Guide » Grinding concrete - That's how it's done!
Grinding concrete can often be done by yourself.
We show you:
- Where concrete usually needs to be sanded
- What work you can do yourself
- Machines and tools required for grinding concrete
Table of contents
- 1. This is how concrete grinding works
- 1.1 What is needed for concrete grinding?
- 1.2 How much does concrete grinding cost me?
- 1.3 Which sandpaper do I need to sand concrete?
- 2. Grinding concrete - areas of application in modern residential and industrial construction
- 2.1 Grind concrete floor
- 2.2 Grind concrete wall
- 2.3 Grind concrete pavement
- 2.4 Grind concrete stairs
- 3. How can I grind down concrete?
- 3.1 Grinding concrete by hand
- 3.2 Grind concrete using a floor grinder
- 3.3 Grinding concrete with the Flex
- 4 Sanding concrete smooth - step by step instructions
- 4.1 Preparation
- 4.2 Cleaning the concrete surface
- 4.3 Determine grit
- 4.4 Grind down concrete with a floor grinder
- 4.5 Grind down concrete with an angle grinder
- 4.6 Cleaning the concrete surface
- 4.7 More grinding passes
- 4.8 Polishing concrete
- 5. Conclusion - grinding concrete:
Difficulty: Easy | Costs for 20m²: approx. 350-400 euros | Workload for 20m²: approx. 8 hours
The building material concrete is used in many areas. The areas of application range from the foundation of a building to special constructions such as bridges or tunnels. Concrete is also being used more and more frequently as a floor in modern living areas and industrial rooms due to its stylish appearance. Good processing of the concrete floor in the form of concrete grinding plays an important role in this. In this article we explain in detail how you can turn a newly poured concrete floor in a new building or the old concrete floor into an eye-catcher.
Figure 1: Sanding the concrete floor - this is how it's done!
1. This is how concrete grinding works
In order to be able to successfully grind concrete, you should obtain the necessary tools and machines in advance. In addition, due to the high level of dust and noise, certain equipment is required to protect your health.
1.1 What is needed for concrete grinding?
As described above, certain protective equipment such as a respirator, safety goggles and hearing protection are necessary for concrete grinding. Depending on the size of the area to be treated, a floor grinder should be used. This is used for large areas such as a floor in a living area. This will save you a lot of time and effort. In addition, an angle grinder is required for the surfaces that cannot be reached with the floor grinder. With an angle grinder you can work on small areas such as corners and stairs. An industrial vacuum ensures cleaning between the individual grinding processes. You can usually rent these machines at any large hardware store. In order to protect the concrete floor from mechanical and chemical stress, you should apply a seal after sanding it down.
At a glance:
- respirator
- safety goggles
- ear protection
- floor grinder
- angle grinder
- grinding wheels
- diamond cup wheel
- industrial vacuum cleaner
- sealing material
- brush and roller
1.2 How much does concrete grinding cost me?
Concrete grinding depends on the size of the area to be treated and the number of grinding passes required. For a floor area of approx. 20m² and three sanding passes with a grain size of 80, 160 and 320, you can calculate around 350 - 400 euros for your project:
Personal protective equipment (approx. 27 - 43 euros):
- Respirator mask about 20 - 30 euros
- Goggles about 1 - 3 euros
- Hearing protection approx. 6 - 10 euros
Machine rental (approx. 160 euros):
- Floor grinder approx. 110 euros (daily rate)
- Angle grinder approx. 12 euros (daily rate)
- Industrial vacuum approx. 38 euros (daily rate)
Tools (approx. 165 - 205 euros):
- Sandpaper set approx. 80 - 100 euros
- Diamond cup wheel 125 mm iynx Tools 24.90 euros
- Synthetic resin / epoxy resin (10 liters) approx. 50 - 70 euros
- Brush and roller about 10 euros
Prices are from current internet research (20.11.2022).
1.3 Which sandpaper do I need to sand concrete?
Which abrasive paper is necessary for grinding concrete depends on the expectations of the individual operator. For example, sanding concrete floors requires multiple sanding passes. Here you usually start with the first sanding pass with a coarser grit of 80. In the second sanding pass you continue working with a 160 grit. Double the grit of the sandpaper after each sanding pass until the desired finish is achieved.
2. Grinding concrete - areas of application in modern residential and industrial construction
The fair-faced concrete is used more and more frequently in modern residential and industrial construction. The optically stylish exposed concrete can appear in offices, living rooms, kitchens and bathrooms in the form of floors, walls, ceilings and stairs. In order to be able to use the full potential of the fair-faced concrete, different machines, tools and grinding techniques are required depending on the area of application.
Figure 2: Fair-faced concrete in modern residential construction
2.1 Grind concrete floor
A floor grinding machine is used for fair-faced concrete with a large area, such as floors in industrial halls or offices. Due to the large diameter of the grinding disc of the floor grinding machine, many square meters can be ground down in a short time and with significantly less effort than with an angle grinder. You can read about how the grinding of a concrete floor works in detail in our instructions under point 4 "Sanding concrete smooth - step by step instructions".
2.2 Grind concrete wall
When grinding concrete walls, special hand grinders, which are closely related to conventional angle grinders, are used. Since, in contrast to grinding concrete floors, the "floating" of the floor grinding machine cannot be used due to its own weight and the machine's own weight has to be carried when grinding concrete walls, this grinding work is one of the more complex variants of concrete grinding.
2.3 Grind concrete pavement
In advance, you should be sure that grinding the concrete surface is really necessary. Due to the overhead work and the weight of the machine, the grinding of a concrete pavement is associated with great exertion and correspondingly tiring work. The entire concrete surface of the ceiling is processed with a concrete milling machine in several grinding passes. An angle grinder with a diamond cup wheel can be used for the edge surfaces.
2.4 Grind concrete stairs
The grinding of a concrete staircase is often necessary during renovation work due to old material residues such as adhesive from carpets or tiles. The concrete surface must be thoroughly sanded down. Only then is it possible to lay the new floor on the concrete staircase due to the required adhesion between the concrete staircase and, for example, the new carpet. An angle grinder with a diamond grinding disc is advantageous here, as this can be used perfectly for small areas.
3. How can I grind down concrete?
There are several ways to sand down a concrete surface. This usually depends on the size and also the accessibility of the concrete surface to be processed. Devices such as a floor grinder or an angle grinder, also known colloquially as a flex, are used. Another option for very inaccessible areas is to grind the surface by hand using diamond hand grinding pads .
3.1 Grinding concrete by hand
Diamond hand grinding pads can be used to grind small areas that are difficult or almost impossible to reach with an angle grinder. Thanks to their ergonomic shape, they are easy to hold and are available with different grit levels, from 50 for renovation sanding to 3000 grit for high-gloss polishing. However, grinding concrete by hand is a very tedious and sweaty activity and is therefore rarely used.
3.2 Grind concrete using a floor grinder
A floor grinder is often used to smooth large, rough concrete surfaces. Due to the large sanding disc and its own weight, this is able to work on a large area in a very short time with little effort. In order to produce a homogeneous grinding pattern on the concrete floor, it is essential that the floor grinding machine is guided evenly. Depending on the application of the concrete surface, several grinding passes with different grit grades of the grinding wheels are necessary.
3.3 Grinding concrete with the Flex (angle grinder)
The angle grinder, also known colloquially as a flex, is suitable for grinding small concrete surfaces such as corners, edge areas or stairs. The Flex is equipped with a diamond grinding cup, which can process the hard material thanks to the robustness of the diamonds. One of the major disadvantages compared to the floor grinder is the higher grinding effort and the associated effort due to the smaller grinding disc. An increased risk of injury must also be expected due to the open grinding wheel.
4 Sanding concrete smooth - step by step instructions
Grinding and sealing concrete smooth can be done successfully even by inexperienced people by following the steps involved. Grinding and sealing the concrete is divided into three steps. These are the grinding, vacuuming and sealing of fair-faced concrete.
Figure 3: Grinding a concrete floor using a floor grinder
4.1 Preparation
Before starting your forthcoming work, ensure occupational safety. You should put on a breathing mask and safety goggles because of the dust that develops during sanding. In addition, your hearing should be protected with hearing protection.
4.2 Cleaning the concrete surface
First clean the surface to be treated with an industrial vacuum cleaner. Be careful to ensure the concrete floor is free of loose debris before sanding. Large loose residues of material could scratch deep grooves in the floor during the grinding process.
4.3 Determine grit
Equip the floor grinder with the appropriate sandpaper for your application and start the floor grinder. Important: When using the sandpaper for the first time, pay attention to the increased frictional resistance of the sandpaper, which can affect the floor sander.
4.4 Grind down concrete with a floor grinder
Sand the surfaces evenly using the floor sander. Care should be taken to keep the handle of the floor grinder flat. This ensures better gliding of the floor grinder on the concrete floor. Check the sandpaper after certain time intervals and change it if necessary to prevent the sandpaper from wearing through.
4.5 Grind down concrete with an angle grinder
If you can't get to all the places in the room with the floor grinder, then you should use the angle grinder. In combination with the right diamond cup wheel, the angle grinder is a good alternative for working on surfaces such as edges, corners or stairs.
4.6 Cleaning the concrete surface
After the room has been completely sanded, the increased occurrence of dust must be counteracted by cleaning with an industrial vacuum cleaner. You should make sure that before each new grinding process, the surface to be processed must be free of particles in the form of dust or material residues from the previous grinding process.
4.7 More grinding passes
Repeat steps 4 to 6 until the desired finish is achieved.
4.8 Polishing concrete
After the desired micrograph has been achieved, the fair-faced concrete must be sealed due to the sensitive surface. Mix the sealing medium (e.g. synthetic resin or epoxy resin) thoroughly and apply to the fair-faced concrete with a brush or roller. You should make sure to apply thin and even layers. Usually at least two jobs are required to get a good result. The drying time before walking is approx. 24 hours. Complete drying of the seal is achieved after 72 hours. Good ventilation and a minimum temperature of 5°C are required while the seal is drying. Direct sunlight should also be avoided during drying.
5. Conclusion - grinding concrete:
The areas of application of fair-faced concrete are increasingly being used in modern residential and industrial construction. Therefore, the processing of the concrete surface in the form of concrete grinding is increasingly becoming part of the everyday activities of a craftsman. The use of the machines depends on the size of the area and the accessibility of the surface to be sanded. A floor grinder is used for large areas. An angle grinder or, in rare cases, a diamond hand grinding pad can be used for hard-to-reach areas such as corners and edge areas.
6. The most common questions about grinding concrete
1.