Painting Vertical Heating Pipes

The painting itself is quick. Most of the time goes into preparation and waiting for each coat to dry. The work usually goes like this:

• Let the pipes cool down: paint only goes on a cold, dry surface, otherwise it bubbles and does not stick well
• Protect the surroundings: the floor, the wall behind the pipe and nearby furniture are covered with sheeting or paper, and edges are masked with tape
• Clean and degrease: dust, grease and loose old paint are removed
• Remove rust and sand: a wire brush or sandpaper gives the new paint something to grip
• Prime: wherever bare metal or rust has shown through
• Apply two thin top coats: working from top to bottom and keeping to the drying times on the tin

Why two thin coats rather than one thick one? On a vertical pipe a thick coat runs, takes a long time to dry, forms drips around the brackets and is more likely to peel later.

Heating pipes warm up and cool down again and again. Ordinary wall emulsion or a standard wood gloss cannot cope with that. Choose a paint that is clearly labelled for radiators and heating pipes. The tin usually states its heat resistance. For common radiator paints this is typically around 100 to 120 °C according to the manufacturer, which is enough for a normal central heating system.

Water-based acrylic radiator paints

They have very little smell, dry quickly and white shades stay white for longer. They suit lived-in homes, children's rooms and offices. On rusty metal they need a suitable primer underneath.

Solvent-based (alkyd) paints

These form a hard, durable gloss film that stands up well to knocks. They smell stronger while you apply them and take longer to dry, so good ventilation matters. A white alkyd paint that is not made for radiators tends to yellow on a warm pipe over time.

Primers and colours

Rusty steel pipes need an anti-corrosion primer. Copper and galvanised pipes need a primer made for that kind of surface, otherwise the paint will not hold. The colour is a matter of taste: white or the wall colour makes the pipe blend in, while anthracite or black deliberately turns it into a feature. A gloss finish is easier to wipe clean, a matt finish hides unevenness in the old surface better.

How much work the job takes, and therefore what it costs, depends mainly on the condition of the pipes and how easy they are to reach:

• Condition of the surface: a pipe with one sound layer of paint only needs a light sanding, while rust and thick flaking layers mean far more preparation
• Distance from the wall: a pipe tight against the wall or in a corner is hard to paint at the back and needs a narrow radiator brush
• Number of brackets, branches and valves: every detail has to be painted slowly by hand
• Furniture and fittings: cupboards, kitchen units or a bath next to the pipe mean more covering and masking
• Dark or strong colours: when changing colour a third coat is sometimes needed

In a block of flats the vertical pipes, known as risers, are often part of the shared heating system. During the heating season they stay warm and you cannot cool them down from inside your flat. Plan the painting for outside the heating season. If anything is unclear, for example whether a pipe may be moved or boxed in, ask the building management or the owners' association. Painting the pipes needs no permission. Any change to the pipework itself does, and that work belongs to a heating engineer.

A reasonably handy person can paint pipes within reach from the floor. You are not touching the heating system, only renewing the surface. Work only on a cold pipe and keep the room well ventilated.

1. Switch off the heating or wait for the end of the heating season, and let the pipes cool completely.
2. Cover the floor and furniture, and protect the wall behind the pipe with a piece of card or sheeting.
3. Scrape off loose paint and rust with a wire brush or coarse sandpaper.
4. Lightly sand the whole pipe so the surface is dull and slightly rough.
5. Remove the dust, degrease the pipe with a suitable cleaner and let it dry thoroughly.
6. Prime bare metal and rusty patches, then let the primer dry as the manufacturer states.
7. Apply the first thin top coat from top to bottom, using a radiator brush for the back of the pipe.
8. Let the coat dry according to the instructions on the tin and give it a light sanding if needed.
9. Apply the second thin coat and check brackets and joints for paint collecting in them.
10. Turn the heating back on only after the time the manufacturer gives, usually not before one or two days.

In older houses the original layers of paint may contain lead. If you have to sand such layers, keep the surface wet, wear a suitable respirator mask and never sweep up the dust dry.

• Painting a warm pipe: the surface skins over too fast, bubbles and cracks later
• Skipping the preparation: new paint does not bond to grease, dust and rust and starts peeling within a year
• The wrong paint: wall or wood paint turns yellow, stays tacky and flakes off a pipe
• One thick coat: runs, an uneven finish and long drying times
• Painted valves and thermostatic heads: a clogged thread or a head that will no longer turn
• Turning the heating on too early: the paint has not cured yet and changes colour or gets damaged

In practice it often happens that pipe insulation or plastic sleeves get painted too. They should be left alone, because paint does not hold on them and can damage the material.

Once the paint is dry, look at the pipe in good light, ideally from the side, and check for:

• An even colour with no old paint showing through
• The back of the pipe near the wall painted as well as the front
• No runs or drips, especially at brackets and joints
• No rust breaking through the paint
• Clean valves, heads and threads that still turn freely
• A clean wall, floor and surroundings without paint marks
• No bubbles, cracks or obvious colour change after the heating has run for the first time