Neutralize no , just wash off completely with a hose. But acid is
toxic you need good ventilation outdoors, a big fan. A cartrige
respirator , old clothes and gogles. It will burn lungs. You use a stiff
plastic bristled brush on a pole to scrub down after it stops foaming,
about 5 minutes. You also apply acid with the brush.
Just use mortar mix.
How thick no more than 1/2 inch, but im not sure on that, maybe a
Paint over with latex. Or if you have moisture comming through and with
effloresence you do use UGL. a Portlant cement , rubber based paint.
Wait time , read the ugl can or 30 days or more for latex.
The key is cleaning bad mortar from the joints even if its deep. Old
stuff turns to sand if its continualy water damaged.