When we had a new door inserted in a wall of our house by some builders, they fitted a RSJ and then covered this with mortar and painted the mortar to match the painted, rendered finish of the rest of the outside wall.
But they didn't do a very good job of getting the mortar smooth - there are a few grooves in it as if something something gouged the mortar before it set.
We want to fill in those grooves with mortar and repaint that section. But what is the best way of making mortar stick to masonry paint when the grooves are probably about 3 mm wide and maybe 1-2 mm deep? Is it necessary to rub the paint off with a wire brush to get back to bare mortar and maybe deepen the grooves so the new mortar has a better chance of getting a "grip" on the existing mortar?