Question
I'm wondering what is the best way to clean flagstone. I've tried pressure washing, which doesn't work well and damages the stone. I also tried diluted muriatic acid (less than 5%), but that doesn't seem to work well either.

Any other ideas?

Answer
Hey, David.

I think you've hit on the two best methods. Another one, though, is a good brush and some diluted Clorox bleach. None of them work real well, though. I've finally given up, believing that Mother and Father Nature don't want me to clean it. Alas....

If you don't like the natural look of weathered flagstone, you might consider having it cleaned real thoroughly and then have it sealed. That can get expensive, though, and sometimes will change the look and color of the flagstone.