Compressive strength of the sand:

The compressive strength of the sand is measured by eliminating the rammed specimen from the tube and placing this in a mechanical testing device. Then a compressive load is applied till the specimen breaks, typically in the range of 10 to 30 psi (0.07 to 0.2 MPa). While there is too little moisture in the sand, the grains are weakly bonded and strength is poor. While there is excess moisture, the additional water behaves as a lubricant and strength is again weak. Therefore there is a maximum strength and optimum water content shall vary with the content of other materials in the mix. A same optimum also applies to permeability. Sand coated along a uniform thin film of moist clay gives the best moulding properties. A ratio of 1 part water to 3 parts clay (by weight) is frequently a good starting point.

The hardness of the compacted sand might provide a rapid indication of mould strength and give extra insight into the strength-permeability characteristics. This can be measured by an instrument that measures the resistance of the sand to penetration from a 0.2-inch (5.08-mm)-diameter spring-loaded steel ball.

Compactability is find out by leveling off the column, sifting sand into a steel cylinder, striking it three times along a standard weight (like in the permeability test), and after that measuring the final height. The percent compactability is the modification in height divided by the original height, times 100%. The value might frequently be correlated with the moisture content of the sand, with a compactability about 45% indicating a correct level of moisture. A low compactability correlates with too little moisture.