Wall Putty Calculator: How Much Putty and POP for a Room

What it calculates

The calculator gives, for a room or an area you enter:

• the area to putty, walls less doors and windows, plus the ceiling if chosen;
• the wall putty in kilograms and whole bags, for the number of coats chosen;
• the POP punning in kilograms and whole bags, if chosen.

Putty comes before primer and paint. Once the putty is estimated, use the paint quantity calculator for the primer and finish coats on the same room.

Inputs

Area chooses whether the area comes from the room size or is entered directly.

Room length, width and wall height are the inside dimensions in feet. Use the height to the false ceiling where there is one. Surfaces chooses walls only, or walls and ceiling. Doors and windows are counts; their sizes are in the assumptions panel.

Area to putty, when entered directly, is in square feet and should already be net of doors and windows.

Putty coats is the number of coats in the specification.

POP punning adds a plaster of Paris levelling coat before the putty.

The assumptions panel holds the putty coverage and bag size, the door and window sizes, the wastage allowance, and the POP thickness, consumption and bag size.

Method

1. Area to putty = 2 × (length + width) × height − doors × door width × door height − windows × window width × window height, plus length × width if the ceiling is included.
2. Area in m² = area in sq ft × 0.092903.
3. Putty = area in m² × coats ÷ coverage for one coat × (1 + wastage).
4. Putty bags = putty ÷ bag size, rounded up.
5. POP = area in m² × thickness in mm × consumption in kg/m² for each mm × (1 + wastage).
6. POP bags = POP ÷ bag size, rounded up.

If the POP data sheet gives coverage as square metres for each kg at a stated thickness, convert it: consumption for each mm = 1 ÷ (coverage × that thickness).

Assumptions

Coverage is the input that matters most. Data sheets give it for a reasonably level surface; on rough or uneven plaster, site coverage is usually lower.

Limitations

• Rectangular rooms only. Add walls of other shapes separately, or enter the area.
• Openings are averaged. Rooms with full-height glazing or many doors should use their real opening sizes, or enter the net area.
• POP thickness is an average. Badly out-of-plumb walls vary in thickness from place to place; measure before relying on the figure.
• Products are sold in fixed bag sizes. Round to the packs available, and buy from one batch where the finish matters.
• It does not choose the system. Whether a wall needs POP punning, putty, or neither, and how many coats, is a decision for the finish specification.

Worked example

A 20 ft × 15 ft room with 10 ft walls, one door and two windows, walls only, two coats of putty at 2 m² for each kg a coat, 40 kg bags and 10% wastage:

The room needs about 66 kg of putty, or 2 bags of 40 kg. Puttying the ceiling as well adds 300 sq ft, taking the area to 947 sq ft (88 m²) and the putty to 96.8 kg, or 3 bags. With POP punning on the walls at 3 mm and 1 kg/m² for each mm, the POP is 198.4 kg, or 8 bags of 25 kg.

How engineers use it

On a fit-out, wall finishes are measured from the drawings in square metres for each finish, and the specification sets the full system: surface preparation, any POP punning, putty coats, primer and finish coats. Material quantities then follow from the manufacturers' coverage for that system. A calculation like this one is the quick check that a supplier's or painter's material estimate is in the right range.

When a professional design must replace it

Use the calculator to estimate how much putty and POP to buy for a room or to check an estimate. Replace it with a measured take-off and a written finish specification for a whole office or building, where surfaces, backgrounds and finishes vary from room to room and where the preparation work is a large part of the job.