A shear test for structural adhesives used in the consolidation of old timber

A test method was developed specifically for structural adhesives used in t hick joints. It is based on compressive shear loading of glued joints (GJ) and solid wood (SW) specimens, before and after a suitable accelerated agei ng cycle. The evaluation of results is based on the ratios of wet strength to dry strength and on the comparison of Gl specimens to SW specimens which are prepared from the same batch of wood, in order to minimise the influen ce of the variability in wood characteristics. On a group of 10 epoxy-based adhesives, specifically marketed for the consolidation of old timber struc tures, the method has proved to be effective to differentiate the performan ces of each product. Among the adhesives tested, only two types combine a d ry strength of the GT which is equal or higher than that of SW and a wet st rength which is >50% of the dry strength. Three other types have a wet shea r strength >40% of the dry strength. Three types showed significantly lower performances when wet, and two types delaminated completely during the acc elerated ageing cycle. The test method has been proposed for standardisatio n.