Re-pointing old stone wall? We have a beautiful exposed stone wall in our dining room. It's more than a hundred years old. The wall is in great condition, there are no loose stones. I do notice some dust/silty-looking stuff on the floor build up after a few weeks if I don't vacuum. I've also seen some house centipedes crawl into a crevice or two.

So i wanted to re-point this basically for cosmetic reasons and dust, plus I want a smoother looking mortar. Do I need to scrape out all the exposed mortar first even though its not cracking or loose, or can I simply apply the new mortar on top of it?