Depending on the background wall, if its high suction, plenty of water until the brick/block doesn't absorb any more, apply your hardwall , feather it of when setting then float up with the float flat to the wall. No need for pva prior to skim unless you have left it for a few days.

How long before you can float plaster?

After applying the plaster, wait around 20 or 30 minutes for it to start firming up (also known as going off) before using the float. You need to time it just right. If you start too soon, the float will pull bits of wet plaster off the wall and spoil the finish. If you wait too long, the plaster will have set hard.

What does floating mean plastering?

3 Answers from MyBuilder Plasterers

the term float and set refer to the traditional style of plastering sometimes known as wet plastering. the system requires a wet undercoat plaster such as sand and cement or browning/bonding coat which troweled onto the walls usually around 11mm thick.