Ting into timber beams

[robbbin]

Hi guys

Got a bathroom to tile problem being round the bath area the client wants to tile to the ceiling because a shower is being fitted. but there are vertical 4 oak beams that have small various size holes.... from bath to ceiling flush with to finish plaster, they are 8ins wide. He wants to tile between them, can they be sealed with a product to stop water penetration, it can not be over boarded its a grade A listed Manor house

Thanks

 

[White Room]

The wall must lime mortor by the sound of it, what tiles is he having fitted..