What materials do I need to fill this hole on my 2nd floor balcony? It's deeper than it looks. There's nothing for bondo or caulk to adhere to do not sure how to create a backing.
Looks like some bricks fell out (or in?). A mason or a DIY mason could put the bricks back in, perhaps.
A possibility: Try taking out the schmutz X'd out here:
Then see about either adding bricks from below (can a mason do bricks upside down?) or fill the hole with some pressure-treated wood or plywood.