Plaster is a building material used for coating walls and ceilings. Plaster is manufactured as a dry powder from raw gypsum and is mixed with water to form a paste when used. The reaction with water liberates heat through crystallization and the hydrated plaster then hardens. Plaster can be relatively easily worked with metal tools or sandpaper. These characteristics make plaster suitable for a finishing, rather than a load-bearing material.
Plasterers use a wide range of plasters depending on what the job is. If its just a re-skim then he is most probably going to use "Thistle Multi Finish" this will achieve a smooth background prior to decorating.
High or Low Suction
If you are not sure whether the background is high or low suction splash a small amount of water on it. If the water runs/drips down that is most probably low suction. With low suction, thistle bonding should be used prior to plastering with thistle multi finish. If, on the other hand, it dries very quickly, it is probably going to be high suction. If it is high suction, Thistle hard wall should be used with Thistle Finish.