Why Is There White Staining Under My Lead?

If a new flashing went in recently and white marks have followed, the link is direct. Bright lead is reactive. In the first weeks of exposure it builds up a surface of lead carbonate, a pale powder that forms when the metal meets rainwater and carbon dioxide from the air.

Why does it end up on the wall?

Rain dissolves and loosens the powder, then runs off the sheet carrying it. The white streaks follow the water path: down the slates, across the face of the brick, or over the render below a chimney apron. Where the water repeatedly runs, the marks build up into a stripe. A south-facing wall that dries fast can leave the streak crisp and white.

The powder is a by-product of the metal beginning to protect itself. Once a stable grey skin has formed, the run-off slows or stops, which is why the same flashing looks clean a year on. Older lead that has long since weathered does not usually behave this way, so fresh white staining under old lead points elsewhere, as the last section explains.

The best time to deal with staining is before it starts. The remedy is a thin film of patination oil, applied to new lead once it is fitted, and it controls the early reaction so less powder forms and less is washed off.

Does the oil stop it completely?

It reduces it rather than guaranteeing a clean wall. Heavy rain soon after fitting, a very exposed position or an uneven coat can still leave some marking. But a lead flashing that has been oiled usually weathers more evenly than one left bare. Our answer on patination oil on lead explains how it is applied and why it is worth asking for in the quote.

The film is only a finish. It does not alter how the flashing is made or fixed, and it does not make a poor job sound. It is a small, sensible protection for the wall, applied by the roofer at the end of the job.

Where an owner is about to have lead fitted above pale stone, light render or a painted wall, it is worth agreeing the oiling before the scaffold goes up, since it needs dry weather.

If the streaks are there already, patience is the first remedy. Much of the powder is washed away by further rain over a season or two, and the marks fade as the lead settles down.

Can I scrub it off?

Go gently. Dried carbonate can cling to porous brick and soft stone, and harsh scrubbing or strong chemicals can damage the surface and drive the stain deeper. Start with clean water and a soft brush on a small test area. Never use a pressure washer at close range on old mortar or soft stone. On a listed building, or an older wall of unknown material, ask a specialist before cleaning anything.

Use a ladder only where the ground is firm and the reach is low, and never lean on the lead, which creases easily. For marks high up, beside a chimney or on a steep slope, wait for a visit from someone with proper access. A ground-floor wall is the only place worth tackling yourself. The marks are not urgent, so waiting for a proper visit costs you nothing.

Run-off from fresh lead is harmless, but a few white or pale marks mean something else, and it is worth telling them apart.

Is any white staining a sign of a leak?

It can be. White crystals that appear inside the house on a wall below a flashing, or a powdery bloom on brickwork that returns after cleaning, are efflorescence, a sign of water moving through the masonry. If the staining is on the inside or on an old wall beside old lead, the flashing or the pointing may have failed. Our guide to the signs of failed flashing sets out what else to check.

The test is simple. Is the lead new, and are the marks only outside, under the sheet, in the path of the rain? Then it is almost certainly cosmetic. Are there damp patches inside as well? Then a survey is worth booking. We photograph the lead and the wall, show you the pictures, and explain what we see before anything is priced. The full range of work is on our lead work page, with a single written price.