If you are finishing a concrete floor, you need to prepare it first. Etching the concrete by using acid to strip the top layer is one way to do this. However, it does have its downsides and many people wonder whether you can sand or grind it instead.
Yes, you can sand or grind concrete instead of etching. Sanding is not very effective but grinding is often the best way to prepare the surface for painting or epoxy.
This article will give you all of the information you need about etching, grinding, and sanding your concrete floor.
Table of Contents
- Why is Etching, Grinding, or Sanding Concrete Even Important?
- Can You Use a Sander on Concrete?
- Can You Use a Grinder on Concrete?
- Should You Sand or Grind a Concrete Surface?
- The Pros and Cons of Grinding Concrete:
- What’s the Best Way to Grind a Concrete Floor?
- The Verdict – Is Grinding Concrete or Etching Concrete Better?
Why is Etching, Grinding, or Sanding Concrete Even Important?
Etching, grinding or sanding concrete is a crucial step when painting it or coating it with epoxy. When you are painting a wall or a wooden surface, you usually sand it to create a rough surface that the paint sticks to. It’s no different with concrete and if you don’t prepare it properly first by roughing up the surface, the end result will not be as good. The paint will not adhere properly and it’s more likely to chip and peel.
Preparing the surface properly is especially important when using an epoxy coating. Epoxy is much thicker than paint, so won’t soak into the concrete as easily. During the preparation stages, you open up the pores as well as creating a rough surface. This allows the epoxy to fill the pores and bond to the concrete properly. Failing to prepare the surface properly by etching, grinding, or sanding is one of the most common reasons that epoxy or paint fails on concrete.
Sanding concrete can also be used for aesthetic reasons. If you strip back the top layer of concrete, you can get a black and white speckled ‘salt and pepper’ effect, which looks similar to polished granite. People often use this for concrete worktops. It can also help you achieve a smooth, polished finish.
Can You Use a Sander on Concrete?
Yes, you can use a sander on concrete, but only if you use the right pads for it. The aluminum oxide or ceramic sandpaper that you would use for wooden floors, for example, won’t do much to concrete. You need specific diamond sanding or polishing pads that fit your sander if you want to strip the surface layer and prepare the concrete for paint or epoxy.
However, using a standard sandpaper pad can help you smooth the surface of concrete and get a nice finish. If you are not planning to paint or epoxy over the top, using a sander can get you the finish you want. However, you will find it much easier if you use fine diamond encrusted polishing pads.
Bear in mind that manufacturer’s often use the terms ‘sander’ and ‘grinder’ interchangeably when talking about concrete tools. So, you may be able to use an all-purpose sander on concrete as long as you can get the right diamond pads to fit it, but this will be the same as using a concrete grinder.
Can You Use a Grinder on Concrete?
Yes, ideally you should use a purpose-built concrete grinder to prepare the surface. These use the same diamond pads that you would put on your sander. They come in different grades, like the grit on sandpaper. The diamond pad you should use depends on whether you are stripping back the surface or trying to polish it and get a smooth finish.
Upright concrete polishers will help you cover a large area quite quickly and prepare the surface for painting or epoxy. However, these are quite harsh machines and they are not ideal for fine work like polishing. So, if you are going to put a finish over the top of the concrete, go for an upright polisher.
However, if you want to maintain the surface of the concrete and polish it up, you will need to finish it with a handheld grinder.
Should You Sand or Grind a Concrete Surface?
In most cases, grinding is the best method. It’s much more effective and far quicker than sanding. As long as you use the right diamond grinding pads for your purposes, it’s the best way to prepare a surface for paint or epoxy.
Sanding is sometimes preferable if you just want to smooth the surface and remove small imperfections in the concrete, but aside from that, grinding is the best choice.
The Pros and Cons of Grinding Concrete:
The biggest pro of grinding concrete is the finish that you get afterwards. Grinders are very efficient at taking off the surface layer of the concrete and opening up the pores, so it is ready to be finished in whatever way you like. Ultimately, this means that the paint or epoxy will last much longer.
Concrete grinders also offer a lot of customization options because you can change the diamond pads. If you were etching, for example, you don’t have that much control and the results are very varied depending on the state of the concrete when you get started.
The composition, hardness, and texture of concrete can be very different and a grinder allows you to change the pads to account for that, so you get the best finish. Etching, on the other hand, is a one-size-fits-all solution and the results are not always great.
There are a few downsides to grinding concrete. Firstly, concrete grinders can be quite expensive, especially once you buy all of the pads on top. So, if you’re looking for the cheapest option, consider etching instead.
There is also a bit of a learning curve with large concrete grinders. It’s still possible for a home DIYer to grind a concrete surface well, but if you are using a large upright grinder for the first time, it can be tricky.
That said, concrete grinding is still an excellent way to prepare the surface for finishing.
What’s the Best Way to Grind a Concrete Floor?
When grinding a concrete floor, you have two options; wet grinding and dry grinding. With wet grinding, water is applied to capture dust from the concrete, and it also gives a different finish. Dry grinding gives you a glossier finish, while wet grinding doesn’t give you the same sheen. If you are keeping the concrete uncovered and polishing it, you need to decide what kind of finish you want.
However, if you are just preparing it for paint or epoxy, it doesn’t matter as much. Dry grinding is usually easiest because it doesn’t create a slurry of concrete to clean up afterwards. Just bear in mind that it creates more dust.
If you want to grind your concrete floor, follow these steps to get the best results:
1. Remove existing coating
If there is an existing coating on the concrete floor, this needs to be removed first. A 16 to 20 grit grinding blade will take off paint or epoxy very easily. Once you have taken off the existing coating, you can repair the concrete floor underneath.
2. Seal cracks and joints
Old concrete floors are likely to have some cracks and joints in. These need to be sealed before you grind the floor so they don’t show up once you paint or apply epoxy. Use an epoxy filler or a concrete patch solution for this. Use a scraper and fill the cracks, trying to smooth the top as best you can. But bear in mind that you will grind it anyway, so don’t spend too much time trying to make it perfect.
3. Grind with 30-40 grit pad
Once the filler is dry, you can start grinding the floor. Use a 30-40 grit diamond grinding pad and start working up and down the concrete floor. Move it slowly side to side to ensure even grinding across the whole floor. Make a few passes, and then change the pad.
4. Increase the grit of the pad and continue
Change to a finer pad and do another pass over the floor. Do this a few times until you get to 100 grit. You should notice the floor is becoming smoother and has a nice even surface, but is still a bit rough.
If you are planning to put an epoxy coating or paint on the floor, you can stop at this point.
5. Polishing concrete flooring (optional)
If you want to polish the concrete instead of painting or using epoxy, you need to continue grinding it. Use a 150 grit pad to prepare it for polishing. You will then need to use a chemical hardener on the concrete before you can start polishing.
Once the hardener has done its work and dried fully, you can start polishing, increasing the grit of the pad each time. Start with 200 grit and work your way up to 400, 800, 1500, and finally 3000 grit to polish the floor.
The Verdict – Is Grinding Concrete or Etching Concrete Better?
Overall, grinding concrete is better than etching. Etching involves using acid to eat through the top layer of concrete and expose the pores underneath. While it does do a good job of exposing the pores and it doesn’t create as much mess as grinding, it cannot get rid of old finishes, glue, or stains. It’s also more unpredictable because you can’t easily adapt the process depending on the state of the concrete.
With a grinder, you can get rid of everything easily and you can use your judgment to decide which grinding pads to use, so you get the best possible finish.
If you are preparing a brand new floor with no blemishes, acid etching might be the easier option. But, in most cases, grinding your concrete floor is better.
Read related concrete articles:
- How Long After Sealing Concrete Can You Walk on It?
- What Is Etching Concrete? (The Ultimate Guide)
- How Long to Wait After Etching Concrete Before Painting?
- How Thick Should a Concrete Patio Be? (All You Need to Know)
Jamie is the founder of The Backyard Pros. When he was 15 years old he started working at a garden centre helping people buy plants, gardening products, and lawn care products. He has real estate experience and he is a home owner. Jamie loves backyard projects, refinishing furniture, and enjoys sharing his knowledge online.