Question answered
What are lead wedges?
The short answer
Lead wedges are small folded or rolled strips of lead tapped into a raked joint to hold the top edge of a flashing tight against the wall. They stay put and do not rot. The joint is then pointed with mortar, or finished with sealant, over the top. A flashing without wedges relies on the filling alone, and the filling is usually the first thing to fail.
Wedges are tiny and almost never seen, yet they decide whether a flashing stays in its joint. Here is what they are and why a good repair always includes them.
What a lead wedge is and how it looks
A wedge is a short piece of lead, folded over on itself or rolled into a small tapering plug. It is made from offcuts of the same sheet as the flashing, so it is the same metal and weathers the same way.
The fitter folds the top of the flashing into a slot raked along one of the wall mortar courses. Wedges are then tapped into the groove at regular spacing, pinching the lead tight against the back of the joint. Because they are lead, they are soft enough to bite into the brickwork and grip without cracking it.
The fitter folds them to suit the width of the joint, so a wedge for a narrow brick course is smaller than one for a wide stone joint. Once the joint is pointed, you cannot see them. From the ground a good flashing and a poor one look the same, and the difference is inside the wall. That hidden detail is why two quotes for the same flashing can describe very different repairs.
What they actually hold
The wedges, not the mortar, carry the load. They hold the lead against the back of the joint and stop it dropping or springing out under its own weight and the pull of the wind. The pointing is applied afterwards to lock the wedges in and close the groove to rain.
This division of labour is important. Sealant on its own gives the lead nothing to bear against, so any weight on the edge falls on the bead. Mortar by itself is brittle and will crack as the wall and roof move; lead is flexible and will not. When wedges hold the lead, the mortar can crack without letting go of the flashing. When there are no wedges, a cracked joint means the flashing is loose within weeks or months.
The same logic explains why a flashing that was only pointed can look sound for a year and then rattle in the first strong wind. The failure that results is described in lead flashing pulling out of the wall, which also covers how the joint is rebuilt.
Why other fixings are poor substitutes
You sometimes find a flashing held with something else. Bits of timber rot and shrink, leaving a loose joint. Nails punched into the mortar do not grip a soft sheet and can tear it as it moves. Fillets of cement hold the lead rigidly, then crack when the wall moves.
Lead wedges avoid those problems because they are the same metal, they do not rot and they allow the sheet to flex slightly while keeping it in its seat. That is why traditional work uses them and why we use them on new and repaired joints alike.
If you are tempted to push the lead back in yourself, the real fault is the missing grip, not the gap. Our page on fitting lead flashing yourself explains why that is better left to a roofer.
Where wedges go missing
We find wedges absent after past repointing, when old mortar was raked out and the wedges were never replaced, and where a roofer relied on a bead of sealant. Old cement pointing hacked out roughly can also take the wedges with it, leaving nothing to grip. Stolen lead leaves the wall groove open, and new lead put back without wedges has the same weakness from the start.
A lead-lined parapet gutter is another place where it matters. The upstand at the back is turned into the wall and needs the same wedged joint to resist wind and ponding, as covered in lead parapet gutters.
On a survey, we look along the joint for gaps, loose pointing and a lifted edge, and we photograph what is there. A close view of the wall joint will often show a flashing resting in the groove and not gripped by it.
Wedges, sealant and the finished look
Once wedges are in, the joint is closed. Pointing in a mix to suit the wall is the traditional finish. Sealant is sometimes used as a final skin, where the brickwork is uneven or the weather is unkind, and our page on sealant for lead flashing sets out when it helps and when it does not.
Because the wedges are lead, they take on the same grey as the flashing, the soft grey lead takes on as it weathers. Nothing about them spoils the appearance of the finished wall.
Expect the quote in writing after the survey, as one figure. If your flashing is loose, ask whoever is quoting whether wedges are part of the repair. It is a short question, and the answer says a lot about the standard of the work. More on the metal itself is in our lead roofing section.
Lead wedges: two more questions
How do I know whether my flashing has any wedges behind the pointing?
You cannot tell from the ground. A roofer can see the joint close up, check for lifted edges and tap the lead gently. On a survey we photograph the joint and say whether the lead is held by wedges or only by the filling.
Can wedges be added without replacing the whole flashing?
Often yes, if the lead is sound. The old pointing is raked out, wedges are tapped in and the joint is repointed. If the lead is split or thin, that run is renewed in the same visit.
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
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