The short answer
To fix a leaking gutter joint, clear the gutter, clean and dry the joint, then replace the rubber seal or apply gutter sealant and make sure the clips hold the two sections tight. A single weeping joint on a low run is reasonable DIY. If several joints drip, or the run is sagging or corroded, the sections need refixing or replacing.
Why a joint starts to drip
A gutter is made in lengths that join end to end. Each joint relies on a seal to hold water in, and on the sections staying aligned and tight. When a joint leaks, the cause is nearly always one of a handful of things.
On uPVC gutters the joint is a clip-over union with a rubber gasket inside. Gaskets harden and shrink with age and sun, and the union can be pulled out of line when the run moves with temperature. On older cast iron, the joint is a bolted flange with a putty or sealant bed. The bed dries out and cracks, and the bolt rusts and loses its grip. Aluminium joints are usually sealed with a compound that has the same tendency to shrink.
Movement is the cause under the cause. Brackets that have slipped let a section drop, and a joint under strain will not seal however much sealant is applied. Standing water and debris make matters worse, because wet silt sits against the joint and works through any gap. Clearing the run therefore comes first, as covered in our answer on how often to clean gutters.
How a joint is resealed properly
A lasting repair follows an order. Cutting corners is the reason many patched joints are dripping again within a season.
- Make it safe. Set the ladder on firm ground and have someone foot it. Do not lean out; move it along.
- Clear the run. Remove debris from both sides of the joint, and scrape out old sealant.
- Check the alignment. Look along the run. If one section sits lower or tilts forward, the clips or brackets need refixing first.
- Clean and dry. Wipe the joint surfaces and let them dry. Sealant will not bond to damp or dirty plastic or metal.
- Replace the seal. On a uPVC union, the gasket is lifted out and a new one fitted, then the clip is closed fully. On other materials, a fresh bead of sealant goes along the inside seam.
- Test with water. Pour a bucket along the gutter and watch the joint from below.
A tube of sealant squeezed over the outside of a failed joint hides the leak for a few weeks and then peels. The seal has to be remade on the inside, where the water actually runs.
When a DIY fix is reasonable
Repairing one weeping joint on a low run, reached safely from a short ladder, is a job many people can do. The materials are cheap, and the worst outcome of a poor attempt is that the joint drips again.
A useful habit is to mark the joint with a pencil line across the seam before you start. If the line has shifted when you come back after a few weeks, the section is moving, and sealant alone will not hold it. Also keep the old gasket or a photograph of it, so you can match the profile when buying a replacement. Gutter systems differ between makers, and a gasket from the wrong range will not seat properly, even if it looks close.
Be realistic about height and access. A gutter over a first-floor window, above a porch roof or beyond a conservatory is not a place for a stretched arm and a sealant gun. Anything out of comfortable reach is better left to someone with a tower or platform, because no joint is worth a fall.
Stop and look more widely before you start. A leak at a joint may be the first visible sign of something else, such as a sagging bracket line, a rotten fascia behind, or an old run reaching the end of its life. If water has been spilling behind the gutter, the board it hangs from can be soft, and fresh clips will not hold in rotten timber. Our guidance on looking after fascias and soffits explains what to check.
When the joint is not the real problem
Resealing suits a sound gutter with a tired seal. It is the wrong answer in several cases.
- Several joints drip along one run. The run has probably moved, or the whole set of seals has aged out together.
- The gutter is bowed or cracked. A split along a section cannot be fixed by sealing the end.
- Cast iron has rusted through at the flange. Bolts that snap or flanges that crumble need new sections.
- Water backs up at the joint every time it rains. That is a blockage or a fall problem.
Where any of these apply, inspect the whole run instead. Which material you have matters for the choice, and we compare them on the page about gutter materials. Our answer on repairing or replacing gutters gives the rules we use to choose between a patch and new sections, and our note on clearing gutters shows how debris builds up behind a joint.
Having it done
We repair gutter joints where a repair will hold, and we say up front when it will not. A visit starts with clearing the run and checking the fall, because a joint under strain will leak whatever is applied to it.
We photograph the joint and its fixings at the survey, so you can compare what is there with what we say before deciding. If the work is a straightforward reseal, it is priced as such. If the brackets and fascia need attention, we show you why. Meanwhile, jot down which joint drips and whether it shows in light rain or only in heavy storms, since that tells us a lot about the fall and the seal before we arrive.
Our gutters, soffits and fascias page covers the other roofline jobs we take on. If you would rather start from photographs, WhatsApp them to us and we will give you a view on the likely cause.
