Problem #1 - We found a soft-spot in the ceramic tile near the bottom faucet in the bathtub. I warned my wife not to push on it...the next day she somehow put her foot through it. About a week later, another soft-spot appeared a little higher than the first. Total, there are about four 4-1/2" square tiles broken/missing horizontally and five vertically (about 20 tiles total).
What do I need to do to replace the old drywall? Most of it was soft and crumbling apart so i removed what wasn't firm. There was black stuff (mold or mildew) all over everything back there. A couple inches above the tub there's a 2x4 running horizontally.
Do I have to buy a whole 4x8 sheet and cut it down? If so, how do you cut drywall?
How do I secure the drywall in the wall?
What goes between the tiles and how do I do that? (I saved the tiles that I removed)
The hole is about 5-6" deep to the wall of the other bathroom and not accessible from the basement due to wooden beams and furnace pipes, etc.