Waterproofing exterior garage wall

[stratford_noob]

Hi,
I have long going dampness issue on one of my garage wall as big part of it is under the ground level as it makes border with my neighbour who has his ground level higher then me. I have finally managed to dig a trench around the wall in my neighbour garden and now I need to seal it, and would greatly appreciate any advice on that.
From the digging it looked like it wasn't dampproofed as originally when they built the garage they haven't expected to for neighbouring ground to be high. The joint between concrete slab, and brick was sealed with a rubber/felt (?)

but as this was done long time ago, I doubt it was working anymore, as it fell of very easily while digging the trench.

Before digging, I was planning to do something like this

using trowel on bituminous mastic for Roofs to treat the slab/brick joint and then paint the bricks with liquid rubber up to the ground level.
But there is no lip between the slab and brick, so I'm not sure if the mastic would do. So what would be the best approach for that?

Also what would be the best way to clean the bricks? I was planning to just let it dry and clean with steal brush, but maybe I would need to pressure wash it, or something else?

thanks a lot for any advice.

 

[dontbelieveawordofit]

pressure wash the bricks , tank the below ground level wall twice all the way down to and including as much of the foundation as you can get to with cementitious slurry.
after it’s dry lay a dpm up against the tanked area making sure it sits as low over the dpc as possible and backfill the trench.

 

[catlad]

I'd backfill with gravel.