I have a Large balcony here in france, With floor tiles bedded onto 1cm thick species flexible floor glue specially for the purpose. The problem is that after 3 years of summers and winters the grout has come loose and water is getting under neath exacerbating the problem. I need to remove the grout(I have bought the tool to do this) and replace with a more flexible alternative adhesive/ sealant. Can anyone suggest a suitable very flexible product to do this? It needs to be pretty hard wearing and immune to sun and cold. Cheers