Table of contents:

Laying concrete foundations: simple instructions
Laying concrete foundations: simple instructions

Video: Laying concrete foundations: simple instructions

Отличия серверных жестких дисков от десктопных
Video: How to Build and setup a Concrete Foundation for Garages, Houses, Room additions, Etc Part 1 2023, February

One does not see concrete foundations, but they have the supporting function in every building. When it comes to the foundation, good planning and precise work are important - errors can only be fixed with great effort afterwards. With these instructions you can create simple foundations.

Table of Contents Table of Contents Creating Concrete Foundations: Simple Instructions for Do-It-Yourselfers

  • Which concrete do you need?
  • Concrete foundations with and without reinforcement
  • Lay the concrete foundations yourself
  • 1. Materials: You need that
  • 2. Different types of concrete foundations
  • 3. Process structural steel mats
  • 4. Smooth the concrete foundation and base plate
  • Save costs

Table of Contents Table of Contents Creating Concrete Foundations: Simple Instructions for Do-It-Yourselfers

  • Which concrete do you need?
  • Concrete foundations with and without reinforcement
  • Lay the concrete foundations yourself
  • 1. Materials: You need that
  • 2. Different types of concrete foundations
  • 3. Process structural steel mats
  • 4. Smooth the concrete foundation and base plate
  • Save costs

Whether slab foundation, strip foundation or point foundation - one foundation anchors and supports the entire structure, distributes its weight and thus the resulting load evenly on the surface. Therefore, it is usually built from concrete. To avoid frost damage, concrete foundations have to be laid down to frost-free soil depths, i.e. at least 80 centimeters. When building a concrete foundation, you also have to assess its load due to the subsequent construction. With simple foundations for a smaller garden shed, this is not so dramatic, you can do it yourself. For larger buildings from garage sizes upwards, you definitely need a structural engineer who will then also determine the type of concrete and decide on a possible reinforcement, i.e. the pouring of structural steel elements into the concrete.

Whether you need a building permit to build the foundation depends on the region and depends on the size of the building. Therefore, be sure to ask your city or municipality.

Which concrete do you need?

Concrete is a mix of cement, sand or gravel and water - the respective construction project determines what should be added and in what quantities. The guidelines on the subject of concrete are laid down in the standards DIN EN 206-1 and DIN 1045-2, which of course also apply to foundations.

For foundations, use so-called normal concrete with sand and gravel. The gravel gives the concrete the necessary hardness, while the sand makes the mass homogeneous and cement - mostly Portland cement - acts as a binder.

Concrete is divided into different compressive strength classes (C), which are determined by two different test methods: one test determines the strength of a standardized concrete cube, the other that of a likewise standardized cylinder. The results are given with two numerical values, about 20/25. The first number characterizes the compressive strength of the cylinder in Newtons per square millimeter, the second that of the cube. The higher the number, the more stable the concrete. Concrete of the compressive strength classes C 20/25 is more stable than a concrete of class C 8/10 and well suited for concrete foundations - if the structural engineer does not want another one.

For smaller projects you can buy ready-mixed concrete in bags, for larger projects it costs less to mix the concrete yourself. A robust mixture for garden walls or houses as well as terraces consists of one part of cement, five parts of gravel (0 to 16 millimeters grain size) and a good four liters of water.

Beton gießen
Beton gießen

Concrete is a mixture of cement, sand / gravel and water. The respective construction project determines the ratio in which everything is mixed.

Photo: iStock / saravuth-photohut

Concrete foundations with and without reinforcement

Concrete not only has to be pressure-resistant and load-bearing, but also has to cope with lateral or vertical tensile forces, depending on the requirements.

Therefore, the concrete is reinforced by reinforcement with mats, rods or baskets made of Monier steel to form what is known as reinforced concrete, which is particularly used for floor slabs and foundation slabs. The steel either disappears completely or protrudes from the foundation - depending on what is supposed to be on the concrete. Outstanding steel provides additional stability for walls.

It doesn't work just to tip the concrete into a sufficiently large hole in the floor. Instead, formwork is required that keeps the initially viscous concrete in shape until it sets and prevents it from slipping off the ground on sandy soil. The formwork is comparable to a cake pan from baking and is particularly necessary for large foundations. Often only the upper part of the foundation is shuttered, because the shuttering greatly facilitates horizontal installation and smooth removal of strip foundations. The formwork usually consists of boards that are placed directly on the leveled floor at the level of the finished foundation and stabilized from the outside using pegs. The next step is to add construction film as moisture protection to the formwork, then fill in the concrete. Alternatively, so-called formwork blocks are used.

Lay the concrete foundations yourself

1. Materials: You need that

  • concrete
  • Scarf boards
  • Nails
  • Wall cord
  • Spirit level
  • shovel
  • wheelbarrow
  • Folding rule
  • Benchmark
  • Pegs

In addition, you need other materials, especially for reinforced concrete:

  • Monier mats
  • Monier bars
  • Concrete binding wire
  • Monier pliers
  • Angle grinder
  • Bolt cutters
Stahlbeton herstellen
Stahlbeton herstellen

Reinforced concrete is really hard. In addition to cement, sand / gravel and water, monier mats are also installed here.

Photo: iStock / Vladimir Kokorin

2. Different types of concrete foundations

Point foundation

Point foundations are built when a carport is built, terrace roofs or other structures such as a pergola or garden fences only selectively load the floor with piles or piers. A frost-proof foundation is then placed under each post. A garden shed can also be placed on a point foundation if the load-bearing floor timbers are attached to the posts or rest on the point foundations. Of all concrete foundations, point foundations are the quickest to build because they do not require much earthwork:

They level the ground, define the foundation points, dig the holes with an earth auger and attach the formwork - for smaller foundations, this can also be PVC pipes (KG pipes), such as those used for sewage pipes. All foundation formwork must be precisely aligned and at one level, so check the position of the formwork again and again with a spirit level and a masonry cord or a long straight edge. If you use pieces of pipe as formwork, they are simply driven vertically and to the correct height into the ground with a piece of roof batten and a fistula and remain in place even after being filled with concrete.

Strip foundations

Strip foundations are suitable for walls or larger buildings. Depending on the size of the building, they require more construction work and a solid, load-bearing floor. However, you do not have to box out the entire base area, the foundation strips usually only come under load-bearing walls. In large buildings, a 10 centimeter thick floor slab can be concreted between the strip foundations or a basement floor slab that is also not load-bearing.

Mark the outline and the load-bearing walls of the building exactly with a batter board made of pegs, battens and masonry cord. Then lift a strip 80 centimeters deep and, depending on the thickness of the wall, at least 30 centimeters wide, and put on the casing. Depending on the building, perimeter insulation made of XPS panels is also installed on the outside. If you build a garden wall yourself and have solid, loamy soil, there is no need for cladding, the foundation usually closes off at ground level anyway.

You pour half of the trench with concrete, compact it with a tamper or squared timber and fill in the rest, which is then also compacted. Reinforcing steel is required for larger buildings and less load-bearing floors so that the strip foundation does not tear and there are no settlement cracks in the masonry. In the case of reinforced foundations, the reinforcing steel must be surrounded by a layer of concrete at least 3.5 centimeters thick to reliably protect it from corrosion. After filling, the concrete is compacted in layers with a so-called vibrating bottle in order to avoid voids between the steel bars.

Concrete slab as a foundation

A solid concrete slab runs under the entire floor plan of the building and also supports entire residential buildings. Such a foundation slab is often built on sandy, less firm soils because it evenly distributes the load on the building. This foundation is like a snowshoe that distributes the weight of the hiker in deep snow over a larger area so that he does not sink.

Gegossene Bodenplatte
Gegossene Bodenplatte

A concrete floor slab is often used on sandy soils to better distribute the weight of the house.

Photo: iStock / foto-ruhrgebiet

Foundation plates are always made of reinforced concrete, so they have mats made of reinforcing iron for reinforcement so that they are sufficiently tensile and shear-resistant. They lie on a layer of gravel or gravel - the so-called cleanliness layer. The thermal insulation is also installed under the foundation - either from XPS panels or foam glass gravel. On top of that comes a construction film as protection against rising soil moisture. The thickness of the foundation slab depends on the weight and the statics of the building and must be calculated by a structural engineer.

For terraces with slabs in the concrete bed, a continuous, reinforced foundation slab is also built, which, however, can be less thick - 10 to 12 centimeters are usually completely sufficient, since the static loads are low. In residential buildings, the non-loadbearing floor slab still rests on the strip foundations, which, however, are no longer visible under the cast concrete. Their position is specified in the structural engineer’s foundation plan. This plan also specifies the location and type of reinforcement and specifies the positions of the necessary connections and drains for the building.

In a building with a basement, the floor slab is more stable than in buildings with no basement, where the slab only serves as the floor. If you build a building without a basement, the floor slab is given a so-called frost protection - in principle a circumferential strip foundation. This prevents the floor from freezing at the edge of the floor slab and thus cracks in the concrete. The frost apron also has a load-bearing function, which is why it must be taken into account in static calculations. However, if it serves as pure frost protection, it can also be built from gravel.

Lift the surface according to the plan's specifications. For example, in a small garden house it is 40 centimeters, in large buildings it must be 80 to 120 centimeters. The surrounding frost apron must in any case reach 80 centimeters deep. The pit must always be slightly larger than the dimensions of the base plate so that there is still enough space for the formwork. Level and compact the subsurface and set up the formwork boards. These close exactly with the planned surface of the floor slab. Since you can easily compensate for later differences in height with the screed and mortar of the masonry, the boards must be aligned as precisely as possible. Attention: This does not work with so-called thin-bed mortar.

Fill in a 15 centimeter thick sand-gravel mixture as a layer of cleanliness and compact it. In residential buildings, gravel or crushed stone is often used instead of a layer of cleanliness. This is followed by a PE film that protects the concrete foundation from moisture from below. The reinforcing steel must be completely enclosed on all sides by the concrete. First fill in a good five centimeters of concrete, lay the reinforcing steel mats on top and fill in the rest of the concrete or place the mats on plastic spacers and then fill the entire concrete in layers and compact it several times.

Beton gießen mit Verschalung
Beton gießen mit Verschalung

In order for the casing to find space in the floor, lift the pit slightly larger than the floor slab.

Photo: iStock / photo

3. Process structural steel mats

The reinforcing steel often has to be cut and adjusted. There are special tongs or bolt cutters with long handles or you can use an angle grinder. If you need several mats, let them overlap and connect them with the monier wire, which you twist with a pair of pliers. Sometimes it may be necessary to bend a monier bar. The best way to do this is to slide a piece of copper pipe over the rod from both sides and then bend the rod in the middle using the leverage effect.

Tip: Don't forget the foundation earth electrode!

4. Smooth the concrete foundation and base plate

Concrete slabs in particular must be completely flat and smooth. The formwork guarantees a flat surface as long as they are precisely aligned. If there are still bumps, place a long, straight square timber over the formwork boards and pull off the surface. Make sure that there is always some concrete in front of the wood as a "bow wave" that immediately fills in the depressions.

The concrete can only be smoothed as long as it is still viscous and malleable. You can easily level strip foundations with a short wooden board and then smooth them with a float - simply use the top edges of the formwork boards as a guide to pull them off. For large areas there are special concrete trowels or concrete slippers available. You can also screw a 60 cm wide, planed board to a roof batten and smooth the concrete with it: Walk backwards through the still fresh concrete and slowly pull the board over the concrete at a flat angle. So-called wing smoothers are available for smoothing mature but already hard-wearing concrete. They resemble sanding machines for parquet floors and smooth the concrete surface so well that it is suitable as a floor covering without a screed layer. In this case, the concrete has to be sanded after drying and then waxed.

How can you save costs on the concrete foundation?

The foundations of low walls or small garden houses can be mastered on your own and thus save costs. Foundations for residential buildings or the floor slab should only be ventured if you have the know-how and the manual experience. In any case, this will save you the external wages, which are not insignificant. You then only pay the material costs for the concrete foundation.

Possible defects in the foundation are serious and repairs without dismantling are only possible to a very limited extent. In addition, the contractors often assume no liability for subsequent trades if the preparatory work has been carried out in-house. It can quickly become expensive if there are problems. Where laypeople can also save costs is when digging the earth and building the formwork. Both are very labor intensive and therefore expensive.

Thomas Hess

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