Mayor de Blasio just can’t get enough of nonprofits: He’s setting up a new one, the NYC School Support Services Corp., in what looks like another union payoff in the name of ending the long-running scandal of profiteering custodians.

For decades, school custodians were kings: independent contractors given a flat budget of up to $750,000 to buy supplies and hire and pay staff — including themselves.

In 2009, Phil Portelli, a custodian at West Side HS, got caught stealing $99,000. The next year, Trifon Radef, the custodian at Roosevelt HS in The Bronx, was accused of using school staff and supplies to renovate 10 houses he owned.

The Empire Center found city school-custodian engineers were the highest-paid group of city employees in 2014, earning an average of $109,467.

And their union contract made it impossible to fire them unless they were jailed. Some custodians did stellar work — but many schools looked like dumps.

Mayor Mike Bloomberg tried to fix the mess. He wanted to start privatizing the system, but the custodians union, Local 891, wouldn’t play — it just refused to negotiate a new contract after 2007.

In response, Bloomberg refused to replace custodians who left and instead had temporary hires do the work.

That Temporary Care program had its own problems, with excessive overtime and other management issues, but at least it moved the union to accept some reform. Last year, de Blasio inked a new contract to cover 2008-2016 in which Local 891 finally gave up some of its power — lump-sum budgeting is gone.

But now he’s giving away those gains to please the unions for the janitors and other custodial staff, 32BJ and Local 94.

They’re to receive the “prevailing wage” — a term of art that has nothing to do with market-rate pay and means a raise of perhaps 25 percent.

And they’ll all theoretically be employed by this new nonprofit — though insiders expect the city Department of Education’s Facilities Management team will actually call the shots.

The mayor estimates the start-up costs of his scheme at $40 million but promises the long-term savings will more than offset the outlay. Savings from a 25 percent pay hike?

One thing the scheme will do is remove all these jobs from the official head count of city employees — which, as it happens, is up more than 8 percent under de Blasio.

Of course, just contracting out all school custodial work would’ve truly saved money and cut the city head count — but privatization’s not “progressive.”

© 2016 New York Post