# Building Stone Selection
Natural stone is among the most durable, prestigious, and environmentally responsible building materials available — buildings constructed in stone routinely survive for centuries. For the practicing architect, stone selection requires balancing aesthetic aspiration with technical performance: durability in the intended exposure, structural adequacy, dimensional stability, compatibility with adjacent materials, and increasingly, embodied carbon and ethical sourcing considerations.
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## Table of Contents
- [Stone Types](#stone-types)
- [Properties and Testing](#properties-and-testing)
- [Selection Criteria](#selection-criteria)
- [Stone Finishes](#stone-finishes)
- [Stone Fixing Systems](#stone-fixing-systems)
- [Detailing Principles](#detailing-principles)
- [Sustainability](#sustainability)
- [See Also](#see-also)
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## Stone Types
| Type | Formation | Characteristics | Common Building Stones |
|------|-----------|----------------|----------------------|
| **Granite** | Igneous (crystallised from magma) | Very hard; durable; resistant to pollution; wide colour range | Aberdeen granite; Cornish granite; Rajasthan granite |
| **Limestone** | Sedimentary (marine deposits) | Moderate hardness; warm tones; weathers beautifully; soluble in acid rain | Portland stone; Bath stone; Jaisalmer stone; Clipsham |
| **Sandstone** | Sedimentary (cemented sand grains) | Variable durability; warm earthy tones; bedding planes | Yorkshire stone; Darley Dale; Red Agra sandstone |
| **Marble** | Metamorphic (recrystallised limestone) | Polishable; luxury; acid-sensitive; stains | Carrara; Makrana; Statuario; Pentelikon |
| **Slate** | Metamorphic (compressed mudstone) | Fissile; impervious; excellent roofing/cladding | Welsh slate; Cumbrian; Burlington |
| **Basalt** | Igneous (volcanic) | Very hard; dark; durable; difficult to work | Indian basalt; Italian basalt |
| **Travertine** | Sedimentary (precipitated limestone) | Porous; warm; characteristic voids | Italian travertine; Turkish travertine |
| **Quartzite** | Metamorphic (recrystallised sandstone) | Extremely hard; weather-resistant | Indian quartzite; Norwegian quartzite |
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## Properties and Testing
| Property | Test Standard | Significance |
|----------|-------------|-------------|
| **Compressive strength** | BS EN 1926 | Structural capacity; typically 30-250 MPa |
| **Flexural strength** | BS EN 12372 | Cladding panel design; wind loading |
| **Water absorption** | BS EN 13755 | Frost resistance; staining susceptibility |
| **Bulk density** | BS EN 1936 | Self-weight calculation; 2,000-2,800 kg/m³ |
| **Frost resistance** | BS EN 12371 | Suitability for external use in freeze-thaw climates |
| **Salt crystallisation** | BS EN 12370 | Resistance to salt weathering (coastal, de-icing) |
| **Abrasion resistance** | BS EN 14157 | Floor and paving applications |
| **Petrographic analysis** | BS EN 12407 | Mineral composition; potential durability issues |
| Stone Type | Compressive Strength (MPa) | Water Absorption (%) | Density (kg/m³) |
|-----------|--------------------------|---------------------|-----------------|
| Granite | 100-250 | 0.1-1.0 | 2,600-2,800 |
| Limestone (Portland) | 20-60 | 4-12 | 2,000-2,400 |
| Sandstone | 20-150 | 1-15 | 2,000-2,500 |
| Marble | 50-150 | 0.1-2.0 | 2,500-2,800 |
| Slate | 100-200 | 0.1-1.5 | 2,700-2,900 |
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## Selection Criteria
| Criterion | Key Consideration |
|-----------|------------------|
| **Durability** | Match stone durability to exposure — highly exposed positions require the most durable stone |
| **Compatibility** | Adjacent stones and mortars must be chemically compatible; avoid iron-bearing stones next to limestone |
| **Bedding orientation** | Sedimentary stones must be laid on their natural bed (horizontal) for walls; edge-bedded for copings and sills |
| **Colour consistency** | Natural stone varies; specify colour range from sample panels; agree acceptance criteria |
| **Availability** | Confirm quarry supply for project duration; visit quarry before specifying |
| **Replacement** | Consider future repair — specify stones that remain available |
| **Mortar compatibility** | Use lime mortar (not cement) with soft stones — see [[Heritage Conservation Principles]] |
| **Pollution resistance** | Limestone is attacked by acid rain (sulphation); granite resists |
| **Ethical sourcing** | Child labour risks in some quarrying regions; specify ETI-audited supply chains |
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## Stone Finishes
| Finish | Process | Texture | Application |
|--------|---------|---------|------------|
| **Sawn** | Diamond saw cut | Smooth; matt; saw marks visible | Cladding; paving (non-slip when wet) |
| **Honed** | Progressively finer abrasives; sub-polish | Smooth; eggshell sheen | Interior floors; cladding; countertops |
| **Polished** | Full mirror finish | Reflective; reveals full colour | Interior walls; floors (slippery when wet) |
| **Flamed/thermal** | High-temperature flame spalls surface | Rough; textured; slip-resistant | Paving; external cladding |
| **Bush-hammered** | Pneumatic point tool | Uniformly rough | External cladding; paving |
| **Split-face** | Cleaved along natural plane | Rough; natural; irregular | Feature walls; rusticated base courses |
| **Sandblasted** | Abrasive grit blast | Matt; uniform texture | Cladding; signage; restoration |
| **Tooled (chisel)** | Hand or pneumatic chisel | Parallel grooves; traditional | Heritage; restoration; bespoke |
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## Stone Fixing Systems
### Cladding Fixings
| System | Description | Typical Thickness |
|--------|------------|------------------|
| **Mechanical cramp and dowel** | Stainless steel restraint fixings into stone edges | 40-50mm stone |
| **Kerf clip** | Continuous kerf groove in stone edge; clip engages | 30-40mm stone |
| **Undercut anchor** | Drilled and undercut hole in stone back face; anchor bolt | 30-50mm stone |
| **Adhesive fix** | Structural adhesive to carrier frame or substrate | 20-30mm stone |
| **Rainscreen bracket** | Stone panel on aluminium carrier system with ventilated cavity | 30-50mm stone |
**All structural fixings** for stone cladding must be stainless steel (austenitic grade 316 minimum for external use) to prevent corrosion and staining.
### Design Loads
| Load | Assessment |
|------|-----------|
| Self-weight | Stone density × thickness × panel area |
| Wind load | Per BS EN 1991-1-4; zone pressure on facade |
| Thermal movement | Coefficient × temperature range × panel dimension |
| Seismic | Where applicable; per local seismic code |
| Impact | Ground floor: consider vehicle and pedestrian impact |
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## Detailing Principles
| Detail | Principle |
|--------|----------|
| **Joints** | Open joints (10-15mm) with backer rod and sealant; or pointed mortar joints (8-12mm) |
| **Weathering** | Slope all horizontal surfaces (copings, sills, string courses) minimum 1:40 outward |
| **Drip grooves** | Continuous drip groove on underside of all projecting elements; minimum 15mm from edge |
| **DPC** | Physical DPC beneath copings, sills, and at base of stone walls |
| **Movement joints** | At maximum 6m centres (limestone/sandstone); 12m (granite); at all structural movement joints |
| **Mortar** | Lime mortar for natural stone (NHL 3.5 or NHL 5); never ordinary Portland cement (too hard, cracks stone) |
| **Staining prevention** | Avoid contact with iron, copper, or dissimilar metals; use non-staining fixings |
| **Cleaning** | Specify cleaning method in maintenance manual; avoid acid cleaning on limestone/marble |
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## Sustainability
| Metric | Stone vs Alternatives |
|--------|---------------------|
| **Embodied carbon** | 0.06-0.12 kgCO₂e/kg (quarrying + cutting); low compared to manufactured materials |
| **Design life** | 100-500+ years (far exceeds most alternatives) |
| **Maintenance** | Minimal if correctly specified and detailed |
| **Recyclability** | 100% reusable; historically, stone is salvaged and re-dressed |
| **Local sourcing** | UK and European quarries reduce transport impact; specify local stone where possible |
| **Waste** | Offcuts used for aggregate, walling, or landscaping |
When assessed on a whole-life carbon basis (embodied carbon amortised over design life), natural stone is among the lowest-carbon cladding materials available.
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## See Also
- [[Architectural Detailing Principles]]
- [[Heritage Conservation Principles]]
- [[Concrete Properties and Mix Design]]
- [[Structural Steel Properties]]
- [[Waterproofing Systems and Details]]
- [[Material Weight Tables]]
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#materials #stone #cladding #durability #heritage #detailing