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How to Properly Sand Concrete

How to Properly Sand Concrete

When we hear someone talk about sanding concrete for the first time, it sounds near impossible but, we can hone concrete into a smooth, attractive surface.

If we have concrete floors, walls, or patios, sanding them will save us a lot of money in the long run as we won’t need additional tiles, marbles, or granites to make our surface look spiffy or it can also be taken as a foundation for flooring option later on

 We can achieve smooth concrete surfaces with a bit of DIY or hire a professional to do it for us. We can either use electrical sander machines or sanding pad and give it old-school elbow grease.

Why Should We Sand Concretes?

Concrete Sanding is an attractive choice for the following reasons:

  • Normal concrete floors are dull. Sanding them can bring a certain gloss and aesthetic feel to the place. Sharp protruding clunks and bumps of concrete are removed during this process. These bumps can puncture tires or cause accidents when found in driveways and patios.
  • Improves durability, wear, and tear of concrete.
  • It can be a precursor to more aesthetic developments in the future, like marbling tiles as the surface gets smooth.
  • Sanding helps to remove stains and scuffs as the process eliminates the concrete’s affected layer.
  • Sanding Concrete will give a consistent look to our surface after we repair them, like patching holes, cracks, etc.

Should I Sand Concrete by and or Get a Machine?

There are two major ways to sand concrete. For specific small areas, we recommend sanding them by hand. It will require effort, but we will be more precise on the project.

For larger surfaces, we recommend renting a sander/grinder machine or getting it at your local hardware store if you have a bit of money to spare. These machines cover large areas quickly.

The method we choose should depend on the amount of work we are planning to do. We recommend using a sander or grinder machine as Sanding by hand can be time-consuming.

What Machines to Get?

We can find a lot of sanders and grinders for rentals at our local hardware stores. Buying them might be a big purchase. Please note that we need only those machines with at least 7A amperage. Anything lesser than that won’t be powerful enough.

We have options with handheld or walk-behind sanders in terms of machines. Larger floors will need the walk behind sanders and grinders.

These have abrasive wheels that rotate significantly and are optimal for maximum layer removal. This machine will be the most effective tool if we are sanding large floors.

 For smaller areas, the handheld will be the best. For ceiling, walls, and countertops, we have no option except for orbital sanders / orbital random sanders, or other handheld sanders.

These machines generally will either have sandpaper changing attachments or will come with discs that we can change after its use if complete.

Note : When we buy or rent these machines, we need to specify it’s for concrete sanding as we can only use specialized sanders made for concrete. There are a lot of sanders for woodworking. We need to be careful with our rentals or purchases.

diamond grinder options
Foundation Armor/Youtube

Things to Remember Before Sanding

What Sandpaper Should We Use At What Grit

Always buy wet/dry diamond sandpaper made from natural or synthetic diamond grits. These sandpapers are specifically made for works relating to concrete or masonry.

We can also get attachments of these abrasives for our machines and handheld diamond sandpaper pads.

Start with grit levels of 40-60 for basic Sanding. Get grit levels 80-120 for smooth surfaces with minor imperfections here and there. End with a grit level of 200-400 or higher. This process will result in a perfectly smooth and shiny concrete finish.

Other General Tips

  • Be sure to get safety goggles, proper masks, and gloves. Concrete dust is harmful to our lungs. Some sealers also contain toxic fumes.
  • Buy Sponges, squeegees, and bristled brooms as they will be helpful in the cleaning process.
  • If the surface to sand is large, get some tape to the section of that area to sand evenly.
  • Suppose we are sanding an indoor concrete floor; it’s best to plastic off things we want to preserve. Cement dust damages materials.
    cleaning tips
  • Get a level checker to maintain uniformity all around.

How to Properly Sand Concrete?

 The whole process of sanding concrete ranges from preparing the surface to sanding it and sealing it with proper sealants. Learn how to do it with the steps below:

Preparation for Sanding Concrete

The first thing to do is prepare the surface we are trying to sand. The effort we put into this step will ensure our level of finishing.

  • Use a chisel or a handheld concrete grinder to cut off any clunks and bumps of concrete sticking out from the surface. Our goal should be to make the surface perfectly even.
    grinding concrete surface
  • We also need to fill up any cracks or holes on the surface. There are plenty of ready-made concrete patch slurries in the market with instructions on using them. The mixture and additives might differ from product to product, but the goal is the same. Patch everything you can find.
    cracks or holes on the surface
  • After the surface is even, sweep the area squeaky clean with a broom or a vacuum.
  • Once the areas are swept, mix 1/4 cup of trisodium phosphate with a gallon of hot water in a bucket. Use a stick or a long-handled spoon to mix it till the phosphate completely dissolves. We can also add chlorine bleaches or degreasing dish soap for some extra kick to the solution. Change the volume from ¼ to ½ trisodium phosphate for extremely dirty surfaces.
  • We recommend using a stiff-bristled broom. If we don’t have it, a mop do it too.
    stiff-bristled broom
  • After the surface is clean, rinse it with a garden hose and let the surface air dry completely. We are now ready to sand.

Begin the Sanding Process

  • If we have a large space, do not attempt sanding it by winging it. The process must be evenly distributed, so we recommend sectioning the surface to distribute our effort on each section evenly.
  • Begin sanding using sanding paper or a mechanical sander. We need to sweep up the dust and debris periodically as we go along. We will also need a bit of water on the surface during this process. We always start with the coarsest grit of paper or disc on our sander. Lower the grit number, higher the coarse level.
  • Once we have finished all sections, clean it, start with a finer grit, and repeat the process. Be sure to use a level checker to maintain uniformity in removing layers of concrete all around.
    sanding concrete
  • We continue this process each time using finer grits of sandpaper than the last until we have our desired level of smoothness.
  • Use sandpaper pads on areas where it’s hard to reach by machines.
    Sanding by hand

Apply Concrete Sealer After Sanding as Protection

Once we have the desired amount of smoothness from the concrete, we need to lock it in with a concrete sealer. Remember to use sealers only after the surface is completely dry. A good sealer will preserve the surface appearance, prevent moisture, and provide resistance to stains and scuffs.

What Type of Sealer Do We Use?

  • Indoor Surfaces : For indoor surfaces, we use film-forming sealers. We have options of either epoxy or acrylic. Epoxy is considered the most durable, whereas soft acrylic sealers are more affordable and require floor wax.
    Try to find a water-based sealer as they contain less harmful fumes.
  • Outdoor Surfaces : We need to use a penetrating sealer rather than the film-forming sealers mentioned above as they will last longer and look more realistic. We can find outdoors sealers labeled according to the location of use. Some of the types are mentioned below:
  • Driveway Sealers : We can get acrylic resin bases sealers for our driveway. These sealers are often blended with epoxies, polyurethanes, and silicones. Try to get pure acrylic resin as it will last longer than styrene acrylics found in the market.
    We can also get epoxy or polyurethane sealers, but they may cost a bit more than acrylics.
  • Patio Sealers : We should be looking for solvent or water-based acrylics sealers. These sealers will also help us provide a certain gloss to the surface.
    If we do not want a sheen, we need to use penetrative sealers that protect our surface from outdoor exposure. Whether we choose the patio to shine, be decorative, or have a matte finish entirely depends on us.
  • Exposed Aggregate Sealers : This sealer is used for exposed aggregate surfaces. We generally need film-forming acrylic sealers for this area. There are plenty of brands like expo gloss or concrete sealer X, Super seal 30.
  • Stamped Concrete Sealers : This works for concrete that has been stamped. We can find the labels to specify stamped surfaces while buying them. They are supposed to enrich the colors of the stamped concrete and provide resistance from stains, chemicals, etc.
    We can get sheen levels from satin to gloss. Some brands include super seal 30, super seal 25 semi-gloss, supreme shield SB 600, etc.
  • For Countertops : There are plenty of counter sealers with varying sheen levels in the market. We need to look for heavy-duty sealers that are food-safe, scratch-resistant, and possibly don’t have any harmful fumes.
    We can buy specific countertop sealers at our local hardware stores. We can use brands like polyaspartic 745 for coating or sealers like the countertop 880.

If we plan to use countertop 880, we need to use a countertop wax later to maintain the sealer around 24 hours after the sealing is complete.

Frequently Asked Question

Can we use normal sandpaper for sanding concrete?

Wood sandpaper and concrete sandpaper are very different things. Please do not confuse the two. We will most likely be sanding for hours without the desired result if we get normal sandpaper.

Normal sandpapers are generally used for wood surfaces. Always opt for diamond sandpaper abrasives specifically made for concrete surfaces. You can get diamond sandpaper handheld pads too.

What is the difference between orbital sanders & random orbital sanders?

An orbital sander sands in a circular motion. A random orbital sander sands in circular motion plus back and forth. This movement will help in removing any swirl patterns created.