Fixing spots where outside render has fallen off

[sfjnet]

Hi - I have moved into a place that is partially rendered on the outside front wall. It looks like once upon a time some of the render came loose in a few patches of varying sizes (from about a 50p size to a few inches across). The previous owners repainted the render without filling the missing patches (they are about 1/8th of an inch deep I would say). Looks OK from a distance but when you get up close it's really noticable so I want to fill in the patches so the wall is smooth. I've never done this sort of thing before. Is there some pre-mixed plaster/render I can buy that would do the job? Also, I'm assuming I have to somehow sand the paint out of the patches I want to fill so the new render will hold - is this right, and is there anything else I should be conscious of? Thanks!