Replacing joists... New mortar on wall?

[JP_]

Ok, so now have removed rotten wood and cut new pieces. I'd it best to remind old mortar on walls and put new, or just just to up with a little and press all down to level?

Still got one rotten bit to sort.... Tend to leave it soaking in preservative as it's tricky to get to... In the bay area.
The new air brick I've started cutting out is on the left. Might put one on right too....

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[Newboy]

Clean the old mortar off and lay a new bed - a piece of DPM between the new joists and mortar wouldn't do any harm - likewise on the joist ends where they are touching the brickwork.