Updated: May 6, 2022
Oxidation of paint on aluminum and vinyl siding is an old problem. Oxidation is paint failure due to the sun's ultraviolet rays. What is new are that manufactures are turning out many more colors than the old days. With the traditional white, tans and greys the telltale sign of oxidation is a simple physical test. You run your finger along the surface. If you wind up with chalky dust on your finger you have an oxidation problem.
Here comes the disclaimer, There is no way to tell how extensive "paint failure" is until after the surface is cleaned and dry. As a general rule, oxidation is worse on aluminum and other metals but it can also be bad with vinyl that is over ten years old. And the problem does get worse when left untreated for a period. Additionally there may be permanent fading from the sun which cannot be altered with cleaning and/or oxidation removal. In the old days, with fewer options of exclusively lighter color vinyl and aluminum siding the problem existed, but it just not as noticeable as it is with with darker colored vinyl. Since the products and process involved in removing oxidation are expensive, oxidation removal just wasn't practical for most budgets.
The good news is that the oxidation removal process does remove the failed paint and therefore it will prep the surface for repainting if necessary. However, the repainting process is between you and your painter. In most cases, with vinyl at least, the oxidation removal process will solve the problem and repainting will not be necessary. With aluminum, in contrast there have been cases where the treatment takes off the failed paint down to bare metal when the oxidation is really bad.
With the darker colors the oxidation test is the same, (but to an untrained eye the dust can be confused with dirt). With oxidation there will be “tool marks” left on the siding when cleaning. Using a pressure washer, or a brush and garden hose for that matter, both are forms of agitation, will leave marks on freshly cleaned siding. This happens because the paint is not water soluble, unlike natural things like, tree sap, insect excrement and soil. The detergent mix used to clean chemically binds soils, but it cannot hold paint in suspension in the same way. So jettying or brushing the siding inevitable pushes the paint around physically but cannot lift it from the surface.
For some people this ordinary cosmetic wear in the maintaining siding from organic invaders like algae, mold, tree sap, insect excrement and the like is worth the tradeoff. Even your favorite tee shirt wears over time in the washing machine. However, for those who find that prospect unacceptable, there is a solution to the problem. The oxidation itself must be addressed with the proper application of the right product. The product must be formulated specifically for vinyl/and or aluminum. The correct order of application, agitation tools, rinsing and dwell time are essential to success. If you find that you have this problem, (typically begins at around ten years from installation) it is best to call a company that employs certified pressure washing technicians. Once the oxidation is dealt with the siding can be pressure washed once again.