This is oxidation and it is usually chalky. This can be cleaned off but it takes a lot of time and labor to remove this from your siding there is no easy way to get it off. This can be a pain in the you know what because when it rains depending on how bad it is it can start running off the house and onto your pavers or driveway. The process to remove this can be costly because more times than not it has to be scrubbed off, Now imagine scrubbing your whole house…. Yes that does not sound like fun. Power washing this usually does not do the trick and can cause more of a headache. Hiring a company that has the experience and a company that is professional like power wash unlimited is the key to solve all your headaches.