What is the best way to seal wall slots?

The plumber installed some pipes flush with the wall and chiseled slots into the HBL bricks. How do I best close these openings? Can I use regular plaster with mesh for that? Is there special mortar for this? I have the same situation in the bathroom, and I am concerned about possible crack formation later.

Rotband is always an option.

Rotband is always an option.

But then in two coats, otherwise it oozes out? Is there no cracking at all?

For all I care, even in 10 courses. Something like that is always situation-dependent and must always be decided on site whether to add another finish or if it's enough as is.