Once the slab is clean, stripped, and patched, it’s time for the first true grind: 30 grit metal bond. This is the aggressive removal phase — it evens out high spots, removes trowel marks, opens the pores, and starts your floor’s journey to polish. Done right, it sets the foundation. Done wrong, and you’ll see every flaw all the way through to 1500 grit. This guide walks you through the proper technique, tooling, and checks for grinding concrete with 30 grit diamonds.
Before you even load up 30 grit diamonds, check that the surface is fully clean and dry. Any residual grease, sealer, or wet patch will affect grinding and clog the segments. The floor should be free from loose debris and dry enough to create dust under foot, not sludge.
Concrete varies — soft slabs need a hard bond diamond, while hard slabs need a softer bond so the diamonds expose properly. Get this wrong and you’ll either glaze the tool or wear it out too fast. If you’re unsure, start with a medium bond and adjust after a small test grind.
Attach segments securely and evenly to your planetary grinder or single-head machine. Avoid mixing old and new segments — it’ll lead to uneven wear. Always balance the machine. For 3-head setups, use full-triangle placement; on single-heads, centre weight over the disc.
Start with medium pressure and slow your forward walking speed to allow segments to cut deep and evenly. Don’t rush — this isn’t polishing. Use the dust pattern behind you to verify cut quality. Increase head pressure only if the slab is soft and you’re not seeing enough removal.
Run in north-south passes, then follow with east-west passes to ensure full coverage. Overlap each run by at least 30%. Watch for lines or missed patches — you shouldn’t see untouched trowel marks or glossy sections after the second pass. Stick to a methodical pace — don’t race.
After your north-south passes, vacuum the floor thoroughly before switching to east-west. Dust masks defects and low spots — removing it lets you spot issues before it’s too late. It also prevents dragging dry slurry or grit into the next pass.
Use a hand grinder with matching 30 grit metal bond tooling for edges, corners, and around joints. Try to match depth and pattern. Feather out at least 150–200mm into the main floor to blend edge work with your main runs. Don’t leave harsh lip lines or tool marks.
Use a light and get down to slab level — check that your grind is even. You want a consistent scratch pattern, no swirl, and no glazing. Any skip marks, high patches or glossy spots need a second pass. Don’t move on until this cut is flawless — the next steps can’t fix it.
30 grit metal bonds wear quickly on hard slabs. Check your segments every 50–100m² and swap them before they round out. Dull segments glaze and leave streaks. If the machine starts vibrating, pulling to one side, or the sound changes — stop and inspect the plates.
Once 30 grit is complete, vacuum again and log your cut quality. Take photos or notes for future steps — especially if you’re doing full aggregate exposure. Now you’re ready to move to 50 grit metals and begin refining your scratch pattern into a polishable surface.
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