I've not used them but people have praised Rawlplug Wet n Fix - could help stabilise the fixings so they don't wobble and work loose over time. If it's just a normal shelf with no real force pulling out of/away from the wall, it'll likely be fine. e.g. I wouldn't mount a TV into mortar, where there's a huge weight on a long lever pulling away from the wall.
I've not used them but people have praised Rawlplug Wet n Fix - could help stabilise the fixings so they don't wobble and work loose over time. If it's just a normal shelf with no real force pulling out of/away from the wall, it'll likely be fine. e.g. I wouldn't mount a TV into mortar, where there's a huge weight on a long lever pulling away from the wall.