Extrusion-based 3D concrete printing has become increasingly widespread in recent years. While using this technology, it is important to monitor the fresh properties of concrete in its fresh state, as the extruded walls must retain their shape without formwork support. Unless automated testing methods for fresh concrete are utilized, it is impossible to achieve full automation of 3D concrete printing. The penetration test (PT) is one of the most suitable methods for this purpose: It does not require manual sample preparation and can be performed directly on a printed structure without destroying it. This article proposes a method of automating PT by mounting a penetration tip on a robotic arm equipped with a load cell, allowing automatic movement from one test location to another. Cleaning the cone between tests is also done automatically by wiping the penetrator against a sponge soaked in water or oil. In this study, experiments were conducted to investigate the effect of coating the cone with these fluids, which showed that in both cases it led to a slight decrease in the results. The use of a robotic arm allows PT to be performed not only vertically, but also from any other orientation, enabling testing not only of the uppermost but also of the layers beneath it. The test results presented in this research showed that the values obtained with PT in the horizontal direction were higher than the values obtained with PT in the vertical direction. Furthermore, the results of PT in the horizontal direction increased proportionally to the height of the wall above the penetration point.