# Natural Stone Cladding — Granite, Sandstone, Marble

> Natural stone cladding is dimension stone, such as granite, sandstone, limestone, marble or slate, cut into slabs and hung on a facade with stainless steel anchors in a drained, ventilated cavity. Slab thickness and anchor design follow from tests on the supplied stone batch, because strength varies between quarries and even between blocks.

## What it is

**Dimension stone** — granite, sandstone, limestone, marble or slate — cut into
slabs and hung on a facade with stainless steel anchors in a drained,
ventilated cavity.

Indian projects have exceptional access to domestic granite and sandstone,
which is why stone remains commercially viable here at scales that would be
prohibitive elsewhere.

## Specification at a glance

| Property | Typical specification |
| --- | --- |
| Stone | Identified to IS 1123, named quarry and batch |
| Thickness | 25mm — 40mm typical, by calculation |
| Finish | Honed, flamed, bush-hammered, polished |
| Anchors | Stainless steel, grade by exposure |
| Fixing | Kerf, undercut or dowel, into a drained cavity |
| Testing | Flexural, compressive, absorption, pull-out |

## The anchor is the design, not the stone

A stone facade fails at the anchor, not through the slab. Everything that
matters structurally is in the fixing:

- **Anchor grade.** 304 stainless pits in coastal and heavily polluted air;
  316 is the grade for those environments.
- **Edge distance and kerf depth** control whether the anchor pulls through the
  slab edge.
- **Pull-out testing on the supplied stone** is the only evidence the anchor
  capacity is real.
- **Each slab independently supported**, so a single failure is not
  progressive.

## What drives the cost

Stone type and rarity · slab thickness · finish · panel size and yield from the
block · anchor type, with undercut costing more than kerf · wastage, which is
high for stone · testing programme · handling, weight and crane time.

## Where projects go wrong

- **Thickness copied from another project.** Wind pressure and stone strength
  are both project-specific.
- **Test values taken from quarry literature** rather than the supplied batch.
- **304 stainless near the coast.** It stains and pits within a few seasons.
- **Wet fixing above low rise.** Mortar adhesion is not a facade support system.
- **No breakage allowance.** Stone chips and cracks in transit; the order must
  carry margin.

## Standards referenced

Stone identification under **IS 1123**. Compressive strength testing to
**ASTM C170**. Wind loading on cladding and anchors under **IS 875 (Part 3)**.

## Frequently asked questions

### How thick should a stone cladding slab be?

It follows from the stone's tested flexural strength, the panel size and the design wind pressure for that building, not from a standard number. Granite at 30mm and sandstone at 40mm are common starting points on commercial facades, but the thickness must be confirmed by calculation against tested values for the specific stone batch being supplied, because strength varies significantly between quarries and even between blocks.

### Why is dry cladding preferred over wet fixing?

Wet-fixed stone relies on mortar adhesion that degrades, and it gives water no drained path. Dry cladding hangs each slab on stainless anchors within a ventilated cavity, so each panel is independently supported, movement is accommodated, and water that passes the joint drains out. On any building above low rise, dry cladding is the correct method.

### What testing should a stone supply have?

Flexural strength, compressive strength, water absorption and, for the anchor condition, anchorage pull-out on the actual stone. Test values must come from the batch being supplied. Quarry literature describing the stone type in general is not a substitute, because the same named stone varies between blocks.

## Sources

- [IS 1123](https://standards.bis.gov.in/website/published-standards/department-wise) — Identification of natural building stones
- [ASTM C170](https://www.astm.org/products-services/standards-and-publications.html) — Compressive strength of dimension stone
- [IS 875 (Part 3)](https://standards.bis.gov.in/website/published-standards/department-wise) — Wind loads on buildings

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Source: https://hagerstone.com/materials/natural-stone-cladding