Did a job the other week customer had tubs of Unibond tile and grout he got in a sale £3.90 a tub did not want to use it but would have lost the job so had a compromise just used it on the floors but used powdered grout it was a bit like Bal-flex could not grout for 48 hours but it did stick. And regarding Bal fast flex had a major fail with that stuff had to do a grp balcony did every thing by the book as never tile to grp before, in two weeks started to lift, stuck to the tile but came clean away from the grp, called in the Bal tech guy ,he turned up and together we both fixed a few tiles went back a few days later and they failed, the result from Bal was,the fixer was to blame so will not use the stuff again,have since found out from a boat builder that in the process of using grp it forms a wax on the surface so this in his opinion is what the adhesive was sticking to.