Orange streaks on siding usually start at one point, and that point is often at the eave. This guide shows how to trace a rust stain to its source, fix the source first, and then clean the stain without damaging the siding.
In This Article
Follow the streak to its source
Rust travels with water, so stains run downhill from where the iron is. Start at the bottom of the streak and follow it up with your eyes, or a phone camera, until it stops. The place it starts is the culprit.
| Where the stain starts | Likely source | Fix |
|---|---|---|
| Below a seam, end cap or downspout joint | A rusting steel trough, or a leaking joint carrying rust | Reseal, touch up or replace the section |
| Below a screw head or bracket | A steel fastener rusting in the wet | Replace it with a fastener suited to the trough's metal |
| A broad fan below a corner that overflows | Overflow washing rust from roof metal or the trough | Stop the overflow, then look up at the roof |
| Below a roof vent, chimney cap or flashing | Rusting metal on the roof above the gutter | Ask a roofer to repair or replace it |
| Low on the wall near a tap, sprinkler or air conditioner | Iron in water, or rusty equipment | Fix it at the source, and this is not a gutter problem |
| Under a nail head in the siding | A nail that has started to rust | A siding repair, best left to a professional |
A single streak is a point source. A broad stain across several boards points to overflow. Colour helps too: orange-brown with a powdery edge suggests rust, a green or black film suggests algae or mould, and a white crust on brick or stone suggests mineral deposits carried by water.
The magnet and the flashlight
Two cheap tools narrow it down in a few minutes.
- A fridge magnet. Hold it against the trough and against each screw and bracket. If it sticks, the part is steel and can rust. Aluminum troughs will not rust, so the source is probably a fastener or something else.
- A flashlight. Look along seams, at the bottom of the trough and around screw heads for orange dust, flaking paint or pinholes.
- A camera. Photograph the stain and its start point, with the date. It shows whether the streak is spreading.
If the trough is steel and rust has eaten through, cleaning the siding will not last. The stain will return with the next rain.
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Fix the source before you clean the stain
- Stop any overflow. Clear the trough and downspouts, and fix any low spot, so water stays where it belongs.
- Replace rusted fasteners. Use ones made for the trough's metal, following the manufacturer's guidance.
- Treat surface rust on steel. Remove loose rust, prime and paint with products made for the metal, following the labels. For a leaking seam, see repairing leaking gutter joints.
- Replace what is beyond saving. A steel section with holes will keep staining the wall behind it.
- Ask a roofer about roof metal. Vents, flashing and chimney caps are roof work, not gutter work.
Fixing the source first matters, because a spotless wall under a leaking seam is stained again by the next storm.
Cleaning the stain without harming the siding
- Test a hidden spot first. Wait for the result before you treat the visible wall.
- Use a rust remover labelled for your siding. Many rust removers use oxalic acid. The label will say which surfaces are safe, and some acidic products can etch aluminum and dull painted finishes.
- Skip chlorine bleach. It does not dissolve rust, and it can make some stains worse.
- Protect plants and yourself. Wet the plants beforehand, wear gloves and eye protection, ventilate the area and never mix products.
- Rinse well, using a hose on a gentle setting.
- Keep the pressure low. A pressure washer can strip paint and force water behind vinyl and wood siding.
Fresh stains lift most easily. Old stains that soaked into porous surfaces such as brick, stucco or concrete may not come out fully, and those surfaces are worth leaving to a professional.
When it is not rust, and when to call
Not every dark streak is rust. Green, black or grey staining on siding is usually algae or mould. Black streaks on gutters describes a related look on the trough itself. D&D Home Services offers gutter cleaning from $125 and soft washing from $350 for typical Kitchener-Waterloo homes, with free written quotes before work begins. Rust needs a rust-specific product, so tell the crew what you have found.
Key Takeaways
- Follow the stain upward to where it starts. A seam, a screw, an overflow corner or a piece of roof metal each have a different fix.
- A magnet shows whether a trough or fastener is steel. Aluminum does not rust, so check the fasteners first.
- Fix the source before cleaning, or the next rain will stain the wall again.
- Test any rust remover in a hidden spot, avoid chlorine bleach and keep pressure low.
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