A method for testing a porous material under test at a field site, the method comprising: deploying a test apparatus on the porous material under test, the test apparatus comprising one or more electrodes (28, 50, 60, 88, 102, 104, 132, 134, 138, 140, 142, 162); providing one or more input electrical signals to the one or more electrodes (28, 50, 60, 88, 102, 104, 132, 134, 138, 140, 142, 162); receiving one or more response signals from the one or more electrodes (28, 50, 60, 88, 102, 104, 132, 134, 138, 140, 142, 162); calibrating the test apparatus by comparing the one or more response signals to one or more empirically derived correlations for the type of the porous material under test; determining, from the comparison, one or more parameters of the porous material under test; characterised in that the method further includes the step of determining the one or more empirically derived correlations for the type of porous material under test comprising conducting a laboratory controlled test of the porous material under test using the test apparatus and accounting for the effects of the test apparatus in the empirical correlation; wherein the laboratory controlled test comprises: iii) measuring at least one physical character of a laboratory sample of the material under test, including at least one of density, moisture content and temperature, through a series of standardized test procedures; ii) measuring at least one electrical parameter of the laboratory sample using the test apparatus, the at least one electrical parameter including at least the complex impedance of the laboratory sample; iii) empirically correlating the at least one physical character and the at least one electrical parameter. deploying a test apparatus on the porous material under test, the test apparatus comprising one or more electrodes (28, 50, 60, 88, 102, 104, 132, 134, 138, 140, 142, 162); providing one or more input electrical signals to the one or more electrodes (28, 50, 60, 88, 102, 104, 132, 134, 138, 140, 142, 162); receiving one or more response signals from the one or more electrodes (28, 50, 60, 88, 102, 104, 132, 134, 138, 140, 142, 162); calibrating the test apparatus by comparing the one or more response signals to one or more empirically derived correlations for the type of the porous material under test; determining, from the comparison, one or more parameters of the porous material under test; characterised in that the method further includes the step of determining the one or more empirically derived correlations for the type of porous material under test comprising conducting a laboratory controlled test of the porous material under test using the test apparatus and accounting for the effects of the test apparatus in the empirical correlation; wherein the laboratory controlled test comprises: iii) measuring at least one physical character of a laboratory sample of the material under test, including at least one of density, moisture content and temperature, through a series of standardized test procedures; ii) measuring at least one electrical parameter of the laboratory sample using the test apparatus, the at least one electrical parameter including at least the complex impedance of the laboratory sample; iii) empirically correlating the at least one physical character and the at least one electrical parameter. iii) measuring at least one physical character of a laboratory sample of the material under test, including at least one of density, moisture content and temperature, through a series of standardized test procedures; ii) measuring at least one electrical parameter of the laboratory sample using the test apparatus, the at least one electrical parameter including at least the complex impedance of the laboratory sample; iii) empirically correlating the at least one physical character and the at least one electrical parameter.