Grinding Concrete Floors

There are many reasons to grind concrete. It usually is the initial step in a process. The process might be installing a coating or mortar, resinous or cement-based, or removing an old vinyl tile floor. You can also flatten an area or remove a hump or bump. When polishing a concrete floor, the grinding step typically is the first step. Whether it be in a residential, commercial, or industrial setting, the process is all the same. The same equipment and tooling will be used. Although the process appears to be simple, operating the equipment and tooling selection will initially take some guidance.

Understanding the Purpose of Grinding Concrete Floors

When grinding concrete, you will be removing a weak surface, exposing fine or coarse aggregate, or ridding the surface of an unwanted coating, adhesive, or contaminant. Grinding prepares the surface for the next step in a process.

When a coating is to be installed, the manufacturer of the coating will call out a level of surface preparation (groundwork) required before the coating can be applied. There might be a CSP designation in the installation instructions that will need to be followed.

CSP, Concrete Surface Profile, developed by the International Concrete Repair Institute, is a guide to help manufacturers, installers, and specification writers understand the different levels of the surface profile (roughness) that need to be obtained. The guide visually explains the different levels and manufacturers decide which one they need for the individual product. Having a manufacturer state they require a rough surface for their coating, the word “rough” will have different meanings to different people. When they state they want a CSP 2, that is a specific profile. When grinding a concrete floor with the correct tooling, you can obtain a CSP 1-5.

Essential Tools

To grind concrete, you will need a mechanical device (concrete grinder) that spins while holding an abrasive. The abrasive that is typically used is an industrial diamond. A grinder comes in many sizes. They can be handheld or walk-behind machines. They are powered by electrical motors or propane engines. The size, weight, and power source of the grinder will depend on the project. Using a handheld grinder to prepare a garage floor for a coating will take forever. A 32” grinder in a bathroom will be difficult to maneuver. Niagara Machinehas knowledgeable Field Technicians to help determine what size, weight, and power source best fits the work.

A diamond tool is what grinds the concrete. The type of tooling that is used during the process is a metal-bonded tool. The industrial diamonds are secured to the tool base with a metal alloy. As the tool grinds, the diamonds will become flat and unusable. At this point, the metal alloy will wear away, exposing fresh diamonds. This process will continue until all the diamonds have been used up. Not all metal alloys have the same hardness. This is where some professional guidance from Niagara Machine will help. Hard metal alloy is used on soft concrete and soft alloy is used on hard concrete. The concrete hardness needs to be determined before any grinding starts.

Anytime there is concrete grinding going on, there will be dust generated. No matter if you are using a 32” walk-behind grinder or a small 5” handheld unit, you will produce dust. Concrete dust is extremely harmful to breathe. It contains silica. Exposure to silica dust can lead to the development of lung cancer, silicosis (an irreversible scarring and stiffening of the lungs), kidney disease, and chronic obstructive pulmonary disease. Each year more than 300 U.S. workers die from silicosis and thousands more are diagnosed with the lung disease. Silica dust is just as lethal as asbestos. The dangers are the same, yet we cannot afford for the results of exposure to silica dust to be the same as what occurred with asbestos.

The grinder you select, and the tooling used to grind are very important but the dust extractor, for health concerns, is the most critical piece of equipment on the job site. Dust extractors (vacuums) attach to the grinder to minimize airborne dust. They have a means to capture the dust and bag it without being in contact with the dust. DiamaPro Systems manufactures several dust extractors. They come with 2 or 3 motors, 110v or 220v power requirements, and manual or automatic filter pulsing features.

When a dust extractor picks up dust from the floor, the air moves through a series of filters capturing harmful dust particles within the unit. The main or primary filter captures much of the dust from the air moving through the unit. After the air moves through the primary it moves on to the HEPA filters. This is where the ultra-fine particles are removed before the air leaves the machine into the atmosphere. This type of air filter can theoretically remove at least 99.97% of dust, pollen, mold, bacteria, and any airborne particles with a size of 0.3 microns (µm).

When using a handheld grinder there needs to be a dust shroud attached. There will be a tremendous amount of dust produced within arm’s length. The shroud has an exit port where the dust extractor is connected. The shroud contains the generated dust enabling the dust extractor to move it into the vac.

Although a highly efficient extractor with be used, there are times when dust will escape under the grinder shroud. An air scrubber works like your home furnace. Outside air is drawn through a series of filters and back into the room. Air scrubbers are characterized by how much air will move through the unit in cubic feet per minute (CFM) measurement. If you have a small room, a 500 CFM unit might be sufficient. A large area might require a 2000 CFM scrubber. By contacting Niagara Machine, they will be able to direct you to the correct size.

Personal Safety Precautions

Anytime power equipment is being operated, proper Personal Protection Equipment (PPE) must be properly used by everyone in the immediate area. Airborne dust, flying debris, moving equipment parts, and high levels of noise are all health hazards. Leather gloves and boots, hearing protection, eye protection, dust masks, and long-sleeve shirts and pants (not shorts) need to be worn.

How to Grind Concrete Floors

The first task is to contact a Niagara Machine Field Technician. They will help you determine which grinder will be best fit for the job, the tooling suitable to obtain the profile required for the project, match a dust extractor with the grinder, all the PPE that will be needed, and answer any question that you might have. Having a resource available you can count on is a very valuable tool in your bag.

With grinders and dust extractors, you can rent or purchase. If purchasing, discuss your options with Niagara Machine. If renting makes more sense, Sunbelt Rentals carries everything you will need.

Once the grinder size has been determined, the concrete hardness needs to be tested. If you do not have a Mohs Hardness Testing kit, contact the person who supplied you with the grinder. You can purchase a kit from them or have them test it for you. If they test it, make sure they explain the testing process so you will not need their assistance the next time. The hardness correlates to the metal alloy bond of the tooling.

Normally, you will start with a 16-grit or 30-grit metal bond tool if there are no coatings or adhesives to be removed. If there will be, contact the Niagara Machine Field Tech to direct you in the right direction. There are numerous options available depending on the coating or adhesive type and the final surface profile you need to achieve.

When grinding, there will be some dust that is not extracted from the floor that needs to be picked up. DO NOT USE A BROOM TO MOVE THE DUST. Brooms will kick up dust and make it airborne. This is a health hazard that needs to be eliminated. The dust extractor will be supplied with a wand attachment. Connect the wand to the vac hose and vacuum the floor. This should be done after every grinding pass.

After the floor has been cut with a 30-grit metal bond tool, evaluate the floor for a uniformly ground surface. Match the surface profile to the CSP value to make sure it meets the final intent.

Finishing and Clean-Up

Once the floor has been ground with the walk-behind grinder, there might be some hand work to do. Edges, around pipe protrusions, corners, and under cabinet kick plates might need to be addressed. This is where you use the handheld grinders. With hand-held grinders, you can match the tooling that was used to grind the floor. This enables you to obtain the same surface profile throughout the entire floor.

Possible Common Issues

Grinder

• Size – too small or too large for the area
• Weight – cannot get it to the area that will be ground. Down a flight of stairs or the freight elevator is not operating yet.
• Head Pressure – there are times when a special tool is needed but the grinder will not have enough down pressure on the tool to perform at an optimal production rate.

Not Cutting:

• Incorrect Metal Alloy – If you use a hard metal alloy bond tool to grind hard concrete, it will initially cut but soon will stop cutting.

Tooling Wearing Fast

• Incorrect Metal Alloy – If you use a soft metal alloy bond tool to grind soft concrete, the metal will wear away before the diamonds wear out. Tooling will not last long but will grind very well.

Dust Extractor:

• Dust left on floor - A large amount of dust is being left on the floor. Extractors come in different sizes and power requirements. Select one that matches the grinder’s output. Dust Extractors are tested for CFM and water lift. These two values are important when comparing one unit to another. You want to make sure that you have enough vac for the amount dust that will be generated.
• Reduction in Suction – As the dust moves through the vac, the filters capture some of the dust. As it is used, the filters fill up with dust. The filters need to be cleaned or in industry terms, “purged”. There are two types of dust extractors when it comes to purging, manual and self-purging. The manual unit needs to be manually purged on a regular basis. The self-purging model will automatically shake the filter on a preset time interval. Although it helps clean the filter free from dust, it still needs to be manually purged. This could be every time it’s turned off or every 3-4 hours. The time frame is dependent on how much dust you are generating.
• Tripping Circuit Breakers – Most 110V extractors are rated for 20 amps of electrical power. Most residential outlets are wired for 15 amps. If you plug a 20-amp rated vac into a 15-amp service, the circuit breaker could trip. Make sure if this is the situation you have, only run the vac on that circuit and no other power equipment. If it keeps tripping, locate a 20-amp outlet, or find a generator to run the vac.
• Dust Bags are Heavy – With a commercial Dust Extractor, there will be a continuous bag system capturing the dust. The bag needs to be removed before it gets too heavy to carry. Never fill a bag greater than the size of a 5-gallon pail, preferably smaller. This will make it easy to remove and dispose of.
• Dust Extractor Electrical Plug – The Extractor draws 20 amps and has a legal 20-amp plug. This will not fit in a 15-amp residential or commercial outlet. Without exchanging the plug for a 15-amp style or using a plug adaptor, neither are recommended, a generator to power the Extractor will be the best option.

Grinding concrete entails much more than getting a grinder, putting tooling on it, and beginning the grinding process. There is science behind it. Determining the concrete hardness, selecting the hardness of the metal alloy in the tooling, and operating the grinder at a speed to fully process the surface. It takes knowledge, practice, and a resource that you can count on.

Once you have developed a relationship with a resource, the rest of the process will fall into place. Selecting a grinder, dust extractor, and tooling, with the help of your resource, will not be intimidating. Many distributors have demo machines they use to train with. This is the perfect situation for you to try before you buy. Each Field Technician at Niagara Machine has access to every piece of equipment they sell to demo. You wouldn’t buy a car before a test drive, no different than buying a grinder package.