How do I prevent this from happening to my flagstone again?

by Derek
(Burke, VA)

Over the summer I had a brick walkway removed from my driveway to the front door and it was replaced with flagstone on a new concrete base set in mortar, with a concrete mortar combination grout. All was well until the grout was applied. It left a residue that cleaning could not remove. It looked like a frame was around the entire stone, and all were effected. Acid was used, grout residue cleaner was used, lots of power washing again and again, and then more acid. I have since learned that this framing effect is the result of the flagstone being extremely porous and when the grout was applied the stone absorbed the moisture from the grout while also pulling the grout into the stone itself, locking it in. Had the stone been sealed before this, I was told this would not have happened in the first place. The contractor believes that it is because we asked to use a color additive to make the grout a darker gray to match the stones. I don't think that should matter, but does it? However, that is not all of my woes. The next thing we're experiencing, only with some stones, is what looks like a constant look of wetness. Is water trapped beneath the stones? Which leads to my next problem of efflorescence. I can understand this at the grout joints but coming through the entire flagstone and resting on top of it? Is this possible? My photos hopefully will help. The only thing my contractor can do and has agreed to do it to rip up the entire walkway and redo it at his cost. He says he has never seen anything like this in all of his years, how lucky am I? I don't what this to happen again and I want it done right, he's only going to redo it once more. I have been researching and talking with stone sealer manufactures, and would like to get your opinions and what steps to take to eliminate these problems so it never happens again. What can be done to eliminate and prevent this from re-occurring? The walkway is only months old and has too many issues so soon. I would be happy to provide more details about this project if would be able to lend your expertise. Thank you. Derek