Wow. quick reply
If the walls aren't straight enough to tile, you need to fix that before tiling. And you can use the Aqua-panel to do it.
My usual method:
1. Primer ALL the plaster with an acryllic primer such as BAL APD (reason to follow shortly).
2. Mark the walls and the boards for the screw holes. Drill them and plug them. (How you do it and what you use is up to you as that is all dependant on what's behind the plaster)
3. Using a slow setting Cement based powdered adhesive, spread the walls and the back of the board using a 6x6mm notched wall trowel. If the wall is too far out, consider using a bigger depth trowel. Put the boards up. Spirit level them to make sure they are straight and screw it to hold it in place while the adhesive sets.
This would be recommended for all the walls around the bath area. Where the boards meet, apply a very thin lay of adhesive over the top and flatten in either some BAL WP1 Tape. Scrape of any excess adhesive so that its smooth and flat, and leave to dry. 24 hours should be good.
Or, if the walls are straight enough to tile, you don't need the Aqua-panel.
Whether the Aqua Panel is used or not, TANK IT! (Safest option)
The bare plaster walls still need priming with the BAL APD. Not just in the bath and shower area, but everywhere you are sticking tiles. But if we just concentrate on the bath and shower area, get yourself some BAL WP1 Membrane and about some more of the BAL WP1 Tape.
1. Make sure that the bath is fixed into its final position and siliconed to the wall.
2. Fill it full of water to weigh it down so that you can cater for any dips.
3. Whether the area is your primed plastered walls or the Aquapanel, paint the membrane into all the internal corners and around the top of the bath. While its wet, flatten the WP1 Tape into it. Just above the bath, the WP1 tape needs to overlap the bath by about 3-4mm.
4. Paint the membrane over all the surfaces and the afore mentioned tape. Leave it to dry for another 24 hours just to be sure. You now should have a completely watertight bath and shower area.
Next job, tile it. Trowel the adhesive using a 6x6mm trowel. If the wall is slightly out and you need to keep it level, after spreading the wall, spread the back of the tile too.... DO NOT DOT AND DAB TO LEVEL TILES! The reason you primed the plastered walls is due to the size of the tile you have, you need to use a cement based adhesive. Not ready mixed as it won't dry properly. Problem is, without the primer, the cement adhesive reacts with the gypsum in the plaster, and causes crystallisation which prevents the adhesive from bonding correctly. So the APD is essential.
Anymore questions? I'm happy to answer them. (ps. Sorry about the CAPS with the dot and dab bit.... pet hate. anyone dots and dabs tiles should be shot!)