The large number of new ceramic tiles and substrates used in construction has brought difficulties to traditional mortar materials in relation to adhesion and flexibility, resulting in low durability in the built environment. Numerous reports have evidenced pathological manifestations of tile peeling in facades, kitchens and bathrooms, which may be related with the stiffness of the adhesive mortar. For conventional Portland cement mortars, polymer admixtures can be added to increase their flexibility. The concept of alkaline activated materials, also known as geopolymers, is an ecological alternative to the use of Portland cement. However, geopolymers are also rigid and brittle. In this study, the effects of the addition of a vinyl acetate-ethylene copolymer (VAE) on the mechanical properties of a metakaolin-based geopolymer mortar were investigated. The geopolymer mortar samples were prepared using commercial metakaolin, quartz sand, cellulose ether, alkaline solution, and with and without VAE. For comparison purposes, samples of conventional cement mortar (adhesive mortar type ACII), with Portland CPIIF40, were also prepared. The samples were tested for measurement of strength (compression and bending), transverse displacement in flexure, Young’s modulus by impulse excitation technique, and apparent density. The samples were also characterized by X-ray diffraction and scanning electron microscopy to understand the microstructural changes with VAE admixture and to correlate with the mechanical properties.