400 grit is the first true polishing stage in the concrete refinement process. It produces a tight, smooth surface with a low-sheen matte finish — ideal for spaces that want durability without gloss or reflection. At this stage, pad pressure, polish timing, and floor prep all matter. This guide walks you through how to polish concrete to 400 grit properly, using the right tools, pace, and sequencing for a clean, professional result.
Before beginning your 400 grit polish, the slab should already be honed to 200 grit and densified. This step hardens the surface and preps it for a cleaner finish. Never densify after polishing — it won’t absorb. Vacuum all dust or clean slurry before moving forward. Inspect for remaining scratches, haze, or swirl — they’ll only become more visible from this point on.
Use 400 grit resin-bond pads designed for either wet or dry systems. Wet polishing will give slightly better clarity, while dry may be faster in large spaces. Attach pads evenly and match pad type to machine speed and downforce. Avoid aggressive hybrids — true resins give better clarity and refinement at this stage.
Work methodically in a crosshatch pattern — north to south, then east to west — overlapping each pass by at least 30%. Use slow forward speed and medium head pressure. You want a consistent matte sheen across the full slab. Keep pads clean and avoid stopping in one place — resin pads can heat and burn if held still.
Use a 400 grit flexible resin or burnishing pad around walls, pillars, and tight spots. Match the machine-polished look across the perimeter — mismatched edges are highly visible under raking light. Feather by hand at least 150mm into the main slab to blend the transition seamlessly.
Whether polishing wet or dry, remove all residue before inspecting the finish. Slurry can dull the appearance, and dry polish dust can mask problem areas. Use a clean wet vac or auto-scrubber for wet jobs. For dry work, vacuum fully and wipe with a microfiber pad to reveal true sheen.
After cleaning, inspect under low-angle light or overhead reflection. You should see a smooth, even finish with soft reflectivity — not gloss. Any visible swirls or hazing means 200 grit wasn’t fully removed. Re-run 400 if needed to correct those areas. Matte polish should feel tight and sealed, not dusty or rough.
If applying dye for colour, do it immediately after polishing. Apply with a sprayer and microfiber mop, following manufacturer guidelines. Let it dry, then polish lightly again with 400 grit to lock it in. This is your last chance to blend colour or correct light/dark patches. Dye applied too early or too late can result in uneven tone or lift.
For additional stain resistance or a tighter finish, apply a penetrating sealer or guard product after polishing. Use a pump sprayer and microfiber mop. Some contractors finish matte floors with a light burnish using a high-speed buffer and white pad to tighten the surface without adding gloss. Test on a small area first.
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