Presumably old brick, not new build block?
correct
Okay, hacked off to bare brick.
Day before plastering, brush down with wet brush to get all dust off, getting into any chases or old switch box holes etc. Fill with s/c holes, loose beicks chases etc.
To render, use 5:1 mix with waterproofer (check drum for waterproofer mix).
You can brush down the wall with water to kill the suction, or a weak PVA or SBR solution, 5 :1 just before you render. You should be able to get then walls in one coat, but you may find it easier to give the wall or two a tight scratch coat and then come straight back on to it with a float coat.
The waterproofer will do three things:
keep out damp
kill suction for easier skimming
improve workability.
Don't use lime with waterproofer.
You will need to keep the stuff in the mixer for a while to get it nice, but be careful not to leave it in too long or it will get too runny and have no body. It should sit up nice on your hawk, and hold a pattern if you pull a trowel through the spot board.
Depending on your experience, coat teh wall in sections and rule off, or pull screeds first and then infill. If right handed , always apply floating from right to left . Rub up with devil float, and clean off ceiling lines etc.
Flatten with trowel when gone off a bit to leave nice for skimming.
Skim after 24 hrs