In a few months, my garden should have patio slabs and walkways laid. I really like the lighter color stone. In my experience, stones with open pores (like sandstone) get very overgrown with algae and moss over the years, especially in shady areas. Light-colored sandstone looks great in a new stone, but unless you constantly treat it with a high-pressure cleaner, the pleasure won't last.
Can anyone recommend types of stone that are almost immune to algae infestation (like granite or something similar)? Are there also suitable types of light colored stone?
P.S.: I know you can also seal stone. But that's too much work for me, especially because the sealer needs to be renewed regularly.
This can also be countered by hydrophobic impregnation. The idea – simplistically – is that there is less water in the substrate because of the hydrophobicity, and therefore growth is at least hindered and delayed. This works well on facades, although, of course, individual characteristics must be taken into account. Here you can often observe a kind of self-cleaning.
For example, we waterproofed our wall so that water just rolls off of it. The resistance to freezing/thawing should also increase significantly. It works great on a clinker facade too :)
However, it can be problematic if the water stands on the substrate due to hydrophobicity and freezes in the winter.
I think that frequent high pressure cleaning makes the moss come back faster is a misconception. If the moss was already there, it would show up faster, that's true.
If the stone is altered by high pressure and the pores open, that may be true, but otherwise the most useful thing with moss is to remove it as completely as possible, as it may grow back from the remaining plant parts (which are easier to preserve in open materials than in closed ones).
An effective enemy of moss is dryness ...
Algae and moss will grow on any unpolished surface in moist, shaded corners. And the more often you clean natural stone with a pressure washer, the faster algae and moss will repopulate it. Natural stone looks like freshly laid only if it is cleaned every month. This, by the way, applies to concrete as well.
The more open the pores of the stone, the better mosses and lichens can take root. For those who are less tolerant of dirt, the differences are not serious, as they have to act either way to satisfy their desire for bare stone. Pressure washing is a shortsighted option, working with a sealer is more feasible.
Right now I've settled on granite. The stone has a dense structure and has no open pores, so it is less susceptible to mosses and algae. The expert advised refraining from cleaning with a high-pressure cleaner. This is supposed to promote algae overgrowth.
Last year we switched from pressure washing with just water to brushing after pretreatment with caustic soda in the courtyard (concrete block paving), water comes from a hose with a spray nozzle. So there is less pressure. In my opinion, the high pressure cleaner has a double effect: the high pressure only sprays a little more of what was previously sprayed deeper into the pores. The caustic soda reaction loosens the dirt better than a rough attack with a high pressure machine.