Fresco Secco Plaster Calculator

The lime plaster, pigment and water for a fresco secco panel, from the area, the coat thickness and the pigment load.

Fresco secco is painted onto a dry lime plaster ground rather than into wet lime, so the plaster panel has to be planned and finished before any pigment is mixed. This calculator works out the plaster volume and weight from the area and the thickness, the number of coats, the bags of dry powder to buy, and the pigment load as a percentage of the plaster weight. It is a quantity and coverage estimate, not a recipe or a plastering instruction.

At a glance

What you enter: Panel length, Panel height, Number of plaster coats, Thickness of each coat, Density of the mixed plaster, Dry powder yield of the mix, Pigment as a percentage of the plaster weight, Density of the dry pigment, Mixing and application waste, Bag size of dry plaster, Price per bag
What you get: Area to plaster, Area to plaster, Total plaster thickness, Volume of plaster, Weight of mixed plaster, Dry plaster powder needed, Dry powder to buy, Bags to buy, Pigment for the plaster, Pigment volume, Pigment per square metre, Water to allow for, Cost of the plaster, Plaster cost per square metre
Formula shown: Yes, every step, right below your results.
Cost and privacy: Free, no account needed, and nothing you type is stored.

See worked examples ↓ Read the FAQ ↓ Share this calculator ↓

Panel length mm

The panel or wall being plastered.

Panel height mm

Number of plaster coats

A panel on board usually takes two or three coats, a wall three or more with a scratch coat beneath.

Thickness of each coat mm

Lime plaster is applied at 3 to 8 millimetres per coat.

Density of the mixed plaster kg per litre

Mixed lime plaster is roughly 1.6 to 1.8 kilograms per litre. Use the figure from the product data sheet if it gives one.

Dry powder yield of the mix kg of powder per litre of plaster

Dry powder makes about 1.2 to 1.4 kilograms per litre of mixed plaster, because the mix is largely water.

Pigment as a percentage of the plaster weight %

Five to fifteen percent gives a strong colour in lime. Above fifteen the set and the strength can suffer.

Density of the dry pigment kg per litre

Earth pigments are roughly 1.5 to 2 kilograms per litre. A light organic pigment is lower.

Mixing and application waste %

Plaster lost in the bucket, on the board and on the floor.

Bag size of dry plaster kg

Lime plaster is usually sold in 25 kilogram bags or in tubs of putty.

Price per bag

Optional. Used for the plaster cost.

Reset

Results are estimates for general information only, always verify with a professional or official source before acting on them.

How to use the Fresco Secco Plaster Calculator

1 Enter Panel length (mm), The panel or wall being plastered.
2 Enter Panel height (mm)
3 Enter Number of plaster coats, A panel on board usually takes two or three coats, a wall three or more with a scratch coat beneath.
4 Enter Thickness of each coat (mm), Lime plaster is applied at 3 to 8 millimetres per coat.
5 Enter Density of the mixed plaster (kg per litre), Mixed lime plaster is roughly 1.6 to 1.8 kilograms per litre. Use the figure from the product data sheet if it gives one.
6 Enter Dry powder yield of the mix (kg of powder per litre of plaster), Dry powder makes about 1.2 to 1.4 kilograms per litre of mixed plaster, because the mix is largely water.
7 Enter Pigment as a percentage of the plaster weight (%), Five to fifteen percent gives a strong colour in lime. Above fifteen the set and the strength can suffer.
8 Enter Density of the dry pigment (kg per litre), Earth pigments are roughly 1.5 to 2 kilograms per litre. A light organic pigment is lower.
9 Enter Mixing and application waste (%), Plaster lost in the bucket, on the board and on the floor.
10 Enter Bag size of dry plaster (kg), Lime plaster is usually sold in 25 kilogram bags or in tubs of putty.
11 Enter Price per bag, Optional. Used for the plaster cost.
12 Press Calculate. You get Area to plaster, Area to plaster, Total plaster thickness, Volume of plaster, Weight of mixed plaster, Dry plaster powder needed, Dry powder to buy, Bags to buy, Pigment for the plaster, Pigment volume, Pigment per square metre, Water to allow for, Cost of the plaster, Plaster cost per square metre, and every intermediate step stays visible under "How is this calculated?"
13 Change one number at a time to see what moves the result, that is usually the most useful thing a calculator can tell you.

Worked examples

Real numbers run through this calculator. Open any example to load it into the form above and change it.

A 1200 by 900 mm panel in two coats

Two 5 millimetre coats with 8 percent pigment and 10 percent waste.

You enter

Panel length: 1,200 mm
Panel height: 900 mm
Number of plaster coats: 2
Thickness of each coat: 5 mm
Density of the mixed plaster: 1.70 kg per litre
Dry powder yield of the mix: 1.30 kg of powder per litre of plaster
Pigment as a percentage of the plaster weight: 8%
Density of the dry pigment: 1.60 kg per litre
Mixing and application waste: 10%
Bag size of dry plaster: 25 kg
Price per bag: $22.00

You get

Area to plaster: 1.08 sq m
Area to plaster: 11.63 sq ft
Total plaster thickness: 10.00 mm
Volume of plaster: 10.80 L
Weight of mixed plaster: 18.36 kg
Dry plaster powder needed: 14.04 kg
Dry powder to buy: 15.44 kg
Bags to buy: 1
Pigment for the plaster: 1.47 kg
Pigment volume: 1.01 L
Pigment per square metre: 1,496.00 g
Water to allow for: 7.02 L
Cost of the plaster: $22.00
Plaster cost per square metre: $20.37

1.08 square metres at 10 millimetres is 10.8 litres of plaster, which is 18.4 kilograms mixed and 14 kilograms of dry powder, so one 25 kilogram bag. The pigment is 1.47 kilograms, about 0.92 litres.

Open this example in the calculator →

A wall panel in three coats

A 2400 by 1400 millimetre panel with three 6 millimetre coats and a stronger 12 percent colour.

You enter

Panel length: 2,400 mm
Panel height: 1,400 mm
Number of plaster coats: 3
Thickness of each coat: 6 mm
Density of the mixed plaster: 1.70 kg per litre
Dry powder yield of the mix: 1.30 kg of powder per litre of plaster
Pigment as a percentage of the plaster weight: 12%
Density of the dry pigment: 1.70 kg per litre
Mixing and application waste: 10%
Bag size of dry plaster: 25 kg
Price per bag: $22.00

You get

Area to plaster: 3.36 sq m
Area to plaster: 36.17 sq ft
Total plaster thickness: 18.00 mm
Volume of plaster: 60.48 L
Weight of mixed plaster: 102.82 kg
Dry plaster powder needed: 78.62 kg
Dry powder to buy: 86.49 kg
Bags to buy: 4
Pigment for the plaster: 12.34 kg
Pigment volume: 7.98 L
Pigment per square metre: 4,039.20 g
Water to allow for: 39.31 L
Cost of the plaster: $88.00
Plaster cost per square metre: $26.19

3.36 square metres at 18 millimetres is 60.5 litres, so 102.8 kilograms of mixed plaster and 78.6 kilograms of powder: four bags. A 12 percent pigment load is 12.3 kilograms, which is a serious amount of colour.

Open this example in the calculator →

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Frequently asked questions

How thick should a lime plaster coat be?

Three to eight millimetres per coat is the usual range, and thinner coats are the norm rather than the exception. A thick single coat shrinks, crazes and can fail to bond, which is why plaster is built up in layers with time between them and a scratch or key coat beneath. A 4 square metre panel in three coats at 5 millimetres is 60 litres of plaster, which is about 102 kilograms of mixed material and 78 kilograms of dry powder before waste.

How much pigment goes into lime plaster?

Five to fifteen percent of the plaster weight gives a strong colour, with the exact figure depending on the pigment and the depth wanted. Below about 5 percent the result reads as a tint, and above about 15 percent the pigment can interfere with the set and reduce the strength of the plaster. Pigment is normally mixed into the final coat rather than every coat, so calculate it against that coat if the build up underneath will not be coloured.

Which pigments work in lime?

Earth pigments and pigments sold as lime fast, because fresh lime is strongly alkaline and some modern organic colours are not stable in it. Iron oxides, ochres, umbers and terre verte are traditional for a reason. Always make a small test panel and let it cure fully, because a lime colour continues to develop as it carbonates over days and weeks, and it will look lighter when dry than it did when wet.

How much water does lime plaster need?

Roughly 0.4 to 0.6 litres of water per kilogram of dry powder for a workable mix, but the correct consistency is judged by the mix rather than measured, and a lime putty based product is different again. The water figure here is for planning how much you have to carry and store, not a mixing instruction. Use the water ratio on the product data sheet, and add water to the powder rather than powder to water when the manufacturer says so.

Is lime plaster safe to handle?

Wet lime is caustic and will burn skin and eyes, and dry pigment powders and set plaster dust are respiratory hazards, so gloves, eye protection, skin cover and suitable ventilation or extraction are needed as set out in the product safety data sheet. Lime also reacts with some metals and with aluminium in particular. This tool calculates quantities only and gives no mixing, application or curing instruction: follow the manufacturer data sheet and, for a panel of any size, work with someone experienced in lime.