Grinding Concrete with Hand-Held Grinders: How to Choose for Your Project

A handheld angle grinder is a power tool for cutting and grinding. It is among the most prevalent power tools seen in workshops and construction sites. You can use it for a wide range of tasks due to its versatility. Concrete grinding is one of them.

When polishing concrete, the entire surface needs ground, honed, and polished. Using a 30” grinder with the appropriate tooling, the surface can be ground, honed, and polished to perfection. When running the big grinder across the floor, uniformity can be produced except for one small narrow area on the floor, the edges.

If there is a wall associated with the floor that is being polished, the wall-floor intersection will not be touched by the large grinder. Floor grinders will always leave a small part of the floor untouched next to the wall. This area needs a different approach, it needs to be done with a completely different walk-behind machine or by hand with a hand grinder.

With the use of a standup edger, the edges can be done. On most floors, edges will turn out and blend into the main field. Using a hand grinder is the only choice to perform the work when the edges are not blended. Walk-behind edging machines have a tough time “floating” with the contour of the floor.

Diamond Abrasive Cup Wheels

Abrasive cup wheels have a blend of an abrasive and a bonding material that is attached to a holder or wheel. The bonding material can consist of a metal alloy or resin composite. The type of bonding material is based on what the cup wheel is used for.

When grinding concrete, you will need the cup wheel to remove stock. The abrasive needs to be large, angular, and hard. The grinding process is aggressive requiring a durable cup wheel. The bonding material needs to be tough with the ability to hold the abrasive when grinding concrete. If it’s substandard or incorrect material, the service life of the wheel will be shortened. Even if the price tag shows a good deal, it doesn’t mean it is.

Metal alloy bonding material is produced in different hardnesses. The hardness of the metal correlates to the concrete hardness. When grinding hard concrete, the metal alloy needs to be soft. With soft concrete, a hard bond will be needed. This is especially important if the cup wheel is not cutting very well. Collaborating with a supplier, like Niagara Machine, which has everything needed will increase your production.

To hone or polish a concrete surface the bond material will not have a metal alloy, it will be using a resin composite to bond the abrasive to the wheel. The abrasives are smaller and do not need to be aggressive. The amount of surface that will be removed is minimal. That is why there is no need to use metal bonding material.

Choosing the Right Hand-Held Grinder

Hand grinders come in varied sizes based on what they will be used for. Some grinders can be fitted with a 5” or 7” abrasive cup wheel. Typically, a 7” hand grinder is for grinding and a 5” hand grinder is for honing and polishing.

The revolutions per minute (rpm) the arbor spins need to be decided by the cup wheel used. All cup wheels will work best at a speed best suited for the specific substrate. Some perform well at high speed and others work well at a lower speed.

Obtaining the proper tools when working on any construction project is valuable. Everyone understands that having the right tools can make the project. Granted, not all tools are creative equal when evaluating quality.

When it comes to hand grinders, or angle grinders as they are called in the industry, no matter which one is selected, they all do the same thing. A diamond abrasive wheel is attached to an arbor, the electric motor spins the arbor spinning the wheel to abrade a surface. One of the key attributes that separates one from another is long-term durability.

Hand-grinding concrete is very abusive on the equipment. Dust, long operating times, and the way it is used all have an impact on how long it will last. When grinding, an operator puts pressure on the head of the grinder to stabilize it. The amount of pressure exerted varies from operator to operator. If the operator puts more pressure on the grinder head than it was designed to manage, the stress on the motor will shorten its life. The operator needs to allow the grinder to do its job and more pressure will not allow that without sacrificing the life span.

Warranties are provided for most hand grinders by the manufacturer. The key is to have an understanding of the parameters of the warranty. The length of time the warranty covers is critical and what they take care of. When you buy a hand grinder, you are not only are buying a piece of equipment, but you are also buying a manufacturers reputation to uphold their warranty.

Hand Grinder Basics

The electric motor is the heart of the hand grinder. The motor is what performs the work. Some may say it is the abrasive wheel but if the wheel doesn’t turn, the grinder is useless. Motors are rated by the amount of amperage needed to perform at its best level. A 15-amp motor has more power than a 12-amp.

Variable speed is a nice and valuable option. There will be times when having the ability to slow down or increase the grinding speed will increase production. A non-variable speed hand grinder speed will be 6000-7000 rpm. This speed will provide for fast stock removal. A variable speed will run from 300-3000 rpm. It works well when polishing or honing.

Safety is always a concern when running power-driven equipment. No matter what the size is or the power it produces, any piece of power equipment can be dangerous if care is not taken during operation. A grinder is fueled by electricity, the electric motor turns at a high rpm, and it produces cement dust. These are the main concerns.

Anytime electricity is involved, there is a potential for electric shock. Having a well-grounded power supply is the first step. Grounding the grinder won’t eliminate the issue but it will reduce most of the concern. Wearing leather gloves and boots will add extra protection from potential shock. All newer electrical outlets will have a ground to plug into. Just make sure the cord attached to the grinder is undamaged and the outlet is wired correctly.

A dust shroud connects to a hand grinder just above the exposed arbor. It performs two duties; it is a shield around the spinning cup wheel reducing hand injury and it connects to a dust collector to hold dust. A dust shroud is made from a tough, composite material. It is adjustable allowing it to be moved up and down adjusting for the height of the cup wheel. This is important when capturing generated cement dust.

HOW TO CHOOSE THE APPROPRIATE DIAMONDS

It's essential to choose the correct diamond cup wheel when hand grinding. Developing an understanding of what each type does is the place to start. When hand grinding edges the goal is to have the edges look like the main field that was ground and polished with a walk-behind grinder. No matter the level of aggregate exposure or gloss, a hand grinder in the hands of an experienced operator and the correct cup wheel can produce a seamless transition on the floor.

Let’s start with grinding. Grinding is when the top surface will be removed exposing a level of aggregate. It’s an aggressive process that can cause a high level of damage if not performed correctly. Selecting a cup wheel that produces the exposure that is in the main field is the goal. The more aggressive wheel will grind faster. This is great for production. It will remove stock in short order. Using a less aggressive cup wheel can produce a similar look but slower. Gradually exposing aggregate to match the field under control might be a better scenario unless the operator is extremely experienced. Once the surface is removed, it cannot be put back on.

Once the level of exposure has been obtained, honing and polishing begins. With every step the walk-behind grinder completes, the hand grinder needs to duplicate. The tooling type on the walk-behind grinder can be the same as the hand grinder. Whether the bonding material is copper, hybrid, ceramic, or resin, they are all produced to be fitted on a hand grinder. No one can provide a prescription for which one to use. It will depend on the substrate, operator, and expectations approved by the client.

Before use, assessing a particular cup wheel on concrete is a brilliant idea. Rely on your manufacturer for help. You won't believe the improvements in the end result when selecting the right one for the job.

A SAFE APPROACH

When using a hand grinder, your top priority should be safety as much as creating an acceptable concrete surface. That should be with all power equipment. When using power tools, vigilance is needed to prevent accidents and other issues. A typical hand grinder rotates at 7,000 RPM. To be safe, you need to adhere to the following guidelines:

Personal Protection Equipment (PPE)

• When using any power equipment personal protection must be addressed. Leather gloves and boots, long pants, and a tight-fitting long-sleeved shirt. With all clothing, it should be close fitting to minimize it getting wound up in the piece of equipment.
• Dust will be generated. The hand grinder will be connected to a dust extractor, but it cannot capture all the dust. An air scrubber is a vacuum for the air. It is considered the second line of dust defense. The third line of dust defense will be a dust mask. It is designed to filter the air you breathe just before you breathe it in. A Half Facepiece Reusable Respirator uses disposable cartridges to filter the air. Cartridges come with different filtering capabilities. Selecting one for dust only will be the best line of defense. Most are familiar with N95-rated masks. During COVID, everyone was buying up the available N95 masks. While the FDA did grant temporary emergency-use authorization to KN95s to allow US healthcare workers more options for high-quality protection, as of June 2021, KN95s are not approved by the FDA.
• Grinders grind and produce incompressible objects that can go airborne. Wearing safety glasses with side shields will protect your eyes from flying projectiles. A full-face shield would be added protection.
• When other people are around, avoid working if they are not wearing the proper PPE.
• Verify that nothing combustible will contact any potential sparks.
• If possible, always hold the hand grinder firmly with both hands.

Changing Cup Wheels

• The first thing to do is to unplug the grinder from the power outlet.
• When changing cup wheels, always visually inspect the wheel coming off and going on. Check for cracks, missing segments, and other damage.
• There will be cup wheels that will need to be dressed before use. Dressing removes any coatings that have been used in the manufacturing process and expose the abrasive to enable clean, efficient cutting.
• Before using the wheel, evaluate it on a concrete surface of your work area. This will help figure out if it can perform the task at hand.

Electrical Power

The power requirements of a hand grinder have a wide range.Power is a calculation with voltage being one part. They all need 110 volts from a standard wall outlet. The amperage is the key. The more powerful grinders will require 15 amps and on the lower end 10 amps. Typical residential electrical wiring is designed to supply 110 volts and 15 amps.

Why this is important is that when a hand grinder is working, a dust extractor should always be connected. The dust extractor runs on 110 volts and draws 10-15 amps. If you plug both the grinder and vac into the same circuit, the circuit breaker will trip. When hand grinding, two separate circuits need to be found and used - one for each piece of equipment.

Preparation Before Grinding

Check List

• All safety precautions have been taken.
• Evaluate all cup wheels on concrete before use.
• Adjust the shroud according to the height of the cup wheel.
• Run the vac and hand grinder at the same time to make sure you have two separate circuits.

Hand Grinder Maintenance

Maintaining equipment, and keeping it in like new working condition, increases field production. Ten minutes at the end of the day will extend the service life of the grinder.

Concrete dust is very detrimental to moving parts. It is a fine, abrasive material. It can work its way into the smallest void and cause havoc. If dust gets into the motor or arbor bushings, it will shorten their life. By vacuuming or blowing the dust from the motor and other moving parts, minimizing the potential hazard. If using compressed air to remove the dust, take precautions to protect yourself and others from the airborne dust.

The electrical cord is fragile, it can be cut easily. Inspecting the cord regularly will provide a safety step within the maintenance procedure.

Conclusion

Angle grinders are useful for smoothing concrete surfaces. Nearly all building and construction projects make use of them. The success of the project will depend on high-quality diamond tooling. Power tools typically have multiple uses, but even the most seasoned users are surprised by how versatile an angle grinder can be.

Though their costs can vary, angle grinders are reasonably priced instruments. When working an angle grinder, your top goal should be safety as much as creating a smooth concrete surface.

During your selection process, Niagara Machine can connect you with one of our field representatives. We can show you the available tooling that best suits your project.