Question answered
White powder on new lead: is it a problem?
The short answer
Usually not. New lead reacts with air and rain and forms a pale, chalky film, mostly lead carbonate, on its surface. That film is the start of the grey patina that protects the metal underneath, not a sign the lead is failing. The powder can wash down onto brick, stone or paintwork and leave streaks. A patination oil applied when the lead is fitted limits it, and the staining fades as the sheet weathers.
A bright new lead flashing often turns chalky within weeks of being fitted. It looks like a fault, but it is usually the metal settling into its working finish.
What the white film actually is
Freshly cut lead is bright and silvery. Within hours it begins to dull as the surface reacts with oxygen, moisture and carbon dioxide in the air, and in time that reaction produces a layer of basic lead carbonate. In its early stages the layer is pale and powdery, which is the white you see.
As the sheet weathers, the film thickens and turns the familiar soft grey. That grey layer is stable and clings to the metal, so it slows further change. Old church roofs and Victorian flashings owe their long lives partly to it.
The change carries on for as long as the lead is exposed, which is why a roof laid years ago has a layered grey surface that would take effort to scrape off. So the powder is a stage and not a defect. It is the visible side of a process that has to happen before lead looks and behaves like the lead on an old building. Our guide on lead patination goes further into how it develops.
Why new lead looks its worst at the start
The white shows most on a new job because the metal has had no weathering at all. The film is loose and has not yet keyed to the metal, and every shower can lift some of it. A sheltered area, such as the underside of a flashing or a spot under an overhang, gets less rain to rinse it, so the powder lingers longer there.
Streaks are patchy for the same reason. A flashing that has been dressed and handled will show finger marks, tool marks and creases in a slightly different shade, because each of those marks changes how fast the surface reacts. The pattern evens out as the whole sheet weathers together.
That is also why a flat roof or a new valley can look uneven for some time and then settle. Welded seams do the same.
Run-off and the marks it leaves below
The practical nuisance is run-off. Rain carries some of the loose powder down the wall, and on pale render, brick or stone it can leave whitish streaks under the flashing. They are surface marks, and they usually fade as the lead stops shedding powder.
A patination oil, brushed on by the fitter before the roof is exposed, gives the metal an even coat that reduces both the chalky look and the run-off. It is a routine finishing step on visible lead, and worth asking about if the flashing sits above a light wall or a freshly decorated surface.
Where the flashing sits above a light wall that matters to you, ask the fitter to oil the lead before the roof is exposed. It is a small extra step. If streaks have already formed, rinse the wall with clean water and a soft brush while they are fresh. Avoid scrubbing hard or using strong chemicals on stone, since that harms the wall more than the powder does.
When white on a roof means something else
Not every white mark near lead is lead. A pale crust on brickwork, especially along the chimney or at a damp mortar joint, is often salt carried out of wet masonry as it dries, and it points to water in the wall. If the crust appears with a damp patch indoors, look at the flashing joint; see lead flashing pulling out of the wall.
Zinc and some other metals also develop white deposits. On zinc near the coast they are the metal reacting to salt in the air, and one zinc maker notes that they form mainly on surfaces not rinsed by rain. That is a different metal with a different behaviour, covered in lead or zinc.
Pitting, holes or a surface that flakes away in layers on lead is a separate matter and worth having looked at.
What to do, and what to leave alone
In most cases the right action is none. Let the lead weather, and keep the gutters and the wall below clear so the run-off drains cleanly. Do not abrade the film to make the metal look new again, because it will only start the process over.
Treat the powder as you would any lead dust. Avoid breathing it, do not eat or smoke after handling it, and wash your hands. If you are tidying up around a fresh flashing, wipe it with a damp cloth and do not sweep it into the air.
If you are unsure if what you are seeing is patina or a fault, send us photographs. We will say which it is from the picture, or look at the lead and the joint on a survey. Our lead roofing pages cover the other metals and details.
White deposits on lead: two more questions
Can a pressure washer clean white patina off a lead flashing?
It is best avoided. The jet strips the weathering you want the lead to keep, can force water behind the edges, and can damage delicate tiles nearby. Clean water and a soft brush on the wall below are gentler and enough.
Will the white streaks on the wall below fade by themselves?
Usually, yes, as the lead stops shedding powder and rain rinses what is left. If the marks are on soft stone or pale render, a gentle rinse while they are fresh helps and avoids them setting.
Tell us about your roof
Describe what is happening and we will call you back to arrange a visit.
- Photographs of what we find
- A written quote with one total price
- Or call 01903 299063
10-year workmanship guarantee, in writing.