This dataset contains the experimental results supporting the research article "Effects of PDADMAC Solution Pretreatment on Beech Wood- Waterborne Coating Interaction". This study investigates the use of poly(diallyldimethylammonium chloride) (PDADMAC) as an alternative cationic polyelectrolyte to polyethyleneimine for beech wood surface pretreatment prior to waterborne coating. Beech wood was treated with 1% aqueous PDADMAC solutions of low and high molecular weights, with and without NaCl. Changes in surface chemistry, wettability, water absorption, roughness, coating penetration, and adhesion were evaluated using FTIR, fluorescence microscopy, SEM/EDS, and standardized tests. PDADMAC pretreatment modified wood surface properties, reduced water absorption and surface roughness, and formed a uniform surface layer that limited coating penetration, without significantly affecting adhesion strength. NaCl addition further improved surface smoothness. These results demonstrate that cationic polyelectrolyte pretreatment enhances the performance of waterborne coatings and offers an environmentally friendly strategy for improved wood–coating compatibility.