When building a country house, there's a component that's not included in the basic scope of work: the concrete blind area. Its construction is often put off until later, and the design is often flawed. A concrete blind area is essential for diverting rainwater and meltwater away from the house walls and foundation and onto the land. The impact of groundwater on the building's foundation leads to subsidence and cracks. To prevent the structure from collapsing, it's important to follow five key rules.
Compliance with geometric parameters
The blind area is constructed around the perimeter of the building. Its width ranges from 0.8 to 1.2 meters, but it must extend at least 20 cm beyond the roof overhang. Raindrops running off the roof should not fall onto the ground. If the structure does not include drainage, the width is increased to 40-50 cm. If the building has protruding parts, such as a porch or veranda, the rain protection zone must be expanded to ensure the foundation is protected from water damage.
The foundation depth depends on the climate where the building is located and the type and extent of ground freezing. Soil heaving must be taken into account when creating a drainage system. This can be found in reference tables. If the soil is subject to deformation during cold weather, the trench for the blind area is dug below the frost line. For sandy soils, this parameter can be ignored.
You may be interested in:Formation of drainage slopes
Puddles on the surface of the blind area indicate errors in its slope. Builders poured concrete or laid paving slabs horizontally. This can lead to stagnant zones, and in some cases, water seeping under the foundation. Regulatory documents stipulate the formation of a transverse slope for the water-repellent layer. It is installed at an angle of at least 10° from the building's foundation.
To ensure the desired slope, it is determined during the construction of the blind area. To achieve this, the edge of the drain near the foundation is raised by at least 10 cm for every meter of gutter width. In addition, drainage channels are installed along the perimeter to drain liquid away from the building frame. These can be either prefabricated drainage system components or metal pipes cut to length.
Compliance with the rules for pouring concrete
The appearance of cracks, delamination, and spalling on the concrete surface is the result of errors in the composition of the concrete mixture itself. This allows water to penetrate under the monolithic screed and foundation. At subzero temperatures, moisture turns to ice, which destroys the concrete base. Cracks can also occur due to the absence of expansion joints between the drain and the building's foundation.
Ensuring the strength of concrete depends on strictly observing the proportions when mixing it. The composition has long been known: cement, crushed stone, sand, and water. However, not everyone knows the correct ratio in the finished mixture, or they measure the required quantities "by eye." Mixing concrete isn't something you can rely on luck. The weight of the components in the mixture is indicated per 1 m³:
- cement grade M400 – 330 kg;
- crushed stone with a fraction size of up to 20 mm – 1100 kg;
- sand – 750 kg;
- water – 215 l.
The duration and order of mixing influence the structure of the finished product. Initially, all dry ingredients are placed in a container. Mixing time is two minutes. When mixing by hand, continue mixing until a homogeneous mass is achieved. Then water is added and mixed for another two minutes. The finished mixture is evenly distributed, compacted, and sloped.
Insulation of the blind area
If the drip cap has lost its shape, warped, or begun to peel off in layers, this is a sign that it is being subjected to the buoyant force of soil heaving. This occurs due to a lack of insulation between the foundation and the surrounding soil. As a result, moisture accumulated in the ground during the fall freezes and crystallizes and expands, thereby pushing out the concrete screed.
You may be interested in:A layer of thermal insulation material can help prevent this process. The following is the sequence for installing the insulation:
- They dig a trench near the foundation to a depth of 0.5 m (the width depends on the size of the roof slope).
- Thermal insulation boards are attached to the foundation.
- A cushion of sand and gravel is poured onto the bottom and compacted thoroughly.
- Thermal insulation is laid on top.
- The last layer is a concrete blind area.
Waterproofing of soft blind areas
A damp foundation when constructing a soft concrete apron is the result of a lack of waterproofing. The finishing coating for such a drainage system is crushed stone, lawn grass, or Mettlach tiles. These are purely decorative and do not prevent water from penetrating the foundation. A damp concrete base, saturated with moisture, deteriorates at subzero temperatures. This is noticeable by chips and cracks in the concrete mass.
Using a hydrophobic material at the base of the drainage system prevents moisture from penetrating the foundation. Specialized membranes or roofing felt are used for this purpose. The waterproofing installation procedure is as follows:
- Sheets of material are laid on a prepared sand and gravel bed.
- One edge is placed on the foundation at a distance of 15-20 mm, the other is lowered into the drainage channel.
- They pour crushed stone on top or lay decorative tiles.
You may be interested in:Creating a high-quality blind area is simple. The key is to avoid common mistakes and use high-quality materials. Don't skimp on the drainage system, as the strength of the structure depends on how well it protects the foundation.