You’ve polished the slab to a clean 800 grit — but under raking light, swirl marks appear, or a rogue scratch shows up near the wall. Do you continue, or go back? This guide covers exactly how to identify and remove scratches or swirl marks during the concrete polishing process. We’ll also break down why they happen, and how to avoid making the same mistake again.
First, don’t continue polishing. Examine the direction, depth, and pattern of the scratch or swirl. Often, swirl marks mean your previous grit wasn’t fully removed — for example, if you jumped from 100 to 400. A deep, singular scratch could be caused by debris or a damaged segment. Identify where in your sequence the problem occurred, so you know where to return to.
If you see swirls at 400 grit, go back to 200. If the scratch appears at 800, return to 400. Re-polish the affected area with slow, overlapping passes. Don’t spot-grind — blend at least 1–2 square metres beyond the defect to maintain uniformity. Check under raking light before moving forward again.
Damaged, worn, or clogged pads are a major cause of swirls. Remove your pads and inspect the diamond face — if it’s smooth, rounded, or glazed, it won’t refine properly. Replace worn pads immediately. Rotate pads between heads regularly to even out wear patterns and extend pad life.
Swirls often result from dragging fine dust or slurry over the slab between passes. Always vacuum thoroughly between grits, and never polish over a dirty surface. If wet polishing, clean standing slurry quickly before it dries. If dry, inspect for residue buildup at pad edges and baseplate rings.
Uneven pressure or high speed can cause pad bounce, chatter, or heat glazing — especially with resin pads. Lower your speed slightly and reduce downforce on finer grits (400+). Let the pad float and refine, not cut. You should hear a smooth, consistent hum — not a grind or squeal.
Run one full set of north-south passes, then follow with east-west at the same grit. Crosshatching eliminates directional scratch buildup and helps even out pressure zones from multi-head machines. If swirl is directional, this usually fixes it by blending those angles together.
After polishing, you may use a high-speed burnisher with a polishing pad to further blend the surface. This can remove light haze or swirl left behind from resin pads and bring out uniform reflectivity. This won’t fix deep scratches — it’s only for mild surface inconsistencies.
Every slab is different. Once resolved, document what caused the issue — skipped grit, pad age, machine tilt, etc. That feedback helps improve your next job. Most swirl or scratch issues come down to rushing steps or inconsistent pad maintenance — both avoidable with process control.
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