Quick Answer
Rake marks (also called chatter lines or washboard streaks) are caused by the grinder bouncing or skipping across the floor, usually from worn bearings, a too-aggressive bond, incorrect pressure, or a warped plate. Fix the machine, soften the bond, and grind flatter and slower. Do not try to polish them out.
What Causes Rakes
- Worn bearings or drive belt: the head wobbles and chatters.
- Too hard a bond: the diamonds cannot protrude, the tool skips instead of cutting.
- Too much downward pressure: the plate digs in and bounces.
- Uneven subfloor: over a slab joint or hump, the plate rocks.
- Worn tooling: segments that are half gone no longer cut consistently.
Fresh, sharp metal-bond discs like our double-S segment discs cut smoothly; old, glazed discs chatter.
How to Remove Rakes
- Inspect the machine: bearings, drive belts, plate flatness.
- Switch to a softer bond. Hard concrete needs a softer bond.
- Reduce downward pressure. Let the weight of the machine do the work.
- Slow the feed. Overlap passes by 30%.
- Take one coarser pass across the rakes, then resume normal sequence.
How to Prevent Them
- Always start with a flat, clean plate.
- Use matched sets of tools; never mix worn and new discs on the same turret.
- Check the plate for warping after dropping the grinder.
- Diamond grind rather than speed grind: slower feed gives a flatter result.
Browse the full range in our concrete grinding discs category.
Frequently Asked Questions
Q: Will a finer grit remove rake marks?
A: Sometimes, if they are shallow. Deep rakes need a coarser pass first. Trying to polish them out usually wastes a pad set.
Q: Are rakes caused by the floor or the machine?
Mostly the machine or tooling. A well-tuned grinder on good tooling should not leave rakes.
Q: Do I need to re-grind the whole floor?
Usually a single coarser pass across the affected area, then step back through the grit sequence.
Conclusion
Rakes are a tooling or machine problem, not a concrete problem. Fresh sharp discs, correct bond, and light pressure are the fix. contact JOY TECH if rakes persist despite new tooling.
