Noticed some grout voids in shower tile, scraped away to re-grout and found bottom row of tiles had some wiggle. Figured I should assess underlying cause and removed tiles.

What was under the tiles was a dry-papery substance and behind that some course powdery bits, maybe just dried out mastic. House was built in the 70's, not sure of conventions at the time or if it was tiled since.

The gap shown seems problematic, but do I need to cut away material and apply new backerboard, or should I just put a little moisture barrier over this section to protect the gap? I'd like to avoid re-tiling the whole shower for now as will be doing that in the next few years, but also want to fix it properly so that it will last a while. Any thoughts?

shower tiles

1 Answer 1


In those years, wonder board (cement type backer board) was not in general use yet. Green board was still widely used with a couple of coats of paint over it. And as you are very well seeing, it did not stand up to moisture for the long haul as was expected. If the tile sealing was not maintained and or the grout lines, within 5 to 8-years the whole shower was falling apart.

The gap was intentional. It was meant as an air gap. Water was not supposed to wick across the gap up into the drywall board and thus last longer.

No easy answers here. Recommend you simply tear it all out and start again. The new cement type backer board is far superior to what you now have. P.

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