ABSTRACT: The flatjack technique is a solution used to evaluate masonry structures. It is a non-destructive technique which allows obtaining real in situ structural properties, with efficiency and precision to test masonry structures made with solid units, as stones or bricks. The technique is part of two American standards: ASTM C1196-09 and ASTM C1197-09 and other European recommendations: RILEM MDT.4-04 and RILEM MDT.5-05, being both about tests in masonry with solid units. Brick or stone solid units are common in old structures, however modern masonry also needs to be evaluated due to material quality questioning or to changes in its designed use. Usually, those structures use hollow concrete or clay blocks and the usual flatjack cannot be used in these situations. This paper presents the development process of new flatjacks for hollow blocks. Prototype models explore the ideas of testing only one face shell or both face shells. Preliminary calibration and testing issues are presented, using the new jacks to load blocks and prisms against a testing machine. Results so far indicate a new path for the use of this technique in the non-destructive evaluation field, focusing on modern masonry structures. As a conclusion, it is possible to say that the new flatjack model can be applied on hollow concrete blocks.