Tiling

Grey grout has darkbrown patches and what looks like white salt on the grout

Anonymous user 23/02/2024 - 3.21 PM

We had porcelain tiles put on the floor by our builder using the ~Mapei Flex Fast Set Adhesive (Grey)~ and ~Mapei Grey Anti-Mould flexible grout~ (bought from B&Q). We had electric and wet underfloor heating done in the areas. Where the wet underfloor heating is done I see the grout lines has got dark brown patches and at places with what looks like white salt on the grout. My builder has since raked out the grout where it was dark brown and regrouted the area, however it didn't rectify the issue. He says the adhesive under the tiles is still wet and he can see it while raking, hence the issue and to let it dry completely. It's been over two months with underfloor heating on and it has made no difference. I also contacted Mapei to know what could be the issue and they told me one possible reason of the issue could be that the grout was not mixed with correct amounts of water. However, if this was the case then the whole area where the grout was done should have the problem and not in patches. They could not give me a convincing solution and directed my to buy their product called "Fuga Fresca" which is a grout reviver pen, to fix the problem which has to be applied to all the grout lines for consistency rather than the problem area - turning out to be a big job. **Update**: Tiling on the wet underfloor area was put 3 days after the screed was laid down. Could this be the reason that the grout is getting moisutre from underneath?