Proper surface pre-treatment plays an important role for good compatibility between the wood and the coating. The present study aimed to determine the correlations between the type of surface pre-treatment and the wettability for unmodified and thermally modified beech (Fagus sylvatica L.) wood with water and water-based coatings. A new approach to evaluate the water permeability of coating systems was developed by investigating the wettability of wood samples using the multicycle Wilhelmy plate method in combination with immersion of the coated samples in water. The treatment with non-thermal plasma made the wood surfaces more hydrophilic and treatment with organic solvent made the surfaces more hydrophobic. The poorer wettability and sorption with water and coatings in thermally modified wood was clearly related to the altered chemical composition of wood. As the water content in coating increased, the amount of absorbed coating in the wood decreased. The surface pre-treatments had no effect on the colour of the coated wood. The higher water content in the coating negatively affected the water protection performance of the coated wood. The thinner coating films correlated with greater water absorption in the coated wood, generally resulting in microscopic delamination between the wood substrate and the coating films. © 2022, The Author(s)