Natural Granite Slab – Technical Material Specification
Comprehensive technical specification for natural granite slabs used in Canadian countertop fabrication, monument work, and architectural cladding. Covers standard slab sizes, physical properties, tooling requirements, common defects, and handling guidelines for shop-floor accuracy.
Material Overview & Common Uses
Natural granite is an igneous rock composed primarily of quartz, feldspar, and mica, offering exceptional hardness, compressive strength, and aesthetic variety. In Canadian fabrication shops, granite slabs are the primary material for kitchen countertops, bathroom vanities, fireplace surrounds, and commercial reception desks. Due to its high density and low porosity, granite is also specified for exterior cladding, paving, and monument applications. Standard slab thicknesses are 2 cm (3/4 in) and 3 cm (1-1/4 in), with 3 cm preferred for countertops to eliminate the need for plywood underlayment. Common Canadian suppliers include Cosentino, Daltile, and local quarries in Quebec and Ontario. Granite is classified as a dimension stone and must meet ASTM C615/C615M standard specification for granite dimension stone.
Core Technical Properties & Sizing
| Property | Value |
|---|---|
| Density | 2.63 – 2.75 g/cm³ (164 – 172 lb/ft³) |
| Compressive Strength | 130 – 250 MPa (typical 180 MPa) |
| Modulus of Rupture | 10 – 20 MPa |
| Water Absorption | < 0.4% by weight (ASTM C97) |
| Abrasion Resistance | 25 – 40 Ha (hardness index per ASTM C241) |
| Flexural Strength | 8 – 15 MPa (ASTM C880) |
| Coefficient of Thermal Expansion | 4 – 8 × 10⁻⁶ /°C |
| Standard Slab Sizes (Canadian stock) | 120 in × 60 in (3050 mm × 1525 mm), 108 in × 54 in (2745 mm × 1370 mm), 96 in × 48 in (2440 mm × 1220 mm) |
| Thickness Tolerances | ±1.5 mm for 2 cm slabs, ±2.0 mm for 3 cm slabs (calibrated face) |
| Flatness Tolerance | ±1.0 mm over 1 m (ASTM C485) |
| Edge Profile | Typically eased or bullnose; full bullnose requires 3 cm thickness minimum |
| Finish Options | Polished (gloss >85 units), Honed (gloss 30–50 units), Flamed (textured), Leathered (low-sheen textured) |
Machinability, Tooling & Feeds
| Parameter | Recommendation |
|---|---|
| Spindle Speed (Sawing) | 3000 – 4500 RPM |
| Spindle Speed (Polishing) | 6000 – 8000 RPM |
| Feed Rate (Sawing) | 2 – 4 m/min (80 – 160 in/min) with water cooling at 15 – 25 L/min |
| Depth of Cut (CNC Router) | 0.5 – 2.0 mm per pass |
| Stepover (CNC Router) | 0.5 – 1.0 mm |
| Polishing Pad Grit Progression | 50 → 100 → 200 → 400 → 800 → 1500 → 3000; final buff with 3000 grit |
| Water Flow for Drilling | 10 – 15 L/min, feed pressure 20 – 40 N |
| Common Tooling Brands | Weha, Alpha, Diaplus |
| Safety | Full-face respirator and wet cutting to control silica dust (OSHA PEL 50 µg/m³) |
Granite is extremely abrasive and requires diamond tooling. CNC bridge saws and waterjet systems are standard. For edge profiling, use continuous rim diamond blades (grit 30/40 for roughing, 60/80 for finishing). Avoid overheating; maintain water flow to prevent thermal shock.
Common Defects & Quality Control
| Defect Type | Acceptance Criteria | Rejection Criteria |
|---|---|---|
| Fissures (hairline cracks) | Minor fissures not penetrating full thickness | Open fissures wider than 0.5 mm |
| Pits | Small pits up to 2 mm diameter, <5 per sq ft | Large pits >5 mm diameter |
| Cracks from edge | — | Cracks extending from edge >25 mm |
| Delamination or structural voids | — | Any delamination or void |
| Checking (fine surface cracks) | — | Visible thermal stress cracks |
| Flatness deviation | ≤1.5 mm over 1 m (straightedge/feeler gauge) | >1.5 mm over 1 m |
| Polished gloss | Minimum 85 gloss units (gloss meter) | <85 units |
| Honed finish | No scratch marks under raking light | Visible scratches |
| Iron oxidation (rust spots) | — | Any staining from iron |
| Resin fills | Small pits only, colour‑matched, no bubbles | Large resin patches >10 cm² or mismatched colour |
| Structural integrity (tap test) | Clear ring | Dull thud indicates delamination |
Natural granite exhibits inherent variability. Acceptable defects include minor fissures (hairline cracks not penetrating full thickness), small pits (up to 2 mm diameter, <5 per sq ft), and colour variation. Reject slabs with large resin patches (>10 cm²) or mismatched colour. Always inspect both faces and edges. Canadian standard: CSA A440.2 for window and door applications, but for countertops, follow NKBA guidelines.
Storage, Handling & Racking Guidelines
| Parameter | Guideline |
|---|---|
| Storage Orientation | Vertical in A‑frame racks |
| Rack Padded Support Bars | Rubber or felt, spaced at 600 mm (24 in) centres |
| Rack Angle | 10 – 15 degrees from vertical (prevents tipping) |
| Maximum Stack per Rack | 10 slabs for 2 cm, 6 slabs for 3 cm |
| Slab Separators | Cork or foam between slabs to prevent scratching |
| Flat Storage | Never store flat – risk of cracking from weight |
| Handling | Slab cart with suction cups (min 4 for 3 cm, 6 for 2 cm), rated for 150 kg each; two people or mechanical lift |
| Transport | Padded truck with vertical straps and edge protectors |
| Climate Control | 15 – 25°C, 40 – 60% RH; avoid temperature extremes |
| Outdoor Storage | Cover with breathable tarp to avoid moisture trapping |
| Receiving Inspection | Check for chips, cracks, water stains; use moisture meter (<0.5% acceptable) |
| Stock Rotation | FIFO to avoid colour variation from UV exposure |
| Personal Protective Equipment | Cut-resistant gloves and steel‑toed boots when handling |