| Material | Advantages vs. Sandstone | Disadvantages vs. Sandstone | |----------|--------------------------|-------------------------------| | Cast stone | Uniform properties, lower cost, no bedding-plane weakness | Artificial appearance, higher thermal movement, less repairable | | Limestone | Easier to cut, consistent color | Lower acid resistance, often weaker in thin sections | | Granite | Extremely durable, zero porosity | High cost, difficult to carve, very dark color absorbs heat | | Precast concrete | Any shape/color, reinforced possible | Cracking from steel corrosion, efflorescence, carbonation | | Fiber-cement | Lightweight, low maintenance | Lacks mass, feels hollow, limited historic authenticity |

| Failure Mode | Visual Indication | Primary Cause | |--------------|-------------------|----------------| | Laminar spalling | Detachment of thin sheets parallel to bedding | Expansion from iron pyrite oxidation (rust bursting) | | Edge crumbling | Rounded, granular loss on front edge and drip groove | Freeze-thaw + salt action | | Mid-span cracking | Vertical or diagonal hairline crack | Overload or insufficient bearing (lack of support beneath) | | Under-side bowing | Downward sag visible from below, often with tensile cracks | Long-term creep under sustained load + wetting/drying cycles | When specifying a window sill, sandstone competes with several substitutes: