Paint
Always water base on masonry. The alkali in masonry is the natural enemy of oil based colors like One Shot.
You can use house paint, but the pigments are not as pure as a mural paint like Nova Colors. House paints have lots of titanium dioxide diluting the pigments. Of course, if the client specifies a house paint color, it is still far better than an oil base color. I would double coat all colors. Prime the area to be painted if you wish. Colors will cover better. (I like Zinnser 1-2-3).
https://www.homedepot.com/p/Zinsser...ior-Exterior-Primer-and-Sealer-2001/100398391
If the masonry is fresh (weeks old), any painting contractor will say to acid wash first to remove any effervescence (white salts residue). Four parts water, one part muriatic acid. Scrub with a log-handled brush and then rinse and allow to dry.
Clear coating is unnecessary and it may trap moisture, which you do not want. Water based paints will allow any residual moisture to exit.
Brushes
Yes, you can use bristle fitches, but natural bristles tend to swell in water base paint. You'll get cleaner lines from synthetic sables and the water doesn't affect them. I like the angled ones by Royal Langnickel (dark silver handles, at Michaels). They are a little softer than real sables but still stiff enough to work well on masonry, allowing you to pull straight lines and create clean corners. I think they are Taklon or a mix.
Taping off concrete does not work well. Better to use pounce patterns and hand cut all the lines with brushes. Fill in with larger brushes or roller.
Knock it out. And have fun, like Tammie said.
Brad in Kansas City
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https://novacolorpaint.com/
Nova is pricey but if you need bright colors it's great. They have metallics, too. And a blending medium.