Need to grind paint off concrete, grind glue off concrete or grind down high spots? Learn how to use a concrete grinder. This handy machine features horizontally rotating discs embedded with abrasives that grind concrete to level and smooth out concrete surfaces.

Concrete grinders are commonly used to level off a slab, to remove paint, epoxies, stains and other coatings from concrete in order to prepare for new floor coverings, and to polish concrete surfaces to perfection.

How much will a concrete grinder remove?

A grinder can take off up to 1/8 of an inch of material with each pass — less than a concrete scarifier, which cuts into surface coatings and the underlying concrete and can cut about 1/4 of an inch with each pass.

Switching out grinding attachments, which vary by grit and type, gives you the ability to tackle different surface prep or surface finishing tasks with the same machine.

Follow these tips to get the best results.

Recommended materials and tools

• Abrasive grinding wheels
• Silica sand
• Water for pre-soaking floor if needed
• Dust mask or respirator
• Plastic sheeting
• GFCI or appropriate extension cord
• Wet/dry vacuum
• Knee pads
• Face shield
• Steel-toed boots
• Ear protection
• Gloves
• Broom/dustpan

Before you start

Before you start your project, set yourself up for success.

Choose the right grinder

Choose the right grinder for the project. Handheld grinders are great for working in tight spaces or corners. Walk-behind grinders can cover large surface areas quickly and are perfect for applications involving sidewalks or large slabs.

Walk-behind grinders come in two main categories: rotary grinders and planetary grinders. Rotary grinders generally feature one or two large discs that rotate and directly grind the floor. Due to their significant weight, they’re reserved for intensive applications, such as removing thick rubber coatings or layers of paint. Planetary grinders have multiple discs that spin simultaneously but at different speeds. This allows them to remove material and finish a floor at the same time. They’re generally used for less intensive grinding tasks, like smoothing a concrete slab or preparing a surface for an epoxy coating.

Choose the right cutting tool

Silicon carbide stripping wheels work well for topical concrete floor cleaning and scraping jobs. Diamond wheels can handle both light and heavy-duty jobs. Use a diamond wheel with a lower grit when aggressive grinding is required, and a higher grit for general-purpose grinding jobs and polishing. PCDs, or polycrystalline diamonds, are used for very aggressive applications such as removing industrial coatings.

Choose the right bond

Softer bonds are good for less abrasive surfaces, such as concrete made with river rock. Harder bonds are ideal for concretes with high sand content. Not sure what you’re working with? Start with a medium bond.

Check the level of the grinder discs

The goal is to have 100% surface contact. Hold the machine in place for several seconds, then look at the pattern it leaves. You should see a full circle ground into the surface. If you see a half-circle, follow the directions for adjusting the level of your grinder. If you’re working over a large area, perform the level test periodically and adjust the grinder level as necessary.

Plan your path

Electric cords and hoses can get in the way when you’re using a concrete grinder. Plan your path to make sure you stay connected without getting tangled up.

Create a plan to control dust

It’s important to understand how to reduce dust when grinding concrete. If you’re working indoors, seal doorways with plastic sheeting and remove or protect furniture. Consider moistening the floor with a water sprayer. Use an industrial dry/wet concrete dust vacuum to suck up any debris and dust.

Wear appropriate PPE

Wear safety glasses or goggles, and add a face shield if necessary. Safety boots, knee pads and gloves are also smart. To protect your lungs from crystalline silica, wear a dust mask or respirator.

Using a concrete grinder: Technique matters

When grinding concrete, take your time and allow the machine to do its work. If you move too fast, odds are you’ll end up redoing some areas. The way you move the grinder depends on the type you’re using.

• Single disc or duel-disc rotary grinder: Swing the machine from side to side.
• Planetary grinder: Walk forward and backward, as you would with a lawnmower.

Keep the concrete grinder operating efficiently

• If your diamonds begin to glaze and become ineffective when you’re working on a hard, dry surface — use silica sand as a secondary abrasive to keep them sharp.
• If you’re removing tacky tile glue or other adhesives — add sand to the surface. Adding sand will ball up the material to make it easier to remove.
• Consider adding weight to your dual-disc grinder if the grinding process is taking too long. The more weight, the more aggressive the grinder will be. But don’t go overboard; adding too much weight can bog down the motor and damage the machine.
• Watch the belt tension. Unusual noise, high machine temperature and premature belt and pulley wear can be indications that the belt tension needs adjusting.
• Grease the bearings and perform other maintenance as outlined in the manual. (If you’ve rented the machine from a reputable equipment provider, it should be ready to go.)

Browse United Rentals’ full lineup of concrete grinders available for rent here.

Freelance writer Mary Lou Jay writes about business and technical developments in a variety of industries. She has been covering residential and commercial construction for more than 25 years.