Communication presented at the 17th International Congress on Acoustics, Rome, 2-7 September 2001.Premature damage of mortar and concrete structures, due to environmental action, demands procedures to estimate durability of this type of components. Mortar or concrete composition (e.g., grain size, type and percentage of sand) may have some influence in the durability, but it is mainly related to porosity, which determines the interaction between aggressive agents and material. In this work, several NDE ultrasonic methods to estimate porosity of mortar are presented and evaluated. In these methods porosity is related to (1) the material structural noise, (2) sound velocity and (3) ultrasonic attenuation. In all these methods mortar is consider to be formed by only two phases: solid and pores.This work has been supported by Spanish Administration under grants CICYT TAP97-1128 and DPI2000-0619.Peer reviewed