Published December 2007

One Tough Coat

By Jim Force (page 54)

Polyurethane protective lining system from Sprayroq Inc. helps utilities quickly protect manholes against structural failure and corrosion.

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Faced with deterioration of manholes and other underground infrastructure, utilities are looking for lower-cost and less intrusive alternatives to tearing up streets and disrupting neighborhoods. One option is to apply a fast-curing protective coating to existing surfaces, renewing structural integrity while sealing out hydrogen sulfide and other corrosive agents.

One such offering is the Spray Wall quick-setting resin-based polyurethane liner system from Sprayroq Inc. The material is manually sprayed on below-ground surfaces by certified technicians.

Through independent third-party tests, the system is guaranteed for a design life of 50 years. Commonly, the liner is sprayed onto the surface at a thickness of 250 mils (1/4 inch), providing a monolithic seal of the entire invert, wall, and bench structure. The company says more than 150,000 manholes have been rehabilitated with the liner system.

On Oct. 25, a crew from Team Elmer’s, Sprayroq contractor for Michigan, demonstrated the Spray Wall system on a manhole in downtown Traverse City. The crew consisted of John Prescott, supervising engineer; Dan Strehlke, applicator; Erik Seaburg, operations coordinator; and Brandon Nickerson, laborer. Mike Vaughn, utility systems specialist for the city, observed. The weather was clear and calm, and the temperature was 35 degrees F.

Walk-Around

The manhole, 2 feet in diameter at the top, widening into a 6-foot diameter chamber at the bottom, descended 17 feet to an 18-inch trunk line. It was located at the rear of a busy hardware store parking lot.

The Team Elmer’s rig consisted of a Ford 6000 six-wheeled box truck (plated at 36,000 GW) containing the polyurethane system and associated equipment, a one-ton Jet Heater utility truck with a small heater cart, and a confined-space tripod, which the crew placed over the hole.

Inside the truck, 55-gallon drums contained the polyurethane resin (Part A) and hardener (Part B). The chemicals were heated by three Graco Viscon HP heaters to the application temperature of 150 degrees F. (One heater warmed the thinner Part A, while two heaters were used for the thicker Part B.)

Circulating pumps kept the fluids warm during setup. A Graco Bulldog piston pump delivered the two chemicals through separate heated 1/2-inch hoses to the Graco Probler spray gun, where they were mixed at the nozzle to proper ratio (2-to-1) and sprayed onto the surface at 100 to 110 psi. The hoses could be extended to 150 feet if necessary, although the Traverse City project required only about 35 feet of hose.

The system’s compressor and generator were located on a bay between the truck cab and box. A DeVilbiss clean air dryer trapped and dried moisture from the compressor air. The heater trailer could generate 100,000 Btu/hour and produced 90-degree F air that was blown into the manhole to dry it before lining application. “A big blow dryer,” commented Prescott.

The confined-space tripod was equipped with a safety winch and wire cable that would be clipped to a harness worn by the applicator. It also had a “fall protector” that would automatically stop the cable should the applicator suddenly drop. Various lines were used to lower a light, camera, and other equipment into the hole. An air supply system and a face mask were also onsite to be worn by the applicator.

The parking lot remained open during the manhole lining operation, and customers drove freely in and out of the property.

Operation

Team Elmer’s is part of a network of certified Sprayroq partners experienced in municipal, industrial and commercial applications.

Manhole surfaces must be cleaned and prepared before the Spray Wall lining system is applied. Beginning at 7 a.m., two-and-a-half hours before the demonstration, Team Elmer’s had plugged the sewer inflow line with a rubber pig, cleaned the manhole with 2,500-psi water, and patched the surfaces as necessary.

The team used a cementitious grout from De Neef Construction Chemicals to stop minor water infiltration — the manhole had experienced periodic infiltration and inflow in the past. The grout has a compressive strength of 1,800 psi at 30 minutes, 4,000 psi at 24 hours, and 5,000 psi at seven days (ASTM C 109).

To fill voids and other substrate defects, the crew used a Precor cementitious compound with a compressive strength of 1,000 psi at one hour, 3,500 psi at 48 hours, and 5,000 psi at 28 days (ASTM C 109).

After these operations, the heater blew warm air into the hole via a large diameter hose to dry all surfaces. Finally, the crew checked air quality in the hole for adequate oxygen and the absence of harmful gases, in compliance with local, state and federal confined-space guidelines.

The liner spraying began at 9:35 a.m. First, applicator Strehlke checked the pumps and heaters in the truck to make sure all systems were operating properly. Next, he put on a Tyvek suit, rubber gloves, and face mask and sprayed a test batch of the polyurethane liner onto a large piece of plastic. Within seconds, the sprayed material hardened into a smooth coating about 1/4-inch thick. Prescott tried to poke the tip of his pocket knife into the surface, but it was impenetrable.

Seaburg and Nickerson then helped Strehlke into the safety harness and lowered him slowly into the manhole. A digital camera was lowered so that pictures could be taken of the coated surface and reviewed for any remaining defects. Next a light was lowered, and then the spray gun.

Strehlke worked around the bench area first, holding the light in one hand and the trigger-activated spray gun in the other. He judged the thickness by the number of sweeps he made over the area, working upward from the bottom, signaling to Seaburg and Nickerson when he needed to be raised to the next level.

Once the lower wall areas were completely coated, Strehlke came to the surface, replaced the removable lens of his face mask with a clear one, and knelt over the manhole to coat the upper 2 to 3 feet of the cylinder. Finally, he went back down to finish the last section of the upper wall area. As he did this, Seaburg and Nickerson placed a sheet of plastic over the hole to prevent any of the spray from getting on the manhole sealing flange. “It really sets up fast, and it’s hard to get off,” Prescott noted.

When Strehlke was finished, Seaburg hooked up to the safety harness and went down the hole to inspect the work and photograph results. As he did so, Nickerson put the equipment away so that the crew could move on to the next spray location. Seaburg was finished inspecting, the sewer plug was pulled, and the manhole cover was placed back on the hole at 11:23 a.m.

Observer Comments

It was hot in the hole, as the reaction between the chemicals being sprayed can reach 200 degrees F. In that atmosphere, a trained, stalwart applicator is the key to successful sealing of the surfaces. One wonders if a remote-controlled application system would be an improvement over the manual approach.

The down-hole environment can be tough on equipment, too. During the Traverse City demo, the light failed, and had to be pulled out of the hole and repaired, although the fix consumed little time. The tear-away lenses Strehlke used on his mask are a good idea, since they restore clear vision when the initial lens coats up.

Communications between the applicator in the manhole and his crew on top are shouted back and forth. Some kind of audio system might be an improvement.

In this instance, the sewer inflow was blocked with a rubber pig and the flow was directed to an existing bypass line. Prescott said that if such a bypass is not available, his company uses a vacuum truck to take flow while the spraying operation is in progress. He pointed out that since the operation is completed so quickly, the vacuum truck’s storage capacity is always more than adequate.

The product worked as the company described it — the spraying operation was quick and unobtrusive. The hardware store customers coming and going across the parking lot were probably unaware that a manhole was being repaired only a few feet away. The lining system cures almost instantaneously, and the sewer trunk line was fully flowing again just two hours after the start of the spraying operation.

Manufacturer/user comments

Prescott noted that an automated spraying system was something to consider, but he felt that the manual application and inspection produced the best and most complete coating of the bench and walls. He added, “A lot of underground structures are odd-shaped, and an automated spray system might not achieve good coverage.”

As a certified application contractor, Prescott pointed out that his firm had selected the Spray Wall system because of ease of application, fast cure times, and the durability and corrosion protection of the polyurethane system. He credited Sprayroq Inc. for strong support. “We’ve benefited from their seminars, and they’re very responsive if we call with a question.”

Prescott said the low cost, when compared to removing and replacing a complete manhole, was another benefit. An information sheet showed the approximate cost to rehabilitate an existing 4-foot manhole with the Spray Wall system at $325 to $575 per vertical foot, compared to $625 to $950 per vertical foot for manhole removal and replacement. (These estimates do not include the potential additional costs for traffic control, bypass pumping, and dewatering).

Vaughn said Traverse City has committed to this approach for manhole repair. “We think it’s the way to go, and we plan to launch an annual program to use the lining system to rehabilitate manholes across our system.”