There is a spot on the front of a house in Martinez where the paint has been peeling in the same two-foot patch for three years. It is directly under an outside corner of the gutter. Everywhere else on that elevation, the gutter is fine. It has held water through every storm since it went up. But that one corner drips a steady line down the fascia and the corner board every time it rains hard, and the homeowner has caulked it twice.
That pattern is so common it is almost diagnostic. A gutter leak is rarely a leak in the gutter. The long run itself is a single formed piece of aluminum with no holes in it, and unless something physically punctured it, there is nothing there to fail. Water gets out where two pieces of metal meet, and on a typical house there are only a handful of those places: the inside and outside corners, the end caps, the outlet holes where downspouts drop in, and on sectional gutter, every joint along the way. Those junctions are held closed by sealant. Sealant does not last as long as aluminum does.
What Actually Breaks Down Up There
Aluminum moves more than people expect. It expands and contracts about 0.0000128 inches per inch for every degree of temperature change, which sounds like nothing until you do the math on a real gutter. A 40-foot run swinging from a 25-degree January morning to a gutter surface temperature of 140 degrees on a July afternoon moves roughly five eighths of an inch over its length, and a smaller version of that happens every day the sun comes around. The joints absorb all of it, and sealant is the only thing up there being asked to stretch. It does that well for a while, then goes brittle, loses its grip on one side, and opens a hairline gap. You will not see the gap. You will see the stain below it.
The second thing that shortens sealant life around here is moisture that never leaves. Debris and shingle grit hold water against a seam long after the roof has dried, and standing water at a corner does the same thing on a bigger scale. A joint that stays damp fails several times faster than one that dries out between rains.
The third reason is the one nobody likes hearing: the wrong product was used. Silicone is what most people have in the garage, and silicone does not bond well to painted aluminum. It will look like a repair for about a season and then peel off in one rubbery strip. Gutter sealant is a different chemistry, usually a butyl or a tripolymer, made to stay flexible and stick to metal. It costs a few dollars more per tube and it is the entire difference between a repair that lasts a decade and one that lasts until October.
Why Re-Caulking Stops Working the Second Time
Here is the part that frustrates homeowners who have already tried to fix it. New sealant does not bond to old sealant. It bonds to whatever the old sealant is stuck to, which is nothing, because the old sealant is the thing that failed. So the second application traps a little water behind it, holds it there, and often makes the joint worse than it was.
A real repair means getting the joint dry, scraping the old material completely off both faces, cleaning the aluminum, and then sealing from the inside of the gutter rather than the outside. Sealing the outside is treating the symptom. Water sits on the inside, and that is the side that has to be closed.
Corner construction matters too. A box miter is a factory-formed corner, so the bend itself is continuous and there are two straight seams where it joins each run. A strip miter is two gutter ends cut on an angle and sealed to each other, which puts the seam right where the most water is turning. Strip miters go up faster and they are the first thing to leak. When somebody says a house needs new gutters because of one bad corner, ask which kind it is.
When the Corner Is Not the Real Problem
Sometimes resealing a corner is genuinely the whole job and the gutter has another fifteen years in it. Sometimes it is not, and the tell is what the leak has already done. Water running down an outside corner lands on the fascia, the corner board, and the soffit return, and those are wood. In Augusta humidity, wood that gets wet at that frequency does not dry out between events. If the fascia behind the gutter has gone soft, sealing the joint stops the drip but leaves you with a rotted board that the gutter is screwed into, which is worth handling at the same time rather than a year later.
Worth noticing where that corner is aiming, too. Outside corners sit near the ends of the house, which is frequently where a patio meets the foundation or where a screened porch ties in. A slow leak there has been putting water into the ground next to the exact structure you spent money on. The stain on the fascia is annoying. What is happening four feet below it is the part that costs something.