I have just used a hammer and chisel for the fine stuff. If you whack it right the big stuff pops off.
Hi, Acid wash with wire brush after big stuff came off and of course good protection and don't forget to neutralized with backing soda mixed with water and spry and rains it after cleaning stage. . you tube can be good teacher, I left several clip on that regards to these kind of stuff. Happy ending
The first thing is to remove as much of the mortar as possible with a scraper without scratching the brick. Dampen the bricks before cleaning. Before using any acid, cover all exposed skin, where glasses, cover shrubs......anything it could get on. Scrub the brick with diluted muriatic acid, mixing one part of the acid with ten parts water. If you can, try a test area somewhere inconspicuous.
Little bubbles will start to form. Let it sit 5-10 minutes then scrub them with a scrub brush. It may take a few tries, but keep at it. Use lots of water to rinse it off.
Use a masonry hammer with a pointed chisel end. It works well to knock off large lumps. You can also use a grinder to clean it off, but I would use caution with something like that. As designing Home says, an acid wash will also work on finer stains and residue. You can find such a cleaner at a building material (stone and brick) or landscape supply house typically. They should be able to suggest tips for use as well.