Mortar is an important material in old masonries. Its repair is leading to the conservation of buildings and structures of our cultural heritage. Old mortars are mainly made of pozzolan, sand, brick powder, lime and water. Repair mortars are made of the same materials whereas cement is often added in small quantities in order to improve the strength development. This paper presents preliminary results of a systematic experimental study on the effect of aggregate type and ratio on physical and mechanical characteristics of repair mortars. Four mortar mixtures were prepared with different pozzolan/brick powder/sand ratios. Compressive strength, flexural strength, weight loss and shrinkage measurements were taken for a time period up to 90 days. Different type and dosage of aggregates strongly affects the mortar's mechanical characteristics mainly due to the different specific surface area and physical properties of sand and brick powder.