Plaster coverage for walls and ceilings — how many 25kg bags of multi-finish you need.
A 25kg bag of multi-finish plaster covers roughly 10 m² at 2mm thickness (a typical skim coat). Multiply your wall area by the thickness and divide to get the bag count. Always allow for two coats and some waste.
A standard 4m × 4m room with 2.4m ceilings has roughly 38 m² of wall — about 4 bags per coat, 8 for two coats.
Skimming is done in two coats — a first coat then a finishing coat. Budget double the single-coat quantity.
Usually yes if the surface is sound. Loose or blown plaster must be hacked off and the wall re-boarded or bonded first.