Install insulation without misalignments compressions gaps or voids in all exterior wall cavities behind tubs and showers.
Rotten wall behind bathroom enclosure.
Drop those pieces into a bucket of hot water to separate the gypsum backing from the tiles.
If any of the wood studs appear wet and moldy you can clean them with a water bleach solution.
Cover the wall cavities with a rigid air barrier or other supporting material to prevent cavity insulation from sagging and to create a continuous thermal barrier.
If you find that the wood is rotted you will need to replace it.
Then pull the tile and small squares of drywall out together.
Any insulation that is wet or moldy will also need to be replaced.
Fiberglass and acrylic tub and shower enclosures come with a flanged edge that attaches directly to the wall studs and the proper way to hide this flange is to install drywall over it.
Install an air barrier behind showers and tubs installed on exterior walls.
Position the cut drywall sheet on the wall.
Leave some of the old drywall exposed where it will meet the new backerboard.
Make sure the bottom side edge of the drywall sheet extends down over the thin lip of the tub s mounting flange.