If your eavestrough leaks, it’s probably faulty joints, right? Then again, there might be nothing wrong at all, especially if water cascades from the eavestroughs only during heavy downpours. Few systems can handle the volume. But before you smear goo all over your eavestrough, eliminate other possible leak sources first.
A faulty overlap?
Sometimes the trouble is between the roof and the back of the trough—the shingles or the metal drip edge don’t project far enough over the back of the trough. Get up on a ladder with a hose, turn the water on and look for water flowing behind, not into, the eavestrough. Sometimes, it’s enough to remount the eavestrough higher to correct a back-of-trough leak, but it’s usually better to cut strips of aluminum flashing to tuck under the drip edge and over the back of the trough.
These can also cause eavestrough overflows and leaking, even during moderate rains. Check the slope by looking for standing water in the trough after a rain. If more than half the height of the eavestrough is filled with standing water, raise the low spots to correct the water flow.
A leaky joint?
For reals? Wait until your eavestrough is completely dry, clean out all debris and remove the existing tar or caulking from the faulty joints. Polyurethane caulking is one of the best joint repair options because it sticks so well and lasts so long. Squeeze a healthy bead on the joint, then use your finger to work it into every crevice.