Key takeaways
- Coating prep uses coarse metal-bond diamonds; new grinders typically ship with 30-grit, medium-bond tooling, and 30-grit metal diamonds are the standard choice for stripping old coatings that aren't epoxy.
- Match the bond to the concrete: soft bond for hard concrete and hard bond for soft concrete, so the bond wears at the rate that keeps fresh diamonds cutting.
- Test hardness before you grind; Mohs scratch kits rate concrete from 2 to 9, and most US concrete falls between 5 and 7.
- PCD tools strip epoxy, glue and mastic; resin-bond pads are for polishing, not coating prep.
- A six-piece set of 30-grit Double Dyma-Dots for a dual-disc grinder costs $240 at list; full sets for an EDCO dual-disc run about $195–530, and planetary tooling varies by bond and grit.
Concrete grinding tools for coating prep are coarse metal-bond diamonds matched to the hardness of the slab, PCD tools for stripping old coatings and mastic, and diamond cup wheels for the edges. New grinders typically ship with 30-grit, medium-bond tooling, and a six-piece set of 30-grit Double Dyma-Dots for an EDCO dual-disc costs 2 × $120 = $240 at list. The rule that saves the most money: soft bond for hard concrete, hard bond for soft.
This guide explains grit, bond and segment shape, how to test concrete hardness, when to switch to PCDs, why resin pads don’t belong in coating prep, and how to work out what tooling costs per square foot. For the machines themselves, see concrete grinders for epoxy prep, part of the epoxy flooring equipment list.
What a diamond tool is
Every grinding segment has three parts that matter:
- Diamonds, sized by grit. Lower numbers are coarser: 16 and 30 grit cut aggressively; 400 and up polish.
- The bond, the metal (or resin) matrix that holds the diamonds. As it wears, it exposes fresh diamonds. How fast it wears is what “soft” and “hard” bond mean.
- The shape: single or double buttons, bars, arrows. Aggressive shapes cut faster and leave deeper scratches.
The three families divide the work: metal-bond tools grind, hybrids bridge the scratch pattern from metal to resin, and resins polish.
Grit for coating prep
Coatings need tooth, measured as concrete surface profile, and coarse metal-bond grits create it:
| Situation | Tooling |
|---|---|
| Bare concrete, standard prep for a high-build system | 30-grit metal bond, medium bond unless the concrete is unusually hard or soft |
| Previously coated floor, coating that isn’t epoxy | 30-grit metal diamonds until the old coating is completely gone |
| Very hard or very smooth concrete that won’t open up | A coarser 16–18-grit set |
| Thick epoxy, paint, glue or mastic | PCDs first, then metal bond |
Finer grits are for polished concrete, a different end product. Polishing doubles the grit at each step (30, 70, 120, 200, 400, 800, 1500); for a coating, you stop at the coarse end and check the profile against CSP chips.
Match the bond to the concrete
This is the part that confuses people, because it runs backwards. Use soft-bond tooling on hard concrete and hard-bond tooling on soft concrete, and test the concrete’s hardness to know which you have.
Why it works: a soft bond wears away quickly and keeps exposing fresh diamonds, which is what hard concrete needs. On soft concrete the reverse applies, and a hard bond is the one that lasts. Get it wrong and you pay either way. Soft diamonds on soft concrete cut fast but can be used up within a few hundred square feet; a hard bond on a hard floor stops exposing diamonds and glazes until the tools are no longer usable.
Makers label tooling by the concrete it’s for, not by the bond. EDCO sells the same 30-grit Double Dyma-Dot in “Soft Concrete” (yellow), “Medium Concrete” (grey) and “Hard Concrete” (red) versions, plus a “Dyma-Rapida” for extremely hard concrete. Order by the concrete you’re grinding.
Testing hardness
| Test | How | Reading |
|---|---|---|
| Mohs scratch kit | Drag picks rated 2 to 9 across the slab; the hardest pick that scratches it is the rating | 7–9 hard, 5–6 medium, 2–4 soft; most US concrete rates 5 to 7 |
| Knife or screwdriver scratch | Press and drag a pocketknife or flathead screwdriver along the slab | No dust: hard; a little dust: medium; a trench: soft |
Mohs kits are inexpensive; some prep packages for new contractors include one, priced around $150. Test in more than one spot, and write the reading on the job sheet.
Glazing
When the bond is too hard for the floor, the diamonds stop being exposed and stop cutting: the tools glaze and production drops. The fix is a softer bond for that concrete. Water mist on the tools also reduces the risk of glazing on machines built for it, such as Husqvarna’s PG 5.
PCDs for coatings, glue and mastic
Old epoxy, paint, glue and mastic melt and smear under ordinary diamonds. Polycrystalline diamond (PCD) tools chip them off instead, quickly and aggressively, without smearing or gumming up, which keeps production high. For EDCO’s Magna-Trap grinders, PCDs with a backing segment cost $210 per pack of three.
PCDs cut deep. An aggressive PCD shape on a soft concrete floor leaves deep gouges, so after stripping, go back over the floor with metal-bond diamonds to even out the profile before you coat.
Resin bonds: polishing, not prep
Resin-bond pads refine and polish a surface; they’re the later steps of a polishing sequence. They don’t belong in coating prep: they’re too fine to create the profile a coating needs, and polishing makes the surface smoother, not rougher. If the job is a densifier and polish rather than a coating, that’s a different system and a different tooling budget.
Cup wheels for edges
Hand grinders use diamond cup wheels or grinding discs. The same bond-and-grit logic applies: a coarse metal-bond cup wheel for edge prep, a PCD cup wheel for stripping coatings at the walls. A 7-inch, 8-segment PCD cup wheel lists at about $525. An edge grinder kit with a cup wheel and shroud runs about $640–716.
What tooling costs per square foot
Tooling prices are easy to find; tooling life isn’t, because it depends on the concrete, the bond, the pressure and the operator. Sets for an EDCO dual-disc cost about $195–530; planetary tooling varies by bond and grit. At the long end, EDCO’s Dyma-Serts are rated for up to 30,000 sq ft of grinding on standard 3,500-psi concrete.
Work out your own cost per square foot as set price ÷ square feet ground. For a $240 set of Double Dyma-Dots, the cost changes like this with the life you actually get:
| If the set lasts | Cost per sq ft |
|---|---|
| 5,000 sq ft | $240 ÷ 5,000 = $0.048 |
| 10,000 sq ft | $240 ÷ 10,000 = $0.024 |
| 20,000 sq ft | $240 ÷ 20,000 = $0.012 |
Even at the short end, tooling is a few cents a square foot, small next to materials at about $1–5 per sq ft. The expensive mistake is the wrong bond: segments that glaze waste labor hours, and segments that wear out in a few hundred square feet waste the set. Rental shops usually bill tooling separately, so it belongs in every job cost whether you rent or own.
Tooling has to fit the machine
Attachment systems differ. Trapezoid tooling fits EDCO Magna-Trap and Lavina grinders; Husqvarna’s Redi Lock system takes rectangular tooling. Before you buy tooling, confirm the attachment, the rotation direction where it matters (EDCO sells left- and right-hand PCDs for its dual-disc heads), and that your supplier stocks replacements.
A starter tooling set
- A set of 30-grit metal-bond segments for your grinder, in the bond that matches most local concrete.
- A second bond, or a coarser 16–18-grit set, for the floors that don't respond.
- A set of PCDs if you'll remove old coatings or mastic.
- A coarse metal-bond cup wheel for the edge grinder, and a PCD cup wheel if you strip coatings.
- A Mohs scratch kit.
If you rent your grinder, ask what tooling the shop stocks before you buy your own (the rent-vs-buy calculator shows when owning the machine starts to pay); the concrete grinder rental guide lists the questions to ask, and the rent vs buy guide shows why tooling costs the same either way.
Reading concrete is learned on concrete. Feeling a bond glaze, seeing when a floor has enough profile and knowing when to switch to PCDs come fastest when you’ve watched it done. In The Epoxy Playbook you watch the full installation, replay any step as often as you need, then do it on the slab in a hands-on class. The Playbook also covers how to price prep and tooling into each job.
Questions
What grit should I use to prep concrete for epoxy?
Coarse metal-bond diamonds, chosen to reach the profile on the coating's data sheet. New grinders typically ship with 30-grit medium-bond tooling, 30-grit metal diamonds are the standard choice for removing old coatings that aren't epoxy, and some new-contractor prep packages add a 16-grit set and PCDs.
Do I need a soft bond or a hard bond?
It's the opposite of what you'd guess: soft bond for hard concrete, hard bond for soft concrete. A soft bond wears away quickly and keeps exposing fresh diamonds, which hard concrete needs; on soft, abrasive concrete a soft bond would wear out too fast, so you use a hard one.
How do I tell how hard my concrete is?
Use a Mohs scratch kit: picks rated 2 to 9 are dragged across the slab, and the hardest pick that leaves a scratch is the rating. 7–9 is hard, 5–6 medium and 2–4 soft. For a quick check, drag a pocketknife or screwdriver across the slab: no dust means hard concrete, a trench means soft.
What are PCD tools used for?
Polycrystalline diamond tools remove coatings, glue and mastic, which would gum up or smear ordinary diamonds. They cut aggressively and quickly, but they also cut deep, so follow them with metal-bond diamonds to get back to an even profile.
How long do diamond grinding segments last?
It depends on the concrete's hardness, the bond, the pressure and the operator. Long-life inserts can last up to about 30,000 sq ft on standard 3,500-psi concrete, while a bond that's too soft for the floor can be used up in a few hundred square feet. Track your own: divide the set's price by the square feet it ground to get your cost per square foot.
Keep reading
Concrete grinders for epoxy prep: types, brands and what fits the job
Which concrete grinder to use for epoxy prep: hand-held, single-disc, dual-disc and planetary machines compared, with EDCO and Husqvarna examples and costs.
Concrete surface profile (CSP): the ICRI scale and what your coating needs
ICRI's concrete surface profile (CSP) scale: CSP 1–10, the profile thin and thick coatings need, and what grinding, shotblasting and acid etching produce.
Rent or buy a floor grinder? The break-even math, worked out
Rent or buy a floor grinder? Break-even tables from published rates ($90–142 a day) and prices ($8,488 dual-disc), plus extractors, tooling and insurance.
Concrete grinder rental: what to rent, what it costs, how to use it
Concrete grinder rental rates for hand-held, dual-disc and planetary grinders, what's charged extra, power and OSHA dust rules, and a garage step by step.