How to seal a leaking gutter joint
A twenty-dollar tube of sealant and an hour usually fixes a drip that would otherwise rot the fascia behind it. The trick is entirely in the preparation.
- Doing it yourself
- $15–$45
- Typical contractor price
- $150–$400
This job puts you on a ladder
- Set the base one foot out for every four feet of height. Steeper than that and it slides out from under you; shallower and it tips backwards.
- Extend the ladder at least three rungs above the gutter and tie it off, or have someone foot it. Never rest a ladder on the gutter itself — aluminium will fold.
- Keep your hips between the rails. Reaching sideways past the rails is what puts people on the ground; move the ladder instead, however tedious that gets.
- Stay off it in wind, rain, or on wet grass. A ladder on soft ground sinks unevenly as you climb.
- Standing on the top two rungs is how most ladder falls happen. If you cannot reach from the third rung down, the ladder is too short.
Tools
- •Extension ladder
- •Wire brush
- •Putty knife or scraper
- •Caulking gun
- •Rags and denatured alcohol
- •Work gloves
Materials
- •Gutter and flashing sealant (not general-purpose silicone)
- •Replacement gutter screws if any are loose
Step by step
Find the leak with water, not by eye
Run a hose into the gutter and watch from below. Dried mineral streaking shows where water has run in the past; it does not reliably show where it is escaping now.
Strip the old sealant completely
Scrape every trace of the old bead out with a putty knife, then go over it with a wire brush. New sealant bonds to metal, not to old cured sealant, and this is why most reseals fail within a season.
Watch out: Leaving a thin film of the old material is the single commonest reason the repair leaks again by spring.
Clean and dry the joint
Wipe with denatured alcohol and let it flash off. Any oil, grit or moisture left in the seam stops the sealant keying to the aluminium.
Apply from inside the gutter
Lay a continuous bead along the seam on the inside, roughly 3mm thick, and work it into the joint with a gloved finger. Sealing from outside looks tidier and does almost nothing — water sits on the inside.
Watch out: General-purpose silicone will not bond to aluminium for long. The tube needs to say gutter, flashing or roof.
Let it cure before it gets wet
Most gutter sealants need 24 to 48 hours dry. Check the forecast before you start; a shower four hours in will wash the bead out of the seam.
Stop and call someone if
- More than three or four joints are leaking — at that point resealing is a losing battle against a gutter near the end of its life.
- The metal is pitted through, or you can see rust holes rather than a seam leak.
- The fascia behind the gutter is soft or discoloured.
Or read more about gutter repair.
Common questions
- Why did my last repair fail?
- Almost always one of three things: old sealant left in the joint, a wet or dirty surface, or general-purpose silicone instead of a gutter-rated sealant. Preparation is most of this job.
- Should I seal or replace the section?
- Seal an isolated joint on gutter that is otherwise sound. If the run sags, the metal is pitted, or several joints leak, you are maintaining something that has already failed.
Last reviewed September 19, 2026. General guidance only — your house, your roof and your local building code are what actually govern the work.