EVERETT — The main runway at Paine Field Airport will close temporarily after maintenance work performed earlier this month failed to achieve the desired results.

The runway was shut down from July 1 to July 8 for scheduled maintenance. As part of the project, an oil-based fog seal treatment was applied to the runway by an outside contractor.

The sealant, however, isn’t performing as expected, airport officials said Friday.

At times, it’s resulted in a slipperier-than-normal surface, as well as an unusual amount of loose material on the runway.

The 9,010-foot long runway is used for take-offs and landings by Boeing and other airport tenants.

Of the airport’s three runways, the main runway — the airport’s largest — would accommodate commercial passenger flights. Commercial airline service is expected to begin this winter at the airport’s new passenger terminal, pending approval by the Federal Aviation Administration.

Although the problem is intermittent — planes are still able to take off and land — the runway needs to be fixed, county officials said Friday. Paine Field Airport is owned and operated by Snohomish County.

The project, which will shut down the main runway for five days, is expected to cost about $5.5 million. The FAA has offered more than $1.3 million to help pay for the work.

The remainder is likely to come from previously budgeted airport funds that were set aside for work that was scheduled but never undertaken, airport officials said.

“We are thankful to receive additional money from FAA for our important runway rehabilitation project,” airport engineer Ken Nichols said in a news release. “The additional money from the FAA is a reflection of a good relationship with the FAA Airports District Office and the high priority of runway rehabilitation projects nationally.”

County spokesman Kent Patton said the first priority is getting the runway in shape.

“Afterwards we can look at what other actions we need to take. An outside contractor performed the work and put down the sealant,” Patton said.

Airport officials are conferring with tenants to determine the best time to undertake the closure.

“We want to minimize the disruption to our tenants,” Patton said.

Boeing said, so far, there are no impacts to its operations.

“We are aware of the issue and are in close communication with Paine Field regarding the remediation plan,” Boeing said in an email Friday. It will reassess the situation once the plan to repair the runway is developed, the company said.

In the meantime, airport crews continue to monitor the runway and conduct friction tests to make sure “conditions remain safe.”

A few days after the sealant was applied, the airport closed the runway for part of the day July 12 after tests determined that surface friction levels dipped below what’s acceptable, airport officials said. It reopened the next day.

Initially, it was hoped the treatment, which is intended to prolong the life of the runway’s asphalt surface, would eventually “cure” and the problem would disappear.

When that didn’t occur, airport officials — in discussion with engineers, paving experts and the Federal Aviation Administration — determined that additional repairs were necessary.

Janice Podsada: jpodsada@heraldnet.com; 425-339-3097. Twitter: @JanicePods.