Manhole chimney seals: Do we really need them?

Is it really necessary to include the chimney seal portion of a manhole when considering rehabilitation? This has been a topic of debate in the manhole rehabilitation industry for years. The answer is, simply … yes!

chimney ring

The area that connects the concrete or brick cone section to the metal adjustment ring, known as the manhole chimney, is often neglected when carrying out manhole rehabilitation. Some say that because the chimney area has an external liner when constructed, it does not need to be sealed or protected. However, the reality is that often times, as the manhole settles and ages, that liner deteriorates making this part of the manhole the most vulnerable to Inflow and Infiltration (I&I), and to neglect it can often lead to bigger problems.

Here are a few of the forces acting on a manhole chimney:

  • impact due to traffic
  • freeze/thaw cycles
  • infiltration of water
  • thermal expansion and contraction of the surrounding areas

The deterioration caused by these elements can often lead to inflow and infiltration (I&I), thus compromising the integrity of the manhole. It is the first joint of the manhole, closest to the surface, and vulnerable to excess inflow and infiltration (I&I) from rainfall.

The cost of sealing and protecting this area is minimal compared to the cost of rehabilitating the entire manhole due to its exposure to these elements.

The careful selection of a product designed for this application is important, due to the many factors that must be considered. A urethane-acrylate hybrid epoxy would be suitable for this application because it has a high elongation property and sufficient tensile strength to handle movement and change. In addition, the product must be highly defensive against corrosive gases such as hydrogen sulfide (H2S). When addressing the chimney seal, look for products that:

  • are designed to prevent leakage of water into the manhole through the frame joint area and the area above the cone of the manhole
  • are flexible in order to deal with movement caused by the freezing and thawing cycle as well as from the traffic above
  • protect the metal ring from exposure to H2S

Other factors to consider are the ease of application and high bond strength. A product can have all the necessary properties to protect against corrosion and deal with changes of the infrastructure, but if it’s not easy to apply, applicators will tend to shy away from it. Consider products that are:

  • fast and simple to apply
  • applied by hand, so that they can be used in any structure regardless of its shape or  size
  • compatible with any existing coating that might have been used to protect the walls
  • applied inside the manhole structure avoiding the need for costly excavation or pavement replacement.

When rehabilitating a manhole, consideration of the chimney seal in addition to the walls and grade rings will create a solid, complete rehabilitation. This additional step should not be neglected, in order to fully seal and protect the manhole and maximize the integrity of the infrastructure.

Contact CLADLINER for a complete manhole rehabilitation system including a high-quality chimney seal.
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Silvia Caputi, Marketing Coordinator for CLADLINER
October 17, 2017