Why are there so many different types? We have just bought some flexible rapid set adhesive from wickes 2 x 20kg bags for £35 I have looked and you can get some that's cheaper but some isn't flexible? Some isn't rapid set? How do I know which on to get? We are doing downstairs shower room - wall and floor - same tiles. Do you need different adhesive for floor and wall? Is ready mixed better than powder? Totally confused 