How Do You Fix a Leaking Gutter Joint?

A plastic gutter is made of lengths joined by short sections called union clips, with a rubber seal inside each one. The seal does the sealing; the clip simply holds the two ends together and presses them against it. Over the years the rubber dries, hardens and loses its spring, and then a thin trickle gets past on every wet day.

Movement is the other cause. Plastic grows and shrinks with the weather, and a joint fitted tight can open a little on a cold morning. Add a gutter that has dropped between brackets, and the two ends are pulled away from each other and from the seal. Debris makes it worse, because grit trapped in the joint wears the rubber and stops the clip closing fully.

Look at where the water goes. A drip from the underside of a joint, a dark streak down the wall below it, or green growth running from one point are the common signs. A stain on the brickwork under a joint shows how long it has been leaking. Our look at why gutters overflow helps tell a leak from a spill over the lip.

Start by emptying and drying the gutter around the joint. Water makes a repair impossible, and a wet seal never settles. Open the clip, lift out the old rubber, and wipe both gutter ends clean so no grit sits where the new seal will go.

Fit a new seal of the right type for the gutter profile, close the clip firmly and check that both ends sit square in it. Many fixes stop here. Where the clip itself is cracked or has lost its grip, replace it, since a weak clip cannot press the seal flat.

Then look at the support. A joint sitting right at a bracket is stronger than one between two, so make sure there is a bracket close on each side. If the gutter has pulled away because the fascia behind has gone soft, adding a bracket into rotten wood will not last, and the board needs sorting first. Once everything is closed, run water through from the high end and watch the joint. It should stay dry along its whole length, and the water should carry on to the downpipe without lingering. A thirty-second test with a bucket saves a second visit.

Gutter sealant has a place. On a joint where the seal is sound but a tiny gap has opened, or on a hairline crack in an otherwise good section, a bead of suitable sealant can stop the drip for a while. It has to go on a clean, dry surface, and it works best as a short-term measure while a proper repair is arranged.

It does not last on a joint that moves. A bead across a gap that opens and closes with every temperature swing will crack away within a season or two, and it can hide a failing seal while the real fault gets worse behind it. Silicone smeared on from a ladder, over dirt and in the wet, rarely holds at all.

Be wary too of a repair that keeps recurring. If the same joint, or the same run, needs sealant every year, the cause is something else: a sagging bracket, a poor fall or a worn-out gutter. Our answer on the fall a gutter should have explains the first of those, and sagging gutters cover the second.

Not every gutter has rubber seals. Older cast iron gutters are bolted together with putty or mastic in the joints, and when that dries out, the repair is to take the joint apart, clean the faces and rebuild it. Our answer on cast iron gutter repair goes through that.

Concrete gutters of the Finlock type, found on some 1950s houses, are a different case. The RICS defects record says leaking joints have done serious harm to many of them, but it adds that a close look can separate the gutters needing major work from those that will stay sound with proper care, and that taking them out should not be assumed. Have one of these inspected in person.

For ordinary plastic gutters, renew the section when the plastic is cracked, brittle or bowed at the joint, since a new seal cannot cure a damaged end. If several joints fail in the same season, the run is probably near the end of its life and a new one may cost less than repeated callouts. Send us a photo of the leaking joint and the wall below it, and we will tell you if a seal, a section or a run is the answer. Our gutters, soffits and fascias page lists the full range of work.