Before you do any plastering back onto the old wall, give it a good clean down, brush off all the dust etc, and wet the wall from top to bottom, using a brush. You can then PVA the wall, but let it dry,, that will seal the wall and help control any suction, especially if you are not too sure of the job..... After that coat of PVA has dried, give the wall another coat of it, but this time plaster straight onto it while it is wet/tacky.... "Never" plaster onto PVA that has dried out.
Roughcaster.