Efflorescence is something I’ve mentioned before on this website. It is the movement and deposit of salts on masonry surfaces. That movement is because of the presence of water. This is the reason that efflorescence is a good indication of having a potential water problem. If you discover this on your basement walls, you have water coming through the wall and need to address the source of the problem. Sometimes it is as simple as extending your down spouts away from your home or cleaning out your gutters.
We recently had an interior commercial job and discovered this problem. The walls we were working on were high up from the ground. Actually 20 feet up on a second floor; so the source of the problem was a roof issue. It was obvious the issue was old. The walls were dry and we could see the the efflorescence was old.
The best way to deal with this is to scrape the surface to remove as much of the efflorescence as possible. I recommend putting something down on the floor to catch as much of the debris as possible. You will also need a shop vac after you are done. The best tool for this is a drag scraper.
After the areas are scrapped they should be sealed/primed with a masonry sealer the painted. We used an exterior grade product for some extra kick.
Products like drylok are great but a waste of time if the surface has been previously painted. They are only effective on 100% bare surfaces.