Driveways, walkways and house exteriors on the postwar streets.
Downey filled in during the 1950s, and it still reads that way: block after block of houses built to the same plan, with the same setback and the same driveway. On a street like that, one stained slab stands out from four doors down.
It also means the neighbours are working with the same surfaces you are, so what fixes one driveway fixes the whole row.
Oil, transmission fluid and rust rings from a planter are the three we pull out most often here. All three sit below the surface, so all three need the concrete pre treated and given time before pressure does anything useful.
The walkway to the door is worth doing at the same time. It is a small area, it is the piece every visitor actually walks on, and cleaning one without the other leaves the difference on display.
Houses of this age usually have a low roofline and wide eaves, which keeps rain off the top of the wall and lets a grey band build up underneath it instead. That band is not paint failure and it comes off with a soft wash.
A stain that has been there for years will lighten a great deal and may not disappear completely, and how far it goes depends on how deep it went and how long ago. We will tell you what we expect to get before we start rather than after.