Tiling directly onto blockwork walls chimney breast

[area tiling]

hi, their am a tiler working in co. antrim n. ireland and, this is my first post on this forum so any advice will be gratefully appreciated!

got a job coming up which might involve tiling directly onto blockwork depending on what is the best advised , its an internal chimney breast wall , where the client will be burning a fire most of the year!
can i tile directly onto the blocks, or do i need it plastered first?
my main concerns are that if i do tile straight onto the blockwork, with the heat their has to be alot of movement, and i dont want any cracked tiles, also what special sealer or primer is best to use on these porus walls?

cheers

 

[Spud]

prime with sbr bond mixed 3/1 with water then render with sand and cement