If you are somebody who likes to take the DIY approach, that is really cool because you always get to learn something new, plus you get to feel a sense of accomplishment too. One of the things that you may do on your own is pouring concrete, which in itself is easy enough. However, that being said, doing a project with concrete usually doesn’t end with just pouring it and letting it cure because, for many purposes, you will also need to sand it down.
Concrete is a hard material once cured, so sanding it does require the right tools and know-how, which is exactly what we are here to talk about today. Let’s get right to it .
Can You Sand Concrete?
One question that many people have is whether or not it is even possible to sand concrete to begin with, and the answer is a definite yes, it is more than doable. This is true both for indoor and outdoor concrete, as with the proper tools, both can be sanded.
In fact, there are three common finishes that concrete is brought to, particularly when it comes to indoor applications, such as for floors, walls, and countertops too, and they all require a certain degree of sanding.
The first of these finishes is the smooth finish, where you don’t remove much or any of the concrete at all, but are just smoothing it out to make it look smooth and shiny. The second of these concrete finishes that require sanding is the salt and pepper finish, which is an intermediate finish that involves the topmost layer of the concrete being sanded off to expose the sand directly under the top layer. The third of these finishes that requires sanding is the exposed aggregate finish, where a lot of material, up to 1/4-inch or more, is removed, thus exposing the aggregate below.
Do also keep in mind that a smooth finish can usually be done with high-quality sandpaper or a hand grinder (or handheld sander), whereas an exposed aggregate finish is more or less impossible to achieve without a powered sander or polishing tool.
What Is the Best Type of Sander and Sanding Paper for Concrete?
Ok, so something that we definitely need to cover here is what kind of tools and items that you can and need to use for sanding concrete. First off, let’s talk about the type of sandpaper that works best for sanding concrete, and then we will talk about what the best tools for this job are.
One question that many people have is whether or not it is possible to use normal sandpaper to sand concrete. Now the simple reality here is that while it is totally possible to sand concrete using normal sandpaper, which you would usually use for wooden surfaces, it is not going to be fast or easy. Normal sandpaper just usually isn’t tough enough to handle concrete sanding, especially in terms of longevity and durability.
For one, you will go through a whole lot of normal sandpaper if you choose to use it on concrete, and second, even if you do choose to go with this method, you will end up taking a whole lot of time to complete the job. Using normal sandpaper to sand concrete is a difficult and painstaking task. With that being said, if you choose to use normal sandpaper, if you want to achieve a very smooth finish, go for grit between 200 and 400, but for basic sanding, a grit between 40 and 60 will do just fine.
When it comes to sanding concrete, the much better type of sandpaper to use is known as diamond sandpaper. And yes, this stuff is actually made with very small bits of diamonds as opposed to sand that is used for normal sandpaper. Diamond grits are extremely hard and durable and therefore last much longer, can remove harder material. They offer the user a good deal of speed too.
That said, when it comes to diamond sandpaper and sanding concrete, do remember that for the process to go as smoothly as possible, the concrete does usually need to be wet, and therefore you need to purchase wet/dry diamond sandpaper, as regular dry diamond sandpaper will break down too quickly when it gets wet.
Now that you know what kind of sandpaper is best for sanding concrete, it is time to figure out what the best tools for the job are. What you need to know here is that which tool you use really depends on the size or the scope of the job in question.
For instance, if you are just polishing a very small surface, you may be able to manually sand it with sandpaper, or you could even use a special concrete sanding block (or a normal sanding block wrapped with some diamond sandpaper).
However, for much larger areas, such as for floors, walls, and countertops, as well as for removing a lot of material at once (such as to achieve those concrete finishes we discussed above), you will need a power tool, so let’s figure out which one you need.
Walk-Behind Concrete Sanders
If you are sanding or polishing a large concrete surface, particularly a concrete floor, then a walk-behind concrete sander is what you need. In terms of appearance, these walk-behind concrete sanders look more or less like floor buffers or floor polishers. They feature very large circular discs that sand or grind away at the floor and come complete with wheels and a handle for easy pushing.
All you have to do is to attach the right kind of sanding pad, turn it on, and walk behind it. When it comes to large surfaces (generally for floors), this is by far the best option to go with. The high-quality models even come with options to attach them to dust vacuums to help keep messes under control.
Handheld Concrete Sanders
Now, those walk behind sanders are fantastic for floors, but it’s not like you can hold them in the air and use them for walls, not to mention that using them on countertops is not easy either. For walls where a floor sander won’t work, and for smaller areas such as countertops, what you need to use is a handheld concrete grinder or polisher.
You can either go for a straight-up handheld concrete grinder, or you can go for a normal orbital grinder and then outfit it with a special concrete grinding pad. You can easily hold these in your hands and use them for any concrete surface whether small or large. Keep in mind that the type of sandpaper you use here will depend on the sanding method (wet or dry).
Although an angle grinder definitely won’t be your first choice (that small wheel can only work on very small areas at a time), if you just need to sand down a small and specific area, an angle grinder outfitted with a diamond cup wheel can definitely do the trick.
If you are going to use an angle grinder, don’t use anything but a diamond cup wheel, because everything else will wear down too quickly.
4 Reasons to Sand Concrete
In case you are wondering why you would sand concrete, this is what we are about to discuss. As you are about to find out, there are four main reasons as to why you would sand concrete.
1. To Make Repairs
One of the primary reasons as to why you might need to sand down concrete is to perform repairs on it. For instance, if your concrete has cracks in it, you will need to add concrete filler, but in order to add concrete filler (to make it adhere to the existing concrete), you will first need to sand down the broken bits. You will also need to sand the surface after adding the concrete filler in order to make the repairs match the original concrete.
2. To Remove Sharp Edges
Another reason why you might need to sand concrete is because there are sharp edges or aggregate that is showing through the surface. Sharp edges and exposed aggregate can be dangerous and cause injuries and should therefore be sanded away. A super rough concrete driveway with sharp edges could even pop a tire on a vehicle and should therefore be sanded away. Of course, you also don’t want sharp edges on your kitchen countertop.
3. To Remove Stains or Paint
While there are many types of paint that can be removed with common solvents, some of them just can’t get rid of paint stains. Whether we are talking about paint stains or other types of stains such as oil stains, that just won’t come away, one of the last resorts you might come to is to sand them away. If you have a big paint stain on a concrete surface, just sand away the top layer to expose the original concrete below.
4. To Achieve a Specific Appearance
The other reason and perhaps the most common reason as to why concrete needs to be sanded is to achieve a specific finish. We already talked about the three major types of finishes that need sanding (smooth, salt and pepper, exposed aggregate). Simply put, concrete just isn’t all that smooth after it has been poured, and if you want to achieve a smooth finish or any other type of specific finish for that matter, you will need to sand it.
How to Sand Concrete: A Step-by-Step Guide
OK, so there are plenty of concrete surfaces that you may need to sand down, but if you’re taking the DIY approach, one of the most common applications that you might require concrete sanding for is to get that countertop looking brand new.
Therefore, for the purposes of this article, this step-by-step guide on how to sand concrete is going to focus on sanding a concrete countertop.
Step 1: Gather Your Tools
First off, you need to gather the right tools, which in this case includes a handheld water-fed variable speed concrete polisher or grinder, a variety of diamond grinding pads (of varying grits), a mask, goggles, earplugs, a squeegee, some water, and possibly some diamond sandpaper pads for hand sanding (for the hard to reach areas). You will also need the concrete sealant of your choosing.
Step 2: Prepare the Surface
Before you can get to work on your countertop, just in case there are any cracks, holes, or flaws, you will first need to fill them. If this is the case, you will need to buy a patching slurry or concrete filler (that matches the color of the existing concrete), apply it to the holes, and then let it cure. I wrote more about fixing cracks in concrete here.
If there is no need to make repairs, you still need to prepare the surface by washing it down and then using a squeegee to remove any grit or debris. The concrete counter must be 100% clean before you start sanding, because if there is sand or dirt present when you go to sand the concrete, you may cause damage to the surface.
Step 3: Start Polishing the Surface
With the surface adequately prepared, you now need to start polishing. Make sure to fit the coarsest pad you have onto the handheld concrete grinder, and then start the water flow (you really do want to use the wet sanding method here as it causes less dust to fly into the air, so you do need to hook up your water supply first). Start sanding and evenly cover the entirety of the surface until you have achieved a relatively smooth finish and your desired result.
Step 4: Keep Polishing with Finer Pads
Once the concrete has been sanded with the coarsest pad, you then want to exchange that pad for a slightly less coarse pad. Keep exchanging sanding pads for the next finest one you have, and continue the process until you have used the finest pad. Make sure to not use each pad too much and to err on the side of caution, because you can’t add the concrete back on once it’s been removed. Now is also the time to do manual sanding for the hard-to-reach areas.
Step 5: Dry and Seal it
Once you have achieved the desired finish, let the countertop dry. Once everything is bone dry, apply the concrete sealant of your choice according to the manufacturer’s directions.
Mistakes to Avoid, Tips & Tricks
While the above should do the job, make sure to go through the additional tips below to make the process smoother:
- Although wet sanding is the better option because it makes less of a mess, if you do want to dry sand, be sure to wear a mask or even a respirator. Inhaling concrete dust is not healthy by any means.
- Always wear goggles when sanding concrete.
- If you don’t want to waste a huge amount of time, stay away from regular sandpaper.
- If you are unsure as to what kind of finish you want, or you are unsure how to achieve a specific finish, you may want to leave this job to a professional.
- To avoid covering your belongings is water and dust, cover them with tarps or large sheets (that you don’t use anymore).
The bottom line here is that if you want to DIY sand a concrete surface, using a simple hand grinder and the right pads will do the trick, and for a floor, a walk-behind concrete grinder is what you need. Just remember to take your time!