You’ve heard the expression “the weakest link in the chain.” The phrase is often used to describe the one specific spot in a process where failure is most likely to occur. In the typical residential gutter system, that spot is the corner of the guttering run.

Why Gutter Corners Are Troublesome

Corners are the places where leaks will most likely form. One reason is because all corners must consist of at least two pieces of guttering that are affixed together; and the seam where they meet is a natural weak point in the system. Also, it’s unnatural for water to flow around a corner; so when a gutter forces runoff water to change direction, it can often result in uneven wear on a specific point over time.

Types of Miters

The corner of a guttering run is often called a miter. Generally speaking there are three different categories of miters that can be utilized in a gutter system. A hand-tabbed miter involves two pieces of guttering that are screwed together at two thin “tabs” that overlap each gutter on the inside; but these tabs can sometimes pull apart during temperature-related expansion and contraction of the metal gutters. A pre-fab box miter is one corner piece that attaches to two perpendicular gutter runs; which of course means two different seams that must be fastened correctly. Finally, a strip miter is a skinny piece of aluminum that fits over the corner gutter seam and screws into both of them; but this strip requires a greater amount of sealant to prevent leakage.

The Importance of Gutter Sealants

In short, each type of miter has its own unique “leak-prone” properties, which is why proper sealant use is so vital. Common sealant choices include caulk, silicone, or roofing tar; although so-called “super-sealants” like Unibond, Geocell 2300, or Vulkem 116 are often used by professionals. One important thing to remember about these products is to never apply a new sealant over an existing sealant material; otherwise, the bond won’t hold well and leaks are much more likely to form.

How to Repair a Leaky Miter

If you do come across a leak in your gutter miter, it’s highly recommended that you seal it promptly before it becomes worse and leads to water damage of your gutter, fascia, or lawn. Here is how to properly seal any type of gutter miter:

1. 1. 1. Clear all debris out of the gutter miter.
      2. If the precise source of the leak isn’t clear, spray the area with a garden hose to identify the crack, hole, or gap where water is seeping out of the miter.
      3. Take an abrasive pad or wire brush and scrub the debris away from the leaky area. Remove any other dirt and grime with an all-purpose cleaner, then rinse the area clean and towel dry it.
      4. Using a putty knife and/or needle-nose pliers, cut away the existing sealant from the miter seam.
      5. Take your sealant of choice and apply it directly over the seam(s) of the miter.
      6. For other holes and cracks, use the sealant to fill them up as well.
      7. For a larger hole, cut a piece of metal flashing that’s large enough to cover it, then apply roofing cement both to the hole and over the edges of the patch that covers the gap. Allow the roofing cement to dry.

Unless you can somehow redesign your home guttering system, you’ll have to live with one or more miter corners. The key is to be vigilant in inspecting them so that they don’t become leaky spots that can compromise the integrity of your gutters.

Written by Del Thebaud