectangular parts, the sides of which correspond to the length and width of the FBS blocks.

After all the preparatory work, you can begin assembling the mold for the fundamental blocks. To do this, all parts are folded onto a flat surface, and the plywood is laid with the painted sides inside. You need to insert metal sheets into the cuts, and rods into the holes. Next to the screed on the inside of the plywood we fix wooden inserts to set the width of the block. Then we tighten the nuts and our form is ready. Remember that the form for the fundamental blocks must be collapsible, otherwise you may damage the product when removing it from the formwork.

Foundation made of FBS blocks for a two-story brick house

Question:

Hello! A two-story brick house 8*12 with a basement under the entire house is planned. The soil is sand. Two rows of fbs blocks 240*5*6 at the -2.00 mark, then with bricks. I plan to lay the blocks like two letters “E” towards each other immediately on the sand without an armored belt, we need two entrances to the basement and a passage in the center, and connect the foundation only from above, under the floor slabs, with three lintels with reinforcement.

Is this option possible? Or you can’t do without a lower arm belt. I broke my head, I'm not a builder myself.

Dmitry, Izhevsk.

Answer:

Hello, Dmitry from Izhevsk

According to the classics of the genre, when building heavy houses, and your future brick two-story house belongs to a similar category, a sand layer is first poured under the FBS blocks (or the soil is leveled if it is already sandy), then a layer of crushed stone. Then laying the foundation slabs, on which FBS blocks are then installed.

The blocks are laid in several overlapping rows so that the upper ones overlap the joints of the lower blocks with their edges. All joints, both on the sides and along the bottom-top between the underlying and overlying rows of blocks, are laid with cement or concrete mortar so that there are no gaps.

If the foundation slabs are not laid, but it is planned to simply install FBS blocks, then in the basement under such houses the base is made in the form of a reinforced concrete screed laid on a sand-crushed stone cushion. And the blocks are laid on this screed using the technology described above.

All this is a guarantee against all sorts of surprises in the form of displacements of the basement walls. If you do not make a reinforced screed in order to save money, then no designer will give you any guarantees.

It is allowed, instead of a reinforced screed for the entire area of the basement under the house, to make only a tape reinforced belt directly under the FBS blocks with the release of the screed on both sides of the dimensions of the blocks by about half a meter. That is, with a block width of 0.5 meters, the width of the tape will be about one and a half meters.

The upper reinforced belt is also made, despite the presence of floor slabs in the future. The structural strength of the building comes first. It’s better to overspend on the foundation in terms of materials and labor costs than to later deal with the negative consequences in the form of wall movements, the appearance of cracks and bulkheads of walls.

All. Good luck!