Sidewalk's "bubblin' brew" leads to costly snowmelt replacement

Remember the opening sequence in "The Beverly Hillbillies" when poor ol' Jed Clampet shot at a rabbit "and up from the ground came a bubblin' brew"? Of course, that was their ticket to the good life in California.

Two years ago, a bubbling brew of a slightly different sort was seeping out from a sidewalk near Minneapolis, and the owner of that property wasn't pleased. In fact, it was twelve thousand square feet of expensive, meticulously snow-melted concrete sidewalk at one of the city's leading corporations. And it was leaking badly.

Black ONIX tubing withstands extremes of  temp-erature, as well as the kind of concrete movements that are inevitable during the infamously hoary Upper Midwest winters.

"Chalk this one up as a job gone bad," said Jim Burns, vice president of the St. Paul-based manufacturer's representative firm, Mulcahy Company. "But the installing contractor rose to the challenge and accepted full responsibility for it. The silver lining in this cloud was that everyone involved learned a lot through the experience, and the installation is now one we can point to as an example of how best to install a large snowmelt system."

The job began in the fall of 2003, when St. Paul-based Harris Mechanical got the call to install a long, 8-foot-wide wrap-around sidewalk for one of the city's leading businesses. The catch: there wasn't much time to get it done. They quickly put in a call to a local supplier and began the system's layout and design. Several days later, the designer reviewed and approved the plans for an extensive PEX layout, even offering some "helpful" hints about how it could be simplified, given the tight time-frame. Hint: this wasn't a good idea.

Stressed out
In fairness to all parties, the time-crunch was a factor. The facility manager stated clearly his desire for the system to be in place, with concrete poured, before the first freeze, judged to be only a few weeks away. It was not an unrealistic request, but one that the wholesaler didn't take into consideration when they shelved the paperwork for two weeks.

That's when push came to shove, and ultimately led to severe compromises at the job site. The design and engineering work was delayed, which led to an uncomfortable rush to get the pour in before winter. Ultimately, the delays made things pretty stressful for the Harris Mechanical installation team, which began the job on a snowy day in early November.

Of course, it didn't help that the concrete installer hurried all of the preparations and apparently neglected to provide a stable stone base of sufficient depth and stability. But these inadequacies were hidden, or not disclosed. And, when the tubing supplier visited the job prior to the pour, they made a cursory inspection and gave it their nod of approval.

"It was one of those 'hind-sight's 20-20' things," said Chris Rzeszutek, the Harris Mechanical project manager who distinctly recalled a 'sinking feeling' as they completed the installation. "Under the circumstances, we pushed hard to get the job done before Mother Nature could pull the rug out from under us. Everyone was stressed. We simply didn't do the best that we could have, and it certainly proved not to be good enough."

It wasn't long before the troubles began. Cracks with oozing glycol pools appeared randomly, reminiscent of Jed's missed shot. Burns wasn't aware of the job, or the problems, until Rzeszutek sought him out, seeking advice. Harris hadn't acquired the PEX tubing and other materials through Mulcahy, but Rzeszutek knew from experience that he could go to Burns for an opinion. By that time, Harris crews had already responded to the facility's numerous complaints about unmelted snow, and oozing leaks.

Burns notes that the mechanical system was installed with primary/secondary piping, though "it wasn't the best layout" he'd seen. Supply temperatures to the slab were set at 140°F, but it appeared that the tubing must have seen much higher temperatures than that.

Sidewalks on the move
When Burns joined Rzeszutek at the job site, the job was much worse than he expected. He saw evidence of the numerous splices, appearing like patches on a quilt. Several of the poorly shored concrete sections were out of place, pushed and pulled by the rigors of an unforgiving Minnesota winter. And they showed him several pieces of failed PEX tubing.

"The tubing was full of a cement-like substance," exclaimed Burns. "It looked like it had melted and stretched. The tubing was badly extended in several places; it was obvious that it had failed."

A proper installation has relatively short runs of ONIX to maintain uniform temperatures, a stable gravel base to reduce frost heaves and sufficient rebar to limit slab movement from cracking.

"We looked at the problem from every conceivable angle," exclaimed Rzeszutek. "What we discovered was that the expansion joints were very inconsistent in placement, and depth. And there was very little rebar in the concrete. What we then found was that the tubing failed at some of the expansion joints, which one might expect, but what surprised us all is that several of the failures occurred at the 'control' or cut joints," he added. "Even in there, sections where there was rebar, the sidewalk cracked and fell at the control joints. They basically became expansion joints. The piping pulled, twisted and sheared at these joints.

"It didn't help that the very long, straight runs of sidewalk had, within them, 400- to 500-foot runs of PEX . . . probably too long to ensure proper heating of sidewalk surfaces," added Rzeszutek. "Well, we know it now."

In the mechanical room - where Harris pros regrettably had little involvement - their technicians discovered that no temperature "safeties" were installed in the system. This gave led them to suspect that the tubing may have been routinely exposed to water temperatures in excess of 180°F.
"No one would fess up to it, so it remains a mystery," added Burns. "The lesson here is this: if it can happen, it probably will. It did in this case, and it won't be the last time."

The concrete fell and the PEX sheared. Burns showed them another job site where Onix, a durable rubber oxygen barrier hose made by Watts Radiant, was installed. Here, too, the concrete had broken and dropped by more than two inches. And though the exposed Onix hose was stretched and crimped, it hadn't failed. It was stretched, but had not broken.

"The facility managers and the installer loved the fact that although no one plans for concrete to fail, the rubber tubing is far more likely not to shear. It also offers the possibility of raising the concrete during repair with the hose remaining intact." Burns sees this as a key difference in the two technologies and is why he always recommends Onix for snow- melt applications.

Movement of the sidewalk sections, says Burns, is the key challenge with un-footered slabs anywhere, though especially in areas where permafrost can lift or heave the concrete sections like dominoes in a line. Sidewalks move because they're rarely poured on footings. In the language of those who toil in the concrete industry, they're "floating" slabs, inherently unstable and most likely to twist, bend, and rock 'n' roll - not exactly the best of circumstances for tubing or hose that's wrapped in stone.

Harris toes the line at a cost of $250,000
So, when Harris Mechanical accepted the responsibility for replacing all of the concrete while also replacing the snowmelt system, they installed nearly 20,000 lineal feet of Onix hose and replaced all of the concrete at a cost of about $250,000. Of course, this time, the job entailed a carefully prepared base, plenty of rebar, no confusion about what was a control joint and what was an expansion joint, and how to route the hose.

The original supplier that sold the tubing, designed the layout and gave the first system their approval wouldn't return calls and refused to visit the "scene of the crime." But it's Harris' policy to guarantee all installations. And they held fast to their promise by making the commitment to tear out and replace the sidewalk and radiant tubing at their own cost.

As Harris made their preparations to replace the sidewalk, all parties agreed that the new hose must be capable of withstanding temperatures in excess of 180°, and that it would need to be far more durable than PEX.

Harris and the client spoke to several vendors and experts in the field. They hired both a mechanical engineer and a structural engineer to be certain that they agreed with what was installed. And it was agreed on that Onix hose would be the best replacement choice.

"Onix also remains flexible for installations, even at very cold temperatures," said Burns. "Ever try to install PEX after, say, September? What a challenge. Onix remains flexible, which is a huge advantage. And it won't weaken at temperatures above 180°. The contractor and owner felt a great deal more comfortable knowing that the hose could withstand intermittent temperatures up to 300° should a control fail."

Onix is cross-linked Durel EPDM, a synthetic rubber that is extruded into a tube and wrapped with an aluminum shield oxygen barrier and two more layers of EPDM. This flexible composite hose is reinforced with aramid cord, the same material used to make fire and bullet proof shields. One of the key advantages is its aluminum barrier: it's unaffected by sunlight, UV radiation from fluorescent lamps, moisture or elevated temperatures. And, sandwiched between EPDM layers, the aluminum layer can't be scraped off or damaged by typical job site abuse.

"The UV issue is one that's often overlooked in snowmelting jobs," added Burns. "Few people know that, with PEX, if the barrier is exposed to sunlight for longer than seven days, a manufacturer's warranty is voided. With Onix, there's really no limit to the amount of exposure.

"Also, sometimes operators are the 'controls' and they can, of course, make mistakes," continued Burns. This could have been the reason for the first product failure and everyone agreed that it would be best to eliminate the possibility of this happening again. The rubber hose is like an insurance plan.
The key point is that we're burying it in concrete. It's worth a few extra bucks to ensure that the product doesn't fail."

The rubber hose's ability to flex, even after it's installed, also played into its specification on the job. Said Burns, "All manufacturers of tubing stipulate that installers must avoid having tubing pass through an expansion joint [generally, they state the need to go under an expansion joint, or for the tubing to be sleeved]. But what happens when a control joint - an actual cut in the concrete - becomes an expansion joint?"

And so it was on a warm day last June that jackhammer crews tore up and removed the old sidewalk, filling several dumpsters with chunks of concrete. PEX tubing hung from the discarded cement sections like torn arteries. The crews had a tightly engineered plan to follow. Weather conditions didn't harass them, and every stage of the job was carefully monitored.

The system operated flawlessly last winter and is now in the midst of the new snowmelt season. "The client is happy and, perhaps as importantly, we know we did the right thing," said Rzeszutek. "We all stand a bit taller because of it."