How to Protect Your Precast Concrete Manholes From Hydrogen Sulfide Corrosion

Precast concrete manholes were first introduced in the mid-1950’s, and by 1970 were widely adopted as the preferred structure for manhole installation in sewer and drainage applications. Those 1970-ish manholes are now 50 years old (hard to believe!), which is probably close to the original, intended design life. It is common for the published ‘war-stories’ or case histories to be about ancient hand-hewn stone structures built by artisan craftsmen, and those manholes do exist in some of our oldest cities. But most of what we deal with are good ol’ precast concrete manhole structures.

A recent U.S. EPA technical report stated that hydrogen sulfide corrosion could remove one inch of concrete thickness in a 10-year period. A four-foot diameter manhole has a wall thickness of 5 inches. That should really give most of us something to think about! In most circumstances, it is unlikely that if you pull the lid off of a 50-year-old manhole it will have mostly disappeared. However, over the years, on more than a few occasions we have observed mother earth in place of what was formerly the manhole wall. So, perhaps the findings of that technical report are not too far off base. If in your municipality or community, you know when your precast concrete manholes were first put in place and you’re approaching the 50-year mark, it might be a good idea to schedule a check of these structures and see what surprises you come across. Your ratepayers will thank you!

OBIC Armor’s multi-layer liner system is the ideal rehab solution for severely corroded wastewater structures. The first high-temperature spray-applied polyurea layer creates a tenacious adhesive bond for the second hybrid polyurethane layer that expands to fill all the cracks, crevices, voids and bug holes, and provides some restoration to the wall thickness. The third and final polyurea layer delivers a protective layer against hydrogen sulfide and microbial-induced corrosion.


The three layers of the OBIC Armor system together form a stress skin panel. Stress skin panels exhibit great strength, which is why they are commonly used in airplane construction, vehicle fabrication, and building construction. OBIC Armor has a 10-year warranty and generally adds 30, 40 or even an impressive 50 years of additional life to the structure.

While this won’t directly affect the prevention of the actual H2S present in your sewer system, it will most definitely protect your structures from it long-term and make them like new again. At OBIC, we’re proud to share before and after stories from the field of how our products help make a positive difference in the communities we serve.

The OBIC team can help you find a cost-effective, no-dig solution to all of your municipal and industrial water and wastewater needs. Complete the Contact Us form, or give us a call at 866-636-4854 to request information or schedule an OBIC product demonstration.