4 Keys To Stone Selection

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Fitness for Purpose is fundamental to the successful use of stone, but how do we evaluate a stone to ensure its suitability for a particular use or location? In this article we will discuss four basic keys to assist in the selection and specification of the right stone for the job. The keys are relevant to all stone users and specifiers, and they provide a useful starting point for choosing the right stone.

The four keys are:
 Stain Resistance
 Strength
 Resistance to Abrasion
 Durability

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4 Keys To Stone Selection

  1. 1. 4 Basic Keys to Successful Stone Selection Jim Mann Stone Consultant www.stonemtg.com.au
  2. 2. Four main performance criteria: <ul><li>Stain Resistance </li></ul><ul><li>Strength </li></ul><ul><li>Resistance to Abrasion </li></ul><ul><li>Durability </li></ul>
  3. 3. Stain Resistance <ul><li>Three main factors determining stain resistance… </li></ul>Water absorption Composition Appearance
  4. 4. Stain Resistance A stone’s ability to absorb stains is directly related to its water absorption. C629 C568 C616 C503 C615 ASTM Spec. 0.45 12 (LD) 7.5 (MD) 3.0 (HD) 8 (S) 3 (QS) 0.20 0.40 Standard Requirement 6 – 0.3 Slate 26 – 0.08 Limestone 12 – 0.3 Sandstone 0.8 – 0.04 Marble 0.8 – 0.01 Granite Water Absorption Typical Range (weight %) Stone Type
  5. 5. Stain Resistance <ul><li>Composition </li></ul><ul><li>Stone containing acid sensitive minerals are subject to etching from substances such as wine, fruit juices, soft drinks, urea and even sweaty palms. </li></ul>
  6. 6. Stain Resistance Note: Impregnating sealers are not effective in protecting acid-sensitive materials from etching Limestone and calcite marbles are particularly sensitive to acid attack and etching. Be wary of using polished marble in entertaining areas!
  7. 7. Stain Resistance <ul><li>Appearance </li></ul><ul><li>The general appearance of the stone can affect the “apparent” stain resistance by hiding the stain. </li></ul>
  8. 8. Stain Resistance Spot the chewing gum!
  9. 9. Strength Stone installations must have adequate strength to withstand both live and static loads that may be encountered in service.
  10. 10. Compressive Strength Unconfined Compressive Strength – ASTM C170
  11. 11. Compressive Strength Compressive strength results can be useful for comparing likely performance of different stones. - C629 200 - 25 Slate 12 (LD) 28 (MD) 55 (HD) C568 150 - 4 Limestone 27.6 (S) 68.9 (QS) C616 120 -10 Sandstone 52 C503 150 – 80 Marble 131 C615 300 – 100 Granite Standard Requirement ASTM Spec. Typical Compressive Strength (MPa) Stone Type
  12. 12. Measuring Flexural Strength Flexural strength ASTM C880 – 4 point loading Modulus of Rupture – 3 point loading
  13. 13. Flexural Strength Adequate flexural strength is essential for satisfactory performance of stone used for paving or ‘dynamic’ wall cladding 49.6 (MoR) C629 50 - 15 Slate 2.9 (LD) - MoR 3.4 (MD) - MoR 6.9 (HD) - MoR C568 21 – 2 Limestone 2.4 (S) – MoR 6.9 (QS) - MoR C616 15 – 3 Sandstone 7 C503 22 – 6 Marble 8.3 C615 30 – 6 Granite Standard Requirement ASTM Spec. Typical Flexural Strength (MPa) Stone Type
  14. 14. Flexural failure of paving under load
  15. 15. Flexural Strength <ul><li>Breaking Load of Segmental Pavers (AS/NZS4456.5) </li></ul><ul><li>BL=(St x 2 x B x D 2 )/( 3 x L) </li></ul>Example 1: Paving unit 600 x 400 x 20mm thick, modulus of rupture 7 MPa - theoretical breaking load 1.4 kN (139kg) Example 3: Paving unit 600 x 400 x 40mm thick, modulus of rupture 7 MPa - theoretical breaking load 5.6 kN (555kg) Example 2: Paving unit 600 x 400 x 20mm thick, modulus of rupture 14 MPa - theoretical breaking load 2.7 kN (275 kg) Recommendation (AS/NZS 4455) – minimum breaking load of 2 kN for residential pedestrian traffic and 5kN for residential vehicular traffic.
  16. 16. Resistance to Abrasion ASTM C1353 “Standard Test Method for Determining Abrasion Resistance of Dimension Stone
  17. 17. Resistance to Abrasion Typical Values – higher numbers indicate greater wear resistance 8 C629 4 - 20 Slate 10 C568 <1 – 20 Limestone 2(S) 8 (QS) C616 4 – 24 Sandstone 10 C503 15 – 50 Marble 25 C615 50 – 150 Granite Standard Requirement ASTM Spec. Typical Abrasion Index (Ha) Stone Type
  18. 18. Resistance to Abrasion <ul><li>Guideline for determining suitability for specific locations </li></ul>Suitable for all uses including high traffic prestige commercial flooring. >25 Suitable for general commercial and domestic applications. 12-25 Suitable only for light commercial or domestic flooring. 8-12 Suitable only for domestic or light external traffic situations. < 8 Appropriate Uses Abrasion Index
  19. 19. Resistance to Abrasion <ul><li>When evaluating the suitability of the Resistance to Abrasion Index consider… </li></ul><ul><li>Surface finish – loss of polish, tracking </li></ul><ul><li>High traffic areas – bottle necks at entrances </li></ul><ul><li>Tracking of particulates – dirt, loose sand grains </li></ul><ul><li>Change in Index across adjacent surfaces – lipping, trip hazards </li></ul>
  20. 20. Durability <ul><li>Resistance to Deterioration due to: </li></ul><ul><li>Freeze – Thaw Cycling </li></ul><ul><li>Dimensional Instability </li></ul><ul><li>Resistance to Salt Attack </li></ul>
  21. 21. Durability – Resistance to Salt Attack <ul><li>AS/NZS 4456.10 Method A - Determination of weight loss following repeated exposure to a salt solution. </li></ul><ul><li>Wetting and drying of samples also tests the stone’s dimensional stability. </li></ul><ul><li>Also gives a basic indication of the stone’s freeze-thaw durability. </li></ul>
  22. 22. Durability <ul><li>Durability is a complex criteria determined by inherent strength and pore space. </li></ul>
  23. 23. A higher compressive strength can mitigate the forces applied on the stone by crystallisation of salts. <ul><li>Compressive Strength </li></ul><ul><li>Pore Size </li></ul>A larger pore size can assist with durability by reducing the pressure applied by salt crystallisation on the walls of pore spaces. Durability <ul><li>Water Absorption </li></ul>A lower water absorption generally correlates to a greater durability, but…
  24. 24. Durability Suitable only for use in sheltered locations free from exposure to salt attack. Additional engineering practices may be required to protect stone. D > 10 Exposed to infrequent wetting and drying or low level salt attack C 6 – 10 Exposed to intermittent wetting and drying or moderate level salt attack B 1- 5 Exposed to continual wetting and drying or moderate salt attack A 0.1 – 1 Aggressive environments, constant wetting and drying and exposure to salt attack AA < 0.1 Environment Suitability Grade Weight Loss (%)
  25. 25. Test methods for determining performance: <ul><li>Stain Resistance – AS4459:14 </li></ul><ul><li>Strength – ASTM C170 / C880 / C99 </li></ul><ul><li>Resistance to Abrasion – ASTM C1353 </li></ul><ul><li>Durability – AS/NZS 4456.10 Method A </li></ul><ul><li>Water Absorption – ASTM C97 </li></ul>
  26. 26. Choose stone that’s “fit for purpose” Jim Mann Stone Consultant www.stonemtg.com.au

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