The second layer of lime plaster sets too quickly - what to do?

Hello everyone, we applied a layer of pure lime base plaster about 10mm thick on Bimsstein (interior wall, well pre-wetted, house built in 1930). Afterwards, it was repeatedly moistened over several days. Now we wanted to apply a fine top plaster, also pure lime plaster, but it sets much too quickly despite the wall being well re-wetted! Does anyone have a tip?