I have a wall that has started to deteriorate. The wall seems to be cast with cement?-sand+stone and there are large boulders on the front. It's supposed to look like it's laid with stones but it's kind of a cheat... It has started to fall apart and the cement looks mostly like sand in several places and just a tap makes it fall off... how do I best repair this?
ps. the wall is from when we had trains on Gotland, so maybe 50-70 years old