Bricks, Masonry, Asphalt and Concrete - Flagstone Courtyard

I told him at least 6 times not to do it. He didn't listen of course. We have a beautiful flagstone courtyard that was originally set in sand with a road-base type grout filler. My husband decided that he was going to fill in the gaps between the flagstone slabs with a cement mortar. He started and eventually saw it was not turning out as he imagined so he stopped. It is horrible looking - He did a half dozen places, very sporatically, with cement wash leaking onto the faces of the flagstones. Is there any way to dissolve or remove the cement both in between the flagstone and on top as well? I am sick that we might have to replace the entire courtyard. Yes, it is that ugly. Help me! :(

You could successfully chip away the concrete and replace the sand.

how wide are the gaps between the stones?

The gaps between the flagstone vary between 1/2 inch to a full inch. While I think I can chip out the cement in the gaps, my main worries are how to get rid of the "cement wash" on the top or face of the flagstones. Thanks for trying to help.