Work out wall plaster quantity instantly with clear inputs, formula shown and shareable results.
Bag coverage is quoted at a reference thickness, so it scales inversely with the thickness actually applied: a bag covering 9 square metres at 10 mm covers only 6.9 at 13 mm. Add 10% for wastage since plaster that goes off in the bucket cannot be reused.
Plaster quantity
coverage at thickness t = quoted coverage x 10 / t; bags = ceil(area x (1 + wastage) / coverage)
Gypsum plaster sets chemically. Once it has started to go off, re-tempering with water destroys the strength and finish.
2-3 mm for a skim over plasterboard, 11-13 mm for a float and set on masonry in two coats.