Large wooden structures of cultural significance, such as the Mary Rose, face the difficult question of how to preserve them against degradation and ultimately structural failure. Over time creep in the wooden members builds up and causes damage and increasing deformation of the structure. Further complications arise from the polyethylene glycol treatment of large waterlogged wooden structures. Polyethylene glycol is commonly used to replace the water that has built up in the pores of the wood and prevent shrinkage. This treatment changes the material properties of the wood, increasing its ability to deform plastically and reducing its strength.
The use of polyethylene glycol is widespread, but the number of archaeological wooden structures of the significance of the Mary Rose are few. This study investigates how the wood of the Mary Rose has changed over time in terms of degradation and treatment and how this effects the global structure. The material properties are very different to pristine oak. The microstructures of samples of the historic oak were analysed and they proved that polyethylene glycol had successfully prevented cracking. The cell walls were shown to be thinning. The changes in microstructure led to reduced mechanical properties, tested by three-point bending in the scanning electron microscope, and the polyethylene glycol treatment further depreciated these properties.
Analysis of laser scans of the ship during the drying process allowed for a greater understanding of how a change in moisture content affects the wood, and how shrinkage and beam deflection affect the overall structural health. Movement was shown to speed up during drying due to the expediated creep effects of a change in moisture content. However, the overall movement appears to be reducing considerably, in part due to the stabilisation of the wood’s moisture content.