Michael Shea, an 11th grade history teacher at Kenwood Academy, said students came into his first period class Thursday morning saying they saw a rat in the library.

“It’s just become a regular thing, and unfortunately, it’s not supposed to be that way. That’s not what a school is supposed to be like,” he said during a news conference Friday morning.

The day before, Chicago Public Schools officials had agreed to hire 200 more custodians over the summer to tackle dirty schools — with 100 of the new custodians remaining on the job in the fall. Total cost of the hiring: $7 million.

On Friday, Shea joined members of the Chicago Teachers Union to decry a “cleanliness crisis” at Kenwood, 5015 S. Blackstone. To dramatize the situation at the South Side high school, several CTU members donned hazmat suits and offered to “conduct an independent inspection for health and safety hazards” at the school.

Shea, who has been teaching at Kenwood for nearly 17 years, said the school has for years been an “excellent example of how systematic problems really do impact a classroom,” adding that teachers “can’t get our classrooms clean.”

He listed problems such as rodents, leaky pipes, tiles falling from the ceiling, a lack of toilet paper and soap, and more.

“We have administrators buying mops and cleaning supplies for custodians, and it’s still not enough,” he said. “They come in on weekends and clean, and it’s still not enough, and we’ve gone to the board twice, and it’s still not enough. It’s sad.”

On Thursday, union leaders reached a new three-year contract with CPS that includes provisions to hire 200 janitors this summer to do deep cleanings of schools, according to the union, SEIU Local 1. Officials also agreed to meet quarterly with the union to discuss school conditions.

The Chicago Sun-Times has documented filthy conditions in schools where the custodians are managed by Aramark, a private contractor for CPS. Of 125 schools examined in “blitz” cleanliness inspections, 91 failed.

Kenwood was one of the schools that failed, with inspectors noting evidence of mold or mildew in the kitchen, pest infestations in the food prep area, food storage area and teachers’ lounge, and leaking and dirty toilets, urinals and sinks, among other things.

“What’s it really going to take is not just 100 custodians — and we celebrate custodians for standing up and demanding more — but 100 is not enough,” said CTU staff coordinator Jackson Potter, one of three union members at the news conference wearing hazmat gear who were ultimately ignored when they knocked on the door at Kenwood.

“That’s only 10 percent of the custodians they’ve cut over the past few years alone. We need a thousand custodians,” Potter said.