I don't have a great experience because I'm a computer monitoring software developer.
On this forum recently since I started home repairs and have questions.
But I searched the Internet for answers and this is what I managed to find out.
If the render on the brick wall has been damaged and needs to be patched before tiling, here are some steps you can take:
Clean the damaged area: Use a wire brush or scraper to remove any loose or damaged render from the brick wall. Make sure the surface is clean and free of dust and debris.
Apply bonding agent: Apply a bonding agent to the damaged area using a brush or roller. This will help the new render bond to the brick wall.
Mix and apply the render: Mix the render according to the manufacturer's instructions. Apply the render to the damaged area using a trowel or float, making sure to fill the area evenly and smoothly. If the patch is deep, you may need to apply the render in multiple layers, allowing each layer to dry before applying the next.
Allow the render to dry: Allow the render to dry completely according to the manufacturer's instructions. This can take several hours or even overnight.
Sand and smooth the surface: Once the render is dry, use a sanding block or sandpaper to smooth the surface and create a flat, even finish. Wipe away any dust or debris with a clean cloth.
Prime the surface: Apply a coat of primer to the patched area before tiling. This will help the tile adhesive bond to the new render.
Tile the area: Once the primer is dry, you can tile the area as planned.
It's important to note that the patch should be level with the surrounding render to ensure a smooth, even finish once the tiles are installed.
Also here is a helpful video
HOW TO RENDER A WALL READY FOR PLASTER OR TILES (OLD WALL)