© 2020 Elsevier B.V. A hydrophobic pure-silica *BEA-type zeolite membrane was prepared using the steam-assisted conversion (SAC) method on a seeded tubular silica support coated with dilute synthetic gel. This study systematically investigates the effects of the synthetic conditions on the membrane formation process and separation performance. Under the optimized conditions, when using a dilute synthetic gel with a H2O/SiO2 ratio of 500, a dense and continuous membrane layer was formed in 24 h. This was attributed to dissolution of the surface of the silica support during the steaming process, which functions as a silica source for the growth of a seed crystal layer. An increase in silica the concentration on the support surface locally enabled the formation of a membrane under the dilute synthetic gel composition. The obtained membrane exhibited selectivity toward n-butanol, in addition to a high flux with a separation factor of 132 and a flux of 1.00 kg m−2h−1 for a 1 wt% n-butanol/water mixture at 318 K. This novel simple membrane formation method combines a dilute synthesis gel with SAC, takes advantage of the dissolution of a silica support, and reduces the consumption and cost of chemical raw materials used for membrane synthesis.