Concrete

Diamond Tooling: Bond Hardness and Grit Selection

How to match diamond bond hardness to the slab, which grit does what, when to use PCD instead, and how to tell your tooling is wrong.

Updated · 2 min read

The rule that decides everything: hard concrete takes a soft bond, soft concrete takes a hard bond. Get that right and the grit sequence falls into place. Get it wrong and the tooling either glazes and stops cutting or disappears in an afternoon.

Silica

Grinding, blasting and scarifying concrete release respirable crystalline silica. Follow the controls in OSHA 1926.1153 Table 1 or measure exposures. See Silica dust and respiratory safety.

Why bond matters

A metal-bond segment is diamonds held in a metal matrix. As it grinds, the matrix wears away and exposes fresh diamonds. On hard concrete you want the matrix to wear quickly, so a soft bond keeps sharp diamonds at the surface. On soft or abrasive concrete a soft bond would wear out fast, so you use a hard bond. Matching the bond to the slab this way prevents glazing and early wear.[1] If segments glaze anyway, lower the speed a step at a time until the glazing stops.[1]

Test the slab first

A quick hardness check tells you which bond to start with.

  • Use a Mohs scratch test kit for a quick read on slab hardness, working up through the picks until one scratches consistently.[2]
  • Test several spots. Troweled areas, patches and edges can differ from the field.
  • If you don't know, start with a medium bond and 30/40 grit, and watch how it behaves.

Grit: what each range does

Once the bond is right, the grit decides how aggressive the cut is.

Grit Use
16 Aggressive removal of coatings, including thin epoxy, paint, adhesive and sealers[1]
30 Removing sealers and prepping concrete for polishing[1]
80 to 120 Prepping concrete for polishing. 120 is typically the finest metal bond[1]
Transitional / hybrid resin Bridge from metal bonds to resin polishing pads; honing steps typically run #100 to #400[3]

Each step should remove the scratch left by the one before it.

PCD: when diamonds aren't the answer

Thick epoxy, mastic, glue and elastomeric coatings load up metal-bond segments. PCD (polycrystalline diamond) tooling scrapes and chips them off instead. Start with PCD, then switch to metal bonds to clean up and condition the surface. Test old black mastic for asbestos before you grind it: Cutback adhesive and asbestos ID.

Segment style

The shape and number of segments also changes how the tooling cuts.

  • Single segment: most aggressive, fastest cut, more chatter. Good on lighter grinders and stubborn coatings.
  • Double segment: the general-purpose choice.
  • Multi-segment and bar styles: more stable, smoother and more uniform scratch.

Reading your tooling

Your tooling tells you when something is wrong. Here's what to look for.

What you see What it means Fix
Shiny segments, machine skates, little dust Glazing: bond too hard for the slab Softer bond, fewer segments, or dress the tooling on an abrasive block
Segments wearing fast, lots of dust Bond too soft for the slab Harder bond or more segments
Segments gummed with coating Wrong tool for the material Switch to PCD for removal
Deep scratches after a finer grit Skipped a step Go back one grit

Tooling we carry

These are the planetary grinder tooling styles we carry.

References

  1. National Flooring Equipment: Grinder tooling guide
  2. Husqvarna: Mohs hardness test kit
  3. Husqvarna: Concrete grinding and polishing guideline

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