Purple discoloration on parged basement walls
We live in a 1920's home in an area that has a high water table. We never have water come up from underneath the home.
We did used to have water seep in from the lowest area around the walls. While ALL neighbors have sump holes/pumps, our house never had one. We had an internal drain installed around our basement walls, and a sump hole/pump put in. NEVER ONCE have I seen any water flowing from the drain into the sump hole, though the water level in the sump hole rises and falls with the water table. Still, the water also doesnt flow in through the walls, so it must have done enough to re-balance the water around the footings to be successful.
Still, the walls are parged from probably 50 years ago. Some of the parging looks great, but due to moisture underneath, some is coming loose. A previous owner had painted all walls with some kind of moisture-resistant paint, and seemingly removed some of the loose parged areas.
Still, we found discoloration that is sort of a purplish color in various areas of the basement. Ive not done a test, but might this be mold or just mildew. There is no sign of mold in the basement on the wood that makes up the floor joists, and the basement does not smell moldy or milewey. At the same time, we run a Santa Fe 1200CFM large dehumidifier down there.
The basement is around 950 sq ft, and if we didnt, humidity would be at least in the mid 60% range. With it running, we keep it down around 52%, and it does run a good amount. It also heats up the basement a bit.
Any thoughts/suggestions on the best path forward? I would guess that we should have the existing parging removed and then the poured walls sealed and then re-parged. The concrete that is exposed from the waterproof paint/parging always looks damp, but we dont get water in there.
In a dire scenario, we could have plastic membranes or something installed on 2.5-3 of the four basement walls. The property is fairly well graded, though surely could be better, and one downspout does dump next to the home (onto a driveway so it does flow away). It does so in an area that was never a water prone one, so I dont think it is a big issus.
So would appreciate any guidance or advice.