Polished concrete is the slab itself, mechanically processed to a high-gloss finish through progressive diamond grinding and chemical densification. Unlike microcement (which adds 2–3 mm of cementitious topping) or resin coatings (which add a film), polished concrete is the existing slab made into a finished floor by removing material in controlled stages. The result is a finish that cannot peel — because there is no separate layer. Cost-competitive, durable, and authentic in a way no overlay can match. This article walks through the system, the grit progression, the densifier chemistry, and where polished concrete fits in IL specification.
What polished concrete actually is
The technique combines two operations: mechanical grinding/polishing and chemical densification. Diamond-tooled grinders cut progressively finer surfaces into the slab — from coarse 30-grit aggressive cutting through medium 100/200-grit to fine 800/1500/3000-grit polishing. Between coarser and finer steps, a chemical densifier (lithium silicate, sodium silicate, or potassium silicate) is applied. The densifier penetrates the open pore network created by grinding, reacts with calcium hydroxide in the cement matrix, and produces additional calcium silicate hydrate (the same compound that gives cured concrete its strength). The result: a harder, denser, less porous surface that responds to further polishing the way natural stone does.
The finished floor's appearance depends on (a) what's in the slab — aggregate exposure level reveals the concrete's interior; (b) how far the polishing goes — gloss level varies from satin at ~400-grit to high mirror at 3000-grit; (c) what colour additives or stains have been applied; (d) what surface treatments lock in the final character.
Aggregate exposure classes
Three standard exposure levels, controlled by how deep the first grinding cut goes:
| Class | Depth removed | Aggregate visibility | Use case |
|---|---|---|---|
| Cream / Class A | 1–2 mm | None — paste only | Smooth modern interior, retail entry, gallery |
| Salt-and-pepper / Class B | 3–5 mm | Fine aggregate visible (sand) | Most commercial floors — the default |
| Large aggregate / Class C | 5–8 mm+ | Coarse aggregate exposed | Industrial-aesthetic, terrazzo-effect, warehouse-retail |
The class is set in the spec by the architect and executed by the polishing contractor with progressive cuts. Skipping the deeper cut on a Class C spec produces a Class A appearance — a quality variance that the contractor cannot recover from once the next finer stages have begun.
The grit progression
Industrial polished concrete follows a defined grit sequence:
| Stage | Grit range | Bond type | Purpose |
|---|---|---|---|
| 1 | 16/30 grit (coarse) | Metal bond | Aggressive cutting, set exposure class |
| 2 | 30/40 grit (medium-coarse) | Metal bond | Refine cut, prepare for densifier |
| 3 | Densifier application | — | Penetrate open pores, react with Ca(OH)₂ |
| 4 | 40/60 grit (medium) | Resin bond starts | Smooth surface texture |
| 5 | 80/120 grit (fine) | Resin bond | Establish initial sheen |
| 6 | 200 grit | Resin bond | Satin level |
| 7 | 400 grit | Resin bond | Semi-gloss |
| 8 | 800 grit | Resin bond | Gloss |
| 9 | 1500 grit | Resin bond | High gloss |
| 10 | 3000 grit (optional) | Resin bond | Mirror polish (showroom-grade) |
Most commercial polished concrete stops at 800 or 1500 grit (gloss to high gloss). The 3000-grit mirror finish is reserved for showroom, gallery, museum, and high-end retail where the aesthetic is the design point. Each step skipped produces a visible quality reduction — and a polishing contractor cannot recover from skipping a step except by going back and re-running every step from there forward.
Densifier chemistry — three families
Lithium silicate
The premium densifier. Smallest molecule size, deepest penetration, lowest residue. Lithium does not crystallise like sodium, so produces fewer surface streaks. Most-cited reference: Prosoco Consolideck LS. Used on commercial premium and high-design polished concrete. Higher per-litre cost than sodium silicate, justified by visible finish quality.
Sodium silicate
The traditional densifier. Larger molecule, shallower penetration but more cost-effective. Tends to crystallise on the surface in unfavourable humidity producing whitish residue ("polishing haze") that must be wet-polished off in subsequent steps. Sodium silicate dominates entry-tier polished concrete. The IL-installer convention.
Potassium silicate
The compromise. Smaller than sodium, larger than lithium. Penetrates well, less haze risk than sodium, lower cost than lithium. Specified on projects where lithium is over-budget but sodium's quality variance is unacceptable.
Sealers and surface treatments
Polished concrete after densification has hardened, polished, low-porosity concrete as the visible surface. Some projects stop there; others apply a topical sealer to enhance stain resistance, lower the risk of marks, and add additional UV protection. The sealer choice:
- Lithium-silicate-only finish: No topical sealer. Lowest maintenance, lowest sheen, most authentic appearance. Resistant to most household stains. Good for commercial floors with daily cleaning routines.
- Penetrating siloxane sealer: Invisible film inside the surface pores. Improves water-, oil-, and acid-resistance without changing appearance. Used in food service, retail, hospitality.
- Topical acrylic or epoxy sealer: Visible film on top. Adds gloss and stain resistance but reduces authenticity. Used in industrial polished concrete where chemical resistance dominates over aesthetics.
Where polished concrete wins
- Existing concrete is sound. When the slab is in good condition (low crack count, adequate strength, stable substrate), polished concrete uses what is already there. No new material added; no separate layer to fail.
- Cost competitiveness. For large-area commercial polished concrete (above 200 m²), the technique is typically 30–50% of the cost of equivalent microcement or premium tile. The cost goes down per-m² with area as fixed machine-setup amortises across the project.
- Authenticity reads in the design vocabulary. Polished concrete is unmistakably concrete. For modernist, industrial-loft, gallery, museum, and tech-office design language, the finish is the design intent.
- Underfloor heating compatibility. The slab itself is the heating mass; no overlay reduces thermal transfer. Polished concrete is the optimal finish over hydronic underfloor systems.
- Service life. Properly polished and densified concrete lasts the life of the slab itself — 30–50+ years with minimal maintenance.
Where polished concrete loses
- Existing concrete is degraded. Cracks beyond 1 mm, hollow areas, prior contamination — polished concrete reveals all of these. Microcement or resin coatings hide what polished concrete exposes.
- Small-area residential bathrooms and kitchens. Polished concrete is large-area economics. A single bathroom or kitchen does not amortise the polishing-machine setup — microcement or tile becomes cost-competitive at this scale.
- Decorative pigment range needed. Polished concrete colour is the colour of the existing slab (typically grey). Coloured polished concrete is achievable via integral-cast pigments or post-polishing stains, but the palette is constrained compared to microcement or tile.
- Thermal isolation is required. Polished concrete has high thermal mass — useful for stable temperatures, problematic when the room needs quick warm-up cycles.
- Wet wet-room conditions. Polished concrete in showers requires careful slip-class specification and densifier choice. Default to microcement or tile for daily-wet residential bathroom work.
IL specification realities
For IL polished-concrete projects:
- Substrate inspection is mandatory. Before specifying polished concrete, audit the slab: crack mapping, sounding for hollow areas, moisture testing. See substrate repair guide.
- Slab strength must be adequate. Polished concrete reveals weak surfaces. The slab compressive strength should be ≥ 28 MPa (typical Israeli residential and commercial slabs meet this). Below this, polished concrete is risky.
- Cost ₪/m² installed [verify]: ₪200–₪400 for large-area commercial (1000+ m²). ₪350–₪700 for residential and small commercial. Premium showroom-grade 3000-grit finish: ₪500–₪1000.
- Service window: 5–10 days for a 200 m² floor depending on grit target and densifier curing schedule. Faster than microcement, slower than tile or LVT.
- Maintenance: Re-polishing (light cut + new densifier) every 7–12 years for high-traffic commercial. Residential rarely needs repolishing.
Polished concrete vs microcement — the recurring question
The most common decision question IL specifiers ask:
- Existing slab in good condition + large area → polished concrete. Cheaper, more authentic, longer-lived.
- Existing slab is uneven, cracked, or contaminated + need to hide it → microcement. Overlay covers what polished concrete would reveal.
- Bathroom or wet zone → microcement (or tile). Polished concrete in wet rooms is possible but not the default; microcement's tanking + sealer build-up is purpose-built for it.
- Small area (under 50 m²) → microcement or tile. Polished concrete economics need scale.
- Coloured / decorative requirement → microcement (or stained polished concrete). Microcement palette is wider; stained polished concrete is the niche compromise.
- Modernist aesthetic + authentic concrete reading → polished concrete. Microcement reads as decorative concrete; polished concrete IS concrete.
Final read
Polished concrete is the right specification when the existing slab is sound, the area is large enough to amortise the polishing machinery, and the design vocabulary calls for authentic concrete. It is the wrong specification for small bathrooms, degraded slabs, or design briefs that demand wide colour palettes. The technique is mature, well-documented, and IL applicator pool is adequate at commercial scale. Read this article alongside the microcement binder chemistry and microcement vs tile vs LVT articles to position polished concrete in the broader finish-selection landscape.
Related: Microcement vs tile vs LVT comparison · Substrate repair guide · ICRI CSP profile guide · Microcement binder chemistry (comparison).
Sources
- ACI 310.1R — Guide for Specifying, Designing, and Installing Polished Concrete.
- Concrete Polishing Council (CPC) — Industry standards documentation.
- Prosoco Consolideck LS lithium silicate densifier
- Concrete Decor Magazine — polished concrete technique articles.
- Husqvarna PG-series polished concrete grinders (planetary head, dust extraction).