What condition should the wall be in that I intend to cover with a glass splashback?
Ideally the flatter the better.
Our glass splashbacks are fitted to the wall using silicone, so any slight unevenness (2-3mm) can be taken up by the adhesive.
Extremely uneven walls will need either boarding out first or skimming with a new coat of plaster and sealing.
+GNU Dr. Lynn Allen+