Sanding concrete is a very important process, whether sanding concrete countertops, concrete walls, concrete floors or any other concrete surface.
While sanding is essential to the concrete finish process, many people get stuck deciding which concrete polishing method is the right choice for their project.
In this guide, we will talk about the most critical steps for long-lasting concrete sanding to provide the smooth finish you’re looking for.
Each concrete polishing method has pros and cons, so we’ll make sure to give you a detailed analysis of the most important factors.
Why sand concrete?
Concrete sanding is a very important process, as it can improve the durability and appearance of a surface.
It is vital in preparing a concrete surface for staining, painting or coating.
The process involves removing debris and stains from the surface of the concrete and smoothing out any rough spots or patches.
Sanding also helps to remove common imperfections such as etches, scratches, oil stains and scuffs.
Concrete sanding is necessary to achieve the best results when applying a coating or another type of surface treatment to concrete.
Without a smooth and clean surface, it can be difficult for these treatments to bond well with the concrete.
This can result in peeling or chipping of the coating and difficulty with adhesion.
When you polish the concrete surface, you create a more uniform texture and appearance.
This helps to ensure that your chosen treatment or coating will look its best.
Additionally, this makes it easier to apply the new finish evenly across the entire surface of the concrete.
When done correctly, concrete sanding can also help to make the concrete last longer.
Sanding removes excess moisture and reduces the risk of damage from water exposure, mold growth or freeze-thaw cycles.
Sanding concrete is a relatively simple process that can be completed in just a few hours.
However, using the right tools and techniques is essential to get the best results.
To sum up, there are many benefits to sanding a concrete surface before applying a coating or other finish.
Some key advantages of this process include improving the overall appearance, creating a smoother texture and extending the life of the concrete.
Keep reading to learn more about the most critical steps of concrete sanding, whether you’re working on decorative concrete, wet concrete, concrete wall or another concrete surface.
How to sand concrete
Perfectly sanded, polished concrete does require some time and patience.
If you want the concrete surface to be polished but durable, here’s what you need to remember when sanding concrete.
1. Decide on the result you’re going for
Before starting the concrete sanding process, deciding what kind of look you’re going for is essential.
Do you want a completely smooth finish or a little bit of texture?
The texture will depend on the type of sanding machine that you choose.
The most common tools for concrete sanding are floor sanders, random orbit sanders (called palm sanders in the construction industry) and belt or disk sanders.
A hand sander can also be used, but it requires much more effort and time.
You must also decide whether to sand the entire surface or just a small area.
If you choose to sand the whole surface, start in a corner and work your way outwards so that you can focus on the task at hand and not get distracted by what’s happening around you.
If you decide to do just a tiny part of the project, ensure it is easy enough to reach without putting too much effort or strain.
Please don’t choose a spot that is in the way of where you are moving materials and ensure that it is an area against a wall because this makes it easier to control concrete dust while sanding.
Ensure all debris, such as dust, wood chips, and loose dirt, has been swept up.
If you have water on the surface, wipe it off with a dry cloth.
2. Choose wet sanding or dry sanding
The next step is to determine if you will be doing wet or dry sanding.
Wet polishing involves using water while making contact between the material and the surface.
This creates a barrier that minimizes concrete dust by collecting it in pools and letting it wash away.
Dry sanding involves using a pressure washer to wash the surface and immediately start sanding thoroughly.
There are pros and cons that both ways of wet or dry sanding have in common, depending on the type of surface you’re working with, like using less power for wet sanding and controlling the dust level with wet sanding.
One common tip for dry sanding is to keep the sander moving parallel with the grain, being careful not to move it perpendicular (perpendicular motion will result in a wider scratch pattern).
By doing this, you can achieve consistent patterns that are more appealing and less noticeable.
3. Fill any cracks before sanding
A step many people forget when sanding concrete surfaces is filling any cracks and crevices beforehand.
Not doing so can make the job much more complex and time-intensive, so perform this before any other sanding.
First, fill any cracks or crevices with a concrete repair material until they are level with the rest of your surface.
You may need to allow this material to dry completely before moving on.
The best concrete patching option is a flexible material, such as fiberglass mesh.
This material will allow your concrete to move without breaking or cracking under pressure.
Next, use a sander or other sanding tool to remove any scratches from the surface of your concrete.
Be sure, to begin with coarse-grit sandpaper and work up to finer grit as you sand the surface.
Finally, wipe away any dust on your concrete after sanding and allow your concrete to dry completely before applying any sealant or staining.
With these steps, you should have a smooth, even surface ready for whatever finish you choose.
Sanding concrete can be tricky and requires care and attention to detail to achieve the best results.
Taking some time beforehand to fill any cracks in your surface can make the job much easier and ensure that your concrete is smooth and free of imperfections.
If you follow these steps carefully, your sanded concrete should be ready to accept any concrete sealant or stain you choose.
4. Remove any bumps on the concrete surface
Another step in preparing the surface for sanding is removing any bumps on the concrete.
If there are any bumps or holes in the concrete, you will need to fill them with a filler.
You can purchase several different types of fillers from your local hardware store.
Some of these fillers also come with colorants that can help to add some dimension and texture to the surface so that it looks more natural.
Once the filler is applied, use an orbital sander to smooth out the surface.
Pay close attention to the edges of any holes or bumps you fill, even with the surrounding concrete.
It may also be helpful to work in small sections at a time, depending on the size and shape of your project.
Once your surface has been sanded to an even, smooth finish, you will be ready to apply a finishing coat.
Depending on your desired look and the type of concrete you are working with, there are several options for your final coat.
Some common options include using a stain or sealer or applying a decorative concrete coating like stamped or etched concrete.
5. Choose the adequate sandpaper grit
Choosing the correct grit of sandpaper is also essential before starting the sanding process.
If you use a grit that is too rough, the concrete will not be smooth and if you use a grit that is too fine, it can create swirls on the surface when heavier particles are embedded in the sandpaper.
To choose an appropriate grit for sanding your concrete surface, you first need to know what concrete you have.
If you have a mixture, such as Portland cement and sand, you need to use a coarser grit, while polished concrete can be sanded with finer grits.
Most concrete surfaces are best prepped with a grit of around 100-150.
6. Use appropriate sanding motion
Once you have chosen the correct grit for your surface, start using light pressure and a circular motion when sanding.
Use long and even strokes so that the entire surface is evenly sanded.
If you find any particularly rough or stubborn spots, use extra pressure for a few seconds to smooth them out before moving on to the next section.
When you are mostly finished with the grit, lightly go over each area again to ensure everything is smooth and even.
To finish the sanding process, you will need to use finer grits, usually no more than 200-400.
It would be best to begin with, light pressure and circular motion again, using the least amount of strokes possible.
With finer sandpaper applied, you should be able to smooth out your concrete surface in just one or two passes before moving on to the next grit size.
7. Sand in the right direction
The sanding motion is significant, but so is the direction of your sanding.
Always sand in the same direction as the previous stroke, careful not to gouge your surface or create swirls.
You should also remember to sand down, not up, when lightening the surface color and adding a more natural look.
This means that you should always sand with the grain of the concrete instead of against it.
Along with all these steps, you should periodically check your progress to ensure that you have not made any mistakes or created uneven patches on your surface.
8. Seal your work
The final step in concrete sanding would be to apply a sealing product.
This will help protect your finished project, prevent stains and give it the sheen you want.
There are many different options for finishing your project to give it just the right amount of shine or matte effect.
One popular option is to apply a concrete sealer which can be done with a paintbrush or roller and will help protect your surface.
Before applying the sealer, you’ll want to ensure that your concrete is fully dry.
This usually takes 2-3 days, depending on the conditions.
Using a broom or vacuum, you also need to make sure your concrete has been cleaned of any dust or dirt.
David Kessler is a CSLB licensed contractor with over 25 years of experience. He is specialized in home building, construction, and electrical works; he also has a keen eye for interior design and, over the years, has collaborated with various architects.
