I have put a thin layer of hardwall plaster over soft red brick but I couldn't complete the wall on the same day. Its now dried out and needs another coat of hardwall, I was wondering if I should pva or just scratch it for the second coat. Any help would be much appreciated.
If it is smoothish surface then both would help. The moral here is to never start a wall you cannot finish - as this can give problems! The main one being that there will be very high suction so you will need a diluted coat of PVA (or two). Put plenty on until you ensure you have controlled the suction.