Hi, water was leaking from upstairs bathroom through the kitchen ceiling downstairs. I took the bath panel off and saw the water stains were running directly from the grouting lines of the tiles around the bath and shower. Would I need to totally re grout the tiling or has anyone used this before https://www.screwfix.com/p/zep-grout-sealer-500ml/913hk - a spray on sealant and if it works at all? or any other ideas to resolve the issue apart from regrouting all the tiles