Indiana Limestone Specifications: The Architect’s Quick Reference

You’re writing a stone specification. You need the data now, not after reading 40 pages of the ILI handbook.

This is the reference sheet architects and engineers keep on file — colors, grades, finishes, physical properties, ASTM standards, and ordering nomenclature condensed into one page.

Everything you need to specify Indiana limestone correctly.

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Colors

Indiana limestone is available in two natural colors determined by mineral content at formation. Color is consistent throughout the stone depth.

Buff: Light tan to cream color with warm undertones. Contains minor iron oxide content. Most widely specified color. Approximately 75% of quarried stone is buff.

Gray: Light to medium gray with cool undertones. Contains carbon and other mineral traces. Less common than buff. Approximately 25% of quarried stone is gray.

Both colors weather to develop natural patina over decades of exposure. Buff limestone typically darkens slightly while gray limestone may lighten in certain atmospheric conditions.

Color variation within grades: All grades exhibit some natural color variation. Select grade shows minimal variation. Variegated grade intentionally includes contrasting color zones within individual pieces.

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Grades

Grading classifies stone by appearance characteristics — primarily the size and distribution of shells, fossil fragments, and natural markings. All grades meet the same structural performance requirements.

Select Grade (discontinued): Historically specified for uniform color with minimal shells or fossils. This grade classification is no longer produced. Projects specifying “Select” grade receive Standard grade material with appropriate sampling.

Standard Grade: Uniform texture with occasional small shells and fossil fragments. Grain size up to 1/8 inch. Most commonly specified grade. Balances appearance uniformity with cost effectiveness.

Rustic Grade: More pronounced texture variation with visible shells, fossil fragments, and natural markings. Grain size up to 3/8 inch. Specified for applications where character and natural appearance are desired over uniformity.

Variegated Grade: Intentional color variation within and between pieces. May include contrasting buff and gray zones, pronounced fossils, and distinctive natural markings. Each piece is unique. Specified for applications emphasizing natural variation.

Grade selection affects appearance, not structural performance. A Rustic grade panel has the same compressive strength and absorption characteristics as a Select grade panel of equivalent density.

The grading system exists to give architects choice in appearance, not to indicate quality differences. All grades perform identically in structural applications.

— Indiana Limestone Institute technical manual

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Standard Finishes

Surface finish affects appearance, shadow lines, slip resistance, and maintenance requirements. Finishes are applied after fabrication.

Smooth (Planer) Finish: Planed surface with minimal texture. Shows natural color most clearly. The standard finish. Clean, even surface suitable for interior and exterior applications.

Honed Finish: Polished to a smooth, matte sheen. Elegant and refined. Shows minimal fingerprints or water spots. Common for countertops, flooring, and interior walls.

Split Face (Rock Face) Finish: Stone split along natural bedding planes. Natural finish that looks as if still attached to the rock it came from. Rough, textured surface. Excellent for exterior applications and building facades. Can only be applied to bed surfaces, not fabricated edges.

Chat Sawn Finish: Slightly textured, granular surface from gang sawing process. Perfect for every application from high-end residential exteriors to backyard hardscapes.

Bush Hammered Finish: Dimpled, rough texture created by mechanical pounding. Hand-applied finish that provides an extremely rough texture. Excellent for slip resistance in paving and stair treads.

Broached/Grooved Finish: Parallel grooves cut into the face. Machine-applied style that allows variety in finishes implementing uniform designs. Provides depth and variety not seen in other finishes. These textures create shadows and visual depth that flat panels cannot replicate.

Machine Tooled Finish: Parallel tool marks create linear texture. Depth typically 1/32 to 1/16 inch. This “vintage” style has been a cornerstone of limestone work for centuries. Provides shadow lines and hides minor fabrication marks.

We developed broached and grooved finishes — like a tweed suit rather than a serge suit. The purpose was to create textures that concrete molds can’t duplicate.

— Fred Barrett, President, Matthews Brothers Inc., 1977

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Physical Properties

Indiana limestone is classified under ASTM C568 Standard Specification for Limestone Dimension Stone as Category II (Medium Density).

ASTM C568 Category II (Medium Density) Requirements:

• Density: Greater than 135 lb/ft³ and not greater than 160 lb/ft³ (2,160-2,560 kg/m³)
• Compressive strength minimum: 4,000 psi (28 MPa)
• Absorption by weight maximum: 7.5%
• Modulus of rupture minimum: 500 psi (3.4 MPa)
• Abrasion resistance minimum: 10 (Ha scale per ASTM C241/C1353)

Typical Indiana Limestone Properties:

• Density range: 135-155 lb/ft³ (typical for Indiana limestone within Category II)
• Compressive strength: Exceeds 4,000 psi minimum requirement
• Absorption: Well below 7.5% maximum
• Thermal coefficient of expansion: 4.4 x 10⁻⁶ per °F
• Freeze-thaw resistance: Passes ASTM C666 testing

Note on ASTM Classifications: ASTM C568 defines three density categories (I-Low, II-Medium, III-High) for all limestone dimension stone. Indiana limestone falls exclusively within Category II (Medium Density). Lower and higher density limestones exist from other geological formations, but are not Indiana limestone.

Indiana Limestone is classified as a Type II Dimension Limestone under ASTM C-568, and meets or exceeds the strength requirements set forth in this classification.

— Indiana Limestone Institute Handbook

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Standard Dimensions and Thicknesses

Indiana limestone is available in custom sizes limited only by quarry block dimensions and fabrication equipment capacity. Standard thicknesses simplify sawing and reduce lead time.

Standard Thicknesses:

• 2 inches (51 mm) — typical for thin veneer applications
• 3 inches (76 mm) — common for residential and light commercial
• 4 inches (102 mm) — standard for commercial cladding
• 5 inches (127 mm) — heavy commercial and institutional
• Custom thicknesses available in 1/2-inch increments

Typical Panel Sizes:

• Height: 2 feet to 10 feet (taller panels possible with structural considerations)
• Width: 2 feet to 5 feet (wider panels require special handling)
• Maximum practical panel size: approximately 50 square feet depending on thickness

Ashlar Patterns: Random ashlar, coursed ashlar, and dimensional ashlar available in various height combinations. Standard heights include 2-1/4″, 5″, 7-3/4″, 10-1/2″, 13-1/4″, and 16″.

Custom Shapes: Curved panels, radiused corners, column covers, window surrounds, and specialty pieces fabricated per shop drawings. Size limitations based on quarry block dimensions and fabrication equipment.

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How to Write the Specification

Complete stone specifications include material, color, grade, finish, dimensions, and reference standards. Use this format:

Alternative shorter format:

Key specification considerations:

• Specify ASTM C568 Category II to reference industry standards
• Identify both color and grade — they are independent variables
• Note finish on all exposed surfaces (beds, joints, backs may differ)
• Reference approved shop drawings for dimensions and layout
• Include installation method (mechanically anchored, mortar set, etc.)

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Ordering and Lead Time

Information required for accurate quotations:

• Total square footage or lineal footage of stone required
• Color, grade, and finish specifications
• Thickness and panel dimensions
• Any special details (carved work, custom profiles, radius work)
• Project location for freight calculations
• Required delivery date

Typical lead times:

• Shop drawings: 2-3 weeks from contract execution
• Simple ashlar with standard finishes: 6-8 weeks from approved drawings
• Complex fabrication or carved work: 10-14 weeks from approved drawings
• Large commercial projects: 12-16 weeks from approved drawings

Lead times extend during peak construction season (spring and summer) and for projects requiring specific color or grade matching. Early material commitment reduces schedule risk.