Our six-unit coop apartment building (brick and mortar) is 82 years old.
Recently some of the inside walls have begun to show water damage, which
indicates moisture coming in from the outside.

Someone told me this indicates we might need to have the building
"repointed." I've never been clear on what this means and what it involves,
but I would guess that it's expensive.

I have also been told that silicone paint might be a less expensive
alternative to repointing.

Any guidance or experience appreciated.