plaster 2 inch thick

Best to use "drywall adhesive" as the backing stage, as plaster is not a good medium to work with in thick stages. Dry wall adhesive can be put on thick and then skimmed with normal plaster ie multifinish.

======================== The instructions on the bag suggest building up with layers of 5mm to 20mm with a limit of 50mm so you would probably get away with 2 X 25mm if you're in a hurry.

On the other hand it does take time to dry out fully. I would suggest that you apply the first coat and let it go hard enough for you to apply the second and then wait until it dries to a proper white colour before tiling. That could be a few days in this warm weather.

Cic.

Just use drywall adhesive and a bit of plasterboard dot & dabbed on top to the finished level if it's going to be tiled. That way it will be set enough to tile onto in a few hours when the adhesive has set. Franko.

Personally, I would make up mortar for that thickness, which you could lay in one go if it's horizontal. You are probably looking at many days for this to dry out, regardless if it's plaster or mortar.

I've bult window sill's up using either using dot and daub drywall adhesive and plaster board off cuts to near the right height, then plaster as well as cement to near right height, then plaster.