Black Stripes Down Your Gutters
You had the house washed and the gutters still look filthy. That is not a bad job — tiger striping is bonded to the aluminium and needs a completely different treatment from everything around it.
What tiger striping is
The vertical black streaks running down a gutter face are a bonded mix of oxidized aluminium, roof runoff residue and airborne grime.
They form where water sheets over the front lip of the gutter during heavy rain, carrying dissolved asphalt residue and pollutants from the roof, then evaporates and leaves the deposit behind. The pattern repeats at intervals, which is where the tiger name comes from.
It is not organic growth, so the algaecide used on the rest of the house does nothing to it. It is not loose dirt either, so rinsing does nothing either.
Why a house wash does not touch it
House washing solutions are formulated to kill and release organic growth — algae, mould, mildew. Tiger striping is inorganic and chemically bonded to the aluminium oxide layer on the gutter surface.
This is the single most common complaint after an otherwise good exterior clean, and it is why gutter brightening is quoted as a separate line rather than assumed.
Anyone promising to remove tiger stripes as part of a standard house wash either has not seen your gutters or is about to disappoint you.
What not to do
Do not attack it with pressure. Aluminium gutter stock is thin. Pressure will dent the face, drive water behind the fascia, and still leave the striping.
Do not use an abrasive pad. It removes the striping and the finish together, leaving a bright scoured patch that oxidizes darker than the stripe you started with.
Do not use harsh acid. It etches aluminium permanently and can run down onto whatever is below.
How we remove it
Gutter brightening uses a dedicated cleaner applied to the gutter face and worked with dwell time, then rinsed. It releases the bonded deposit without abrading the finish underneath.
It is hand work, face by face, which is why it is priced separately from a house wash and takes longer than people expect.
Results are dramatic — gutters typically come back to close to their original colour. On very old aluminium where the finish itself has failed, striping may lighten rather than vanish, and we will tell you which yours is before we start.
Questions we get about this
Why didn't my house wash clean the gutters?
Is gutter brightening the same as gutter cleaning?
Will the stripes come back?
Can very old gutters be fully restored?
Related: Gutter cleaning · Outside house washing · all FAQs