Concrete is hard, but choosing a grinder doesn’t have to be.
Ever removed carpet or tile from a concrete floor and been left with adhesive on the surface? Need to strip thinset or paint from a concrete surface, or grind off sealer or a waterproof coating? A concrete grinder is the tool to use.
Concrete grinders remove material up to one-eighth of an inch below a concrete surface per pass. Horizontal discs on the grinders carry the cutting accessories that do the actual concrete removal.
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There are different types of grinders, including single disc, dual disc, planetary and edge.Some are better suited than others for certain tasks. Tony Calcopietro, national account manager for EDCO, which manufacturers equipment designed for the rental market, outlined the typical applications for each type.
Single and dual disc grinders
A single disc grinder is a good choice for small or residential jobs. It operates on 110-volt, 15-amp power and can be plugged into a standard outlet.
Single disc grinders are the narrowest grinders. EDCO’s model, for example, has an 11-inch pad, which would enable you to grind about 200 to 250 square feet per hour. If your grinding project is under 1,000 square feet, a single disc grinder could get the job done.
Dual disc grinders are commercial- or industrial-grade machines with two discs that spin independently. They are wider and can cover more area, about 400 to 500 feet per hour. Consider a dual disc grinder if you have a job that’s larger than 1,000 to 1,500 square feet.
Electric dual disc grinders typically use 110 volts, 20 amps. Propane and gas powered versions are suited for outdoor use. Larger industrial sizes that run on 230-volt power or propane can tackle the very big jobs, such as floors in manufacturing facilities and food processing plants.
Planetary grinders have three discs. They spin independently while orbiting around a center point, like planets around the sun.
Planetary grinders can be used for large grinding jobs but are more often used as floor polishing machines. “For polishing, you are looking for something with more weight behind it, something with a higher RPM, and with a completely different range of accessories,” said Calcopietro.
Polishing concrete floors is similar to sanding wood. “You have different grits, and you start with the low grit number and work up to a higher number,” he added. To start the process, you might use an 18 grit disc (the roughest), then progress up through 30, 70 and 120-grit discs. 150- to 200-grit discs are considered honing pads, and anything higher would be used for final polishing.
Because of their dust shrouds, regular grinders can get only 1 inch to half an inch from a wall. Edge grindersare designed to work in that small space.
“When contractors need to get right up to the vertical edge for aesthetics or functionality, you often see people working on their hands and knees with right-angle grinders,” said Calcopietro. “Edge grinders get people off their knees and allow them to be four times more productive.” If an operator’s hand-held grinder production rate is 100 linear feet per hour, they might cover as much as 400 to 500 lineal feet in the same time with an edge grinder.
“The most expensive part of a lot of surface prep applications is the edgework because of the amount of labor that’s involved,” said Calcopietro. “So if a contractor can reduce their labor by 75 percent, that’s a significant savings that they can pass along or use to improve their profitability.”
The discs on grinders operate at different revolutions per minute. Usually, the more power the machine requires, the higher the rpm. In low-rpm machines, the disc spin between 250 and 600 times per minute, depending on the model. Turbo grinders have discs that spin at between 1,000 and 1,500 rpm.
“The difference is how aggressive the machine is going to be,” said Calcopietro. “If I’m just doing a topical clean, I don’t want to have a turbo grinder on the application because it might be too invasive into the concrete. In that case, I would stick with a low-rpm grinder to grind maybe 1/32nd of an inch per pass. With turbo grinding, I might want to eat into the concrete, be a little more invasive to get to exposed aggregate, or maybe I just want to go a lot faster. A turbo grinder is more of a pro tool, not for a do-it-yourselfer.”
EDCO refers to the cutting components of disc grinders as accessories. “Choosing the right accessory is always paramount because you have to have the right one for each application,” said Calcopietro.
The carbide stripping accessory is used for removing anything you could scrape off with a utility knife, such as flaking paint, adhesive, and foam carpet backing.
Diamond accessories can be used to remove stains in concrete and can also handle tougher jobs. They are available in a range of grits. Lower grits are for more aggressive concrete removal. Medium grits are for general purpose work, and higher grits are for concrete polishing. One important consideration when choosing a diamond accessory is its bond, which refers to the way the diamond crystals are held in the tool. The type of bond you should choose — soft, medium or hard — depends on the abrasiveness of the concrete you’re working with. Matching the bond to the concrete is an important part of getting the maximum productivity from your concrete grinder.
- In coastal areas along the East Coast, Florida and Texas, the sand content of the concrete makes it very abrasive. Choose a hard-bond diamond accessory for these applications.
- In areas where there’s a lot of river rock, the concrete is less abrasive, so you’ll want a softer bond.
- If you’re unsure of the abrasiveness of the concrete, start with a medium bond.
The quality of the accessory and the type of surface you’re using it on will determine how long it retains its grinding capability. Economy tooling might last for just 400 square feet, while premium tooling could last upwards of 3,000 square feet, said Calcopietro.
Grinding concrete can produce silica dust, which poses a health hazard. Make sure you understand the OSHA regulations for silica dust control and use the proper equipment to reduce your exposure. That could include dust shrouds and dust collection systems and/or respiratory protection that meets the OSHA standard. Look for a grinder with a port that lets you connect it to a dust collection system.
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.