Crumbling basement walls
Our basement is unfinished (not suitable to finish). The house is quite old - built in the 1880s. The exterior foundation walls are made of brick or rock (it varies depending on the portion of the house). The walls are now crumbling. (We began using a dehumidifer in the basement a few years ago, and now I realize that this probably contributed to the problem.) Although the basement will never be finished, I'd like to stop the crumbling so I can place things against the walls. I'd prefer not to do unnecessary disturbing of the walls, as the paint may have lead in it.
How do I repair the walls? Thanks in advance for any advice - I've researched this question but have been unable to find an answer.
(The basement is damp and we get water through the basement floor during heavy rains because there is a high water table under our house. But the walls do not get wet or leak on the inside. We are considering having french drains installed to deal with this problem.)