Cleaning any stone is something to be done carefully. I tend to err on the side of caution and go at it in incremental steps. Limestone and in particular Lueders is highly porous. The use of caustic materials can truly diminish the longevity of the stone and mortar and done incorrectly can completely change the look of an entire project. The best thing to do is go in to your local stone yard and talk to them about what you are trying to do and who they think is the best mason for the job. Dupont makes a line of products for not only cleaning but equally as important in some environs - sealers (pool and cooking environments). Some people like the individual charm and character that stone takes on over time. For others they want to maintain the original look of the stone as first installed and it sounds like you fit into the later. Hope that helps some. Regards