How to repair skim coating on basement walls

I live in a 115 year old house.

It has a brick over concrete foundation. The basement interior was originally skim coated. Unfortunately, much of the skim coating is coming loose and it is letting in some dampness. The majority of the skim coat on the concrete has come off and quite a bit of the brick area is getting exposed.

I have begun the process of scraping the walls, to try to remove as much of the loose coating as possible.

There is quite a bit of scaling on the concrete and I will be needing to fill in several areas with a hydraulic cement on the brick areas.

My main question is how do I repair the original skim coat, and finish waterproofing the walls?

Thanks

The top photo is the wall I am working on now. The pipe was the drain pipe, connected to the sewer. It is plugged and the downspouts divert the water at least 3 feet away from the house. The wall above the pipe is brick and below is concrete.

It is a multi-family house. We assume the walls were skim coated by the builder, since the entire basement is skim coated, then divided for individual storage cellars.

The 2nd photo is the adjacent wall, but I haven't cleared away in front of it to work on it. Too much stuff to move all at once.