Robust Details Ltd (RDL) has been researching the effect of mortar on wall ties. This stems from the difficulties in being able to investigate the causes of lower than expected sound insulation performance in fully-filled separating walls, now commonly used on RD-registered sites. The cavity fill material limits the use of "noninvasive" investigation techniques, such as borescopes.<br> <br> This research has focused on the effect of mortar accumulation on the dynamic stiffness of wall ties and will be used in guidance on the diagnosis of common sound insulation defects through analysis of RDL test data (rather than requiring invasive work on site).<br> <br> This is another example of RDL finding new ways of closing the so-called "performance gap" without causing undue inconvenience or disruption on site.