A Dekati® low pressure impactor (DLPI) is used to determine the mass distribution of airborne particles from 7 nm to 10 µm as a function of aerodynamic diameter. Quantification of wall deposits inside this sampling device was performed for the first time using polydisperse zinc aerosol produced by a thermal spraying process. This aerosol is more representative of the size distribution found in occupational atmospheres than aerosols usually produced in laboratories. Each experiment (3 replicates) was carried out for two durations. The results showed that wall deposits were quite considerable and in relation with aerosol modes. 13% and 14% of the total mass was found on the wall after sampling periods of 5 and 20 minutes, respectively. Relative losses could reach 50% for certain impaction stages and these losses were also quite different between replicates.