Concrete can be highly functional, but sometimes after it dries, you may find that the surface is rough, bumpy, or uneven. When this happens, it is possible to learn how to smooth concrete after it dries so that you can make it even and attractive.
Before you can smooth concrete after it dries, you need to remove all the imperfections using a scraper and broom. Then you can add a fresh layer of concrete and use a trowel to even it out. Sand the surface area and apply sealer and vitrifier as protection.
In this article, you will learn when you should smooth concrete and how to do so even after the concrete is dried. You will also discover how to fix damaged concrete, when you should use a concrete grinder, and how to smooth the edges of rough concrete.
- Can You Smooth Concrete After It Dries?
- What Is the Best Way to Make Concrete Smooth and Shiny?
- Dry Grinding vs. Wet Rubbing
- How to Smooth Concrete After it Dries
- How Long Do You Wait to Smooth Concrete?
- How to Fix Rough or Damaged Concrete
- When to Use a Concrete Grinder
- How Much Does a Concrete Grinder Remove?
- How to Smooth Rough Concrete Edges
Can You Smooth Concrete After It Dries?
It is possible to smooth concrete after it dries, but in many cases, it requires a fresh layer of concrete over the top of the dried surface. This can allow you to keep the surface smooth and even, even though the concrete is completely dry. This is often the easiest option for smoothing concrete, especially if the surface is extremely rough or uneven.
In some situations, it may be possible to sand the surface or use a concrete grinder to smooth the surface of the concrete after it is completely dry. This often requires other products like epoxy or concrete polish to properly smooth the surface. In addition, if you choose this route, you need to make sure that you are careful not to chip the concrete with a grinder.
What Is the Best Way to Make Concrete Smooth and Shiny?
There is no single best way to make concrete shiny and smooth, but knowing the possible methods can help you choose the one that is best for your concrete. Some are easy and only require a little cleaning and shining, while others are more involved in using polishers, grinders, or other products and tools.
The easiest way that often works better than homeowners expect is to thoroughly clean the dry concrete. Washing the concrete regularly using soap and water can remove the dull dust and any other marks caused by dirt, grime, oils, and more. Just make sure to avoid any acidic products or cleaners.
If cleaning it is on the right track, but the soap and water solution does not remove all of the blemishes that dull the concrete, then you can also use a pressure washer to make it shiny and smooth in appearance.
Many times, particularly with outdoor concrete, dirt, dust, sap, leaves, and other materials reduce the shininess of the concrete over time and the pressure washer will eliminate those contaminants. It is important to remember to use the pressure washer on an out of sight corner first to make sure that it does not cause damage, discolor, or otherwise harm the concrete surface.
If the concrete was never shiny to begin with, then it is unlikely that these methods will make it so. If that is the case, you may find more success with using a concrete polisher substance. Make sure to follow the directions for the product you purchase. Usually, they can be applied easily with a cloth or a mop and work best when covering a small area of the concrete surface at a time.
One final option is to use the dry grinding or wet rubbing method, which can be used in the finishing and polishing stage of laying concrete, but may also work with older, dried concrete surfaces.
Dry Grinding vs. Wet Rubbing
A concrete grinder can be a good choice for moderately rough concrete, even when dried. You can use two methods for grinding and polishing your concrete: wet rubbing and dry grinding.
Wet grinding utilizes water to keep down the dust and to grind and shine the concrete at a low luster. This has a few advantages. For one, it can increase the life of a diamond grinder and can work well for aggressive concrete grinding jobs. It may also be faster with less downtime and, in some cases, will help remove scratches left behind by the grinder. However, it isn’t the method that works to create the shiniest concrete surface.
Dry grinding provides more shine with more light reflection on a concrete floor and is the best choice for soft concrete. It does wear out the grinder faster than wet rubbing for polishing a concrete surface and can cause more dust that could be unhealthy or at least unpleasant for you and the environment.
In many cases, you can combine dry and wet grinding methods to smooth and then shine the concrete surface. Sometimes the wet rubbing works best for smoothing out a rough concrete surface and then dry grinding will add the glossy shine.
How to Smooth Concrete After it Dries
While grinding can smooth concrete after it dries, it can be problematic in some situations and may not work for very rough or uneven concrete. Because of this, the best way to smooth concrete after it is done drying is to use another layer of concrete. However, if you do not have the room or if the already dry concrete is in good enough condition and you don’t want to use another layer, skip to step 5. Let’s look at how this is done.
What you need:
- Shop Vacuum
- Muriatic Acid
- Bucket or Tub
- Concrete or Concrete Resurfacer
- Screed or Straight Edge (2×4 can work)
- Orbital Sander
- Sandpaper (80-120 grit for minor irregularities or 200 to 400 for smooth surface)
- Leveling Bar
- Concrete Sealer
Before you can fully smooth a concrete surface, you have to remove all the easily removable imperfections. This can be done using a scraper (for larger concrete surfaces, you can use a long-handled scraper and then go back over it with a smaller putty scraper).
There may be a lot of elements to scrape off, including concrete abnormalities, paint, and other defects. By the time you are done, the surface should be uniform with few if any deformities. If you cannot make the surface free of these types of abnormalities, then you may have to use a power sander or a grinder.
After removing all of the imperfections you can, you need to clean up all the debris and dust left behind. This is best done by sweeping and then using a shop vacuum to remove any residues other materials. Then you need to clean the surface using muriatic acid.
This will remove stains and other substances that could make it harder for the next layer of concrete or sealer to adhere properly, which could potentially weaken the floor or other surface. Make sure to mix 7 parts of water with one part of muriatic acid in a plastic tub or bucket.
After the concrete is fully clean and mostly even, it is time to add a new layer of concrete. The layer does not have to be thick, but it is important to make sure that it will work with a compacted layer on top of the dry concrete. You can use either normal concrete or concrete resurfacer for this step as long as you make sure it is a smooth mixture.
To spread the mixture, you first need to shape the concrete into place. Then, use a 2×4 or a screed to remove the excess by pushing it to the edge. Then, you will want to level any ridges using a darby and this step should also remove any empty spaces or air pockets in the concrete mixture. After this, you have to allow the bleed water to dissipate.
Afterward, you can cut grooves into the surface to prevent cracks caused by expansion. Then, you want to trowel the surface for a smooth finish. You can work a little at a time and trowel in a singular, straight motion. As the concrete dries, you may want to keep an eye on it to ensure it doesn’t shift. If it does, then you can go over the area with the trowel again.
After the concrete is through bleeding water and firm yet malleable (or if it is fully dry if you skipped previous steps), you will have to smooth it out even more by using an orbital sander. If you just want a somewhat even surface, then it should be okay to use 80 to 120 grit sandpaper, but if you are looking for a smooth concrete surface, you will want to use superfine sandpaper somewhere between 200 and 400.
You can start with coarser sandpaper and move toward finer sandpaper to increase the effectiveness for a smooth finish. You only have to use a grinder if there are extreme imperfections. You can use a leveling bar to double-check for inconsistencies.
After the concrete is clean and sanded, you should use a concrete sealer for protective properties. Apply a thin coat and then reapply as needed, but follow the directions on the product you choose. Some products have semi or high-gloss aesthetics depending on the type of smooth concrete surface you desire.
How Long Do You Wait to Smooth Concrete?
While it is possible to smooth concrete when it is fully dry, it is best to do so when the concrete is still in the process of setting completely. Choosing the right time is crucial because if you smooth too early, then you run the risk of ruining the integrity of the concrete by adding crevices and air pockets, among other things. However, if you wait too long, then it won’t be malleable enough to smooth it properly so that it looks attractive and clean.
The amount of time it takes before you can smooth concrete depends on various factors like humidity, temperature, wind, the thickness of concrete, brand and type of concrete, and more. It can take as little as 20 minutes to fully bleed and start to set, or it can take over 4 hours.
The best way to determine if you can begin the finishing process of smoothing the concrete is to use your senses. First, look to make sure that water traces are gone and that the concrete is just beginning to change color due to hardening. Put on gloves and press your thumb onto the surface near one of the edges. If you press hard, the concrete should only leave around ¼ inch mark if it is ready for smoothing and finishing.
How to Fix Rough or Damaged Concrete
If you want to smooth old dried concrete that is rough, uneven, cracked, or otherwise damaged, then there are other steps that you need to take besides the ones listed above for smoothing concrete. The steps below are used after step two in the steps for “How to Smooth Concrete After it Dries” above.
What you need:
- Cold chisel
- Wire Brush
- Epoxy Gel
- Epoxy Resin
- Putty Knife
- Leveling Bar
- Self-Leveling Compound
1. Take note of every damaged area, including scrapes, crevices, cracks, flakes, or shards. Remove what you can by using a cold chisel and a hammer, but be careful not to damage below the imperfections if you plan on keeping the surface. Then you can use a wire brush to remove the debris.
2. Use epoxy gel to brush the sides of the damaged area. Let the epoxy dry before moving on. The purpose of the epoxy gel is to act as a bonding agent between the patching material and the existing dried concrete. Follow the instructions on the product you buy.
3. Now, use epoxy resin to fill all damaged areas up to the surface level of the undamaged portions of the concrete floor. You will probably have to use a putty knife to properly fill the crack or hole in some areas. You can also use the knife to level the top of the resin. Afterward, you need to wait 12 to 24 hours for the resin to completely dry.
4. You can check the plane of the floor using a leveling bar. As you drag it across, examine for any dips or inclines and mark those areas with chalk. Those are the areas that need extra leveling. To lower high spots, you can use a concrete grinder in a circular motion.
For dips, you can use a self-leveling compound. Pour the compound (following label instructions) onto the dips on the concrete floor. To even it out, you can apply up to ½ inch on the rest of the floor as well. This way, it will appear consistent and uniform while simultaneously filling dips. You can even use a squeegee to even out the concrete. It should take 24 to 48 hours to cure before using the surface.
When to Use a Concrete Grinder
A concrete grinder is not always necessary, but sometimes it is the only way to even dry concrete. A concrete grinder may be necessary if the concrete is very rough or has larger imperfections that sandpaper will not smooth out.
A grinder can also be good if you do not have the vertical space available for another layer of concrete. This can grind the floor to make it smooth without adding thickness to the surface. A concrete grinder can also polish the floor to make it smooth and shiny.
Usually, sandpaper will be sufficient for undamaged, rough concrete, but a grinder can be used for larger irregularities, wider dips or flakes, or errors in the evenness. It can also allow you to expose the aggregate for a different look or to resurface.
How Much Does a Concrete Grinder Remove?
Typically, a concrete grinder will move 1/16 of an inch with one pass. Because of this, it should not be used for minor imperfections and may need to be utilized multiple times to even out multiple layers or thick irregularities in concrete.
Two passes will remove about ⅛ of an inch and 4 passes will take off about ¼ of an inch. Calculate accordingly to remove only the amount you need to take off to progress with your project.
How to Smooth Rough Concrete Edges
The edges of concrete often remain rough after finishing because the focus is on the upper surface. However, that does not mean that you want rough edges and they may be very rough if they were blocked using a frame or other reasons.
Typically, you can sand them smooth enough using an orbital sander, but the grit that you use will help you achieve the desired results. If the edges are uneven, that may require a concrete grinder.
For smoothing out mildly rough concrete with little to no noticeable imperfections, 40 to 60 grit may be sufficient. For more substantial irregularities, you may have to use 80 to 120 sandpaper and for very smooth edges, superfine sandpaper from 200 and up grit may be used. You may also need to use a specialized diamond disc in some cases.
Smoothing concrete after it dries is not difficult if you know how to do it. A few different options are available depending on your projects and concrete situation. Sometimes you can use a sander or grinder to smooth out the surface enough. Other times, you may have to resurface or add a new layer of concrete. Just make sure that you have the tools and process laid out before beginning with any concrete project.