/diy/ - Do It Yourself

I have a short wall outside with this finiture on it that is detaching, leaving only bricks. I read it's a pretty simple job to do, gotta mix concrete with sand (depending on granulometry it will get rougher or more slim) and use a dedicated manual machine to splash it directly on the wall.
Is it true? Am i making basic mistakes? Does it need an actual first layer of concrete to grip on it?