Although angle grinders were not initially designed with concrete in mind, concrete contractors have found plenty of use for them. In fact, angle grinders are one of the most versatile tools in the concrete contractor's arsenal.
The tools originally were designed to grind down and smooth out metal welds by tipping the rotating blade at an angle. This process also works well with concrete, especially for removing stubs or seams.
The tools come in several different sizes from 4½-inch blades up to 9-inch blades. Typically, 4½-inch and 5-inch models feature high speeds up to 11,000 rpm, but they tend to have low torque. They are best suited for grinding off stubs from hardened concrete. They also can be used when tuckpointing, though some manufacturers make specially designed tools for this practice.
Angle grinders play an important role in decorative concrete, whether used for improving the look of stamped concrete, engraving, polishing concrete countertops, or freehand scoring.
The bigger models, ranging from 7- to 9-inch blades, are more powerful tools, with lower speeds and higher torque. These larger models, while they look the same as their smaller brothers, are used for slightly different purposes. Along with occasional angle grinding, these tools can be used for cutting joints, much like a saw. The larger the size, the deeper the potential cut, and they can even be used to cut bricks.
The rat tail angle grinder is a modification on the standard tool theme, except that the tool has a longer and tapered body shape and an almost pistol grip. This pistol-like grip provides a more comfortable positioning in the hand, says Ryan Anderson, Bosch Power Tools' product manager for angle grinders. Anderson sees the rat tail grinder slipping into an intermediate position between the larger and smaller tools.
Generally, angle grinders are pretty similar to one another. The features that make any particular angle grinder unique frequently appeal to the user's preference.
For example, the on/off switch can be either some kind of toggle or slide switch that is clicked on and remains on, or a trigger or paddle switch that a finger activates. Some models have a special feature that ensures the switch isn't accidentally activated, sending it skidding across the floor where it could injure workers or damage the floor. Some jobs may specify using a grinder with a paddle switch for safety, Anderson notes.
All angle grinders come with blade guards or shrouds that slip over the rotating wheel to keep particles from flying into the air. However, these guards often limit the visibility of the machine; the user can't see the tool as well. Because of this and the tedium of changing the guards to match the proper wheel leads many users to simply remove them, which is a safety issue manufacturers advise against.
Dust collection systems, tougher guards, and shrouds are making angle grinders safer to work with and around. Anti-vibration handles reduce the amount of strain the user must bear.
Currently, Makita offers the only cordless angle grinders on the market, including the 7.2-V 4-inch 9500D model and the 18-V 4½-inch BGA452. However, the advent of lithium ion batteries may increase the offerings.
An angle grinder takes a lot of punishment. “Concrete is the toughest environment for angle grinders,” says Bill Gallagher, senior project engineer for DeWalt Tools.
Given the dust generated from grinding concrete, some contractors consider it almost a disposable tool. Typically, the motor wears out due to dust getting inside the tool, says Anthony Corwin, product manager for Makita.
Every manufacturer tries to do all that it can to keep the dust out.
To view the comparative chart for Angle Grinders click here.
This article is part of our October "Tools for the Concrete Pro" series. You can read other articles in the series by clicking the links below