Quick Answer

Rake marks and rough surfaces come down to the same root causes: machine condition, tooling match and technique. On a bare concrete slab, start with 16/18 or 30/40 grit stage depending on the slab’s condition: use 16/18 for coarse, troweled, laitance-heavy, or aggregate-exposing work, and 30/40 for clean, level floors that just require opening up before burnishing. Select the coarsest grit stage that removes the defect in one or two passes, then stage down through 60/80, 120, and resin bonds.

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Decide The First Grit: Step-by-Step

A closer look at the details.

Getting this part right saves a full re-pass later.

The “Defect Rule”

What you should know before starting.

The correct first grit stage is the one that removes the worst defect on the floor in two passes.

• Fine scratch marks or faint glue layer→start medium.
• Glossy sealed slab→start fine scuff.
• Trowel marks and heavy cream→start coarse.

Contractors who skip this stage usually end up redoing the floor.

About Bond Matters As Much As Grit

The key points in practice.

A zigzag-segment trapezoid disc clears swarf well on the first aggressive pass, while Single Rhombus Segment Trapezoid Disc (JOY-TP-RH1) tracks smoothly on medium slabs.

This is where most crews get it right - or lose time.

Avoid These First-Pass Mistakes

A closer look at the details.

• Not inspecting scratch mark pattern. After the first pass, inspect under bright light—you should see uniform, fine scratch marks, not swirls or skipped spots.
• Starting too coarse on a clean slab. Creates deep gouges that demand 5–6 later stages.
• Starting too fine. Glazes diamonds, wastes time, leaves the floor uneven.
• Skipping a stage. Jumping from 16/18 to 120 leaves 30/40 scratch marks you cannot hide.

Getting this part right saves a full re-pass later.

Dressing Glazed Diamonds On Site

What you should know before starting.

Even with the right grit stage, a new shoe can glaze on its first minutes against very even concrete.

Contractors who skip this stage usually end up redoing the floor.

Frequently Asked Questions

Q: Should I use 16/18 or 30/40 on a brand new slab?

A: For most jobs, New slabs have a weak laitance layer. Start with 30/40 unless the slab is heavily troweled; 16/18 is for aggressive laitance or aggregate exposure.

Q: Am I able to skip 30/40 and go from 16/18 to 60/80?

A: In short, In most cases no. The 30/40 stage removes the 16/18 scratch mark pattern. Skipping it leaves deep micro-scratch marks that show through the final burnish.

Q: What if my diamonds glaze on the first pass?

A: The practical answer is, Your bond is too hard for the concrete. Drop to a softer bond, or use a dressing brick to open the segment face.

Q: Does wet or dry grinding change grit choice?

A: For most jobs, No—the grit stage decision is based on the floor. Wet abrading reduces heat and fine dust but does not let you start finer than the surface requires.

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Conclusion

Match the tooling to the concrete, keep the machine in good condition, and run even passes - the finish follows. Pick the first grit stage by the worst defect on the floor, not by habit: 16/18 for coarse or aggregate-reveal work, 30/40 for most standard prep, and 60/80 only for clean, already-level slabs.