A leaking gutter joint is unsightly and could become a nuisance. Water seeping and dripping from a leaky gutter can cause slippery conditions on sidewalks or stair steps, particularly during spring thaw when daytime temperatures are above freezing but nighttime temperatures are below freezing. The situation can be rectified without any major rebuilding or gutter realignment. This can be accomplished by using a specialised gutter seam sealant available at virtually any hardware store.
Remove any standing water in a gutter that leaks and needs repair. Soak up the water in a sponge or slightly spread the gutter seam and allow the water to run out.
Mix up a batch of soapy dishwater solution in a bucket. Thoroughly wash the area to be sealed. Remove all grease, dirt and grime, and allow the area to dry before sealing begins.
Apply the gutter seam sealant directly onto the seam that leaks. Many gutter manufacturers specify their own sealant for the job, so if you know the manufacturer's name, use their particular brand of sealant. If you do not know the manufacturer's name, use a generic gutter sealant for the type of material your gutter is made from. For example, an aluminium gutter uses an aluminium specified sealant, while a vinyl gutter will use a vinyl specialised sealant. Many types come in either squeeze tubes, which you can squeeze out with your hands, or caulk tubes which will need to applied with a caulk gun. Choose which type of dispensing type is right for your situation.
Spread the sealant on evenly and smoothly with a putty knife. Cover the entire seam thoroughly.
Plan your drying time with the weather accordingly. If a sealants instructions say that it needs to cure overnight before getting wet, observe the weather pattern in your area to ensure a period of dry weather that correlates to this time frame before you apply the sealant.