The inability to stop severe leaking at the doomed Algo Centre Mall in Elliot Lake was a disheartening mystery for years, but likely the result of a basic design problem, a public inquiry heard Friday.

In a second day of testimony, the man whose company tried to waterproof the roof-top parking deck testified he now believes the designers failed to take into account the heavy traffic — including buses and snow plows — that would use the exposed garage.

"The primary source of our problems was the choice of the hollow-core structural deck and the way it was constructed," Dave Monroe testified.

Dave Monroe, former vice-president of contracting company Harry S. Peterson, prepares for another day of testimony at the Elliot Lake inquiry as Justice Paul Belanger (right) gets the proceedings started. (Nael Shiab/Radio-Canada)

"There were too many slabs of hollow-core precast concrete loosely tied together, and they moved more than we would have expected and in ways we didn't expect."

In hindsight, the roof design was flawed from the beginning, Monroe said.

"It was opening and closing the joints at the beamline that would allow water to enter in more or less a pumping action," he said.

Monroe, former vice-president of Michigan-based Harry S. Peterson Co., said leakage from the parking deck into the stores below proved to be more trouble than the company had ever experienced.

"We realized we had problems we did not understand," Monroe said. "It was very disheartening."

Remedial measures

He described a series of remedial measures — some after a controlled flooding of the parking deck — including replacing seals and caulking.

At one point, he said, they thought they had fixed the problem that began immediately after the mall construction was completed in 1980.

"We felt like, 'Eureka!"' he said.

The euphoria didn't last long, with serious leaks re-emerging within a few weeks.

It would be a decade later — in 1992 — that an engineering-inspection report stated: "The design used for this roof slab is inappropriate in achieving a water-tight condition."

Yet even a seemingly simple solution, such as restricting access to the garage, was never properly implemented and there were no other parking options for shoppers, the inquiry heard.

'I was shocked'

After years of water and salt penetration, the rooftop garage collapsed June 23, 2012, killing two women and injuring several others in the mall below.

'The people of Elliot Lake ... will find it in their hearts to forgive you.'

— Lawyer Douglas Elliott

Monroe said never in his wildest thoughts did he ever imagine the roof deck would create a safety hazard.

"When I heard [about the collapse] I was shocked. I was very sad."

Douglas Elliott, the lawyer who represents citizens of Elliot Lake, praised Monroe for his candid admission that his company's waterproofing system failed.

"I don't want you to think your company was the only one who made mistakes," said Elliott, who called Monroe's testimony a "healing moment" for the community. "The people of Elliot Lake are good people and I know they will find it in their hearts to forgive you."

In later testimony Friday, Henry Jasskelainen, a former Peterson employee, said installation of the waterproofing began late because of project delays.

The inquiry has heard how the temperatures and moisture adversely affected curing of the sealant materials and their bond with the concrete.

"We were basically under the gun to put the system in," Jasskelainen said. "It seemed to always be wet here and we had an early winter. It created a very difficult environment."

'We don't understand'

Monroe said several repairs to the mall's canopy, parking garage and department store failed.

"It was not an obvious problem. I mean you couldn’t go up there and say, ‘Well, here's a hole, water's going in it,’” Monroe said. "That didn't exist.”

Monroe said he told the original owner of the mall — Algocen Realty, the real estate firm that developed the property owned by Algoma Central Railway — his company wouldn’t stop trying to find a fix.

"We're not giving up on these leaks,” he recalled saying. “But we don't understand them at this point, and we can't guarantee you now that it's not going to continue."

Experimental, cheaper system

Analysis of the parking deck’s construction was to continue Friday at the public inquiry launched after two women were killed in the aftermath of a partial roof collapse.

Monroe said a project like this was unique for him. The company he worked for had never constructed a parking lot over retail stores.

As he discussed the construction of the mall and the materials that were used, he pointed out that the waterproofing system he proposed during the design phase was rebuffed by the owners.

"We did comment about the risk involved," Monroe testified. "This was a basic structural decision that was being made, and we had to accept that if we continued wanting to be involved."

Former Harry S. Peterson Co. vice-president Dave Monroe told the Elliot Lake inquiry Thursday that he had reservations about the Algo Centre Mall's design, but that his company wanted the job. (Yvon Theriault/Radio-Canada)

However, Monroe's Michigan-based company already had extensive experience in waterproofing. Among its projects was a parking garage at Toronto's Pearson International Airport — then the world's largest parking structure.

The company also had success with a new method at Toronto landmark Casa Loma. The experimental, cheaper "strip-membrane" system had worked well, Monroe said.

The "Peterson system" involves using a composite sealant and polyurethane membrane only at critical joints in the concrete, rather than applying a membrane across the entire surface.

‘Pressure’ to get work done

However, unlike previous projects, the mall's rooftop garage used precast hollow concrete slabs resting on steel beams.

"The hitch was that we were changing structures — that being new to our experience," Monroe said.

Despite the novelty, he said, the company was confident it would succeed at the new mall by "tweaking" its system.

In his 1979 pitch to Algocen Realty, Monroe urged acceptance of the new system as "the best long-term solution." He cited fewer problems, lower maintenance costs and lower initial expense.

Algocen Realty accepted the proposal for $380,000, saving $150,000 over conventional waterproofing Monroe's company could have installed.

Despite adverse weather, Algocen pressed Peterson to get on with the project,l and Monroe said they proceeded under some less than ideal conditions to satisfy the owners requests and demands.

"There was a lot of pressure to get this work done before the hard winter set in,” Monroe testified.

Monroe said the rooftop garage began showing increasingly serious leakage problems, with water pouring into stores below the parking deck right away.

Wrong material used

A series of letters from Algocen to Peterson outlined the ongoing problems, demanding "urgent action.”

“A complete summer has gone by and your company has not been able to correct these deficiencies and give us what we contracted for — namely a water-tight parking deck and canopy," Algocen wrote Monroe in November 1980.

In part, Monroe blamed the problems on unusual traffic flows across the deck — snowplows and traffic using the garage as a "street shortcut" to avoid backups at a nearby light.

He did, however, admit to a Peterson design flaw — using the wrong material to seal an expansion joint given the traffic. Numerous attempts at remedy failed, with Monroe admitting he couldn't figure out a solution.

Normally, steel enclosed in concrete is well protected by the alkaline environment, but chlorides used on roads lowers the alkalinity.

Investigators believe the result was corrosion of the steel substructure, ultimately leading to the catastrophic failure of a critical weld.

The mall's architect is expected to testify on Monday.

With files from The Canadian Press