Sealing plasterboard/moisture resistant board

[Kevbos]

You don't need to seal plasterboard unless it's in wet areas where's then you should be tanking the plasterboard before tiling.i personally seal plasterboard in non wet areas all the time (SBR/water -1-4)

You shouldn't really tile with most tiles onto plasterboard full stop as it's not strong enough to hold the weight

 

[judge]

As long as the pb isn't skimmed it will hold most tiles except for possibly 10mm porc and above or natural stone