There are two major types of coatings permanent & sacrificial. Which one to use depends what your coating / cleaning. Main reason to coat is to make the cleaning easier (on the surface & on the person cleaning) & cheaper. The following is how I do it.
1.Brick / stone can be cleaned quite easy without damage to the surface and therefore I don't coat them
2.Painted surface (latex) paint it
3.Painted surface (oil based) can be cleaned usually, however depending on the sign I coat them. There are hundreds of coatings out there, and due to
the above analysis I primarily use sacrificial coatings.
Both types of coatings have there own pros / cons.
One of the biggest cons is every coating I have used / tested affects the color of surface applied to. I call it staining they call it enhancement.
I could write a book on this stuff, if you want give me a call and I'll tell you more info.
PS I don't sell any products on this board, I only give advice
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Walt Graner
"Off The Wall" Graffiti