Cheers, I think I'll scrap this Mapei kit. Waste of £40! Too many mentions of it not working so well on cement backer boards, and Mapei's tech advice seems to differ it looks like. Some told not to prime, to prime, some told its fine if it peels (eh!).
What would you prime it with if I get the Tilemaster one please? Only used Mapei stuff until recently. Got loads of Primer G and cementone sbr... No bother buying something else though, the tiles are heavy and will do some serious damage if they come away, so needs to be right.
Will be using the Tilemaster standard set stuff, liked it a lot on floor I just did.