Re: how to prep already painted interior brick wall ?
Welcome to the Bunnings Workshop community @timw. It's amazing to have you join us, and many thanks for your question about preparing a wall to paint.
What condition is the paint in that is there at the moment, is it flaking or degraded at all? Is it gloss paint? As long as the paint is non-gloss and of sound nature, then you can paint over the top of it. You'll need to give it a thorough cleaning with Sugar soap first before flushing the residual soap off with fresh water and allowing the wall to dry. If it's a gloss surface, you should use a specialised primer like Dulux Precision. If it is currently low-sheen paint but a dark or vivid colour and you are going lighter, then you'll need a couple of coats of undercoat to diffuse and block the original colour.