What paint should I use on a concrete block chimney?

Here is my affiliate link for concrete paint. It will help seal the concrete so it's not as porous.

https://homedepot.sjv.io/xvLd3

B....I used Kilz primer first on my concrete floor and block.

I prefer masonry stain. It allows the concrete to breathe and is usually less maintenance than paint

I agree Masonry stain is more maintenance free, I brought a house with a painted one, and have to touch it up practically every year because the paint bubbles and cracks.

Another option would be to have it stucco treated and that can be done in several colors.

You’ll need a paint specifically meant for masonry.