I am about to get ready to tile my new shower, the tiles are large to to avoid to many grout joints. Can I put adhesive directly onto a newly plastered wall or should it be sealed first.

Tar.

Plaster if a normally plastered wall takes a month to dry properly before tiling. Once dry prime the wall with an acrylic primer like BAL APD and then fix tiles using a powdered (cement based) adhesive. Please bear in mind that a plastered wall has a safe weight limit of 20kg/m2 including adhesive and grout.

Have a look here mate for preperation of different backgrounds and other bits and bobs.

All the questions I asked when i joined - Answered

As grumps said, month to dry for new gypsum plaster, and prime with an acrylic primer. Dont be pressured into tiling on plaster thats not fully dryed.