OOPS I chiseled out too much of a concrete wall board behind tiles in the shower

[miamicuse]

In my shower there is a recessed alcove along an exterior wall (concrete block wall). The shower was put in about 4 years ago in place of a tub.

This recessed alcove recenly had a clack on one of the tiles, I don't know if it is because of swelling from behind (*smells trouble*) or just caused normal expansion/contraction. I decided to remove two of the tiles to inspect. One horizontal and one vertical. As seen in the picture below:

The alcove has two sections, one on top and one at the bottom. You can tell I removed a vertical tile at the bottom of the top alcove and a horizontal tile (this is the one that was cracked) at the bottom alcove.

I did not see any moisture under there so I think that's OK.

However, I did a poor job of removing the vertical tile. In an effort to not strain the adjacent tiles I pounded a chisel under that tile hoping to pry it off. Only I also chiseled into the wall board under.

I looked closely at it and the contractor who did this attached a strip of wonder board onto the wood stud behind. Then applied tile adhesive for the tiles. It was probably one single strip of wonder from top to bottom of the entire alcove. I saw one screw in the section I removed. Here is a close up of what it look like right now:

I managed to remove a big chunk of the wallboard. I see a layer of mesh below. What should I do to put back a surface for the tile to adhere to? I see two options:

(1) Mix up some concrete patcher and float new concrete into the wall board to build it back up. Only question here is I don't know how much of the original wall board is left and whether doing this will be strong enough? I have never floated concrete on a vertical surface either my guess is it's not that easy.

(2) Use a grout saw to saw it off top and bottom of that section. Go buy a new sheet of wonder board and break off a 6" x 10" piece and screw that onto the wood stud again. If I did that the problem I see is I don't know how many screws they used to originally attach the wall board to the stud. If they used two and I exposed and remove one, then it means one section of it will not be screwed on.

Are there other ways?

Thanks in advance for any advise.

[Colbyt]

More than likely you will be fine if you just glue the tile back into place with a generous coat of mastic and take care to grout the joint really well. The check the grout line yearly or so.

If you feel you must do more build it back to level using Durobond 20 or 45. The 20 will set much quicker and if mixed a little dry should be easy for the newest newbie to hold in place till it dries.

Colbyt

[siralfred]

I would use concrete patch. Mix it a little stiff and it'll stay. It's hard to tell from the picture, but use some mesh if there's room for it and fill that gap on the right. The cracks were probably caused by normal house movement. A corner like that is especially vulnerable.

[RicodJour]

Clean what's there. Use fiberglass mesh joint tape over the compromised area. Use latex modified thinset to set the tile. You can do it in one step, or you can apply the thinset to the patch, smooth it out making sure that the tile will sit flush with the surrounding tile, and let the patch set up overnight before installing the tile.

It's not a big deal. Go slower with the surgery when dismantling. It'll be much faster in the long run.

You should redo the caulking for the entire alcove while you're in there. Those alcoves aren't very forgiving and they'll leak from tiny gaps you'll never see.

R