Live oaks, Spanish moss, and the tannin stains nobody warns you about
The canopy that makes this city worth living in is also why exterior surfaces here fail differently than they do inland. A mature live oak sheds leaf litter almost year round instead of in one tidy autumn drop, and the tannin that leaches out of that litter - and out of the moss hanging above it - is what leaves the brown and near-black shadows that pool at the low corner of a driveway, under a downspout, and along the bottom rail of a fence. Most owners read those marks as plain dirt and go at them with a garden hose. Tannin behaves more like a dye than a deposit: it has already moved into the pores of the concrete or the grain of the wood, so plain water pushes it around without lifting it. It releases with the right detergent and enough dwell time, sometimes with a mild brightening rinse afterward on concrete, and it comes back if the wet litter that fed it is still sitting there.
The useful takeaway is that clearing the debris line matters nearly as much as the cleaning itself. When a mat of leaves stays packed against a fence rail, or pine straw is banked up against the siding, the staining rebuilds within a season no matter how sharp the surface looked on the day the crew left.
Why the shaded wall goes green before any other
Nearly every house-washing call here starts the same way: one elevation looks fine and one looks like it belongs to a different house entirely. That is not neglect, it is sunlight. The wall that never takes direct sun stays damp for hours after the morning dew has burned off everywhere else, and in tidal humidity that is all the algae needs. The green film you can see is a living colony, which is why scrubbing appears to work and then it is back before the next season - the surface got cleaner but the organism was never killed.
That is the entire argument for treating it with chemistry at low pressure instead of blasting it. A solution that kills the growth at the root buys months of extra clarity over a rinse that only knocks the visible layer down, and it does that without driving water up under the lap of the siding, which is the failure that turns an exterior cleaning into an interior repair.
Downtown masonry is not a pressure job
The historic core is where the wrong equipment does permanent damage. Much of the old brick downtown was laid in soft lime mortar, and aged stucco, tabby, and hand-formed brick are softer still than anything coming out of a modern plant. High pressure will take the face right off a brick and scour joints out of mortar that has held for well over a century, and no amount of repointing afterward makes it look the way it did before. Work on those surfaces belongs at very low pressure with the chemistry doing the lifting, and it belongs to whoever is willing to test an inconspicuous patch and wait to see what happens before committing to a whole facade. If a contractor quotes an old masonry wall without ever asking what the mortar is, that is the moment to slow the conversation down.
Salt, marsh air, and the surfaces out toward the water
Properties out toward the marsh live in a harsher environment than ones a few miles inland, and it shows up first on horizontal surfaces. Salt-laden air settles and holds moisture against pavers, coping, and unsealed concrete, keeping them damp longer and feeding the same growth that thrives in every shaded spot. Metal railings and fixtures nearby bleed rust down onto the stone beneath them, and rust is a separate problem with its own answer: pressure does nothing to it, and turning the pressure up only etches the surface around it while the orange stays exactly where it was. It comes off with a treatment made for that purpose, applied to the affected area rather than to the whole slab.
What actually changes the scope of a job
Square footage matters less than most people expect. What moves a quote is access, height, and what is growing where. A two-story elevation over a planted bed with no room to set up is a different job than the same wall over open lawn. A roof carrying heavy organic growth needs a slow, low-pressure treatment and careful plant protection, not speed. Rust, tannin, and old oil each want their own chemistry rather than more force. We would rather walk the property, tell you which of those you are actually dealing with, and give you a flat number for the real scope than guess at a figure over the phone and revise it on the day.
