Plastering covers a range of types of surface preparation, and the word skimming means to apply two coats of a type of plaster called a ‘finishing plaster’ over existing walls and ceilings where a PVA glue solution is first applied to allow adhesion of finishing plaster to existing backgrounds, but the plaster can also be applied directly onto new plasterboard surfaces which would not require any PVA preparation.
If a ceiling or wall is badly damaged it may need plaster boarding over before it can be skimmed with plaster. I professionally install plasterboard for both walls and ceilings with a flush finish that are perfect for skimming.
Float and set is a traditional two stage style of plastering. The first stage is a wet undercoat plaster such as sand and cement or browning/bonding which is trowelled onto the walls. When this first stage has set to a semi firm state, the second stage
https://petesplasteringservices.co.uk/