Sanding and polishing operations are essential to conditioning and improving the quality of surfaces before applying coatings on wooden parts and wood-based materials. One of the characteristics to evaluate the surface response to coatings is wettability, which is described by the contact angle. This study investigated the effect of surface roughness on the contact angle behaviour of medium-density fibreboards. For this, workpieces were sanded with different grit sizes (P80, P120, and P240), and all other operating conditions were held constant. Fourier transform infrared spectroscopy (FTIR) analysed the chemical composition of the surfaces to rule out the influence of surface polarity on the contact angle. Then, surface roughness was measured by confocal microscopy, and wettability was measured by distilled water droplet contact angle. The results revealed a non-linear relationship between surface roughness and contact angle, where smoother surface roughness, generated by finer grit sandpaper, correlated with lower contact angles, suggesting better wettability.