A new seeding method, namely, varying-temperature hot-dip coating (VTHDC), is proposed for synthesis of zeolite T membranes by secondary hydrothermal growth. The VTHDC method is composed of hot-dip coating at higher temperature, rubbing off the superfluous crystals, and hot-dip coating at lower temperature. It was found that the method was flexible and effective for combined control over the seed suspension concentration, seed size, and coating temperature, leading to combined control of properties of the seed layer over the seed size, thickness, coverage, and defect. A thin continuous, smooth defect-free asymmetric seed layer was achieved consisting of large and small zeolite T seed crystals. The resulting zeolite T membrane M5 exhibited high pervaporation performance with the flux reaching 2.12 and 2.52 kg/m(2) h for the dehydration of 90 wt % EtOH/H2O and IPA/H2O mixture, respectively, at 348 K. The corresponding separation factor was up to 1301 and 10,000, respectively. (C) 2012 American Institute of Chemical Engineers AIChE J, 59: 936-947, 2013