How Do You Fix a Leaking Gutter Joint?

Why gutter joints leak

A joint is the weakest point in a gutter. Lengths of uPVC gutter are joined with a union bracket, a clip-over piece with a rubber seal inside that presses against both ends. Over time the rubber hardens and shrinks, the plastic expands and contracts with the weather, and grit and silt build up in the seal. Metal gutters have bolted or sealed joints that open as sealant dries and the metal moves. Ice can force a joint apart in winter.

The cause is often not the seal alone. A gutter that sags between brackets tips the water towards the joint and makes it work harder. A bracket that has pulled from a rotten fascia lets the run drop. A joint that is dripping on the outer side may simply have had its clips left unlocked. So the first job is to look at the line of the whole run, not just the drip. Our guide on signs your gutters need replacing lists faults that go beyond one joint.

How to reseal a joint

For a plastic gutter in good condition, a typical repair runs like this. Wait for dry weather and work from a stable platform. Put a bucket or tray under the joint. Unclip the union bracket, remove the old seal and clean both gutter ends and the bracket with a cloth and warm water. Dry them. Fit a new rubber seal, or apply a bead of sealant recommended for the material. Refit the bracket, check that the gutters sit fully in the union, and clip it shut. Run water along the gutter and watch the joint.

A few cautions:

• General-purpose sealant on dirty or wet plastic will not stick; clean and dry first.
• Silicone does not take well on some old plastics, and a product made for guttering is a better bet.
• Do not over-tighten the clips, or the plastic may crack.
• Do not stand on the top rung or lean off the ladder; use a stabiliser or a tower.

Damp patches on the wall below the joint tell you how long the leak has run. Green algae streaks, a dark stain on the render, or flaking paint under the drip point mean the water has been falling on that spot for months. Check the wall and the ground for damage, and make sure the bricks are drying out once the leak is fixed.

When the joint should not be saved

Some leaks come from a gutter that has simply run out of service. A joint cannot be fixed if the plastic is cracked at the socket, if the ends are warped so that they no longer meet, or if the gutter has been resealed repeatedly with a thick layer of old sealant. Cast iron joints with rusted bolts can leak because the metal itself has corroded. On older cast iron, the repair is often a new bolt, putty or modern sealant, which is covered in our page on cast iron guttering on period homes.

If several joints leak on one run, replacement is more cost effective than fixing each one. Costs are on the gutter replacement cost page. Aluminium gutters rolled to length on site avoid joints along the run, and the page on one-piece aluminium guttering explains how that works.

Temporary measures exist. A strip of self-adhesive flashing tape or a gutter repair tape across a dry joint can hold for a short time, which is useful before a storm. Neither is a permanent cure, because tape peels in sun and frost, and a patched joint hides the cause. If you use one, plan the proper repair for the next dry spell. A tub or a bucket under the drip for the time being protects the wall and the path.

Checking the bigger picture

While you are at it, look at the fall. A gutter should drop gently towards the outlet, and a spirit level or a trickle of water will show whether it does. Check the brackets for spacing, because too few allow sag. Check the fascia behind for soft timber. And check that the gutter is not overflowing because of a blocked outlet; our page on why gutters overflow can help sort that out.

Our free survey looks at the joints, the brackets, the fall and the fascia, photographs each issue and tells you which joints can be resealed and which run should go. The guttering, soffits and fascias page explains the service. You receive fixed written figures after the visit.