Nowadays, the construction sector is responsible for a significant part of energy related global carbon emissions. In this context, the wood bio-concrete (WBC) emerges as an environmental-friendly alternative to conventional lightweight concrete by utilizing industry vegetal residues as aggregate, which enhance its energy efficiency. However, due to its organic content, the WBC has a high water absorption capacity that is detrimental to its physical-mechanical properties and durability. Researchers have tackled this issue by integrating a silane-siloxane-based water repellent into the cementitious matrix of the material, which, although mainly beneficial, directly affects the bio-concrete’s workability thus altering its hardened state properties. Therefore, this work aims to optimize the cementitious matrix of wood bio-concrete with incorporated silane regarding its bio-aggregate and superplasticizer proportions, seeking improvements in its workability, mechanical and physical properties. For this purpose, samples were produced in two types: one volumetrically composed of 45% bio-aggregate (WBC45), and the other with 35% of bio-aggregate (WBC35). Both samples had superplasticizer added as additive to the mixture in concentrations varying between 0%, 0.5% and 1.0%. In all mixtures, 2% of water repellent was incorporated. The experimental procedures included the following tests for the fresh and hardened states: flow table, incorporated air content, uniaxial compression, and capillary water absorption. As main results, the addition of 0.5% of superplasticizer resulted in improved rheological behavior for the WBC35 samples and enhanced physical-mechanical properties for the WBC45 samples.