Re: Mosaic Brick mail box and External brick retaining wall (not rendered)
Welcome to the Bunnings Workshop community @suzette. It's to have you join us, and many thanks for your question about rendering a brick wall.
Did you intend to tile mosaic the letterbox? If so, then the advantage of rendering it first would be that you have a nice flat service to work with. If the bricks' mortar lines are not too deep, then it's not a necessity, and you could glue your tiles directly onto them.
I'm keen to hear more about your project and assist with any other questions you have.