I have a 50m2 roof terrasse. The grout has become permeable and rainwater is leaking into the cellar below (this is because the original builder "forgot" to put any sealant on top of the concrete base??).
I can't remove all the tiles and start from scratch, so I simply need to renew the grout. Is it favourite to remove ALL the old grout? What is the best way of doing this? What is the most effective water resistant grout on the market? Thankyou.