Practical application of micro-resistance drilling for timber inspection

Since 1987, recording resistance drilling using thin needles is applied by experts for determining the condition of structural timber and joints by measuring density profiles of wood. Experienced users are able to identify decay, insect damage, and cracks in the profile. In addition, the method allows the expert to find invisible beams below floor and inspect hidden timber (Rinn, 1989a). The information obtained on internal condition of beams and joints helps engineers evaluating historic and modern timber structures (Görlacher and Hättich, 1990) and is the base for repair planning. Meanwhile, nearly ten types and generations of resistance drilling machines are available, differing strongly in many ways. Some types are applicable for timber inspection. Unfortunately, many applications of this method do not lead to satisfactory results, because the selected machines are not appropriate for the given task and because of missing knowledge about how to apply and how to interpret the results. Thus, a basic understanding of the method and knowledge about technical properties of the machines is mandatory for being able to properly select the appropriate machine type and generation for any kind of application.