Recently seeing cracks in the flagstone joints and the stones are starting to loosen up. I would like to repair the joint cracks before they all fall apart. How can I tell what kind of original joint material was it? I noticed a few ant sand hills amongst the cracks and so I figured it was polymeric sand. Do I need to remove all the old existing joints before putting new joints? Or can I just patch up the cracks by putting another layer on top of it? And whats the best material for this kind of repair? Polymeric sand? Mortar? Cement? Or Envirobond? Ill pose a couple of pics.