How to Grind Concrete
Whether you like to have an exposed concrete floor or whether you have recently bought a precast concrete product like a concrete countertop: you might not appreciate the roughness of the concrete surface. However, it does not need to be like that:
You can make the surface of concrete much more appealing yourself with grinding and polishing – read this post, find out what you need for your project and follow our 5 steps to grind concrete.
Besides removing imperfections and roughness of the concrete surface, there are a lot of other reasons why you may want to consider grinding your concrete countertops and floors. For pre-cast concrete projects, grinding is actually a must. For concrete flooring, you can smooth concrete surfaces by removing imperfections and inconsistencies by grinding. Even old damages to your concrete surfaces, paint or epoxies can be removed through grinding.
Whether you are planning to polish the concrete floor, to remove aggressive coatings or whether you want to prepare your concrete surface for some alternative finishing work, continue reading as I will explain 5 easy steps for grinding concrete in this post and share a couple of expert tips that will definitely help you in rendering an even and shining concrete surface.
What Is Concrete Grinding?
Concrete grinding is the process of pulverizing the small rough concrete fragments by the friction of abrasives like diamond tools or silicon carbide.
Concrete grinding is used in almost all (semi-) professional and DIY application areas of concrete technology. This includes but is not limited to pavements, floors of garages and factory warehouses along with countertop and worktops.
Grinding will help you get rid of stubborn tile glue or vinyl glue and, at the same time, expose those shiny aggregates of your concrete to achieve a unique polished look of its surface, which is also quite trendy recently.
How to Use a Concrete Grinder
The only way to smooth rough concrete is using concrete grinders. Concrete grinders are handheld finishing tools that grind and level concrete surfaces and help achieve a smooth finish. This type of grinder is actually somewhat different from grinders used for granite and marble grinding: Concrete grinders are made to be more robust and drive the unit with more power in order to achieve the higher (compared to marble or granite) sliding friction that is required for concrete.
The grinding of concrete is usually performed with diamond grinders, also called “diamonds”. Such grinding machines have grit sanding pads of various sizes attached to the abrasive discs or rotating blades and have diamond particles.
The characteristics of synthetic diamond vary in terms of shape, strength, and size, represented in terms of grit sizes identified as grit numbers. With gradual use of increasingly finer grits of diamond abrasive, it is even possible to come close to a marble- or terrazzo-like appearance.
The grit number and the size of the diamonds are inverse, hence a large grit number refers to a small diamond. For removal of persistent coating, you can use grit of coarser size (16-40) while you better go for the medium (70-80) to fine (140-150) grit sizes for polishing and honing applications. Check out abrasive for concrete on Amazon.
In addition to the grit size, the bond of the material does have an impact on what the final product would look like. The bond of a group as metal-bond, hybrid/semimetal bond, and wet or dry resin bonds defines how effective the diamond tool could hold on to the diamond crystals during the abrasive grinding process. During the grinding, this bond undergoes a preset wearing, so new diamond is exposed during the use of it, without a sudden break of the abrasive.
You will find a comprehensive introduction to grinders and grinding in general in our article How to Use a Grinder.
Now that you know how concrete grinders work, let’s move on to the different types of concrete finishes.
What Types of Concrete Texture Can Be Achieve Through Grinding
Depending on the type of the concrete finishing tool you are using, different textures can be achieved for the concrete surface. You can use trowel or floats as well as a broom or edging tools to get the desired texture of the concrete. Similar to the types of texture for plastic concrete, there are different finishes for concrete surfaces of floors and countertops.
Exposed Aggregate Textured Finish – Full Exposure Finish
This is a classy shining type of concrete finish as the one we can get for terrazzo flooring. As the name suggests, it includes the removal of the top layer of concrete and exposes the edges of the natural stone aggregates mixed in the concrete matrix. This type of finish is best for slip-resistant surfaces as in pavements, for instance. For such a finish, the concrete needs to be be sealed by using a high-quality sealant after concrete curing in order to avoid staining.
This type of finish is rather simple and much easier to achieve compared to the full exposure finish. You are not going to remove anything from the matrix, you are just polishing the top layer for a smooth and shiner surface instead. This type of finish is usually applied for countertops and worktops.
Salt or Speckled Finish
Salt or Speckled finish involves light grinding, so that the fine stones are revealed but the sand is still hidden just beneath the surface. Scratch marks as a result of this polishing are removed afterward aiming to produce a fully polished concrete surface.
Different Types of Concrete Grinders
There are specific concrete grinder tools for the countertops, worktops and floors. These grinders and sanders come in many configurations and sizes, so you will be able to find a grinder that fits for your project. In this section, we will introduce the most common types of concrete grinders and provide you some guidance on how to find the perfect one:
There are two types of grinders when they are categorized by the way of working and the configuration of the grinding stones attached to the base of the equipment:
These type of concrete grinders have a large main disc along with three smaller discs mounted on the main disc. The smaller discs lie in the same plan and have direct contact with the floor while the main disc doesn’t make contact with the floor. Planetary grinders are rather light in weight which allows the user to move the tool in a straight line easily. They are ideal for less demanding jobs such as smoothing concrete floor of a residential garage for an epoxy coating, for instance. Check out planetary concrete grinders on Amazon.
Rotary grinders come in different configurations but all of them have a large disc along with a base that rotates to grind the concrete surface. This type of grinders is ideal for heavy-duty grinding at higher RPM (Revolutions Per Minute). These devices, when equipped with a VFD (Variable Frequency Drive), can be used for high-speed polishing with a superior finish. Rotary Grinders are ideal for residential and light commercial concrete grinding applications as well as for the removal of persistent carpet glue, mastic and epoxies. Find the right rotary concrete grinders on Amazon.
If you prefer classifying grinders by their handling, “handheld” and “walk-back” are the two categories you want to look at:
Handheld Concrete Grinders
Handheld concrete grinders are an affordable and handy choice if you use them casually and only for rather small areas. They have the obvious downfall that they require more effort from the user as they are smaller in size. Handheld grinders are mostly used for smaller floor grinding applications and for polishing concrete countertops. Check the prices of handheld concrete grinders on Amazon.
Handheld grinders are usually equipped with vacuum shrouds for dust-free working. If this does not hold true for your grinder, you can use one of the inexpensive universal dust shrouds in the market, which you will find e. g. on Amazon.
Walk-back Concrete Grinders
This type of concrete grinders is much larger in size compared to the handheld type. Large areas of concrete can be ground with these machines which makes them the unchallenged grinder of choice for large projects and (semi-)professional use. Depending on the application requirements, you are able to choose from 16” to 24” size grinders that are available in the market. These tools can have multiple discs (up to 6) and they are ideal for the quick removal of coatings like epoxy, paint and tile glue.
How to Prepare and Do Grinding
Once you have chosen the desired texture and the fitting tool and equipment, follow these 5 steps to grind concrete:
- As with any tool or machine, follow the ground rules: Before you put your hands on any concrete grinder, you should get to know how it is working and which safety measures you should be familiar with. Concrete grinders are powerful machines, if you do not know or if you are not trained how to use them correctly you will bring yourself in danger.
- Have a thorough look on all the parts of the machine, make sure that all the cables are plugged in and that there is no damage to any part.
- When you and your equipment are ready to start grinding, the next step is to prepare the existing concrete surface. Any visible cracks or humps should be repaired and the existing sealer or coating should be stripped off (as good as possible, at the least).
- After the preparation of the surface, use the concrete grinder that you chose for your project and work your way through the polishing process. Move gradually from coarser grit to finer grit depending on the desired quality and fineness of the finish.
- The final step is sealing the concrete with a suitable sealant in order to protect it from oil, chemicals, staining, and moisture.
Why Should You Grind Your Concrete Surface?
Concrete is a fascinating construction material that offers durability and longevity and can also have an inviting appearance if you choose the right type and treat it correctly. Concrete as a flooring option is much less expensive compared to wood, ceramic or, above all, natural stone. It will also be tougher and more resilient against weather conditions, heavy use or weight from heavy loads. However, without proper grinding, polishing and sealing of the concrete surface, it will be susceptible to moisture penetrations that can lead to freezing thaw and cracks due to differential shrinkages.
All in all, concrete grinding is always recommended to ensure long lasting and classy looking concrete floors and countertops.
Interested in working with concrete? Read our post How to Sand Concrete to learn about other options how you can enhance your concrete surface.