Chicago muralist Jeff Zimmermann’s take on Andy Warhol’s Marilyn Monroe is almost done. No, really.

The Andy Warhol show is up. It opened Oct. 20 at The Art Institute of Chicago.

The huge Warhol mural on North Michigan Avenue publicizing the show, though, is not quite up.

Jeff Zimmermann is working as fast as he can.

“Just a lot of moving parts,” he says. “The city, the alderman.”

Plus: the weather. Pesky OSHA concerns. And the river of pedestrians walking directly underneath him. Care is required.

“Michigan Avenue is right there,” he says. “A million people walking by, and I have not dripped on anybody.”

Then again, Zimmermann is facing a much bigger challenge than Warhol tackled when he took a publicity still from the Monroe movie “Niagara” and silkscreened it.

You can’t silkscreen a wall. The surface at 663 N. Michigan Ave. is 70 feet by 70 feet — nearly 5,000 square feet, a little bigger than an NBA basketball court. It’s also 150 feet in the air.

Santiago Covarrubias / Sun-Times

Working on scaffolding, Zimmermann and his team used a chalk line to create a grid of two-foot squares, a compromise between artistry and deadline.

“The real way to do it is do it on paper. to scale, then transfer it to the wall, rather than the grid,” Zimmermann says. “Things float around on a grid. But there’s just no time. I wanted to do a one-foot grid, but we’d still be up there, snapping [chalk] lines. Something’s gotta give. That would have had us start painting in mid-November in Chicago, and even I don’t try to paint outside after mid-November in Chicago.”

If you get the sense Zimmermann knows his way around the side of a building, you’re right. His murals have gone up across the city — from the Oak Street Beach pedestrian tunnel to along The 606 / Bloomingdale Trail. He’s been doing it for decades, unlike certain, ahem, underskilled newcomers.

“Everyone is a street artist,” Zimmermann says. “Back when I started in 1996, it was me.”

Some might detect a note of criticism in that. Does the new generation of mural artists not meet his standards?

“It’s a just a mixed bag,” he says. “Not everyone should be a street artist. Save it for the canvas in your basement. I want this stuff to be good.”

Santiago Covarrubias / Sun-Times

Casting shade like that, Zimmermann had better be good himself.

Is he?

“This guy’s a phenomenal artist; I admire him a great deal,” says Tony Fitzpatrick, the patron saint of Chicago artists. “He can make paint do whatever he wants it to do. I wish I had the facility Jeff Zimmermann has. He is remarkable. One of the things I love about Jeff’s work is the absolute primacy of it. You can be standing seven blocks away and pick out a Jeff Zimmermann like a fingerprint. He is only like himself, and that’s the highest compliment I can pay an artist. He’s doesn’t play the art world game. He’s on his own mission, his own path.”

A distinctive path it is. Zimmermann, 49, grew up in Westchester, went to St. Ignatius High School, then studied graphic design at the University of Illinois at Champaign.

“I sat in front of a computer for four years,” he says.

Kevin Tanaka / Sun-Times

His Catholic education led, indirectly, to art. He spent two years in Peru, helping street youth with the Jesuit Volunteer Corps. Back in the United States, he continued this kind of work, helping kids paint murals. Before he knew it, he was painting murals himself, and getting paid.

He was never that kid tagging boxcars and dodging police.

“I was chicken,” he says. “I was afraid of my mom and cops.”

He’s less afraid of getting in trouble now. Passersby have called the the police to report a Zimmermann mural, “The Party,” at California and Cortez. Painted in July 2016 to thumb his nose at the Republicans, it seemed there was the image of a noose.

“There’s always somebody who hates my work,” he says. “Every single thing I’ve done. There’s always somebody who creates a stink.”

There is respect, too. Zimmermann was featured in the Museum of Contemporary Art in 2003.

“I had seen his work around. He’d been working with another muralist, Carlos Rolon,” says Lynne Warren, an adjunct curator who picked Zimmermann for the MCA show. “I just thought his style was particularly striking: so naturalist and realistic. Then, I learned he takes photos of people in the different neighborhoods. He didn’t just do some idealized notion of a person. He would do specific individuals.”

Specific individuals can get a guy in trouble, too.

There was an incident in 2009 when Zimmermann was hired to paint a mural at AutoZone Park, a minor league ballpark in Memphis, Tennessee. He included a smiling African American woman with a gold tooth. That tooth caused the gears of outrage to turn. The Rev. Al Sharpton got involved.

Provided photo

Zimmermann’s reaction was that of any sensible artist facing unmerited protest.

“I was [thinking]: ‘Good, this is great,’ ” Zimmermann says. “In the end, they realized, ‘That’s a real person who does have a gold tooth.’ It was about nothing.”

It helped that the mural’s unveiling was attended by Savannah Simmons, an 80-year-old Memphis woman with a gold front tooth — Zimmermann’s model.

The problem, Zimmermann says, is the public can be uncomfortable when challenged.

“People don’t want art to be about anything; ‘Let’s make it about rainbow and flowers!’ I make murals that are about our history. I try and get people puzzled, so they use their imagination. A mural is that close to a billboard. You see a mural, and it’s: ‘Children! Hope! Peace! Our Heroes! Our Problems! Our Solutions!’ My personal work, people look at it and think, ‘I don’t know what the f--- that’s supposed to be.’ ”

Right now, what Marilyn Monroe is supposed to be is finished.

Santiago Covarrubias / Sun-Times

Perhaps the most surprising thing about Zimmermann is that he’s painting that enormous mural not with a spray gun, not with a housepainter’s brush but with a two-inch-wide brush.

“I have to blend all the colors and make it seem like a silkscreen,” he says. “I want it to be an interpretation of the Andy Warhol. It’s gotta look just like the original. But it’s not mechanical. It’s completely painted.”

And it has to be great. If an artist phones in a canvas painting, he can turn it to the wall. A 70-foot-square mural on Michigan Avenue is the definition of obvious.

“Everything has to be awesome,” Zimmermann says. “Reputation is everything. And it’s a small town. There’s a ton of tweaking going on because it’s freehanded. We’ll get it done.”

Click on map below for a selection of Chicago-area murals