Quick Answer

Use a soft-bond grinding shoe on hard concrete and a hard-bond shoe on soft concrete. This is the "opposites attract" rule: a soft bond wears faster and keeps exposing fresh diamonds to cut dense, high-PSI slabs, while a hard bond resists the abrasive pull of soft concrete so the shoe does not disappear in minutes. Match the bond first, then the grit, and your shoes will cut fast and last a full job.

Why Bond Matters More Than Grit

Every diamond grinding shoe holds diamonds in a metal matrix called the bond. The bond's hardness controls how quickly the matrix erodes and releases dulled diamonds:

• Soft bond: matrix erodes quickly, exposing fresh sharp diamonds constantly — correct for hard, dense concrete (high PSI, aggregates exposed).
• Hard bond: matrix erodes slowly, holding diamonds longer — correct for soft or freshly poured concrete that would otherwise rip the diamonds out.
• Medium bond: a compromise for mid-range slabs and mixed conditions; many contractors standardize here and adjust by grit instead.

Choosing by grit alone is the most common mistake. A 30-grit shoe in the wrong bond either glazes over (bond too hard) or burns out in one pass (bond too soft).

How to Test Your Concrete Hardness

Test	What to look for	Likely bond
PSI rating (from mix design or MoH test)	Above ~4,500 PSI	Soft bond
Scratch test with a nail or coin	Hard, no visible scratch	Soft bond
Chalky, dusty, crumbly surface	Low density, weak surface	Hard bond
Fresh pour (under 28 days)	Still releasing water	Hard bond

When in doubt, run one shoe in soft and one in hard bond on a small test area and compare cut speed and wear. The shoe that cuts steadily without glazing is the right one.

Choosing the Segment Shape and Layout

Bond is the matrix; segment shape is the cutting profile. Triple-round trapezoid shoes (JOY-TP-R3) suit general prep on medium concrete, while single-rhombus shoes (JOY-TP-RH1) cut aggressively on hard slabs. Double-round and double-S profiles (JOY-TP-S2) give a flatter finish for the transition passes. Buy the bond that matches your concrete and the shape that matches your machine head.

What Grit Sequence to Run

• Coarse (16-30 grit): leveling, coating and adhesive removal, first pass on rough slabs.
• Medium (40-80 grit): removing coarse scratches, transitioning from metal to resin steps.
• Fine (100+ grit, resin): honing and polishing — switch to resin pads once the metal sequence is done.

Stay within the same bond family for the metal steps, then move to resin pads for the finish. Mixed-bond sequences cause uneven cut and visible color differences in the final floor.

Frequently Asked Questions

Q: How do I know if my bond is too hard or too soft?

A: If the shoe glazes — smooth, shiny, stops cutting — the bond is too hard. If it wears down rapidly with little cut, the bond is too soft for that concrete.

Q: Can I use soft-bond shoes on soft concrete if I just change grit?

A: Not for long. On soft concrete a soft bond erodes fast and the shoe rounds off within a few hundred square meters. Switch to a hard-bond shoe for that slab.

Q: What bond should a rental shop stock first?

A: Medium bond in 30/60 grit covers the widest range of rental jobs; add soft-bond coarse shoes for contractors who report hard, high-PSI floors.

Q: Does machine RPM affect the bond choice?

A: Only slightly. Higher RPM generates more heat and wear, so lean one step softer on hard concrete with a high-speed planetary machine.

Conclusion

Bond first, grit second: soft bond for hard concrete, hard bond for soft concrete, and medium as your everyday default. Test a small area when the slab is unfamiliar, keep the metal sequence in one bond family, and finish with resin pads. Browse the JOY-TP trapezoid shoe range and order the bond your concrete needs.