What type of stones generally require this test?

Stones used for exterior facing and cladding, particularly in industrial or heavily polluted atmospheres, such as limestone, marble, and certain calcareous sandstones.

How is the surface softening quantitatively measured?

By scraping the exposed surface of the stone with a standardized scraping apparatus under a constant load and measuring the loss in weight.

Why is exposure to acidic atmospheres a concern for building stones?

Pollutants like sulfur dioxide react with moisture to form acids, which chemically attack the calcium carbonate in stones, leading to surface degradation, softening, and eventually structural or aesthetic failure.

IS 4122

: 1967

Method of test for surface softening of natural building stones by exposure to acidic atmospheres

CurrentSpecializedTesting MethodMaterials Science · Stones

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This standard prescribes the method of test for determining the susceptibility of natural building stones to surface softening when exposed to acidic atmospheres, simulating industrial or highly polluted environments.

Method of test for surface softening of natural building stones by exposure to acidic atmospheres

Quick Reference Values

weighing accuracy0.001 g

specimen sizeTypically 50 mm x 50 mm cubes or cylinders

exposure agentSulphur dioxide (SO2) or equivalent acidic solution

Key Formulas

Surface Softening (g/cm²) = (W1 - W2) / A — where W1 is initial weight, W2 is weight after scraping, and A is scraped area

Practical Notes

Essential for selecting exterior stone cladding materials in highly polluted, urban, or industrial environments.

Carbonate-rich stones like marble and limestone are particularly vulnerable to acidic softening and should be rigorously tested.

The test involves controlled scraping of the stone surface after exposure to measure the exact material degradation.