Bernal Heights Shower Window Jamb Repair, June 2024

This job came to us through a response on Craigslist, and it was fixing a critical problem: a window in a bathtub surround that had become a waterproofing hazard. It’s also a small world. The owner knew a general contractor I’d worked with years ago, but neither of us realized we knew the same person until the job was done.

The window over the tub had been taken out and reinstalled. When it went back in, it left a gap behind the jambs and header, the tiled sides and top of the window opening. In a shower, that’s a serious problem. Every time the shower runs, water hits the window opening, and any gap behind the tile is a path straight into the wall. A window in a shower is already one of the most vulnerable spots in a bathroom, because it’s an opening in the wall in exactly the place that gets the most water.

The fix had to go back to the structure. First, we demolished the tile that had abutted the old window, opening up the sill, jambs, and header down to the framing so we could see and close the gap properly.

Next, we packed that space with deck mud, a dense, sturdy mortar. It filled the void behind the window opening completely and gave us a solid, shapeable base to build on. Deck mud also lets you set the slope: a shower window sill should pitch slightly toward the tub, so water runs off it instead of sitting against the window frame.

Over the mortar went a waterproofing sealant, a continuous membrane that keeps any water that gets through the surface out of the wall.

Then we installed solid man-made stone pieces for the sill, the jamb risers, and the header. Solid pieces are a better choice than small tiles in a window opening. There are fewer joints for water to work into, and they’re durable enough to take daily soaking.

Finally, we grouted the new stone into the surrounding tile, and used grout caulk where the stone meets the window frame. That joint is where two different materials meet, and they’ll move at different rates, so a flexible seal holds up where rigid grout would eventually crack.

The result is a window opening that’s watertight again, from the framing out to the finished surface.