How Do You Rehab a Manhole? A Day In The Life

Ever wondered about what the manhole rehabilitation process is like for OBIC certified installers? We had a camera crew follow Advanced Lining, an OBIC installer located in Utah, as they worked on a municipal manhole rehab in Moscow, Idaho.

The city of Moscow had 17 aging manholes with groundwater infiltration issues. Although experienced in rehabilitation projects like this, the installation crew was challenged with an unusually cold October. They were also faced with a limited timeframe, as the project was in a residential neighborhood.

Site Safety

Before any rehabilitation work can begin, site safety takes priority. The crew will set up traffic cones and signs to keep the public separated from the work area. Confined space and fall protection equipment is set up on-site and employees don their personal protective equipment.

Manhole Casting Prep

Now that the site and personal safety issues have been addressed, the crew is ready to begin prepping the manhole casting. In this stage, crews use an angle grinder with a diamond blade to remove rust, paint and corrosion from the top layer where the casting lid sits. This not only cleans the metal but also creates a profile to ensure a proper or sufficient bond between the substrate and the OBIC lining system.

Casting prep is important because the metal casting is exposed to extreme weather changes, which changes the temperature of the casting and the ground around it. This is especially important on roads where there is movement and vibration.

Pressure Washing the manhole

Now it is time to remove the debris from the walls by power washing the manhole. Our installers use a power washer that is 3,000 PSI of water pressure. To put that into perspective, the average homeowner has a power washer that is between 300-1,000 PSI. To get even more pressure, the crew uses a rotary tip nozzle that will help them remove even the toughest debris.

Step Removal

The steps found in an aging manhole can have a variety of issues making them unsafe for use. Most often, they are too corroded to leave in place, and just get in the way when crews use safety equipment to lower themselves down into a manhole. When rehabilitating a manhole with the OBIC spray-applied lining system, the corrosion on the old steps can also interfere with establishing a proper bond between the substrate and the lining material.

Substrate Prep

Once again installation crews focus on prepping the substrate. They take this process pretty seriously, and for good reason. They know that, when properly installed, the OBIC lining system can increase the life expectancy of the manhole by 50 years or longer.

Rinsing and Debris Removal

Now that the manhole is cleaned of all debris, crews rinse down the walls of the manhole with a rinse tip on the pressure washer. This rinses any remaining sediment and debris from the wall and ensures the surface is clean and ready for the installation of the OBIC lining system.


For the next 10 minutes to 3 hours, crews will use an indirect fired forced air heater or a blower and torch to remove all moisture from the manhole. The timing on this is largely dependent on the size, age and environment of the substrate. For example, older manholes that have been in moist environments for longer times will take longer to dry. Also, block and brick take longer than a new style precast manhole.

Lining Process

Once the manhole is clean and dry, it is time to begin the lining process.

  1. Steel Primer: The installation begins with a steel primer. OBIC 1503S, Part A and B are applied to the casting with a clean rag and paintbrush.The casting in a manhole, especially in the northern environments, is subject to extreme temperature changes. The increasing and decreasing of the frost level allows for expansion between the steel casting and the substrate below. The steel primer creates a strong bond between the steel casting and the polyurea lining system so as not to allow for the lining to delaminate.
  2. Polyurea Base Coat: The polyurea base coat, or OBIC 1000, is applied using everything from the proportioner pumps to the spray guns. This is the base coat of OBIC Armor, also known as the adhesion layer, and is 50 mils thick.
  3. Rebar for Reinforcement: This step of the lining system is reserved only for manholes that have a large enough bench area. The rebar, in these cases, help to reinforce the transition between the vertical wall and the horizontal bench.\
  4. Polyurethane Middle Layer: A separate proportioner pump and spray gun is used to apply this foam layer of OBIC 1306. This resurfacing layer is a dense foam that helps reinforce the structural integrity of the manhole. OBIC installers use a 6-pound foam which creates the rigidity that helps reinforce the structure.
  5. Polyurea Top Coat: Once again using everything from the proportioner pumps to the spray gun, crews apply OBIC 1000 as a barrier layer. (Fun fact, obic is the root word for barrier in Latin.) This is the final layer of the OBIC lining system for manhole rehabilitation.

OBIC and warranty date stamp

All professionally installed OBIC multi-layer products are backed by a 10-year warranty that covers all material or system failures that are not due to customer negligence.

Post-Installation quality check

Before any OBIC manhole rehabilitation is considered complete, a post-installation quality check is completed. Crews will visually inspect the manhole, looking for any incomplete lining issues such as pinholes, foam showing, or areas missed. This is a priority for everyone on the crew because they all take pride in the quality of their work.

OBIC manhole rehabilitation product demonstrations

Interested in seeing the OBIC lining system first-hand? We offer product demonstrations that may generally be used for CEU requirements. For more information, check out our website, or call our sales team at 866-636-4854 and we will connect you with an installer near you.