Concrete Grinding Guide: How to Select the Right Diamond Grit & Bond

Selecting the right diamond tooling for your project is the most critical factor for a successful concrete grinding job. Choosing the correct diamond grit and bond not only ensures a high-quality finish but also saves you significant time, money, and frustration. Using the wrong tooling can lead to slow progress, premature wear, and a damaged surface, turning a profitable job into a costly headache.

This comprehensive guide will walk you through everything you need to know about choosing the perfect diamond tooling. We’ll decode the terminology, explain the science behind the selection process, and provide a step-by-step framework to get it right every time. By understanding these core principles, you can maximize your efficiency, extend the life of your equipment, and deliver flawless results on any concrete surface.

What Are Diamond Grinding Tools and Why is Selection Crucial?

Diamond grinding tools are specialized abrasive pads, pucks, or segments used with floor grinders to prepare, level, and polish concrete surfaces. These tools consist of two main components: industrial-grade diamond crystals (the “grit”) and a metallic matrix that holds them in place (the “bond”). The interaction between these two elements is what performs the cutting action on the concrete.

The importance of proper selection cannot be overstated. Think of it as using the right key for a lock; the wrong one simply won’t work and might even damage the lock. In concrete grinding, the wrong choice leads to tangible, costly problems. Using a bond that’s too hard for the concrete will cause the diamonds to dull and stop cutting, a phenomenon known as “glazing.” Conversely, a bond that’s too soft for the concrete will wear away too quickly, wasting your expensive diamond segments long before their time.

The financial impact is direct. The right tooling allows you to complete the surface prep faster, reducing labor hours. It also ensures you get the maximum lifespan from each grinding pad, lowering your consumable costs per square foot. Professionals who master this selection process consistently outperform their competition by finishing jobs on time and under budget.

Understanding Diamond Grit: From Coarse Removal to Fine Polishing

The “grit” refers to the size of the diamond particles embedded in the bond. Much like sandpaper, diamond grit is measured on a numerical scale where a lower number indicates a larger, more aggressive diamond particle, and a higher number indicates a smaller, finer particle. Understanding this scale is the first step in planning your project.

What is diamond grit size?

Diamond grit size determines the aggressiveness of the cut and the resulting scratch pattern on the surface. A coarse grit tool with large diamonds will remove material very quickly but will leave deep scratches. A fine grit tool with smaller diamonds will remove less material but will produce a much smoother, more refined surface. The key is to start with a grit coarse enough to accomplish your initial goal and then progressively move to finer grits to remove the scratches from the previous step.

Diamond Grit Size Chart for Concrete Applications

16-30 Grit (Extra Coarse): This is your starting point for aggressive grinding. Use this range for removing thick coatings like epoxy, urethane, or mastic. It’s also ideal for leveling very uneven concrete surfaces and exposing heavy aggregate.
40-60 Grit (Coarse): A common starting point for basic surface prep on floors with no coatings or for the second step after using a coarser grit. It effectively removes minor imperfections and prepares the concrete for a new coating or overlay.
70-120 Grit (Medium): This range begins the transition from grinding to polishing. It’s used to remove the scratches left by the 40-60 grit pass and is often the final step before applying a thin-mil coating. For a simple grind-and-seal project, you might stop at 120 grit.
200-400 Grit (Fine): Now we are firmly in the initial stages of concrete polishing. These grits close up the pores of the concrete and create a smooth, matte to low-sheen finish. A densifier is typically applied before or during these steps.
800+ Grit (Extra Fine): Grits from 800 up to 3000 are used to achieve that highly reflective, “mirror-like” finish. These are resin-bond pads that progressively refine the surface to create high gloss and clarity.

The answer to “What grit is best for concrete grinding?” is that it entirely depends on the starting condition of the slab and your desired outcome. For heavy removal, start low (e.g., 30 grit). For a new, smooth slab, you might start with 60 or even 120 grit.

Decoding the Diamond Bond: What Does Soft, Medium, and Hard Mean?

While the diamond grit does the cutting, the bond determines how effectively the tool works on a specific type of concrete. The bond is the metal matrix that holds the diamond particles. Its primary job is to wear away at a controlled rate, constantly exposing new, sharp diamond crystals to the concrete surface. If it wears too slowly, the diamonds become dull. If it wears too quickly, the tool’s life is drastically shortened.

Bonds are categorized by their hardness relative to the concrete they are designed for:

Soft Bond: A soft bond tool has a metallic matrix that wears away easily. This rapid erosion is designed to quickly expose new diamond segments, which is essential when grinding very hard, dense concrete. The hard concrete abrades the bond just enough to keep fresh diamonds working.
Medium Bond: This is the versatile, all-purpose option. A medium bond is designed for concrete of average hardness (around 3,000-4,000 PSI). It offers a good balance between tool longevity and cutting performance, making it a safe choice when the concrete hardness is unknown.
Hard Bond: A hard bond tool has a very durable, wear-resistant matrix. It is specifically designed for use on soft, abrasive concrete. The abrasive nature of the soft concrete wears down the bond just enough to expose new diamonds without the tool wearing out prematurely.

The Golden Rule: Matching Bond Hardness to Concrete Hardness

This is the most crucial principle in how to select diamond grit and bond combinations. The relationship between the bond and the concrete is inverse. Memorize this rule, and you will avoid the most common grinding problems:

Hard Concrete requires a Soft Bond.

Soft Concrete requires a Hard Bond.

Why is this the case? Imagine trying to grind an extremely hard piece of concrete with a hard bond tool. The concrete is not abrasive enough to wear down the metal bond. As a result, the diamonds on the surface become rounded and dull. The tool stops cutting, heats up, and glazes over, polishing the surface instead of grinding it. You’ll make very slow progress and burn up your tooling.

Now, consider the opposite scenario: using a soft bond tool on soft, dusty concrete. The soft concrete acts like sandpaper, rapidly eroding the soft metal bond. The tool will cut incredibly fast, but it will also wear out in a fraction of its expected lifespan, costing you a fortune in replacement grinding pads. Matching the bond correctly ensures the tool wears at the optimal rate for maximum performance and longevity.

How to Quickly Test Your Concrete’s Hardness (Mohs Test)

You can’t follow the golden rule if you don’t know your concrete hardness. While PSI ratings can give you a clue, the most reliable on-site method is the Mohs Hardness Test. This simple test uses a set of picks with tips of varying, known hardness levels (from 2 to 9 on the Mohs scale) to scratch the concrete surface. It’s a quick, affordable, and accurate way to determine which bond to use.

Performing the Mohs Hardness Test: A Practical Guide

Prepare the Surface: Find a small, inconspicuous test area. Clean it of any dust, debris, or sealers to ensure you are testing the bare concrete.
Start in the Middle: Begin with the #5 or #6 pick from your kit. Press it firmly against the surface and make a 1-2 inch scratch.
Analyze the Result: Examine the scratch. Did the pick scratch the concrete, or did the concrete wear down the pick, leaving a metal streak?
- If the pick scratched the concrete, the concrete is softer than that pick’s number. Move to a lower-numbered pick (e.g., #4) and repeat.
- If the pick did not scratch the concrete and left a metal streak (like chalk), the concrete is harder than that pick. Move to a higher-numbered pick (e.g., #7) and repeat.
Find the Threshold: Continue this process until you find the first pick that will scratch the concrete. The hardness of your concrete is rated just below that number. For example, if the #7 pick scratches the slab but the #6 pick does not, your concrete has a Mohs hardness of approximately 6.5.

Matching Mohs Results to Diamond Bonds

Mohs 2-3: Very Soft Concrete -> Use a Hard Bond.
Mohs 4-5: Soft to Medium Concrete -> Use a Medium-Hard Bond or a standard Medium Bond.
Mohs 6-7: Hard Concrete -> Use a Soft Bond.
Mohs 8-9: Extremely Hard Concrete -> Use an Extra-Soft Bond.

A Step-by-Step Guide to Selecting the Right Grinding Pad

Now, let’s put it all together. Follow these steps to confidently choose the right tooling for any job, whether you’re using equipment with a system like the **Husqvarna Redi Lock vs HTC EZchange** or another brand.

Step 1: Define Your Objective. What are you trying to achieve? Are you removing a thick coating, preparing for an overlay, or aiming for a high-gloss polish? Your goal dictates your starting grit.
- Coating Removal: Start with a very coarse grit (16-30).
- Light Prep / Grinding: Start with a coarse-to-medium grit (40-70).
- Polishing Prep: Start with a medium grit (70-120) if the floor is already in good shape.
Step 2: Test the Concrete Hardness. Use your Mohs kit as described above. This is the most crucial step for bond selection. Do not skip it.
Step 3: Apply the Golden Rule to Select Your Bond. Match the bond to the hardness result. If you have Mohs 7 hard concrete, you need a soft bond. If you have Mohs 4 soft concrete, you need a hard bond.
Step 4: Plan Your Grit Progression. To achieve a smooth finish, you must follow a logical concrete grinding grit progression. A good rule of thumb is to double the grit number at each step (e.g., 30 -> 70 -> 120 -> 200 -> 400…). Never skip more than one grit level, as doing so will leave deep scratches that subsequent steps cannot remove. For more details, explore our guides on achieving the perfect polished concrete finish.

Example Scenario: You need to remove a thin layer of old glue and prepare a floor for a new epoxy coating. Your Mohs test reveals the concrete is a 7 (hard).

Objective: Glue removal and surface prep.
Starting Grit: A 30 or 40 grit will be effective.
Hardness: Mohs 7 (Hard).
Bond Selection: Apply the Golden Rule -> Hard concrete needs a soft bond.
Your Tooling: 30 Grit, Soft Bond Diamond Grinding Pads.