The plastic limit is defined as the lowest moisture content of a soil that will permit a sample to be rolled into threads of 3 mm diameter without the threads breaking. The test procedure has remained, in principle, the same since 1932, when Casagrande proposed to define the various limits by relating the moisture content characteristics of soil under certain conditions. The apparatus required is simple yet effective. 

Glass Plate.

500 mm square x 10 mm thick.

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Rod Comparator

3mm diameter rod comparator to BS1377.

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Spatula 200 mm

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