The influence of methylhydroxyethylcellulose (MHEC) on both moisture distribution and hydration characteristics of glue mortar using nuclear magnetic resonance imaging (NMR) is investigated. MHEC is added to glue mortar in order to control the drying rate by increasing the open time. Besides drying, MHEC might influence hydration characteristics of mortar. In this study, we therefore examined the effect of MHEC on the hydration characteristics of unsealed mortar. Without MHEC, the evaporation time is faster than hydration time and the water distribution is homogeneous in the mortar, resulting in poor hydration. Addition of MHEC > 1.3 wt.% exhibits an evaporation time comparable to the hydration time of mortar. However, in that case, inhomogeneous distribution of water causes differences in the degree of hydration throughout the mortar sample, i.e. the top surface shows poor hydration and the bottom surface shows good hydration, as confirmed by MIP and T2 relaxation analysis.