Wire brush in an oscillating tool

I finally climbed up for a hands-on look and found I was very wrong about the state of the gutter and the likely leak.

The gutter is _not_ rusting through, and the leak appears to be at a seam a foot or two from where the drips were landing. The bumps I took to be rust blisters are just moss stuck to the gutter (convincingly near the point of drippage) and the seam, which looked crude but functional from the ground is clearly cracked in what looks like caulk.

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If only the rust on my vehicles was an illusion! The hole has been taped to keep critters out.

I've had better long term results with silicone instead of acrylic caulk, where it doesn't need paint. Metal and plastic gutters change length with temperature more that the wood of the house and the joints must allow it unless the gutter is free to slide.

Wood has among the lowest thermal expansion rates along the grain, and one of the highest across it.

Great minds must think alike 8-)

After a bit more cleaning it turned out there was a longitudinal crack in the gutter at what I guess was a decorative crease about half an inch above the bottom. The area looked somewhat odd from the ground, but I didn't recognize it as broken.

Given the crack was a couple of feet long, I got some fiberglass ribbon, 4" wide and six feet long. After priming the wire-brushed inner surface with roofing cement cut to pourable consistency with "paint thinner substitute" I laid down the ribbon in the wet primer and worked more of the diluted cement into the fabric, somewhat in the manner of laying up fiberglass on a boat. The nice thing about cloth is that it's fairly limp, so it can be stuck to the contour of the metal by the "glue" and the air bubbles worked out.

I somewhat doubt it's a waterproof patch, but if it slows the leak some I'll be satisfied. The gutter really should be replaced. If it needs rework, I think the cement can be re-softened with solvent and overcoated.

As an aside, does anybody know what the difference is between paint thinner and "paint thinner substitute"? The "substitute" seems to work fine, AFAICT. Since I'm in California it's likely to do with either air pollution or toxic chemicals, but no explanation comes readily to hand.

Thanks for writing,

bob prohaska