The research aims at better understanding the parameters controlling air flow through cracked cementitious material elements. Rizkalla et al. proposed a model that describe gas transport in a cracked concrete element subjected to a pressure gradient. The model includes a flow coefficient, n and a friction coefficient, k that must be determined experimentally. Equations giving the values of n and k were proposed by experimentally analysing air leakage through multi-cracked reinforced concrete panels. This paper aims at validating the model proposed by Rizkalla et al. by analysing the air flow in a single defined crack generated in mortar samples (normal- and high-strength). A permeability cell was developed to measure airflow through a single cracks under controlled conditions. The results confirm the validity of Rizkalla's model. The approach based on single crack measurements has show that, for all the considered cases, airflow in cracks was largely laminar. This lead to a simplification of Rizkalla model and the development of a simple equation that gives air flow as a function of crack geometry, pressure gradient and friction coefficient only. No effect of type of mortar matrix was found on the airflow through a crack.