Product advice for filling gaps on brickwork on flat roof

[Johnny hates jazz]

Hi all
I am wanting to do some minor repairs on filling in gaps/ grouting in the brickwork on a kitchen flat roof extension but am clueless at DIY! Any suggestions on which products I should purchase to fill in the gaps as shown in photos attached? Key issues - needs to be waterproof, fill gaps of up to 10-15mm .
Thank you in advance.
John A

 

[Wayners]

I would mask up (duck tape) either side of a cleaned out joint.
4 to 1 mix with add mix.
Point up.
Polish off smooth.
Pull tape