The morphological description of surface crust is discussed earlier in this chapter. The specimen should be 10 to 15 mm on edge and 5 mm thick or the thickness of occurrence if less than 5 mm. If surface crust, the thickness is inclusive of the crust proper and the adhering soil material beneath. The specimens are small to make the test applicable to crusts with closely spaced cracks. The specimen is grasped on edge between extended thumb and first finger.
Force is applied along the longer of the two principal dimensions.
Table 3-15 contains a set of classes. Compression to failure should be over about one second. A scale may be used to both rupture the specimens directly and develop the finger tactile sense. Force is applied with the first finger through a bar 5 mm across on the scale to create a similar bearing area to that of the plate-like specimen. The specimen is compressed between thumb and first finger while simultaneously exerting the same felt pressure on the scale with the first finger of the other hand.