BERNE — In the process of expanding the high school gym, workers discovered a void under the floor that is now being filled, using a process called mudjacking.

“This technique was developed in the 1930s when they literally used mud to pump under slabs,” said James Denney. He and Michael Ritter own the business, Concrete Raising of Upstate New York, based in Glenville, that is doing the mudjacking in Berne.

While the process is well known and frequently used in the Midwest, Denney said, only a dozen contractors do it in the Northeast. Since mud can erode over time, Concrete Raising uses a Portland cement-based slurry; slurry is like concrete but without any stones, said Denney.

“We’re not trying to match the strength of concrete,” he said. “We’re trying to replace the sub-base.”

The void under the BKW gym floor is about 10 inches deep and covers a surface area of about 750 square feet, Denney estimated.

“It absolutely needs to be filled,” he said. “It’s a problem waiting to happen.”

The school board held a special session on Oct. 14 to approve change orders to have the mudjacking done, said Superintendent Paul Dorward. The board approved two change orders for the work, he said. The first is for $19,215, which should take care of it if the estimates are correct.

“The architect has made an assessment of the void and, short of removing the entire slab, there’s no way to tell if there’s additional void,” said Dorward.

The second change order is for another $20,000 and is to be used only if the void turns out to be bigger than estimated. “You wouldn’t want to be in the middle of work and hit the $19,000 cap when additional work is needed,” said Dorward.

The gym expansion is part of an ongoing $12.7 million building project that BKW voters approved in December 2007. Project bids came in at $1.4 million under budget, giving the district plenty of financial wiggle room to cover unanticipated costs, which often occur when working on old buildings. Even with these latest change orders, Dorward said, expenses are “substantially” under the voter-approved limit.

Drilling began on Monday, Denney said. “We hope to be done this week, but it depends on the actual size of the void. We know it’s full when it comes out the holes we’ve drilled every four feet.”

Denney said the process is much less expensive than ripping out and replacing, which is the norm in the Northeast. “It’s half the cost,” he said, “and typically a business doesn’t have to close while we’re doing our work.”