You need to seal the joints (addy and tape) but they just then need dusting down and you can apply tile straight on to them, ensure you use waterproof adhesive.
Tape/seal as PBD & you will be OK without tanking unless it's a wet room. Always follow your adhesive manufacturer’s recommendations with regard to primer but, generally, it’s not necessary. As far as is possible, avoid tile joints coinciding with board joints.
What size/type tiles are you laying?
What addy are you using?
Sorry for late reply. I'm going to use a BAL adhesive - undecided which one yet, but with teh board costing about £80 alone I certainly wont scrimp on addy
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