Hi all. Hoping for some advice on waterproofing (and perhaps damp proofing) brickwork.

The garage at our place was built against a dividing wall between us and our neighbours. The dividing wall is double brick. The roof rafters sit on top of support bearers bolted against this wall.

There is a good amount of flashing taking away the water that runs down the roof into the valley between the roof and the wall. But I'm still seeing water seep in under the bearers inside the garage. Obviously that's a concern because these are not waterproofed bearers. It's a stupid design but I'm stuck with it for now.

Some sort of ancient mortar has been laid along the top of the double brick wall blocking the cavity, up until a certain point (about 2/3rds of the way along it) but after that point the cavity is wide open to the elements (and actually has stuff growing in it). The seepage occurs inside right from where this mortar cap ends outside.

In other words rain is falling down into the cavity and seeping into the garage.

I want to repoint the top of this wall to keep out the rain. But I think a standard mortar mix would wick in moisture, so I'm asking if anyone can suggest the right mix/compound/material to fill this cavity and keep the rain out.

Ridge tile caps or aluminium are not an option - the neighbour doesn't want anything high profile on top of the roof.