The Filter Paper Method Revisited

The calibration curve for any device or method to infer suction is the most important characteristic to evaluate for reliable measurement to be obtained. Some published literature (e.g. Houston et al. 1994; Bulut et al. 2001; Leong et al. 2002) have presented results in which the calibration for the filter paper method is not unique in relation to the type of suction (i.e., total or matric). A review of the data from the literature is presented, together with data showing the reason that justifies a unique calibration curve for the filter paper. It is also shown that it is necessary to check the calibration curve by performing a quick calibration check. A procedure for calibrating the filter paper for this check is given. Fundamental matters necessary for understanding the concept on which the filter paper method is based are also presented.