>>2920806
Flip the pyramid so the bottom is wider than the top. I used my wife's phone to take a couple pictures for you so you can see yourself. Order of operations is:
>chisel
>clean debris
>wet it down
>apply cement paint primer (with brush)
>apply mortar fill before primer dries
>give it some time to stand, then finish troweling it
>broom it
There is a concrete bonding adhesive that you can buy nowadays. Sika sells it for not much and you replace a portion of the water with it. I think you can apply it to the surface you're repairing to help with adhesion, too. That would be good to use. There was another anon talking about this type of thing in another thread. See >>2918482
So he recommends etching with an acid and scarifying the surface with a grinder. I dunno if you'll want to etch because it might ruin the rest of your concrete, but putting lots of tooth in the surface you chisel (or grind) out is a good idea.
>My question is why use mortar over another type of fill? Would using a sand/cement/epoxy mix be any better or worse?
I don't really know the answer to that. Probably gonna have to do some digging with a search engine to find an answer to that. A mortar might look pretty similar to the existing concrete if you use the same portland cement base, just nix the gravel. I think you can't really go wrong with a mortar fìll, but it's possible the epoxy mixture might have better adhesion. I don't know the full story, though. Good luck.