Why You Don’t Hire Workers From the Big Box Store

I was called out to a shower damaged by an electrician. He was working on the back side of the wall to install a subpanel. Using a reciprocating saw blade, he had cut into the wall all the way through the mortarboard and tile on the other side. He had damaged four large tiles.

Unfortunately, I had to work over a refinished, painted tub surface. Great caution must be undertaken to protect the tub finish because it is as fragile as an automobile finish. I used a half-inch thick lightweight fiber mortarboard to protect the surface directly below the repair.

I also covered the vulnerable edge of the tub with a moving blanket.

When I removed the four tiles, I discovered multiple deficiencies for an area that is subjected to extreme moisture. First of all, the tile did not stick very well to the mortar board. I suspect that they used a very inexpensive, non-modified thinset. Second, as you can see from the grid on the mortar board visible in this picture, quarter-inch thick mortar board was used instead of the required half-inch thick board made for wet installations.

Additionally, the mortar board should be screwed every six inches on the perimeter. As you can see, there’s a much wider, open span between screws. Not surprisingly, the grout in this vertical joint, had cracked out due to movement. While installing screws where they belong, the mortar board visibly cinched up ¼-inch tighter to the studs below.

Also, all of the open seams in this installation were not covered with mesh seam tape.  I also strongly suspect there was no waterproof membrane placed behind the board, and obviously there is no waterproof coating on the front of the board.  One of these two waterproofing options are required in this installation to make it watertight.

Of course, as required, I installed mesh seam tape. The seam tape is then covered with a fine coat of thinset. This further ensures the installation against movement and prevents the grout and tile from cracking.  When the tile and grout cracks, this could lead to water leaks into sensitive areas of the bathroom, walls, and adjacent rooms.