Need to repair some mortar joints on a slate patio set in sand. Not sure what the recommended mortar is for this application. What's currently there doesn't look like mortar, more like a regular cement mix but that was probably from a previous repair.
Easiest to find around me is the Type-S and Type-N mortars as well as the common cement mixes they have at the big box stores.
Also, anything I need to be concerned about as far as staining the slate with the mortar if left on the face of the stone too long or anything along those lines?