Mortar or sealant
Should lead flashing be pointed with mortar or sealant?
The short answer
Either can work, and the better choice depends on the wall. Mortar is the traditional pointing and matches brickwork, while a flexible sealant copes with some movement but needs renewing. What matters most is that the lead is held by wedges first, since pointing only closes the joint. We choose after looking at the wall.
How the top edge of a lead flashing is held and sealed, the strengths of mortar and sealant, and how we pick between them.
What the pointing is actually for
Lead flashing that meets brickwork finishes in a slot raked out along one mortar line, the chase, with the top edge of the lead folded into it. Small lead wedges are driven in to hold it there. The remaining gap is then filled, or pointed, to keep rain out of the chase. That filling can be mortar or a sealant.
The pointing does not hold the flashing up. The wedges do that, and the lower edge of the lead laps over the roof covering. So if pointing fails, the lead should stay put, but water can get in behind it. Our page on lead wedges explains how they work, and why a flashing pointed over missing wedges is only half done. Think of the wedges as the fixing and the pointing as the weatherproofing, two jobs that are easy to confuse because they sit in the same groove. A chase that looks tidy from the ground can still be missing its wedges, which is one reason we photograph it close up.
The case for mortar
Mortar is what the wall was built with, so it blends in and looks right. A mix chosen to suit the brickwork bonds well to the masonry on both sides of the chase. On older buildings the mix matters, because a mortar harder than the existing joints can damage the brick, so we match the mix to the joints already in the wall. If your building is listed, ask the council's conservation officer what they want to see before work starts.
Mortar is rigid. It can crack when wall and roof shift by different amounts, and even a hairline crack lets water in, particularly when the weather drives rain sideways at the stack. It does not need repainting or topping up the way some products do, and a well-pointed chase can stay sound for a long time. For a chimney stack open to the weather, a mortar that suits the brick is the traditional answer, and the one most roofers on older brickwork are asked for.
The case for sealant
A sealant stays flexible, so it can ride small movement without cracking, and it is quick to apply. That makes it popular for repairs and in awkward places. It can also be neat on a modern wall, where a shallow chase has been cut with a disc and the brickwork is regular.
The downsides are age and appearance. Sealants harden, shrink or lose their grip, and manufacturers set out how deep and wide a joint should be for the product to work, so follow the data sheet for whatever is used. Sealant also looks different from the surrounding brick, which shows on an older property. Sealant smeared over a chase that was never cleared and wedged is a repair that will return, as our answer on leaking lead flashing describes. It buys a season, then the water finds the gap again.
How we choose
We look at four things: the age and type of the wall, the width and depth of the chase, how exposed the junction is, and what is already there. A period brick stack gets a mortar to suit. A modern render or cladding junction may call for a sealant detail the manufacturer supports. Where we are unsure, the survey says that, with a photograph of the chase attached, and recommends the pointing that fits the condition we find.
Work should never be pointed over loose or missing wedges, or over a chase packed with old failed filler. The old material comes out, the lead is checked, wedges go in and only then is the pointing done. Finish counts here: the joint should look tidy from the street as well as keep the water out. The whole detail runs from the chase down to the lower edge, and each part has to work for the next to matter.
Cost and next step
Repointing a chase is a small part of most flashing jobs, and our quote follows the survey with a single total price. Checkatrade's roof repair guide, updated October 2026, lists lead flashing repairs at £50 to £70 per metre, plus VAT. Where scaffolding is needed to reach a stack it changes the total, so before you accept any quote, ask whether VAT and scaffolding sit inside the price. A stack that rises above a steep roof is usually harder to reach than a low wall, and that difference can matter more to the total than the pointing itself.
If your flashing has lifted or the pointing has dropped out, send photographs or ask for a survey. You can also read about the small strips that hold the lower edge in our answer on lead clips, and about the wider subject on the lead roofing and leadwork hub. Tell us what the wall is made of and roughly when the house was built, and that helps us arrive prepared for the right mortar.
Related questions
Pointing questions
How often does pointing around a flashing need renewing?
There is no set interval. It depends on the product, the wall and the exposure. Look at the chase when the roof is inspected, and renew it when you see cracks, gaps or shrinkage, ahead of the wettest part of the year.
Can I use ordinary bathroom sealant on a roof flashing?
Check the product's data sheet first, because some sealants are not made for outdoor, sun-exposed joints. We use products suited to the junction and name them in the written quote.