This repair is best done with a 1/4inch tuck pointing blade. Depending on the size of your grinder probably a 4 1/2, or 4 inch blade. You want to remove the joint to a depth of an inch or more. Try to do them all the same depth. Remove from top to bottom, but try not to remove any of the brick. The difficult part is matching the existing mortar. :) More on reddit.com

Those are meant for cutting metal. Do not attempt to cut stone with those blades. More on reddit.com

hes way to use the grinder makes me nervous More on reddit.com

Never take off the guard. The guard should almost always be covering the 4-5 o'clock to the 10 o'clock position, centered at the bottom left quadrant when you're looking at the top of the grinder. You might have to move it a bit, for specific things, but 99.99% of the time it should be like this. Never remove the handle. The handle needs to be on the left hand side of the grinder, always. There's a hole on the right hand side, but you should pretty much never use it. When using a flap disc (and only with a flap disc) you might occasionally use the grinder with one hand. But there's still no reason to remove the handle or the guard. Never use the face of an abrasive cutoff disc to grind things. Only use the edge of the disc. 3 and 4 are diamond cutting blades. 3 has an interrupted edge for more aggressive grinding. 4 is continuous rim. Like with the abrasive cutoff discs, you only cut with the edge of these blades. These are for cutting rock, tile, and other abrasive and hard materials. Be aware of kickback. When cutting, try to keep the cutting between 2 o'clock and 3 o'clock part of the disc. This way the grinder will pull away from you if it binds. (This is why you keep the guard where I mentioned earlier.) If you were to cut at the 9-12 o'clock position and the disc bound up, the grinder would kick into you. The grinder could twist out of your hand, you could get a disc in the face, or you could get your shirt wrapped up in the disc, pulling the grinder into you. The handle on the left side might save you! Always leave the handle on the left side! Some dudes will tell you the handle just gets in the way. No. You almost never want to cut or grind anywhere near the 9 o'clock position where you will leave that handle, always. And notice the guard is covering the back of the disc between the handle and the body of the grinder, so your shirt doesn't get sucked into the disc/attachment. If you know how to use a chainsaw, it's the same thing but sideways. You always want to cut with the bottom of the bar; the kickback happens if/when you foolishly (or taking a calculated risk) cut with the tip or the top of the bar. Ear plugs and full face shield are highly recommended. Gloves are helpful for the vibrations. But if you use the handle and guard, not necessary for quick jobs, IMO. At least they're not as essential as FFS and earplugs. If you are interested in working with steel, welding and surface finishing/painting, you will want a wire cup brush, a grinding wheel, and some flap discs. Wire brush will remove skin and flesh like nothing. A grinding wheel is probably the most dangerous of things you can use. If it breaks, it's a bomb. Use them carefully, and throw away a grinding wheel if it cracks. But should it break, the guard is handy for preventing fragments from removing your knuckles and penetrating your chest or belly. Flap discs can erase skin and flesh, too, but they're probably among the easiest to control and the least capable of causing a serious or life-threatening injury. The most important thing you need to use an angle grinder is a secure vice and a sturdy workbench and metal working clamps. When you cut or grind on something it must be rigidly held in place. Unless the piece weighs 30+ lbs and lays flat and stable, you must secure it with clamps or vises. You're going to break some of these rules, eventually. But absolutely do not even think about it until you have had some hours of experience. And even then, stop and think about it for 5 minutes, before you take off the guard or the handle. 9 times out of 10 you will realize you're a dummy, and there's a much safer and better way to approach the problem. Or you'll figure out and visualize an additional way this could go horribly wrong that you didn't initially consider. It's better to figure that stuff out before you stick the grinder in a tight spot. The more you learn how to use a grinder, the more you will realize that the guard and handle will almost never get in the way when left in this default position. The dudes who don't use the guard or handle? I'm convinced they learned (through luck, close calls, minor flesh wounds, or simply being pretty clever) what not to do, but they still haven't realized that if they were to put the guard and handle back on, in this default position, it would almost never get in the way. So they're not that clever. You could learn to safely use an old chainsaw that doesn't have a brake on it. But you'd be a dummy to remove the brake off a modern chainsaw that already has it. More on reddit.com