Most gutter leaks start at a joint: an inside or outside corner, an end cap or a downspout outlet. A sealant made for gutters stays flexible through summer heat and winter cold, bonds to aluminium, steel or vinyl, and can be applied to a surface that is not perfectly dry. General-purpose silicone and roof cement do not do all three.
Below, the four product types are compared by the leak each one fixes, and the number of joints on a typical two-storey house is worked out with our gutter calculator for a 160 ft eave run.
Pros and cons describe each type from its specifications; this is not a hands-on product test. As an Amazon Associate we earn from qualifying purchases.
Best for: Corners, end caps, downspout outlets and lap joints. Check: Compatible metals, paintability and whether it can go on damp surfaces.
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Best for: Pinholes, small cracks and seams you cannot re-caulk. Check: Butyl adhesive (not acrylic) and a UV-stable backing.
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Best for: Long runs of worn steel gutter with many pinholes. Check: Coverage per container and recoat time.
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Best for: Any cartridge sealant, especially on a ladder. Check: Thrust ratio (higher for thick sealants) and a dripless release.
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Best for: Holding the ladder off the gutter while you work on it. Check: Arm width and whether it rests on the roof or the wall.
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Count the joints before buying sealant: every inside and outside corner has two seams, each end cap one, and every downspout outlet one. The gutter calculator estimates corners, end caps and downspouts from the eave length; the example below uses the same function.
Worked example: A two-storey house with 160 ft of gutter
About 23 joints to seal. Read the bead length each cartridge covers on its label and buy one spare — a half-sealed corner still leaks.
Sectional gutters also have a lap joint every 10 ft or so; add those if yours are not seamless. The gutter size calculator checks whether the gutters are large enough, since overflowing troughs look like leaks.
| Leak | Best fix | Notes |
|---|---|---|
| Drip at a corner or end cap | Gutter sealant | Remove the old bead first |
| Pinhole or small crack | Butyl repair tape, or sealant | Clean and dry the surface |
| Many pinholes along a steel run | Liquid rubber coating | Wire-brush rust; plan on replacement |
| Leak at the downspout outlet | Gutter sealant around the outlet flange | Re-rivet if the outlet is loose |
| Water behind the gutter | Drip edge or gutter apron, not sealant | See the drip edge calculator |
Water running behind the gutter is usually a missing drip edge; the drip edge calculator sizes it. If debris is the real problem, see the gutter guard buying guide.
A sealant sold specifically for gutters and seams, which stays flexible, bonds to aluminium, steel and vinyl and tolerates some moisture. General silicone and roof cement are not designed for the movement at gutter joints.
Some 100% silicone products work on aluminium, but many cannot be painted and some do not bond well to painted gutters. A purpose-made gutter sealant is the safer choice.
It varies by product; many skin over in under an hour but need longer to fully cure. Check the rain-ready time on the label and seal on a dry day.
Some gutter sealants can be applied to damp surfaces, but none bond to standing water. Wipe the seam and read whether the product allows damp application.
Sealant is better for joints because it works into the seam. Butyl tape is better for pinholes and cracks in the trough where there is nothing for sealant to grip.