Assessing Salt-Induced Degradation in Historic Timber-Masonry Buildings Using Micro-Drilling

Abstract

The timber elements of the monumental Sodafactory building in Schiedam, the Netherlands, were investigated to assess the extent of salt-induced degradation. The damage was primarily caused by defibration, a chemical process caused by salt crystallization within the wood structure, which separates the wood cells, induces mechanical rupture, and ultimately results in a complete loss of strength. While the damage is visually detectable, it is difficult to quantify reliably. To address this, micro-drilling measurements were performed in radial and tangential direction on eight wooden beams, which appeared to be severely defibrated. Micro-drilling proved effective for quantitative measurements of decay, supported by a TU-Delft developed algorithm to scientifically determine decay from micro-drilling signals. Results showed that, beneath the layer of defibrated wood, the beams generally remained structurally sound. Only two of the eight beams were found to be severely decayed, with less than 50% of their original cross-section remaining intact. Microscopic analysis of samples from both decayed and intact areas revealed fiber separation and significant salt deposits on the beam surfaces. These findings indicate that the timber elements remain at risk, as the salt-induced decay could still progress over time, causing further degradation and increased safety risks to the historic Sodafactory building.