Render bathroom walls

[HarryUK147]

Hello all hope you are well. I am about to render my bathroom walls, 4:1 Plasterers sand and cement scratch, then 5:1 PS and Cement top coat with plasterciser. I am rendering to brick double skin cavity. Can anyone tell me how to prepare the surface please? I was thinking of adding a slurry of SBR and S+C, or can i just wet the bricks?
The wall is to be tiled with some large tiles

Thank you