Quick Answer

Polishing exposed aggregate is not the same as polishing a sealed concrete slab. The aggregate must first be flattened with metal-bond diamond grinding (30–60 grit), then bridged with a copper-bond hybrid pad (100–300 grit), and only then finished with resin pads at 500–3000 grit. Skipping the transitional step is the main reason aggregate pops out and the floor never glosses evenly.

Why Exposed Aggregate Is Different

Exposed aggregate mixes have large stone chips sitting just under the paste surface. Those chips are harder (quartz, granite, river rock) than the surrounding cement matrix, so a normal resin pad loads on the soft paste and leaves the high stones untouched. The result is a dull, textured floor with loose aggregate. You need a sequence that grinds the stones down to the same plane as the paste, then refines the scratches left by that grinding.

Equipment You Need

• A planetary grinder, 450–700 mm working width, 3–10 HP.
• Metal-bond diamond grinding discs at 30, 60, and 120 grit (soft bond for hard aggregate, hard bond for soft).
• Hybrid or ceramic transitional pads, 100–400 grit, such as the JOY-RFP-T1 ceramic-bond pads.
• Resin polishing pads at 500, 800, 1500, and 3000 grit (JOY-RFP-01).
• Industrial HEPA vacuum or wet polishing rig.

Step-by-Step Grit Sequence

1. 30 grit metal: open the paste, flatten the high stones. Run until every stone is at the same plane as the matrix.
2. 60 grit metal: remove the 30-grit scratches. This step takes the longest; do not rush it.
3. 120 grit metal or hybrid: refine, and begin closing the surface.
4. 100–200 hybrid / ceramic transitional: bridge the gap between grinding and resin. This is where the floor starts to reflect.
5. 400 resin: first true polish. The floor will look "wet".
6. 800, 1500, 3000 resin: build gloss. Skip one and the floor will look hazy.
7. Burnishing: a burnishing pad at high speed brings the final mirror shine.

Common Mistakes

• Jumping from metal to resin: resin cannot cut metal-grit scratches; the floor stays dull.
• Under-grinding the stones: high stones catch the light and read as "holes" once polished.
• Wet polishing too early: water on a 30-grit floor hides scratches; you cannot see what you are doing.
• Using too soft a bond on hard aggregate: the pad glazes in minutes and stops cutting.
• No dust extraction: loose aggregate dust loads every pad you fit next.

Sealing and Maintenance

Polished exposed aggregate is porous between the stones. Two coats of penetrating sealer (acrylic or lithium silicate) are recommended, followed by a dry buff. Re-burnish once or twice a year; do not wet-mop with alkaline cleaners, which dull the gloss over time.

Frequently Asked Questions

Q: Can I polish already-sealed exposed aggregate?

A: Yes, but strip the sealer first. Resin pads glaze instantly on cured sealer.

Q: How long does a 100 m² floor take?

A: A 2-person crew on a 5-head grinder typically takes 3–5 working days from 30 grit to final burnish.

Q: Can I do it with a single-head angle grinder?

A: Small repair patches, yes. A whole floor will show swirl marks and uneven gloss. Use a planetary grinder.

Q: What about pop-outs and loose stones?

A: Knock out loose stones before starting, fill the voids with epoxy mortar, and let them cure 48 hours. Grinding over a pop-out opens a bigger hole.

Conclusion

Exposed aggregate polishing rewards patience: flatten the stones at metal grit, bridge with hybrid pads, and only then let resin do the gloss. If you need a full pad set sized to your aggregate hardness, contact JOY TECH — we supply contractors with matched metal, hybrid, and resin sequences.