My recipe for course stuff:
3 parts lime putty
1 part horse hair about 30mm long
6 parts sharp sand
put the lime putty in a mixing tub such as a large trug, add the hair and stir it in so that the hair disperses. add half the sand mix with a plaster whisk then add the rest of the sand and mix again.
Some hair will get tangled on the whisk this needs to be taken off before it is used again.
I use a propellor whisk from Refina
this grabs less hair than a basket whisk.