Planetary vs. Rotary Grinders: The Best for Large Concrete Projects

Before we can compare these two types of grinders, we must figure out the condition of the concrete project we are working on. All floor grinders will grind. If they can grind, they will also hone and polish. So, if you are removing tile adhesive or a resinous floor coating, either type will work. Both will also polish a floor. The key is to decide not if they can manage the task, but how fast and efficient the process will be with each.     

There are two primary grinder types used to prepare a concrete surface for a coating or that are used when polishing. Planetary and rotary grinders both use similar abrasive tooling. The tooling is what performs the work. Since they use the same tooling, they can be somewhat interchangeable. The difference between each is the torque they produce and the down pressure it shows onto the slab.

When evaluating a potential project, knowing what needs to be removed and what the outcome needs to be will direct you to the best piece of equipment to get the job done most efficiently.

Exploring Rotary Grinders

Rotary grinders are the oldest type of grinder. They have been in use grinding terrazzo for well over 90 years. If you look at the general principle of the first rotaries, they are remarkably like the ones built today. The only change is the tooling that is currently available. 

Rotary concrete grinders, in simple terms, are defined by having a single spinning spindle that rotates around its center. On each spindle, there are 3 tool holders attached. For efficiency reasons, there are 2, 4, 6, or 8 spindles on each machine. Each of the three holders is fitted with an abrasive tool.

Rotary machines are highly efficient and perfect for large adhesive or resinous coating removal jobs.  The torque they produce enables them to be fitted with aggressive scrapers designed for the task.  They are often heavy and less mobile than a planetary machine. Using a large rotary concrete grinder takes more effort and training than a planetary grinder.

Rotary machines specialize in heavy removal. They can be considered the tank of the grinding industry. This doesn’t mean they can’t be used to polish; they are just better suited to be used on removal projects.

• PROS:
  • Rotary concrete grinders are best at handling thick coating removal no matter the project size.
  • Their powerful grinding action ensures you can grind a large floor efficiently.
  • Gear-driven spindles.

• CONS:
  • Will require more training for operators to use due to its weight and grinding pattern.
  • The large rotary models are very heavy, making them less mobile while moving on and off the site.
  • The large rotary machines are a larger investment than the planetary alternatives because of their design and grinding capabilities.

Exploring Planetary Grinders

Planetary grinders consist of a main rotating plate. Three, four, or six satellite grinding heads are attached to this plate. The main plate rotates clockwise while the satellite heads rotate counterclockwise. This planetary rotation provides an efficient cutting pattern.

Planetary grinders are available in varied sizes. They range from 16” to 60” with a few that might be larger. With a planetary grinder, you can select one that fits your needs, whether it’s to grind a balcony or a large warehouse floor.

These are generally easier to control, reducing fatigue on the operator while producing an even cut. Planetary action has a well-balanced grinding motion. There are also large platforms that are run remotely. With this, direction and speed are controlled like a video game. For the younger generation, this is very intuitive and comes very naturally.   

• PROS:
  • Easier than a rotary to polish with.
  • Planetary machines have high mobility from site to site.
  • Generally lower in price than their rotary alternatives.
  • Planetary machines are easy to control, and the grinding method is a simple straight line, making it easier for operators to use effectively.
  • When using a Ride-on Grinder with a 60” width, large areas can be completed very quickly.

• CONS:
  • Not as efficient as a rotary when heavy tile adhesive or coating needs to be removed.
  • Drive belts and pulleys are a weak point when under heavy loads.

Best Practices and Recommendations

A rotary grinder will outperform a planetary grinder if the project entails a large amount of coating or adhesive removal. Rotary floor grinders produce more torque, and the drive system is much more robust.

In the early years of polished concrete, rotary grinders were successfully used by many installers. Typically, the contractors in the terrazzo industry understood how to run a rotary grinder to produce the nicest floors. As the polishing market grew, less experienced installers became involved. That’s when the polishing market moved towards the planetary grinder.

Planetary grinders were developed overseas. The exact date is difficult to find, but it was sometime in the 1990s. They were brought to the United States in the late 1990s. These were developed to provide the industry with an easier-to-run machine while producing equal or better results than rotary. The learning curve was much shorter when installing a polished floor. As time went on, the machine’s durability was enhanced, matching that of a rotary system. Since these are belt-driven, tensioning devices were beefed up, the belt material was enhanced, and the process of working on these machines was made to allow the contractor to perform most of the repair work.

Planetary grinders are considered precision machines. There are varied sizes and power requirements available to help choose one that best suits your needs. They can perform the same work as a rotary but specialize in surface preparation for coating installation and polishing.

Tooling that is fitted to the grinder is what does the work. The available tooling is abundant for each machine and at times is interchangeable. For coating and adhesive removal, a PCDorscrapercan be used. These tools are not for surface prep, they are used to remove a thick contaminate from the surface. Metal bond tools prepare a concrete surface for coating or the first steps in the polishing process. Hybridor diamond transitional tools are used to bridge the gap between metal bond tools and resin polishing pads. Again, all these tools are available for both grinder styles.       

Conclusion

There are two types of concrete grinders, planetary and rotary. Both types will remove coatings and polish a concrete slab, but they do have their individual strengths.

Rotary is the tough guy. With the right tooling, it will cut and remove the toughest coating systems. Whether it be a 50-mil elastomeric parking deck coating filled with sand or 10-mil epoxy system, it will remove it. It can be used to polish a floor, but its real strength is removal.

Planetary can perform coating removal but is best suited for surface preparation and polishing. Checking the belts that drive the heads will be imperative if used on a heavy removal project.

When it’s time to evaluate the machines available, give Niagara Machine a call. We carry both grinder types and tooling for each. There will be times when a job site demonstration will help in making your decision easier. Niagara has field representatives spread throughout the United States. Their reps are fully trained and stocked with demo machines available for testing.

If renting better fits your business plan, Sunbelt Rentals, Niagara’s rental partner, will be an immense help. They rent well-serviced planetary and rotary grinders along with a matching dust extractor. This is a terrific way to reduce your upfront cost. For large projects, renting extra grinders to match up with yours will also speed up the grinding process.