Whether you’re after a subtle salt & pepper look or a bold, full-stone polish, achieving the right aggregate exposure during grinding is all about precision. Too light, and it stays dull. Too deep, and you risk uneven stone or blowouts. This guide explains how to grind concrete to the correct depth and pattern for the finish you want — and how to avoid the most common exposure mistakes.
Exposure depends on how the concrete was poured and finished. Hard-troweled slabs may have less exposed fines for salt & pepper, while soft-finished slabs may reveal sand too easily. Full exposure is easiest on thicker pours with rich stone mix. Always test a small grind area to understand how deep you’ll need to go and whether the aggregate is consistent.
To expose fines without hitting large stone, use a 100 grit metal bond on a medium- to soft-bond plate. This shallow grind reveals just the sand and fines from the trowel zone. Watch closely — you only need to kiss the surface. Going too deep removes the salt & pepper entirely and jumps to medium stone. Use multiple light passes instead of one deep cut.
To expose full aggregate, use 30 or 50 grit metal bond segments and increase head pressure. Make multiple crosshatch passes to evenly remove the paste and reach stone depth. Most slabs require removing 1.5–3mm to hit full stone. Softer slabs may show stone faster — monitor depth carefully to avoid uneven patterns.
Whether going light or deep, consistency matters. Use full-width, overlapping passes in both directions. Mark where each section finishes and avoid “haloing” from inconsistent contact. If your machine rides too fast or the slab undulates, you’ll get a patchy exposure that’s hard to fix later.
Use a handheld grinder with matching metal bonds to cut edges, corners, and columns. Match the depth of the main grinder and feather at least 150–200mm into the main grind field. Unmatched edge exposure is the first thing clients spot — especially in polished commercial settings.
Before jumping to 100 grit (or resin pads), vacuum and visually inspect your exposure. For salt & pepper, you should see consistent sand/stone speckle with no blotches. For full aggregate, you want 70–90% of the surface showing uniform stone without sharp edges or pits. Re-grind any weak sections before densifying or refining.
Once the correct exposure is achieved, apply a lithium or sodium densifier. This hardens the open pores and locks in the finish before resin polishing. Applying densifier too early (before exposure) wastes product, and applying it too late lets the slab dust during refinement.
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