Gutters rust from the inside out, under wet debris, where nobody looks. By the time it is visible from the ground it has usually been running for years.
This post covers how to tell what stage you are at, and the awkward situation where a clean reveals a hole that was already there.
Why gutters rust where they do
A gutter is designed to be wet briefly and then dry. Debris changes that.
Wet leaf litter sitting in the trough holds moisture permanently against the metal. Decomposing organic matter is also mildly acidic, which accelerates it. So the corrosion starts under the debris line, along the back of the trough and in the low points, and it works outward.
Three things make it worse:
Salt. On the coast, chloride in the air accelerates everything. The pattern to know is that corrosion is worst where salt lands and rain does not wash it off — so the underside of the gutter, behind the fascia, and sheltered sections corrode before exposed ones do. See what coastal Sydney does to a home’s exterior.
Dissimilar metals. A copper pipe, a lead flashing, or copper runoff draining onto a Zincalume or galvanised gutter will cut a corrosion line straight through it. Covered in Zincalume vs Colorbond.
Treated timber. Runoff from CCA-treated pine or some hardwoods is corrosive to coated steel.
Assessing what you have
Surface staining only. Orange marks on the inside of the trough with sound metal underneath. Clean it, keep it clean, and it may run for years more.
Scaling and flaking. Rust lifting in layers. The metal is being consumed. Treatable in the short term, but the clock is running.
Pinholes. Small perforations, usually in the low points or along the back seam. The gutter is at end of life, though patching can buy a season or two.
Perforation along a run, or at the joints. Replacement.
The test is a gentle press with a screwdriver on the rusted area. Sound metal resists. If it gives or punctures, there is nothing left.
Check the back of the gutter and the fascia behind it as well. Water getting behind a gutter rots the fascia board, and a rotten fascia means the gutter is no longer properly supported regardless of its own condition.
The awkward part: cleaning reveals leaks
This happens often enough to be worth stating plainly.
A gutter packed with compacted debris can be holding water back from a hole that is already there. The debris is acting as a plug. Clear it, and the water now runs through the perforation it was blocked from reaching.
The homeowner sees a leak that was not there before the clean, and the natural conclusion is that the cleaner caused it.
The honest way to handle this is to inspect and photograph before starting, flag any corrosion found, and show the condition of the metal rather than just the result. On our jobs that is part of the photo report, and it is the reason we take before shots as well as after.
If your gutters are visibly rusted and someone quotes a clean with no mention of their condition, ask.
Repair options
Rust converter and a gutter sealant on isolated pinholes. Clean back to sound metal, apply converter, seal, and accept it is a holding measure of a year or two.
Gutter liner or membrane systems coat the inside of the whole run. Can extend life meaningfully on a gutter that is scaled but not perforated. Not a fix for a gutter already full of holes.
Section replacement where one run has gone and the rest is sound. Colour matching on an older roof can be a problem.
Full replacement. On a house where the gutters are of an age, replacing the lot is usually better value than chasing failures around the roofline for five years.
Worth doing at the same time: check the fascia, and get the downpipes and underground line flow-tested while the gutters are off — see blocked downpipes.
Making the next set last
Clean on a schedule rather than on discovery. Under canopy that is two to three times a year — how often gutters need cleaning in Sydney.
Fresh-water rinse the gutters, inside and underneath, if you are within a few hundred metres of surf. It is the single most effective coastal maintenance measure and it costs nothing.
Think carefully about gutter guard. Done well it reduces debris load substantially; done badly it traps a damp layer of fine material against the metal and accelerates exactly the corrosion you were trying to prevent. We go through the trade-offs in are gutter guards worth it.
And cut back the branches dropping into them, which fixes the cause rather than the symptom.
For cleaning and an honest assessment of what condition yours are in, see gutter cleaning.
