Earth mortars are present in several building materials markets because of numerous advantages, particularly economic and ecological. Portugal has a vast earthen built heritage and these mortars are the most suitable for their rehabilitation and conservation. However, although some studies have been carried out on the behaviour of this type of mortars, little is known about their durability when applied outdoors. This study aims to assess the influence of adding low amounts of limes (air lime or natural hydraulic lime) and using washed sand on the durability of earth-based mortars applied as external wall renders. The results obtained did not show any improvement on the mechanical and physical characteristics of earth mortar renders with these additions and the washed sand. Therefore, to improve the performance of this material, namely towards liquid water, other additions, admixtures or surface protections should be studied.