Why is my lead leaving white streaks?

Freshly rolled lead is bright and silvery. Once it is exposed, the surface reacts with oxygen, moisture and carbon dioxide, and builds a skin of oxide that slowly turns into lead carbonate. In its finished form that skin is the dull, even grey you see on a roof that has stood for generations, and it protects the metal underneath.

The awkward part is the stage in between. Early carbonate is loose and chalky. A shower can lift it off a flashing, wash it down the face of the building and dry it as a pale trail. Because water follows the same path every time it rains, the trail repeats itself in the same place, often with a clear edge where a drip has run.

So the streak is not a sign of a leak, a thin sheet or a bad batch of metal. It is a sign that the surface is still weathering and that rain is taking part of it away. Our guide to patination oil and why new lead is treated covers how the weathering is managed on a new job. This page is about diagnosing marks that are already there.

The shape of the stain points to its source. A straight vertical streak under a parapet gutter outlet or a sill flashing is run-off from the lead directly above. A broad pale bloom below a long cover flashing means the water is leaving the whole length of metal rather than one point. Streaks that start partway down a wall may come from a lead apron, a soaker or a chimney flashing that you cannot see from the ground.

It also matters what the marks sit on. On limestone and sandstone the powder lodges in the pores and can look as though the stone itself has been bleached. On brick it shows as a pale film, and on slate as a whitish bloom that rain gradually thins. Painted render holds the mark in the paint surface.

Is it lead at all?

Not every white mark below a roof is lead. Salts migrating out of damp masonry leave a white crust of their own, and so does lime washed out of mortar joints. A quick test is the position. Lead carbonate follows a flow path from a piece of lead. Salt and lime deposits sit where the wall is wettest, and often have no lead anywhere above them. A photograph of the wall, taken with the roof edge above it in frame, lets us confirm the source before anyone climbs a ladder.

The lead itself is not harmed. Carbonate loss at this level is a surface effect, and the sheet goes on weathering to its stable grey. MyJobQuote's 2026 guide says flashing lead correctly installed can last over 80 years, and over 100 years in the higher codes, so a streaky first year says nothing about its life.

The building below is a different matter. Run-off that keeps landing on the same stone stains it more deeply each time, and in a damp spot it can encourage algae to grip the pale film. On a conservation area house the visual effect matters more, and it can sit awkwardly beside fresh pointing or a recently cleaned wall. The streaks are a cosmetic fault, but one worth stopping early because the older they get, the harder they are to remove.

One caution: heavy, persistent runs from a roof that is only a few years old can point to something else, such as an outlet that is too small or a gutter overflowing across the lead. That is a drainage fault with staining as the symptom, and we check it on the survey.

For lead that is still pale and bright, the answer is to clean the surface and apply patination oil in dry weather, so the carbonate forms evenly and holds together. That is cheap compared with cleaning stone afterwards. Where the lead has already gone grey and stable, the run-off usually fades away on its own over time, and no treatment is needed.

Existing marks on masonry are a separate job. Start with the gentlest method: clean water and a soft brush, working from the top down and rinsing clear. Avoid acid cleaners and abrasive blasting on limestone, because they can etch the surface and leave a worse mark than the one you started with. On listed buildings, or anything in a conservation area, ask the council's conservation officer before cleaning, since cleaning methods can themselves need consent.

Where staining keeps returning, the lead may need a drip or a stand-off detail so water leaves it clear of the wall instead of running down the face. The detail depends on the roof, which is why we look at it rather than guess. A lead flat roof with a poor fall will throw standing water over its edge, and our answer on patching a lead flat roof covers when the roof, not the wall, is the thing to fix.

Some owners ask whether swapping the lead removes the problem for good. Zinc and copper do not shed white carbonate in the same way, but each brings its own look and its own run-off, and on an older stone building the colour change is obvious. Our head-to-head on lead or zinc for a period roof weighs life, appearance and likely acceptance by a conservation officer.

On most older houses, treating the lead and keeping it is the like-for-like course. Replacing a metal because of a surface effect would be a drastic reaction.

The survey starts with the marks from the ground, then moves to the lead above: which sheets are pale, which have gone grey, and where water leaves the metal. Outlets and gutters are checked for blockage, since overflow is a frequent reason for repeat streaks. Cleaning or oiling on its own appears as a separate line from any repair.

Where lead needs renewing or a different detail, the itemised quote prices each part individually, and our written 10-year workmanship guarantee covers the work. Leadwork in general is described on our lead roofing page. To start, ring 01453 933613, use WhatsApp or the form, and attach a photograph of the stained wall.