IS 1124 : 1974Method of test for determination of water absorption, apparent specific gravity and porosity of natural building stones

IS 1124:1974 specifies the method of test for water absorption, apparent specific gravity and porosity of natural building stones. It is the durability-screening test for any dimension or building stone — granite, sandstone, marble, Kota stone, slate, basalt — used in cladding, flooring, masonry, kerbs, copings and paving.

Water absorption is the single cheapest, most informative durability proxy for stone, so IS 1124 is read with the rest of the stone-test family:

• IS 1121 — determination of compressive, transverse and shear strength of stone
• IS 1122 — true specific gravity
• IS 1123 — durability (and resistance to weathering/abrasion)
• Stone product specs: IS 1130 (Kota), IS 3316 (structural granite), IS 1597 (stone masonry)

From the dry, saturated and suspended (in-water) weights of a stone specimen, IS 1124 derives three linked quantities:

• Water absorption (%) = (saturated − dry) / dry × 100 — the fraction of accessible pore space; the headline durability indicator
• Apparent specific gravity = dry / (saturated − suspended)
• Apparent porosity (%) = (saturated − dry) / (saturated − suspended) × 100

Low absorption means few accessible pores, so less water ingress, less freeze–thaw and salt-crystallisation damage, less staining and better frost/weather durability. As a rule of thumb dense granites absorb well under ~1%, good sandstones are low single digits, and a high-absorption stone is a weathering and efflorescence risk regardless of its dry strength. Specimens must be oven-dried to constant mass and fully saturated or every derived number is wrong.

Specimen weights: oven-dry W₁ = 500.0 g; surface-dry saturated W₂ = 505.0 g; saturated suspended in water W₃ = 300.0 g.

• Water absorption = (W₂ − W₁)/W₁ × 100 = (505 − 500)/500 × 100 = 1.0 %
• Apparent specific gravity = W₁ / (W₂ − W₃) = 500 / (505 − 300) = 500/205 = 2.44
• Apparent porosity = (W₂ − W₁)/(W₂ − W₃) × 100 = 5/205 × 100 = 2.4 %

Interpretation: ~1% absorption with SG ≈ 2.44 is consistent with a sound, durable stone suitable for external cladding/flooring. If absorption had come out at, say, 6–8%, the stone would be flagged for weathering/efflorescence risk and external use would need justification (or rejection) — even if it passed IS 1121 strength.

1. Not oven-drying to constant mass. Residual moisture in W₁ collapses the calculated absorption — dry to constant weight, full stop.

2. Incomplete saturation. Short soaking under-fills the pores and under-reads absorption and porosity; follow the prescribed immersion period.

3. Using absorption alone. It is a *screen*, not the whole story — pair with IS 1121 strength and IS 1123 durability for a cladding/structural decision.

4. Ignoring anisotropy/bedding. Sedimentary stones absorb and weather differently along vs across the bedding plane; sample and place stone accordingly.

5. Wrong stone, wrong use. Specifying a high-absorption decorative stone for external rain-exposed cladding is a recurrent, expensive error caught only if IS 1124 is actually run on the supplied lot, not the sample board.

• IS 1121 — compressive/transverse/shear strength of natural building stones
• IS 1122 — true specific gravity of natural building stones
• IS 1123 — durability of natural building stones
• IS 1130 — Kota stone (limestone) specification
• IS 3316 — structural granite · IS 3622 — sandstone (slabs and tiles)
• IS 1597 Part 1 — construction of stone masonry
• IS 4101 — code of practice for external facings and veneers (stone cladding)

IS 1124 is reaffirmed and unchanged — the physics of pore water doesn't age. It remains the first and cheapest durability filter for stone procurement: insist that absorption, SG and porosity are run on the *supplied lot*, not just a polished sample tile, before bulk despatch, because natural stone varies block to block and quarry face to quarry face.

For imported stone, EN test equivalents (EN 13755 water absorption, EN 1936 density/porosity) are commonly quoted; they are methodologically comparable and acceptable when cross-referenced. The key engineering discipline is to read absorption with strength and durability together — many cladding and flooring failures (efflorescence, spalling, staining, frost damage) trace directly to a stone that passed strength but had unacceptably high absorption that was never tested on the delivered material.