Quick Answer

Deep scratches are usually left by coarse metal-bond segments working with too much pressure, worn-out segments with uneven bond exposure, or a grit jump that skipped the intermediate steps. Stop checking after one pass, drop the pressure, work the floor with a medium metal disc, then step through finer grits so the marks cut down and blend instead of staying as grooves.

Where Deep Gouges Actually Come From

When a plate leaves visible grooves, one of these is almost always happening:

• Segments too coarse for the pass — 30/40-grit metal on an already smooth floor plows channels.
• Too much down-pressure — the machine weight pushes the segment edge into the paste instead of shearing it.
• Worn or glazed segments — half-worn bond leaves protruding diamond that cuts deeper than the rest.
• Skipped grits — going straight from coarse metal to fine resin leaves the coarse scratch pattern in place.
• Dirty floor — sand and debris trapped under the plate act like loose grinding media.

Most scratch complaints on job sites come from pressure and grit sequence, not from a bad plate.

How to Confirm It Is the Plate and Not the Machine

Run one plate on a clean test patch at low speed with normal weight. If the pattern repeats on every pass, the plate geometry or segment exposure is the cause. If it only appears on certain passes, check for a warped backing plate, worn Velcro, or an uneven segment bed before you change tooling.

Step-by-Step Fix for Existing Scratch Marks

1. Run a medium metal disc (around 50-70 grit) diagonally across the scratched area to knock the groove shoulders down.
2. Re-run the same disc with lighter pressure in the opposite direction to level the surface.
3. Switch to a Diamond Trapezoid Grinding Disc (JOY-TP-R3) in the fine-metal range and overlap passes by half a disc.
4. Move to resin pads and complete a full grit sequence — do not skip more than one grit step.
5. Use a water-filled vacuum while grinding so removed paste does not redeposit as scratch lines.

How to Prevent Deep Scratches on the Next Job

• Match segment grit to the concrete hardness, not to how fast you want the job done.
• Keep grinding pressure light — let the diamond do the work.
• Wear plates evenly by rotating them between passes.
• Clean the floor of debris before every grit change.

Frequently Asked Questions

Q: Can deep scratches be polished out completely?

A: Yes, if they are surface grooves from grinding. Level them with medium metal first, then refine with resin pads. Cracks or chips need repair before grinding.

Q: Is 30 grit too coarse for a light grind?

A: 30 grit is for coating removal and heavy leveling. For a light grind or scratch blending, start at 50-70 grit metal.

Q: Do scratches get worse with faster RPM?

A: Usually yes. High RPM with heavy weight makes segments dig in. Lower the speed and let the disc rotate without forcing it.

Q: Should I replace scratched plates or dress them?

A: If segments are uneven, dressing with a rubbing block can re-level them. If the plate is warped or segments are worn past half, replace it.

Conclusion

Deep scratches are a technique and tooling problem, not a permanent floor defect. Correct the grit sequence, lighten the pressure, and use a consistent Double S Segment Trapezoid Grinding Disc (JOY-TP-S2) in the medium range to bring the floor back flat. Need a matched set of metal and resin tooling for your concrete type? Contact JOY TECH for a grinding schedule tailored to your machine and floor.