Thank you my liege! I'd never considered masonry paint, I was just going to mix some fine grit with pva, but I'm almost certain I'll have some in the shed somewhere, thanks for the tip!I really like what you've done wth the EPS. I second using filler or as there are lots of nooks and crannies maybe 3 (or more!) layers of masonary paint with sand mixed in. This will also help give a hard outer coat and seal it so you can use paint from spray cans on it.
Looking forward to seeing the finished article.
Hope I do you proud