Had a very bad failure on a GRP balcony used two part fast flex the tiles were 600x600 the whole lot came lose it had stuck to the
tile but came clean from the Grp and had a reddish colour on the Adhesive did everything by the book even got info from Bal tech guys was even told not to prime the surface just to make sure it was clean which is was,it turned out I had to get a friend who builts boats for a living to have a look and he told me that in the process of laying the GRP a wax forms and that,s what caused the failure cost me a lot of money,and the Bal people said it was not their fault as they always do,will never use fastflex again and will never do a job if I have to fix to GRP again,mind you I have a cabin cruiser and I tiled the shower with mosaic using Weber SPF and have had no problems.