SPF Crew Seals the Deal on Monolithic Dome Home

February 1st, 2009

When spray polyurethane foam (SPF) contractor John Kuchta, Jr. received word he’d won the bid to insulate a new-construction home in Hayes, Virginia, he knew his crew would have to face a few new challenges.

But hey! Kuchta’s crew has a track record of spraying foam in a wide variety of applications. Combat Coatings, LLC, insulates metal warehouses, brick office buildings, wood-frame medical facilities, and has even retrofitted homes in the past. What could be so danged difficult about spraying three inches of NCFI Polyurethane’s (NCFI) two-pound, closed-cell foam to help create a monolithic dome home?

Kuchta was about to find out.

 No Box to Think Outside Of

What do you get when you think so far outside the box that the box disappears? A monolithic dome home! These shell-like structures — with no roofs, no joints, and no seams — are among the most energy-efficient in the world. But they can’t be built without SPF!

According to the Monolithic Dome Institute, the construction technique was perfected in the mid-1970s when founder David B. South sought to create a highly insulated potato storage facility in Idaho. Today, monolithic dome homes, schools, gymnasiums, bulk storage facilities, churches, offices, and other structures are found in 45 states and a handful of foreign countries.

Monolithic dome structures are created without support framing. The process begins when tradesmen attach a giant domeshaped tarp — called an Airform — to a circular concrete foundation. Heavy duty fans inflate the dome to a flattened hemispherical shape. A one-and-a-half-inch layer of SPF is sprayed onto the inside of the dome. Workers press specialized hangers used for rebar into the foam. Then, a second one-and-a-half-inch layer of SPF is applied to anchor the hangers. Tradesmen affix rebar onto the hangers. Spray concrete professionals broadcast four inches of swimming pool-type spray concrete to create an extremely rigid monolithic structure. When the concrete dries, the fans can be turned off. The Airform, which remains in place on the outside of the shell, may receive an exterior coating.

Kuchta had all this in mind when he pulled his 28-foot Gusmer-brand gooseneck SPF rig alongside Joel Emerson’s 2,200-square-foot home under construction. But something caught Kuchta’s eye: Emerson’s foundation looked different from the one seen on Monolithic Dome Institute’s Web site (www.monolithic.com).

“The home was being built by a master mason, and he had the idea of creating a 10-foot-high perimeter wall of brick,” says Kuchta. “It’s a work of art from the outside. I don’t know how he did it, since attaching the Airform to ground-level concrete can be a challenge. But Joel had somehow attached the Airform to the top course of brick and had it fully inflated when we got there. My first question to him was, ‘How the heck do we get our spray foam equipment inside?’ ”

 No Foam, No Dome!

Relatively low air pressure supplied by high-volume fans such as those used to circulate air inside grain elevators supports a monolithic dome throughout the construction process until the final layer of spray-applied concrete hardens. But until that concrete sets up, the only way to get inside an inflated dome is through a two-door air lock.

 The problem was that Combat Coatings’ spray equipment couldn’t fit through the air lock. Kuchta also observed that he couldn’t simply snake the heated hoses through the air lock. Leaving the doors ajar before the final concrete coat sets up invites a complete and catastrophic collapse of Airform, SPF, rebar, and concrete.

For a while, it looked as though this oversight might send the SPF team packing. But Kuchta and Emerson huddled up and came up with a plan.

“Access to the house was easy,” says Kuchta. “We could back the trailer right up to the air lock. But the hoses presented a problem. Joel finally had to chisel out a brick and build a small portal. We passed a section of heated hose through, and Joel sealed the hole with a gasket he’d made. We connected other hoses to that and strung them up to the Gusmer 1600 series air-driven proportioning pump in the trailer. We brought our spray guns (Gusmer GAP Pro with #01 mixing chamber) in through the air lock, hooked up, and were ready to go.”