Beech and poplar were thermally modified, treated with melamine resin and both treatments were combined. The weathering performance (cracks and general appearance) of modified beech and poplar was assessed in natural weathering and correlated to material properties such as work in bending (WB) and Brinell hardness. In addition, the equilibrium moisture content after exposure of 12 months and subsequent climatization was evaluated. Melamine treated beech and thermally modified poplar performed best while still showing serious cracks. The melamine treatment increased the equilibrium moisture content, indicating a rather hygroscopic behaviour of the resin. All treated groups showed increased moisture contents after weathering and subsequent climatization. The thermal and melamine treatment decreased the WB substantially. The melamine treatment of the thermally modified wood (double modification) did not further decrease the WB. WB as an indicator of brittleness could not explain the cracking behaviour. Thermal modification decreased the Brinell hardness, whereas melamine treatment increased it. The increased Brinell hardness of melamine treated groups and the double modified groups can be accounted for the stabilized surfaces without erosion.

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