By Les Shaver
Government finds use for bed liners in buildings
Terrorism may have exploded into the national consciousness with the attacks of September 11, 2001, but that doesn’t mean government decision-makers hadn’t already been thinking about its impact.
Multiple terrorist attacks in the ’90s—namely, the bombings at the American Embassies in Khobar Towers in Saudi Arabia in 1996, the 1998 U.S. Embassy bombings in Tanzania and Kenya, and the 1995 bombing at the Alfred P. Murrah Federal Building in Oklahoma City—spurred the military and government into action.
“If there’s an explosion outside the building, the goal is to protect the people on the inside,” says Tod Rittenhouse, an expert in blast engineering from the New York-based international consulting firm Weidlinger Associates.
Part of the goal is to protect people from the building itself. The force of a bomb blast can propel shards of glass and small wall fragments across a room, piercing anything in their path. The Air Force Research Laboratory (AFRL) at Tyndall Air Force Base, Fla., knew the potential danger caused by these flying fragments. That’s why it initiated a survey to look at ways to limit fragmentation.
What the AFRL found was surprising. The material most effective in trapping wall debris during a blast is something found everyday on the bed of pickup trucks. “They were looking for an off-the-shelf material that could be sprayed on the interior of a building to help mitigate fragmentation from a bomb blast,” says Steve Decker, vice president of PAXCON, a blast-resistant coating manufactured by Line-X, a Santa Ana, Calif.-based producer of spray-on truck bed liner.
It turned out that spray-on bed liner can just as effectively protect the occupants in a building as it can the bed on a truck. But just because the spray-on bed liner is easy to spray on a building, doesn’t mean it’s applicable in every building.
How It Works
How does a product that protects pickup truck beds from scratches and corrosion save lives when a bomb goes off? The answer lies in its polyurea system. The polyurea in the spray-on bed liner, an elastomer, holds fragments together when applied to the inside of a wall of cementations, wood, and/or metal.
“When we apply [spray-on polyurea] to the inside wall,” Rittenhouse says, “those little spalls are caught in this polyurea that holds all of the debris together. The wallpaper holds that together so it doesn’t go flying into the occupied space.”
To fabricate this spray-on polyurea bed liner product, Rittenhouse says the bed liner manufacturers had to overcome issues like off gassing and flammability. Although they met these needs in the late ’90s, it still took a little while to get their product into buildings.
“Part of it was proving that it was a safe environment for a building and that it wasn’t combustible material,” Rittenhouse says. “You can’t use combustible materials in office construction because there are issues with off-gassing or flammability. When burnt, does it give off noxious odor?”
For Line-X, flammability was the main issue it had to address to formulate its product for architectural applications. But Mike Babiarz, vice president of business development for the company, said that was solved easily with a flame-resistant top coat.
Although it’s a very close relative, the product lining the walls of buildings is a little different from the spray coating that you might find on, say, a Toyota Tacoma. “It’s very close but it’s not quite the same,” Decker says. More specifically, he says, the architectural version of his polyurea coating product has chemical strength and higher resistance to heat.
Bob Parsons, a polyurea protective spray coating product marketing specialist for Rhino Linings, says his company’s polyurea for cement walls is a little more elastic than its version for pickup trucks. He says that Rhino’s products for buildings offers anywhere from 250 to 450% more elasticity than the pickup truck version does.
The amount of polyurea spray coating to be sprayed on a wall can vary, depending upon the level of protection needed and the building owner’s budget. The owner can also add elements like Kevlar or an aromatic fabric, which is essentially a weave underneath the polyurea. “If you apply this fabric and spray more polyurea on, it acts kind of like a glue to hold it in place,” says Rittenhouse.
Safe Room Walls Made Possible by Polyurethane Spray Lining
The polyurea spray coating used in truck bed liners isn’t difficult to apply to a wall. But the process begins well before installation professionals start spraying. First, designers must measure the strength of the reaction structure, which consists of the columns and the floor.
“We work with blast engineers who understand the core construction design,” Babiarz says. “They may also have to make some retrofit, especially on existing structures where they may have to do different types of retrofit on top of what we do.”
The design of the surrounding structure is of issue because it will be forced to absorb the increased load when the polyurea spray keeps the wall from releasing the blast load. “All those loads are still going to go someplace,” Rittenhouse says. “They’re still going to gather and they’re going to the frame. The frame has to be substantially stronger than the wall elements. If you have strong elements and a weak reaction structure, the whole thing is just going to fail and just blow over.”
Even after the reaction structure is made secure, applicators can’t pull out their sprays and nozzles. The wall has to be prepared for the polyurea spray. “It will bond to anything,” Parsons says. “All you need to do is prime it correctly so that when you spray [the polyurea], it will bond to [the wall].”
The key is to get down to the core material, whether it’s wood or cement. This process typically includes acid washing, etching, or diamond grinding of the substrate. If an installer, for instance, sprayed the polyurea coating on wallpaper, it would come off with the wallpaper during a blast. But if they are able to apply it to the cement underneath, it can work.
“You have to prep the cement so that it will accept our spray,” Parsons says. “Then we will spray the cement. It will bond within seconds. Whatever you spray onto, you need it to accept the polyurethane or polyurea.”
Once the substance is primed for the polyurea coating, then it’s time to spray it on. “Imagine taking an aerosol can with rubber plastic and you spray it on the wall,” Rittenhouse says. “It just sticks and gets tacky. It goes on thicker and it holds it together. It’s like spraying a rubberized surface.”
The thickness of the polyurea layer can vary. Rittenhouse says it’s normally sprayed between 1/8- and 1/4-in. thick.
“You can spray it to any depth that you want,” Parsons says. “You can make it as thick or thin as you want.” But as the spray-on polyurea lining gets thicker, it also gets more expensive. Also, the product comes in various colors. Add a new color and the price can go up.
“You can also put a top coat on it,” Parsons says. “But that will fade in a three-year period. So you have to put another top coat on it.”
Still, Rittenhouse says in larger application, the polyurea spray-on lining can make sense. “In large applications, [clients] feel they can get the price point down to where it was a practical application,” he says.
There’s even more cost in the preparation. “The cost of the chemical is one thing,” Parsons says. “Then there’s the cost of the substrate to apply it. Then the actual hourly labor of somebody to apply.”
One final cost can come from government regulators. The substances in spray-on bed liners have come under the scrutiny of the Occupational Safety and Health Administration (OSHA). Three of OSHA’s ten regions have been investigating the health hazards associated with exposure to various solvents and a group of compounds known as isocyanides.
But there haven’t been reports of these kinds of issues arising in building applications. “During the spraying of the application, applicators are [breathing] supplied air,” Babiarz says. “The only time there is a risk is while it’s being sprayed. Once the material sets up, it’s completely inert. There’s no danger in long-term exposure, but you do have to use common safety procedures during the installation.”
Specific Uses of Polyurea Protective Coatings
Already, the truck bed liner polyurea has been installed in some high-profile buildings. The most famous? That’s easily the Pentagon. The spray-on coating product was applied to the inside surface of the exterior walls of the building, according to Rittenhouse.
The Department of Defense wouldn’t confirm that it had applied polyurea spray-on protective coating on its walls, though representatives for both Line-X and Rhino say their product shrouds certain walls in the building. “We place a value on the safety and security of our personnel who work here and we use the best means possible to do so,” says Lt. Col. Brian Maka, a spokesman for the Pentagon. Considering the military’s emphasis on security (especially since September 11th), that’s saying a lot.
The military is seeking products that help mitigate the effects of a blast in other buildings, as well. That makes sense, since terrorist groups seem to be most interested in high-profile government or military buildings (such as the Pentagon). In fact, the military is Rhino’s biggest customer. Clearly, the U.S. government has taken a strong interest in the spray-on coatings, according to the manufacturers’ representatives. And, that’s the stream of business Line-X wants to tap into with its PAXCON product.
The reaction from other government agencies outside of the Department of Defense has been mixed. The U.S. General Services Administration (GSA), which influences the management of 8,600 government-owned buildings, hasn’t incorporated spray-on polyurea coatings in its blast mitigation package, though it says it has looked into the application of the spray-on truck bed liners for retarding fragmentation of hollow clay tile and other brittle materials.
“We’ve done some testing and the test results indicated that it does work, but we haven’t found the right circumstance where it makes economical sense to use it,” says Melissa Williams, communications account manager for The Office of Executive Communications in GSA Public Buildings Service. “We don’t have any objections to it other than economic reasons.”
The spray-on bed liner manufacturers aren’t just limiting themselves to the American market. “We’ve had great interest from other countries, starting with military and government interest,” Decker says. “There are also private firms that have approached us as well.”
So far, Parsons says his only client interested in blast mitigation is the military. He says that corporations are interested in his company’s spray-on polyurea linings, but more for their ability to protect against corrosion, abrasion, water infiltration, noise, and sound, and to enhance skid resistance on floors (for these uses the product is sprayed on about 1/8-in. thick, while the layer of polyurea coating designed for blast mitigation is sprayed at about ½-in. thick).
“If you go over a crack or side and up the wall, the connection is totally sealed,” Parsons says. “We’re really marketing [the product as] protection against water leakage or corrosion.”
But corporations are starting to take note of the blast mitigation value of polyurea. “Some people on a lower scale in the private sector have looked into it,” Rittenhouse says.
Line-X has discussed its PAXCON product with private businesses as well. “We have also gotten inquiries from ballistic manufacturers and firework manufacturers—anything that has to do with a potential explosion environment,” Babiarz says.
But even businesses in close proximity to these high-risk facilities may have interest in the spray-on polyurea linings. “If [the businesses] were concerned about these explosions, whether it’s a terrorist or whether they’re in close proximity to a petroleum manufacturer or a gas manufacture, this would be a good solution,” Rittenhouse says.
The residential market for spray-on polyurea coatings has proven to be a bigger challenge. Parsons says Rhino’s product is mainly used to seal garages and driveways. But that doesn’t mean the spray-on bed liner manufacturers aren’t looking at additional ways to infiltrate the residential market.
“We are looking at seismic and other natural disaster issues,” Decker says. “We’re in early testing stages at this point.”
One major hurdle in testing? How to address the weaker frames found in homes. Wood-frame homes aren’t sturdy enough to handle the blast that commercial and government buildings are designed to accommodate.
“What could happen in a residential setting, where you have a wood house, is that overall lateral resistance of the structure is probably not strong enough to carry that load,” Rittenhouse says. “You have to have something to react against.”
While it may seem like a minor difference in forces, Decker says the type of polyurea coating needed for blast mitigation is highly different from what’s required for a tornado or even an earthquake. “The difference with a tornado is that it’s a sustained time of force on the wall,” Decker says. “It’s not as strong [as a bomb blast], but the duration becomes an issue. Initially, we’ve seen some real promising results on that, but it will take some time to get through that.”
One place you won’t find these spray-on polyurea linings, though, is in new construction. In these applications, Rittenhouse says architects will usually just make a wall larger to eliminate danger.
“For upgrading an existing building, we think it’s a wonderful idea,” Rittenhouse says. “We would not do a new building in this stuff.”
But that doesn’t mean the spray-on bed liner manufacturers aren’t working as hard as they can to tap into the retrofit market. “If there’s currently a building that needs to be upgraded, through part of that renovation we go in and do our thing,” Decker says.
With any luck, when these companies do their thing, it may just save lives.