On the final stretch of this lengthy project and would love to hear your views on Flexible cementious or Epoxy grout for wetroom floor with ply substrate, backer board, electric underfloor heat, under screed. Porcelain mosaic 55mm hexagons, 23mm square, 3mm joints, 6mm deep! Would love to know how good cementious grout is as I think Epoxy is difficult -Ardex eg 18 plus has been suggested as better to use? I have seen BAL Micromax mentioned here a lot I can get #2 or #3 locally, does cementious grout need sealing? Local CTD tile company have been great and stock Weber grout and say it's as good as any? Room is 2m x 3m so pretty sure there wont be too much flex overall. Thanks for your help!