Thick hard efflorescence on chimney stack

[Mattg4321]

Just had some scaffolding put up to deal knackered chimney flaunching that is causing water to soak into the chimney. Additionally part of the stack needs repointing, a few spalled bricks replaced and I’m going to apply stormdry to the brickwork. 
 

On the north side of the stack I’ve got some pretty heavy efflorescence in places. I’m not massively fussed about the appearance, although it would be nice to get rid of it. This side doesn’t really take the weather, but obviously hasn’t dried out as quick in the sun as the other sides, which has allowed the efflorescence to form. 
 

Can barely even scratch it with a screwdriver it’s so hard. Estimate 1-2mm thick or more in places. What should I do? Leave alone and stormdry cream over it? Try and remove it? Guess it would need a wire brush on a grinder or some extremely potent chemicals.