Stack bonded masonry is scarcely used in practice, except for aesthetic reasons. Nevertheless, a regular array of units allows placing reinforcement in the joints, which can be of major importance for masonry shell roofs, as proposed by Eladio Dieste. In order to contribute to the knowledge of the behavior of stack bonded masonry under shear loading, which seems not to have been addressed before, an experimental research program using the triplet test was carried out. The specimens incorporate aligned joints along two orthogonal axes, filled with micro-concrete. The main results of the experimental program are here presented and discussed.