Restoring Mosaic Benches

I am charged with restoring / finishing a community art piece that consists of two fixed benches. They were originally made with plates, tiles, small stones, and some glass 'blobs'. One of the pieces has a good deal of calcium build-up (hard water deposit - a sprinkler was nearby) and the sanded grout is splotchy with dirt. I have begun with scrubbing everything with water and green scrubbers. Not much difference. I've read up on using acids and will try lemon juice next. I surely would love some advice!