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Plastering calculator: how much plaster do I need?
Estimate finish plaster, bonding coats, beads and tape for walls and ceilings. Enter the area to plaster and add any preparation coats you need.
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How the calculation works
Skim plaster is usually applied about 2 mm thick, and a 25 kg bag of multi-finish plaster covers roughly 10 m² at that thickness. The calculator adds your wastage allowance and any undercoats, bonding or parge coats you select.
Corner beads are counted by length for external corners, and joint tape is added when you plaster over new plasterboard.
Preparing the surface
Very absorbent or smooth backgrounds need a bonding or priming coat so the plaster grips and does not dry too fast. Uneven masonry may need a thicker undercoat before the finish.
Worked example
Skimming 20 m² of wall:
| Material | Quantity | Price (ex VAT) |
|---|---|---|
| Plasterboard Joint / Scrim Tape 48mm x 90m | 1 | £3.97 |
| British Gypsum Thistle MultiFinish Coat Plaster 25kg | 3 | £32.76 |
| Materials total | £36.73 | |
Today's prices, excluding VAT and delivery. Labour, plant hire and some items are priced when you request a quote. Use the calculator above for your own measurements.
Frequently asked questions
How much does a bag of finishing plaster cover?
A 25 kg bag of multi-finish covers roughly 10 m² at a 2 mm skim, depending on the background and how evenly it is applied.
Do I need to prime walls before plastering?
Often, yes. Absorbent or very smooth surfaces benefit from a bonding or priming coat so the plaster sticks and cures properly.
How long does fresh plaster take to dry?
Typically several days for a skim coat, and longer in cold or damp conditions. Let it dry fully before decorating, and use a mist coat on new plaster.