The Crumb test is a simple indicator test that is recommended for initial field identification of dispersive soils. The crumb test provides a simple, quick method for field or laboratory identification of a dispersive clayey soil. Dispersive clay soils are identified by observing the behaviour of a few crumbs of soil placed in distilled water. The dispersion is classified depending on the degree of muddiness of the water.

Required equipment

•        a 100 ml glass beaker

•        distilled water

Test Procedure

  1. Prepare a few crumbs, each about 6 mm to 10 mm diameter, from representative portions of the soil at the natural moisture content.
  2. Drop the crumbs in the beaker about one-third full of distilled water.
  3. Observe the reaction after allowing to stand for 5 to 10 min.


Observe the behaviour of the crumbs, and classify in accordance with the following guidelines:

Grade 1: No reaction. Crumbs may slake or run out to form a shallow heap on the bottom of the beaker, but there is no sign of cloudiness caused by colloids in suspension.

Grade 2: Slight reaction. A very slight cloudiness can be seen in the water at the surface of a crumb.

Grade 3: Moderate reaction. There is an easily recognizable cloud of colloids in suspension, usually spreading out in thin streaks at the bottom of the beaker.

Grade 4: Strong reaction. A colloidal cloud covers most of the bottom of the beaker, usually as a thin skin. In extreme cases all the water becomes cloudy.

Grades 1 and 2 represent a non-dispersive reaction, and grades 3 and 4 a dispersive reaction.

Typical crumb test results a) Grade 1: No reaction b) Grade 2: Slight reaction c) Grade 3: Moderate reaction d) Grade 4: Strong reaction

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