Drying kinetics and shrinkage in dual-layer earthen buildings: in-situ assessment of CobBauge

This case study investigates the long-term drying kinetics and shrinkage of CobBauge, a wet dual-layer earthen construction system undertaken upon the first UK CobBauge building. The methodology involved the use of Time Domain Reflectometry (TDR) moisture sensors which were laid in a novel dual layer earthen material and enable moisture monitoring within the wall following construction. Average vertical shrinkage during the five-month monitoring period was 43 mm (2.05%), while average Volumetric Moisture Content (VMC) fell from 10.3%vol to 5.0%vol. There was little lateral movement and shrinkage was non-uniform. The study assessed the long-term drying kinetics of CobBauge in a wet, oceanic climate using TDR combined with point cloud coupling for the first time. The study suggests that the design of earthen mixes and initial moisture levels can impact upon the amount of wall shrinkage. Where cob is laid wet, this has significant implications when designing for vertical movement around openings, applying renders and controlling moisture content during construction.