Home Improvement Questions? Ask a Handyman for Answers
The question to be asked is what temperature will the wall get to.
I cannot see how 3 sheets of plasterboard 45mm is better than a 75mm fire wall.
This is what the UK suggests to build a 1 hour fire break.
How do you provide a 30 or 60 minute fire-rated horizontal membrane?
Use CasoLine MF incorporating Gyproc WallBoard or Gyproc FireLine board and insulation. For 30 minutes fire resistance in accordance with BS 476: Part 22, use two layers 12.5mm Gyproc WallBoard overlaid with 100mm Isover Spacesaver Ready-Cut. For 60 minutes fire resistance in accordance with BS 476: Part 22, use two layers 15mm Gyproc FireLine board overlaid with 30mm stone mineral wool (minimum 24 kg/m3).
As you can see its a lot more difficult than just installing a few sheets of board.
Whereas a wall when built properly with the correct materials can give you more than an hours protection.
I understand that a Lime Morter plaster is good for giving the wall a good finish .