How to Sand Concrete

Sanding concrete smooths the surface and creates an attractive finish. There are several methods for sanding concrete, and a variety of tools that can be used for this purpose. This article explains when and how to sand concrete, walks you through each method, and tells you how to stay safe during the concrete sanding process.

When to Sand Concrete

There are four times you should sand concrete:

• In preparation for repairs
• To remove old finish or adhesive
• When the rough surface poses a risk of injury
• When you want a polished finish

Concrete wears over time and becomes uneven, or it could have been installed wrong in the first place.

How to Sand Concrete

The process of sanding concrete is fairly straightforward and is similar to sanding a metal or sanding a wood.

1. Protect yourself. Concrete contains sand, which contains particles of silica. When these particles are inhaled, they can cause scarring of the respiratory tract and lungs.

When working around concrete dust, you must protect your airway at all times. The minimum required protection is a half-facepiece respirator with an N95 filter and air purification capabilities.

2. Plan for dust. Concrete dust can travel through vents to other areas of your home and is abrasive enough to scratch hardwood floors. Containing and minimizing dust requires good planning, but is well worth it. See the section below for dust-control strategies.
3. Choose a sanding method. If you need to sand a small area of concrete, you may choose to keep things simple and sand by hand. Hand-held tools such as angle grinders and orbital sanders are best for vertical surfaces and medium-sized jobs. A walk-behind sander or polisher is best for larger horizontal surfaces such as concrete floors or patios.
4. Acquire sanding paper. Look for sandpaper labeled for use on masonry or concrete. If you are wet sanding, make sure the sandpaper is compatible with that technique.
5. Remove excess concrete. When new concrete is poured, it will have rough edges that can easily scrape your hand. Use a coarse grit sanding paper (60, 80, or 100-grit) or an angle grinder fitted with a diamond cup disc to quickly and aggressively remove material.
6. Smooth the surface. Starting with 100-grit sanding paper, remove smaller imperfections and sanding scratches. When the surface starts to look smooth, switch to finer grits like 120 or 160, and finally 180-grit sanding paper. At this point, the surface of the concrete should feel smooth under your hand.
7. Remove material to expose a pattern if desired. For a salt and pepper effect, about two millimeters of material should be removed from the entire surface. An exposed aggregate effect is achieved by removing a layer of concrete up to one-third the size of the aggregate.

Both patterns require precision removal and may be best left to a professional.

Alternatively, a chemical surface retarder can be sprayed on the surface to expose the aggregate.

8. Continue finishing the concrete. You can continue sanding the concrete with progressively higher-grit abrasive materials, stopping when you reach your desired level of polish, smoothness, and sheen.

To prepare concrete to accept finish, sand to at least 180 grit. 240-grit sanding paper will feel very smooth and is ideal for concrete furniture or countertops. Highly polished concrete effects can be achieved through ultra-fine sanding papers which eliminate all visible scratches.

Concrete Sanding Methods

Concrete can be sanded by hand, with a handheld power tool, or with a walk-behind sander or polisher. The method you choose to sand concrete comes down to the size of the area and your desired results. Some jobs are best left to the professionals.

Sanding Concrete By Hand

Sanding by hand is the most labor-intensive method and is best saved for small jobs.

When sanding concrete by hand, a sanding block or sanding sponge is passed over the surface of the concrete to remove and smooth imperfections.

Sanding Concrete with Handheld Power Tools

The two most common handheld power tools used to sand concrete are angle grinders and orbital sanders.

Sanding Concrete With an Angle Grinder

An angle grinder fitted with a diamond cup wheel efficiently removes excess concrete. This special cup-shaped attachment has diamond segments welded to the surface and can sand concrete without becoming clogged.

You can also use an angle grinder to grind down different parts of concrete.

Sanding Concrete With an Orbital Sander

Orbital sanders are less powerful than angle grinders, but they’ll still get the job done faster than hand sanding. The head of an orbital sander moves in tiny circles, removing excess material and leaving behind a smooth finish. Orbital sanders are used with specially-shaped sanding pads, which attach to the head.

Sanding Concrete With a Walk-Behind Sander

Walk-behind sanders are powerful sanding and polishing tools. It wouldn’t make financial sense to purchase a walk-behind sander for a single concrete sanding job, but rentals are available.

To achieve an even and smooth surface, the walk-behind sander must be used for the same amount of time in each area of the floor. This requires close attention and careful monitoring to avoid over-sanding.

Professional Concrete Sanding and Polishing

When concrete is used as a walking surface, it must be perfectly smooth and even to avoid trip hazards. It is difficult to achieve this level of uniformity without significant experience and precision tools.

In this case, it is best to call in a concrete professional. They can help you achieve a functional and attractive walking surface without damaging the concrete.

Some concrete sanding effects, such as salt and pepper or exposed aggregate, require removing a precise amount of concrete. Concrete professionals have the tools and experience to sand concrete to an exact thickness without sacrificing structural integrity.

Concrete Sanding Dust Control

Sanding concrete is a dusty process. Cleaning the dust isn’t easy, so it’s best to contain it at the source. Use these tips to keep dust under control during the sanding process.

• Work outside when possible. If not possible, use plastic sheeting to seal off your work area.
• Remove window unit air conditioners. Concrete dust will clog the filters.
• Turn off HVAC systems or close vents. Tape over vents using paper and masking tape. Concrete dust can travel through air vents to other areas of your home.
• Use a vacuum with a HEPA filter. An industrial vacuum has the power needed to collect concrete dust efficiently, and the HEPA filter will stop the particles from escaping the vacuum canister.
• Carefully dispose of dust. Once you’ve vacuumed or swept up dust, contain it in a fleece-lined, sealable bag.
• Consider wet sanding. Wet sanding concrete keeps concrete dust from ever entering the air.

Wet Sanding Concrete

Keeping the surface of the concrete wet during sanding prevents silica particles from becoming airborne, reducing your exposure.

The simplest way to wet sand concrete is to use a wet/dry sandpaper on your orbital sander or sanding block, and spray the surface of the concrete with water as you sand.

Some angle grinders can be fitted with attachments for running a stream of water over the work area. Wet walk-behind concrete polishers also control dust through a stream of water.

Wet sanding reduces the friction between the sander and the concrete, resulting in fewer scuffs and scratches. By using progressively finer abrasive material, it is possible to wet sand concrete to a smooth, polished, and scratch-free shine.

To dispose of the slurry created by water and concrete dust, a concrete solidifier can be used.

Conclusion

Concrete can be sanded to a smooth and even finish through a variety of methods. Care must be taken to control harmful cement dust. Wet sanding is a concrete sanding technique that helps control dust and remove scratches. Concrete professionals have the tools and know-how to achieve even walking surfaces and specialty effects.