We moved in our house about 6 years ago and our front bathroom has an enamel tub with tile from the top of the tub almost up to the ceiling. Whoever did the tile work didn't do a great job and water has gotten behind the tiles. I took off the bottom two rows of tiles and the rock behind the tiles has wicked water and is totally rotten and moldy. I would really like to go back with a shower/tub that would go almost to the ceiling. What steps do I need to take and what do I need to use to replace the sheetrock or green board or whatever the rotten stuff is behind the tile. I don't want to spend a fortune and I would like to do as much as possible by myself.