How to use the Plaster Calculator
- 1 Enter the area to plaster in square feet.
- 2 Choose the thickness: half inch inside or three quarter inch outside.
- 3 Choose the mix, such as 1:4.
- 4 Read the cement and sand needed.
Worked example
500 sq ft of inside wall plastered half an inch thick in a 1:4 mix. The wet volume is about 20.8 cft and the dry volume about 27.8 cft, needing about 5 bags of cement and 23 cft of sand.
Features
Dry volume
Wet volume × 1.27 plus 5% wastage.
Cement bags
Based on 1.25 cft per 50 kg bag.
Inside and outside
Half inch and three quarter inch thicknesses.
When to use it
New rooms
Plan plaster materials.
Renovation
Replaster old walls.
Outside walls
Thicker plaster for weather.
Ordering
Buy the right number of bags.
Frequently asked questions
What thickness of plaster is usual?
About half inch (12 mm) for inside walls and three quarter inch (20 mm) for outside walls.
Which mix is best for plaster?
1:4 is common for outside and ceilings, 1:5 or 1:6 for inside walls.
Why is dry volume more than wet volume?
Mortar shrinks when water is added and fills gaps, so about 27% more dry material is needed.
How much area does one bag of cement cover?
About 90 to 100 sq ft of half-inch plaster in a 1:4 mix.
Should I cure plaster?
Yes. Keep plaster moist for at least 7 days to prevent cracks.
Can I use fine sand?
Use clean, sieved sand. Too much clay or silt weakens plaster.
How long does plaster take to dry?
Plaster needs about 7 days of curing and longer to dry fully before painting.
Why does plaster crack?
Too much cement, poor curing, fast drying in heat or bad sand can cause cracks.
Should walls be wet before plastering?
Yes. Wet the brickwork so it does not draw water from the plaster too quickly.
What is the cost of plaster labour?
Labour is charged per square foot and varies by city.
Can I plaster over old plaster?
Remove loose plaster first and roughen the surface for a good bond.
What is chip plaster?
Decorative outside plaster with small stone chips, used on elevations.
How many square feet of plaster can a mason do in a day?
An experienced mason with a helper usually plasters about 150 to 250 square feet a day on walls, less on ceilings and detailed work.
Should I use a ready plaster mix?
Ready-mixed plaster gives consistent quality and needs only water, but costs more than mixing cement and sand on site.
Results are estimates based on the official rates linked above. Confirm important figures with the issuing authority or a qualified adviser before you act on them.
Reviewed by ToolsUnlocked Team · Last updated