If the contractor won’t redo the work, it might be easiest to get used to a little green in the bathroom. (Reader photo)

Q: Two years ago, we had a tile shower bench added to the interior of our shower, which has glass blocks on the side facing the bathroom. The bench is hollow, so you can see through the glass blocks into the interior of the bench. Recently, I've noticed what appears to be a bright green funguslike stream that seems to originate from inside the bench and is spreading along the mortar under the bottom layer of glass blocks. It’s most visible from outside the shower. I have sprayed the mortar with Tilex, both inside and outside the shower, but the problem persists. How can I get rid of this fungus (or whatever it is) and prevent it from returning?

Columbia

A: The growth is probably algae or a form of mold, both of which need moisture to grow. It’s almost certainly there because the grout between the glass blocks wasn’t sealed properly, allowing it to stay damp for long periods of time.

James L. Keilson, president of Maryland Home Inspection Services (301-534-0669), says he has seen hundreds of glass block walls in showers. “This is very unusual,” he said, after looking at pictures of your shower. He suggested you get the contractor who installed the shower and bench to come back and redo the work. Nothing short of that will fix the problem, he said. “It won’t go away, even if you don’t use the shower.”

Dave Collier, director of operations for Metropolitan Bath and Tile in Towson, a bathroom remodeling company, had the same advice but recommended some construction changes the next time around. Having a tiled seat on a shower bench isn’t wise because the grout joints on it can let moisture through if they are not sealed. “The bench should have a solid seat,” Collier said. And rather than having the bench butt up to the glass blocks, the bench should be built first and finished with tile all the way to the floor, including on the end facing into the bathroom. Then the glass blocks can wrap around that, resting on the bench seat, so they shed water rather than trap it.

What if you can’t get the contractor to redo the work and aren’t able or willing to pay for it on your own? Keilson said he is fairly certain the moisture that is allowing the green growth is confined to the grout, not causing rot within the wall or floor framing of your house. So, if you need to, you might just decide to live with it. Keep the green to save some green.

Have a problem in your home? Send questions to localliving@washpost.com. Put “How To” in the subject line, tell us where you live and try to include a photo.

The Checklist Read Jeanne Huber’s roundup of home-improvement tasks you should tackle in February, such as exploring renovation tax credits.