I guess the mould here is worse? I can run a surface cleaner over an area that hasn’t been pre treated and the mould is still partially there. So I either go even slower, plus increase the risk of damage from staying in one spot to get the mould to lift - or, I pre treat and it all comes off nicely.
Pre treat also contains surfactant, this helps the water and dirt run off easier I find.
Again, different side of the world to you my friend
Oh, and post treat - THIS IS MY OPINION ONLY - isn’t to fix stuff. Throwing chems down etc to finish the job.
My concrete (or whatever) is already clean, it’s really just to get a nice even look and even help with a first rain rinse off.
We all have our own ways
I simply see it as a surface. So like a car for example…
You could just get plain water and pressure wash the dirt off, then polish it. But to pre treat with soap, loosen the dirt, then pressure wash it - makes for a cleaner surface. Then add the polish or wax (post treat).
It’s always a three stage process for me, always.
Even if it’s not that bad - it’s a system/process I stick to. Consistency is key. No corners cut. They all get the same treatment
(I batch mix, so it’s not really a hassle or much of a cost increase usinga little of the post treat as a pre treat).