A well loved mural that has graced the side of a residential building at Lexington and 18th since 2002 has reached the end of its life. According to a release sent out Monday by Lexington Standard owners Andrew Soernsen and Mark Lee Morris, whose ground-floor shop faces 18th, the deteriorating facade of the building needs repair and repainting, which means the 15-year-old piece of public art, dubbed Generator, has to be removed. In better news, the two artists who created the original mural, Andrew Schoultz and Aaron Noble, have agreed to paint a new one with a similar avian theme.

SFist featured Generator just recently in our list of the best public and street art pieces in the city, but it sounds like it's already too late to check it out one last time.

Capp Street Crap took a snapshot of a piece of the mural already getting painted over with primer, and the work to fix the building's exterior is scheduled to take several weeks.

Significant dry rot is apparently to blame, and while Soernsen said he really wanted the beloved mural to be saved, it just wasn't possible.

Schoultz says, "The ephemeral nature of public art is one that cannot be denied. Nothing lasts forever and nor should it," adding that he and Noble are more than happy that Generator stayed up as long as it did. "[We] are more than thrilled to have had a mural run on 18th and Lexington for almost 15 years. We would have been happy with five."

Previously, Noble wrote on his own website that he didn't expect the mural to remain for very long. "We used the old decayed off-white paint as our background and only prepped the areas that we painted," Noble explains. "We had a very ramshackle aesthetic going on at that point. I soon became much more precious about my surfaces."

Work on the new mural is set to begin in mid-August, and Shoultz says in the release, "I look forward to creating something new and fresh for this location and neighborhood, as does Aaron."

The new work, they hint, will "depict a flock of birds, referencing the quick gentrification of San Francisco, and the apparent soaring departure of the hard-working middle and lower income artists, restaurant workers, childcare workers & bartenders, etc." Schoultz himself was driven out of the Mission by gentrification, he says, having lost his studio there three years ago and relocated to Los Angeles as a result.

Expect to see the new piece by the end of September.

Related: The 12 Best Public Art and Street Art Works in San Francisco