The short-term hydration and drying response of Nirex Reference Vault Backfill (NRVB) grout is presented. Low-frequency electrical conductance measurements were used in conjunction with gravimetric and internal temperature measurements to study NRVB grout from initial mixing up to 7 days hydration. The grout was subjected to ambient temperatures of 25°C, 55°C and 70°C at relative humidities of 50-55% and 85-90%. By taking measurements at discrete depths from the exposed surface, the influence of the external environment on setting and hardening and drying effects could be studied. An empirical relationship, based on a simplified electrical model, was established between moisture loss and electrical measurements. © 2003 Elsevier Ltd. All rights reserved.