Lawn/turf on concrete: this is how much soil is necessary

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Lay the turf on concrete

Around Lawn Sowing on a concrete base requires some substrate for the grass to take root. Depending on the surface, a substructure may be necessary to protect the concrete surface.

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In a nutshell

  • Check the concrete surface for its load-bearing capacity
  • Apply separating layer and drainage
  • use weed-free substrates
  • Distribute lawn seed evenly with spreaders
  • Always press down the rolled turf with a roller

Table of Contents

  • Load capacity
  • separation layer and drainage
  • substrate type and thickness
  • calculate amount
  • prepare ground
  • sow the lawn
  • Lay turf
  • frequently asked Questions

Load capacity

If there is a building such as a basement under the concrete layer, you must first have the load-bearing capacity of the concrete layer determined. Concrete substrates often must not be subjected to excessive loads because it is only a thin cover. In this case, only special substrates may be used or a thin layer of soil may be used.

Lawn next to concrete slabs

A notice: For example, if you want to green an old driveway that you no longer use, then you do not need any static information.

separation layer and drainage

For example, if you want to green a roof terrace or a ground-level basement with a lawn, it is important that the concrete underneath is protected. Otherwise, water can penetrate over time and even a tiny crack can cause serious damage from freezing water.

To ensure that this is not the case, a separating film must be applied between the concrete and the substrate. Depending on the area, it may also be necessary to ensure suitable drainage to prevent waterlogging.

A drainage is then poured onto the separating film. This usually consists of a layer of gravel. It is important that there are sufficient opportunities for the water to drain away. If no drains are integrated on the concrete surface, they must be created structurally before the substrate is applied.

Cross section of lawn on concrete with drainage system

A notice: If you want a lawn on an old concrete surface that no longer has a function, you don't have to apply a release film, but a water drain is essential. In this case, it is sufficient if you drill holes distributed in the concrete so that the water can seep into the ground.

substrate type and thickness

Lawn, regardless of whether it is seed or ready-made turf, has a root depth of a few centimetres. In theory, a layer of 5 cm of substrate on the concrete would be enough for a lawn, but you would have to water it several times a day because the soil dries out too quickly.

In order to keep the maintenance effort within limits, you should therefore fill up at least a pure layer of soil of 20 - 30 cm.

Suitable substrates are:

  • topsoil
  • compost soil
  • Lawn soil with a high organic content
Hands full of topsoil

A notice: If you use topsoil, it should also come from the composting plant. This is specially prepared beforehand so that it is largely free of weed seeds.

Potting soil, for example, is unsuitable for large areas. It's too loose and would sink in. This will make the floor uneven later.

calculate amount

How much soil you need depends on the substrate you choose. Impact on the crowd and that weight has the grain of the substrate and the moisture content. Earth usually has a fine grain size and a correspondingly high weight. On average, a grain size of up to 15 mm is assumed for a topsoil.

For a square meter with a thickness of 20 cm, there is a volume of 0.2 cubic meters per square meter of 1 meter x 1 meter x 0.2 meters.

With a grain size of up to 15 mm, this corresponds to around 200 liters of substrate per square meter. Depending on the moisture content of the substrate, this results in a weight of around 170 kg per square meter.

Formula for calculating the amount of soil

A special lawn soil is even finer-grained. It usually has a higher dead weight and can be around 190 kg per square meter with a thickness of 20 cm.

A notice: At the Sow or laying the lawn, the ground must always be rolled. As a result, the floor loses volume, which is why it makes sense to add 12% per square meter for the desired substrate in order to achieve the required thickness of at least 20 cm.

prepare ground

As soon as the concrete surface is prepared, the earth is spread on it for the lawn. It is important that the surface is level - use a spirit level if necessary - and that you give the floor a few days to settle.

You can already use one in advance roller go over it to compact the soil a bit.

sow the lawn

Choose one for sowing Period, in which rain is announced. This increases the chance that the seeds will germinate and saves you work when watering.

Sow the lawn correctly:

  • Slightly loosen the soil with a rake
  • lawn seed spread evenly over the surface
  • Press down the lawn seed with a roller
  • water the surface
rolling the lawn

If you accidentally cut too close, you can use a rake or rake to spread the seeds over the surrounding area.

Lay turf

If you choose a rolled turf, this has the advantage that you only have to lay an optimal turf. This significantly shortens the time until you can enter the area.

Laying turf correctly:

  • Surface loosen the surface with a rake
  • Distribute starter fertilizer
  • water the surface
  • Lay the rolled turf evenly and flush
  • Press down the lawn with a roller
Lay turf

A notice: Install turf immediately after you have bought it or it has been delivered. The lawn can only survive a few days without contact with the ground without suffering damage.

frequently asked Questions

How often does the lawn need to be watered initially?

You must water the turf every day for the first 14 days. Sown lawns have to be watered regularly for up to four weeks.

When can I mow the lawn for the first time?

With rolled turf, you usually have to mow the first time after ten days. How long it takes for a seeded lawn until you can mow the first time depends on the growing conditions. As soon as it has reached a height of approx. 10 cm, you can mow for the first time.

Which substrate can I use if the load-bearing capacity is low?

There are roof garden substrates that have a low dead weight. They usually consist of some soil and a mixture of different types of light rock. When using such a substrate, it is advisable to lay rolled turf, as this makes the surface more even.

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