I was told by my La Farge rep that you can use cement that has lumps in it as long as they can readily be smoothed back out again with little effort. If the lumps are very hard discard the mix.
Why not just paint the brown mushroom?
Clean the mushroom of any dirt/soil. Make sure the mushroom has been wetted down with water. It should be damp not wet when you apply the new mix. An acrylic fortifier can be used in this application. The craft paint won't hold up mixed in with the slurry.
Just a side note. You "parge" chimney's not "parch" them. Billie

Thanks Billie, I thought it was parch, like parchment. That would have been embarrassing. I have limited experience with bricklaying. I donÂt know how surface painting would hold up here in 5b. I would think that the paint would flake off, and hide the aggregates. I know this stuff doesnÂt look exactly like stone, but paint would not be the look I am going for. Maybe I misunderstand.
Since we correct each other here, the use of an apostrophe in chimney's implies that it is possessive not plural. I always catch that one.

Just wanted to make sure that you use the correct terminology and not correct your english. I didn't correct your spelling.

I'm surprised that you think that paint would not adhere in zone 5b. Are there no painted chimneys or stucco buildings in your area? You can get some amazing results using diluted exterior paints and dry brushing technique. Just make sure you clean your mushroom well before applying paint. Since you don't want to paint just use my suggestions for applying a slurry coat.
"I would think that the paint would flake off, and hide the aggregates." Didn't understand what you meant "and hide the aggregates". Billie

Acrylic paint doesn't stand up very well mixed into cement.

I tried the QC liquid mineral dye in the portland. I used the lumpy stuff. I screened out most of the powder, then added water to the hard lumps, some the size of small eggs. I waited...mixed...waited... and still had to run/squeeze the mix through a fine screen before i could use it. It was a test, and i don't know how it will cure/weather. It looks good. I was wondering, daisy ny6, what dou you meen acrylic paint doesnt "hold up"? the color is subdued much more than mineral cement dye, but has a nice tone, or do you meen structuraly? Is craft paint colored with minerals? I have beds of mineral clay on a property, I am soon going to excavate some and test it for color/structure/etc. I have greens, yellows, and several other colors.