replying to mm, Rusty wrote:
Basically it's like this. concrete wall or stucco wall is very porous. If you
start at the bottom you're basically filling the pores with clean water. If
you start at the top dirty water will run down and fill the pores below. When
the wall dries what's in the pores is how the wall will look. Starting from
the Bottom clean. starting from the top streaks.

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