The RILEM TC 275-HDB - Hygrothermal behaviour and Durability of Bio-based materials aimed to investigate testing methods of hygrothermal and capillary behaviour on vegetal concrete. Usual protocols were considered in Round Robin Tests (RRT) to assess their applicability and to point out warning aspects. The studies were performed on hemp concrete provided by an industrial partner of the TC (VICAT Group), with density about 330 kg/m3. Regarding the measurement of Moisture Buffer Value (MBV), seven laboratories took part to the study. As the participating laboratories commonly used the NORDTEST protocol to measure MBV, this RRT was performed “as usual”, without additional guideline except initial conditioning of specimens. The results differ more or less between laboratories. Their analysis allows identifying several shortcoming regarding the exchange surface, the moisture flux direction versus the compacting one and the climate chamber technology. A second RRT has to be performed to formulate a more detailed protocol suitable for vegetable concrete and to assess its robustness.