This study introduces, for the first time, air-assisted deposition of cellulose nanocrystals (CNC) to create structured coatings on cellulose-based substrates. It first examines CNC hydration and dispersion at the air-water interface, detailing the transition from agglomerates to individual crystallites and the formation of coating layers. The structural and barrier properties of the resulting composites are then analyzed concerning CNC grammage. Results show that water rapidly penetrates CNC agglomerates, requiring less than a minute to loosen and individualize the CNC, enabling the formation of uniform coatings. CNC layer grammages of up to 90 g/m² are achieved within a short time. The structural characteristics of the CNC layers are assessed and correlated with their liquid and gas barrier properties. These coatings demonstrate exceptional barrier performance when reaching sufficient grammage, with oxygen transmission rates below 1 cc/m²·day, water vapor transmission rates as low as 130 g/m²·day, and air permeance up to 68 Bekk seconds. This innovative method facilitates the processing of complex materials with potential applications in packaging and membrane technologies