The construction sector accounts for approximately 40% of energy consumption and 20% of greenhouse gas emissions in France, primarily due to the use of cement. This could be mitigated by replacing cement with raw earth in many cases. However, performance and processing of raw earth need significant improvements to enable industrial-scale production. It is therefore essential to reduce water content while maintaining consistency. This study investigates the combination of two types of tannins with three different types of soils in both unmodified and alkaline environments, as alternatives to environmentally harmful chemical fluidizers. The pH of the mixing solutions was adjusted using sodium hydroxide. Consistency was quantified using a penetrometer. Results indicated that the addition of both tannins reduced the water content of all soils while maintaining consistency (-17% in average). In an alkaline environment, this effect was enhanced for kaolinite (-42%), whereas it diminished for smectite (-10%). For the one rich in calcite, no significant change in behavior was observed between neutral and high pH levels (-28%). In the presence of too much tannin, a surface-active effect took place, aerating the mortar. This study validates the use of tannins to fluidify kaolinite, however it highlights that various soils react differently. Further investigations, such as zeta potential measurements, are needed to confirm the adsorption behavior of tannins, particularly for kaolinite in a basic environment, and to assess whether the basic conditions inhibit adsorption in the case of smectites.