There are several studies on the application of waste foundry sand (WFS) in mortars, however, it is necessary to study the behavior of this material in relation to its ability to absorb deformation according to movements of the substrate to which it is applied. The aim of this research was to determine the modulus of elasticity (E) for laying and coating mortar with partial replacement of small aggregate with WFS. The results indicated that the increase in WFS content reduces E.