PHILADELPHIA (CBS) — An elementary school in the Germantown section of Philadelphia will remain closed on Friday due to mold issues in the building.

The School District of Philadelphia says John B. Kelly Elementary School will not reopen until the school is mold free.

“The school will not reopen until it’s more free. Currently, there is remediation, but it’s cleanup,” said school district spokesman Lee Whack. “It’s cleanup of mold and condensation that has become an issue in the school.”

The school was closed Thursday after traces of mold were found in several classrooms on Wednesday due to heating, ventilation and air-conditioning issues.

A half-dozen work trucks lined the sidewalks outside the school.

“Working with a highly qualified and experienced environmental remediation contractor, work began to remove the problem at 3:30 p.m. on Wednesday.  At this moment roughly 80 percent of the remediation has been completed,” the school district said in a statement.

Parents said they were frustrated in how they learned about the mold issue at the school.

“I have two kids that go here and it’s scary to know that something like this is going under your nose,” said parent Terry Garrett. “Overall, the school is pretty good, the teachers and all, but this, right here, this is a totally different ball game.”

Grandmother Faith Peart wonders if the mold is contributing to her grandson’s wheezing problems.

“Every morning before he goes to school, he always wheezing, so I have to tell him to take his inhaler,” said Peart. “From what I’m seeing now, it’s probably the mold that was causing him to have more symptoms.”

Experts in mold cleanup and remediation say determining exact health impacts can be difficult and tricky.

This mold incident comes two days after an entire school district shutdown in South Jersey because of a similar problem.

Holly Glen Elementary School will be closed for upwards of three months because of significant mold contamination.

The Monroe Township School District superintendent believes the cause was the HVAC system.