Solve backwards
How much wall will my bag of finish plaster skim?
- 50 lbThe example worked below
- Skim Coat Plaster CalculatorEvery figure is its own
You have
How much finish plaster?
That is 50 lb(22.7 kg). Worked by the Skim Coat Plaster Calculator at the settings below.
The settings it uses
- Finished thickness
- 0.08 in
- Skim coats
- 1
- Applied density
- 78 pcf
- Waste allowance
- 15
What it will do
84.9 sq ft of wall
7.89 m²
One wall. Enough for a wall 10.6 ft long and 8 ft high.
Or several. Less than one wall of the size the Skim Coat Plaster Calculator opens on (a wall 40 ft long and 8 ft high).
Check it forwards
- Area to skim
- 84.9 sq ft
- It asks for
- 50 lb
- You have
- 50 lb
The Skim Coat Plaster Calculator asks for 50 lb at that size.
If you had more, or less
Around your amount
Each worked by the Skim Coat Plaster Calculator at the same settings.
Half
25 lb
42.5 sq ft
a wall 5.3 ft long and 8 ft high
Yours
50 lb
84.9 sq ft
a wall 10.6 ft long and 8 ft high
Half as much again
75 lb
127 sq ft
a wall 15.9 ft long and 8 ft high
Double
100 lb
170 sq ft
a wall 21.2 ft long and 8 ft high
Common amounts
What each amount of finish plaster covers
The sizes it is usually sold in, each worked by the Skim Coat Plaster Calculator at the settings above.
| You have | It covers | As one wall | Average walls |
|---|---|---|---|
| 25 lb(11.3 kg) | 42.5 sq ft(3.94 m²) | a wall 5.3 ft long and 8 ft high | under 1 |
| 50 lb(22.7 kg) | 84.9 sq ft(7.89 m²) | a wall 10.6 ft long and 8 ft high | under 1 |
| 100 lb(45.4 kg) | 170 sq ft(15.8 m²) | a wall 21.2 ft long and 8 ft high | under 1 |
| 200 lb(90.7 kg) | 340 sq ft(31.6 m²) | a wall 42.5 ft long and 8 ft high | 1 |
Ten square metres a bag at two millimetres
Gypsum finish plaster is sold by weight and its coverage published by area at a nominal thickness — a 25 kg bag over about 10 m², 108 square feet, at 2 mm, which is an applied density of about 1,250 kg/m³. The calculator uses exactly that, so at 3 mm over a patched wall the same bag covers two-thirds as much.
Plaster goes off in the bucket
Finish plaster has a working time of roughly 45 minutes to an hour once mixed, and whatever is left when it sets is lost. The calculator carries fifteen per cent for that and for what falls off the hawk, so the wall here is smaller than the bag's face coverage — and a small job, where one bucket too many is a large share, loses more.
A skim is not a levelling coat
Where a background is out by more than about 5 mm, 3/16 inch, the wall takes an undercoat first — bonding on a dense surface, browning on an absorbent one — a separate and much larger order. Joints, angles and patches are taped and filled before skimming, and the background must be prepared or the skim fails by adhesion, not by quantity.
How the answer is worked
Nothing here is a second formula. The Skim Coat Plaster Calculator runs forwards — a size in, a quantity out — and this page grows its own starting wall in proportion until the quantity it asks for is what you have. Where it rounds up to whole containers, the answer is the largest size before the next one would be needed.
Where the calculator adds an allowance for cuts or breakage when you order, the same allowance comes off here, because it is the same calculator: a stack you already own finishes less than its face value. Where it adds none, neither does this page — the settings beside the answer say which.
Skim Coat Plaster Calculator
runs it forwardsBags of finish plaster to skim a plasterboard wall or ceiling, from the area and the finished thickness the background actually needs.
Work out what to buy insteadSolve backwards
Other things you might already have
How big a bed will my bags of mulch cover?
Bagged mulch, worked by the Mulch Calculator.
How much bed will a yard of mulch cover?
Bulk mulch, worked by the Mulch & Gravel Calculator.
How much ground will my gravel cover?
Gravel, worked by the Mulch & Gravel Calculator.
How big a bed will my topsoil fill?
Topsoil, worked by the Topsoil Calculator.
How big a raised bed will my soil fill?
Raised bed soil, worked by the Garden Soil Calculator.
How much ground will my compost dress?
Compost, worked by the Compost Blend Calculator.
Solve backwards
Start from what is already in the yard
Paint, sheets, rolls, bags and pieces, each read the other way by the calculator that orders it.
The calculator's own figures
Nothing is estimated twice: the page runs the same calculator you would order with.
The largest size that fits
Where a calculator rounds up to whole containers, the answer stops before the next one.
Both unit systems
Gallons and litres, square feet and square metres, side by side.
Frequently asked questions
- How much wall does 50 lb of finish plaster cover?
- At the Skim Coat Plaster Calculator's own settings, 84.9 sq ft (7.89 m²) — a wall 10.6 ft long and 8 ft high. Every figure follows the settings, which you can change in the calculator.
- How much wall does 25 kg of finish plaster cover?
- At the Skim Coat Plaster Calculator's own settings, 8.7 m² (93.6 sq ft) — a wall 3.6 m long and 2.4 m high. Every figure follows the settings, which you can change in the calculator.
- How many square metres does a 25 kg bag of finish plaster cover?
- About 10 m² (108 square feet) at 2 mm thick, the figure bags are quoted at. Allowing fifteen per cent for plaster that goes off in the bucket and falls from the hawk, plan on about 8.7 m² per bag — less at 3 mm over a patched wall.
- How thick should a skim coat of plaster be?
- About 2 mm (a little under 1/8 inch) over flat, true plasterboard, applied in two passes and trowelled — that is one skim. Around 3 mm over a patched or bonded wall. Anything that needs more than about 5 mm wants an undercoat first.
- Can I keep a mixed bucket of plaster for later?
- No. Finish plaster starts to set within about 45 minutes to an hour of mixing and cannot be retempered, and an opened bag has a short shelf life. Mix in batches you can lay in the working time, and buy whole bags with a little over.