Do you want to learn how to polish concrete? Grinding a floor down to improve its look isn’t as hard as it can seem at first, though it does take some time to do correctly.
In this guide, you’ll learn about the tools and the process for polishing concrete, then get answers to some common questions people have about this.
What You’ll Need
Everything starts with having the right tools for your project.
You should clean the floor twice during the polishing process. The first cleaning is a pre-polishing pass to remove debris that could get into your equipment, and the second is a cleaning run before you finish polishing and sealing it.
Many people use pressure washers for cleaning concrete, while others have special motorized tools. If you’re not polishing enough concrete for that, you can gather cleaning chemicals, a bucket, some rags, and a bristle brush to do it manually.
Vacuums are also helpful for getting dust off the floor, so use one of those before cleaning with anything wet.
Polishing concrete is relatively simple as long as you have the right equipment. However, make sure to wear durable shoes, gloves, and safety glasses. If you don’t have a way to control the concrete dust, wear a filtering mask throughout the process.
You may also want knee pads if you expect to crouch down and a body-covering jacket to help avoid getting concrete dust on your regular clothes.
Polishing concrete requires frequent visual inspections to check your progress, especially once you get to the high gloss levels where imperfections will be the most noticeable. Make sure you have enough lighting to cover the entire area you’re working in. You may need to use a portable high-lumen lamp to check each section as you pass it.
Proper polishing requires a way to control dust, and how you do this depends on the polisher you get. Some setups use vacuums with HEPA filters to gather particles from the air, while others use water while polishing to catch particles before they become dust. These are important enough that polisher suppliers usually bundle them together.
Crack Filler and Patch
You should repair any damage to the concrete floor before polishing it. For most people, that means using a crack filler or a patch for larger damaged areas. If your concrete floor doesn’t have any cracks or noticeable damage in it, you can skip these.
Concrete Variable Speed Polisher
Variable speed polishers are your primary tool for polishing concrete. These come in handheld and mountable options depending on the size of the area you’re shining up.
You probably don’t need to buy one of these unless you’re running a business, so you can probably rent them from a nearby service center.
The main thing to remember about polishers is that larger ones can polish more concrete simultaneously, but they’re increasingly hard to get into corners and edge areas. You may need polishers in several sizes, each with its own diamond polishing pads.
Diamond Polishing Pads
Diamond polishing pads attach to the bottom of your polisher and provide the actual grinding and polishing.
These are similar to sandpaper, so the higher the grit, the finer the polish. Unfortunately, you can’t just grab the highest polish. Instead, you must grind several times at different levels for the best effect.
In most cases, you’ll go through pads around 50, 80, 150, 200, 400, 1500, and finally 3000 grit to get the best look. The earliest options help grind concrete to a mostly-flat state, enough that the higher grits can polish it better.
Polishing pads wear out, so when deciding how to polish concrete, remember that you may need to get several pads of each grit. Most polishing pads last 5000 to 15,000 square feet depending on their quality, so you may need to buy several packs of polishing pads for larger jobs.
For reference, a typical two-car garage is about 24 x 30 feet, or 720 square feet. That means you should only need one polishing pad of each grit if you’re polishing a garage, even if you need to go over the floor more than once.
A Neighborhood-style Walmart store is closer to 40,000 square feet, so they’ll usually need three or four polishing pads in each grit. Businesses of similar sizes can also expect to go through several pads of each level.
Step 1. Perform a Floor Hardness Test With MOHS Picks
The first step in polishing your concrete is using MOHS picks to determine the hardness of your concrete floor. Different levels of hardness require various pads for the best effect.
Recommendations vary by manufacturer, so stick with a single company when you go to purchase pads and reference their charts. If you can’t figure out which polishing pads are appropriate, don’t hesitate to talk to an in-store expert or contact the manufacturer.
Remember, grit isn’t the only thing to look at when getting pads for your machine. Your polishing pads must match your concrete’s hardness.
Step 2. Prepare and Repair Concrete
The second step for polishing your concrete is getting it in the best shape possible. This means cleaning the surface to remove dust and debris, removing any lingering stains, and filling in cracks and holes.
It’s best to do this at the start because repairing concrete usually leaves rougher patches on the surface that will interrupt the shine of your polish. Doing it right away means you can polish the areas you repair and get a clean, consistent look across the entire area.
Repairs can add to your timetable for polishing concrete. For example, many patches require a minimum of four hours to start hardening properly and may continue hardening for at least several days. It’s best to avoid polishing concrete while repairs are still curing, so take care of this as early as you can and wait until it’s done to move to the next step.
Step 3. Smooth the Concrete With a Grinder
Once your floor is clean and in good shape, you can use your grinder to sand the concrete down and smooth it out. Start with a rough pad of about 50 grit, then progress upwards through 80, 150, 200, 400, and 800 grits.
Do not skip grits. Higher-level pads are shallower and cannot polish a level that’s too coarse below them. Your first grit level will remove the roughest part of your concrete, your next grit will smooth it out further, and so on at each stage.
The exact techniques vary depending on the tool you’re using, so check the manufacturer’s guide for instructions. Generally, single-disc and dual-disc grinders require swinging the machine from side to side, while larger grinders require pushing like they’re a lawnmower.
Be sure to plan your path so you can avoid tangling up cords. Consider practicing with your grinder in an inconspicuous area before doing the primary part of your project. Also, follow the grinder’s instructions for dust control.
This process can take several days (or longer for large floors). You may be able to polish a countertop in a single day, but if you’re looking at a few hundred square feet, make sure to give yourself enough time to complete the project.
Your concrete should still look somewhat rough when you’re using 150 grit. Once you complete the passes with 200 and 400, marks should start vanishing, and you’ll notice a meaningful difference in the overall quality.
Step 3b. Understanding Variables
Five main variables affect the performance of grinders and abrasive pads while you’re using them. Your equipment may have recommendations or guidelines for dealing with these variables, so check for that information before starting your project.
Rotation is the direction that the pads and cutting heads turn. Most home projects use tools called planetary grinders, which have several small pads called satellite heads that all attach to a central rotating section. If the main head and the satellite heads rotate in the same direction, it cuts more aggressively than if the satellite heads rotate in the other direction.
RPM is usually variable on machines, and with good reason. As a general rule, lower grits work better at lower speeds because they need time to bite deep enough into the surface. If you run the machine too quickly, the cutting teeth will only skip over the surface. Higher grits can run at noticeably faster speeds.
Speed is user-controlled and may require some practice to get right. If you go too slowly, you may end up removing more concrete than you intended, creating an uneven dip in the floor. If you go too fast, you won’t cut through enough. This is one of the reasons it’s often best to test your machine in an inconspicuous area before moving to your main project.
Tread refers to how much surface contact your cutting pads have. Pads with less tread cut more aggressively in the areas they cover, but also take longer to reach the whole area. Amateurs often do better with larger treads, which cut slower and have more allowance for errors in speed.
Weight presses down on the abrasive pads and helps determine how well they function. If there’s not enough weight, the abrasives won’t go deep enough to cut. If there’s too much weight, resin from the polishing pads could end up on the floor, making you think it’s polished when it’s not.
Step 4. Densify and Harden Concrete
Densifying is the process of adding silicate materials to a concrete floor to harden and protect the surface layer. Among other things, this can improve strength while reducing dust, and that’s on top of filling in any lingering gaps or tracks that exist after polishing to 400.
A typical slab of concrete is about five inches thick, give or take an inch depending on location. However, most of the wear and damage takes place in just the top 1/16th of an inch. That’s the same area we’re polishing. The top layer is also where problems like dirt and oil tend to accumulate, and by removing the gaps, we can keep it cleaner.
The reason we’re hardening the concrete at this step is that the rougher grits can remove more of the concrete’s surface area, and thus the densified section. Doing it before the final one or two grit levels produces better results.
The correct process for hardening your concrete depends on the material you’re using. Most people use a spray-on option, and you can resume polishing as soon as that’s dry. It should continue hardening for some time after the final polish level.
As always, refer to the instructions that come with the products you buy for correct usage. Deviating from those instructions may not hurt your concrete, but it will stop the product from functioning.
Step 5. Final Grinding Pass
Once you’re done densifying the concrete, you can do the final grinding levels. These include 1500 and 3000 grit, the latter of which gives concrete the best shine. If you’re polishing things correctly, you should see your concrete transform from a reflective surface where you can identify reflections to a mirror-like reflective surface.
Imperfections will become more obvious during your final grinding pass. You may see areas that look duller or rougher in comparison to other sections. If necessary, you can move back down one or two grit levels and polish that section again.
Step 6. Clean, Vacuum All Dust and Debris
Once you’re done polishing, it’s time to clean up any debris in the area. Polishing concrete creates a lot of dangerous silica dust, and your tool should come with guidelines or equipment for sucking in that dust. However, those are often imperfect, so it’s time to clean the area again.
Vacuum up as much dust and larger debris as possible, then use concrete-safe chemical cleaners for an extra layer of cleaning. Make sure to avoid using anything acidic, or brushes that are going to scratch your polished surface. Softer bristles and mops are better at this stage.
Step 7. Buff and Polish the Concrete Until Reaching Desired Glossiness
Once you’re done cleaning the concrete, you can start polishing it to improve the glossiness. Some people use chemicals for buffing here, but you may need to go over rough spots again with your tool. If you have smudges in small areas, you can use a handheld tool instead of using your grinder. Remember to clean things again if you have to grind more.
Step 8. Seal and Protect Polished Concrete
Sealing is an important part of protecting polished concrete. The polishing process makes the concrete somewhat porous, so it can absorb chemicals. You have many options for sealants, some of which can change the appearance of the concrete, so feel free to look at your options before you make a final decision.
If you used a densifier earlier, that should already seal most of the surface and provide the primary level of protection you need. An additional sealer on top of that is mainly to protect the shine of your newly-polished concrete.
Look for a breathable sealer that will let water vapor move through concrete and out into the air. While waterproof sealers exist, they tend to bubble as moisture rises. Some people use wax-based options, but those can be hard to find outside of specialty stores.
Step 9. Wait 24-72 Hours Before Using
Finally, wait at least 24 hours after polishing before you use the concrete, and preferably a minimum of three days. We know it’s not always practical to leave the concrete inaccessible for so long, especially after spending days polishing it, but waiting gives your densifier time to work.
Polished concrete can also give off volatile organic compounds for a few days, and these can be hazardous to human health. If you polish the floor correctly, this should stop soon. Essentially, you’re giving your polished floor time to air out.
Frequently Asked Questions[helpie_faq group_id=’51617’/]
Now that you know how to polish concrete, you’re ready to put it into practice. Before you start shopping, however, let’s quickly review what you learned. Grinders come in several styles, and you should pick one that works well for your project size.
Proper grinding requires going through several pads suitable for your concrete’s hardness, each finer than the last until you reach your desired glossiness. This can take several days, and you’ll need to control the dust while you’re doing it. Testing your tools and getting a little practice in an inconspicuous area can help you avoid making major mistakes while polishing.
Getting the best look for your polished concrete takes time, but you can pause almost anywhere and resume later. You can do the entire project yourself if you want to, but if it sounds like too much work, you can also hire someone to do it for you.