If you wipe your hand across your siding and it comes away white and powdery, you are looking at oxidation. Homeowners often mistake it for dirt, and it is the reason some houses still look dull right after a wash. Here is what it is and what your options are.
What oxidation is
Vinyl siding, aluminum siding and painted surfaces all break down slowly in sunlight. Over years of UV exposure, the top layer of the material degrades and turns into a fine, chalky powder. That powder is oxidation, sometimes called chalking. It shows up first and worst on the sunniest sides of the house, usually south and west, and on darker colors.
How to tell oxidation from dirt
- The hand test. Rub a dry palm or a dark cloth across the siding. Dirt smudges gray or brown. Oxidation leaves a white or chalky color that matches the siding.
- The pattern. Dirt and mildew collect in shaded spots, under eaves and on north sides. Oxidation is even across a whole sunny wall.
- The look. Oxidized siding looks faded and flat rather than stained.
Will a house wash remove oxidation?
No. A house wash removes dirt, pollen, algae and mildew from the surface. Oxidation is the surface itself breaking down. A soft wash will clean an oxidized wall, but it will not bring back the original color or shine. On heavily oxidized siding, washing can also leave uneven or streaky patches where the chalk was disturbed. That is why we note oxidation before a house wash, so there are no surprises.
Why oxidized siding streaks after washing
Chalk washes away unevenly. Where water runs harder or a surface gets touched, more chalk comes off and that area looks different from the rest. Rain can do the same thing over time, and chalk can run onto windows and look like streaks on the glass.
Your options for oxidized siding
- Live with it and keep it clean. For light oxidation, regular gentle washing keeps the house looking its best without making things worse.
- Oxidation removal and restoration. Specialty cleaners and careful hand work can remove the chalky layer, and some restorers add back color and sheen for a while. This is a separate process from house washing and takes much longer. Ask us about it if your siding is chalky.
- Paint. Vinyl and aluminum siding can be painted with the right products once the chalk is removed.
- Replace. If the siding is also brittle, cracked or badly faded, replacement may be the better long-term fix.
What not to do
Do not pressure wash or scrub oxidized siding hard to “get it clean.” It strips the chalk unevenly and leaves blotchy results that are harder to fix. See soft washing vs. pressure washing for why we keep pressure off siding.
Related questions
- How much does house washing cost?
- Soft washing vs. pressure washing: which is right for your house?
- Rust stains on siding and concrete: causes and removal
- Is soft washing safe for plants, pets and kids?
Want us to take a look?
We wash homes across Lake Minnetonka and the west metro. Get an instant estimate, call (612) 770-8221, or see our house washing packages and prices.