What the white layer is
Cut lead is bright metal. Once it meets the air, a reaction starts on its surface. Moisture, oxygen and carbon dioxide combine with the metal to form a thin layer, and in the first weeks that layer can be pale and chalky before it settles into the dull grey of weathered lead. Roofers call the finished grey surface a patina.
The white stage is part of the same process. It is more visible on new lead because the layer is just forming and nothing has yet turned it grey. It shows up most where moisture sits on the surface, such as under a lap, along a fold or where water lies after rain.
That is why a flashing that has been on the roof for a few years does not look the same. By then the surface has settled and the pale marks are gone. Our painting lead flashing page explains why that grey finish is what lead is expected to have.
The white marks are not a fault in the sheet or a sign of poor fitting. They are a surface effect, and they appear on well-made work as well as badly made work.
Why it washes onto tiles and walls
The pale layer on new lead is loose. It is not yet bonded firmly to the metal underneath, so rain can carry some of it away. When a flashing sits above tiles, slates or a wall, the runoff from the lead goes onto them.
That is why the marks are on the neighbouring surfaces and not only on the lead. A new stepped flashing beside a chimney, for example, can leave faint white tracks down the tiles beneath it. A new valley can leave a pale line along the edges of the tiles beside it. A new apron can mark the front of the stack.
Three things make it more noticeable:
- dark tiles or slates, which show pale marks clearly;
- a slope where rain runs freely down the lead and onto the covering;
- a flashing that has gone in during a dry spell and met its first heavy rain a few weeks later.
The staining is on the surface of the neighbouring materials and not in them. It tends to fade as the lead stops shedding the loose layer, which happens as the patina settles.
If the marks stay or spread, show a roofer. A flashing that throws water off badly can leave heavier streaks, and our cracked lead flashing page lists what to look for.
What a roofer does about it
In most cases the answer is to wait. The staining stops as the surface weathers, and the first few months of rain do much of the cleaning. A roofer who has finished a job will often tell you to expect it, so it is a surprise only when nobody has said.
If the marks are bothering you, a roofer can rinse the lead and the neighbouring surfaces with clean water. The aim is to remove loose residue from the surfaces below without scrubbing the lead itself. A hard brush or abrasive cleaner on the lead can damage the surface that is forming and restart the process.
A product that suits one roof may not suit another, and the maker's instructions decide whether a treatment or coating is appropriate. If someone proposes a treatment, ask what it is, who applies it, and whether it is intended for lead.
What does need action is a flashing that is lifting, split or letting water in. Those are repairs, not staining, and the lead flashing repairs page covers them.
When the staining points to something else
White marks are not always the lead. Before you decide, check whether the pattern matches what you would expect from new lead:
- Is the flashing new, fitted in the last year or so?
- Do the marks run downhill from the lead, onto the tiles or wall directly below?
- Are they powdery, easy to wipe and not crusty?
If the answer to all three is yes, it is most likely the surface layer. A white deposit on brickwork that comes from the brick itself, or from mortar that is wet and leaching, looks similar but behaves differently. That kind of staining stays where the damp is, whether or not there is lead nearby, and it points to water getting into the wall.
The practical test is timing. Lead staining eases as the lead weathers, but a damp wall carries on in wet weather. If you are unsure, send photos of the lead and the wall beneath, taken a month apart.
Old lead that has been in place for years and is still staining its surroundings is worth a close look at the whole abutment. The lead roofing page lists the repairs we carry out.
