The tile and backer board had to be removed because of water leaking through the poorly constructed tile installation. It is an old house and backer board wasn't the best option for preparing a tile job in this particular case.
I'll completely rip out the existing backerboard and tiles and start from scratch. I'll be building a mortar bed on the walls.
The dark area of the wall is mold.
The Oriented Strand Board (OSB)behind the tub and the back wall is badly damaged by the growth of mold and must be removed.
After the OSB was removed, mold was still evident in the material underneath, although not quite as bad.
Bleach will effectively kill the surface mold but isn't effective in killing mold in hidden areas such as under the tub or inside the studs or even the floor joists.
I'll have to remove this OSB panel to accommodate a mud bed. Also, there is mold growing here as indicated by the darker areas.
The 2"x4" support will be removed and perimeter supports added about 1/2" lower to allow for a mud bed sloped from 1" to 3/4" giving positive drainage toward the tub.
Vapor barrier and lath has been installed in preparation for a mud bed.
I have installed a gypsum based backerboard to build the wall out and to support a mortar bed. Any backerboard may be used for this purpose, and drywall or green board is much easier to use. Once the mud walls are set they become the strength and support for the tile installation.
I didn't install a backerboard on the back wall to support the mud bed because I didn't want to decrease the distance between the tub and wall anymore than it already is. Applying a mud wall over a vapor barrier and lath without a sheet of drywall to support the mortar can be a little tricky, but the final result is still the same.
The mud wall is complete.
The next stage is to add waterproofing to the lower area of the tub/shower enclosure.
Laticrete 9235 is an excellent product to use for this type of waterproofing. I like to apply a generous application.
Schluter makes a product called Kerdi which also is ideal for serious waterproofing projects.
Immediately after the first coat is applied I installed a fiber membrane provided by Laticrete to ALL the corners. The fiber material ensures that the bridge of the membrane between plane changes remains unbroken.
The walls are now ready for the tile installation. (The waterproofing could have extend further up the walls)
The tile was bonded to the walls using a white modified thinset mortar.
Re-install the plumbing and apply a bit of silicon and it's all done.