Rendering/masonry around external window in Victorian house

[WakeUpAustralia]

I hope this question makes sense, as i'm not sure of the right lingo... The surrounds/frames of the outside of my Victorian sash windows look like they have been rendered and then painted white. I have a new kitchen extension and want to create the same effect on a new sash window. Currently the surround of the window is bare brick. Could anyone advise me on what I use to copy the Victorian render/mortar/masonry surrounding the window frame? If I have to mix the concrete/sand myself what quantities do I use? Is there something ready-mixed I can buy? Do I need to apply some kind of pva or other sealant first? Once it is dry is it just a case of painting with masonry paint? Thanks.