Lift Station, Wet Well and Manhole Rehabilitation with Spray Polyurea

Walk down into any lift station that has been in service for twenty years and you will see it: the concrete above the waterline is soft, the aggregate is exposed, and in the worst cases the rebar is showing. This is not ordinary aging. It is microbially induced corrosion, and it is the single most expensive maintenance problem in a wastewater collection system. Replacing a wet well is a six-figure project with a week of bypass pumping. Lining one is a day.

This guide explains what is happening to the concrete, what a spray polyurea lining does about it, and — most importantly — how to prepare a structure so the lining holds. It is written for public works departments that run their own crews and for the contractors they hire.

What is actually eating the concrete

Wastewater in a collection system generates hydrogen sulfide gas (H₂S) wherever flow is slow, turbulent or held — which describes a wet well precisely. The gas rises to the headspace above the waterline, where a different set of bacteria living on the damp concrete convert it to sulfuric acid. That acid attacks the cement paste, turning sound concrete into a soft, crumbling layer of gypsum that sloughs off and exposes fresh concrete beneath. The cycle repeats until there is no concrete left.

Three things follow from this:

• The damage is concentrated above the waterline — the headspace, the crown of the structure, and the underside of the top slab.
• The surface you see is not sound. A coating applied over the soft layer bonds to the soft layer and falls off with it.
• Whatever lining you install has to resist sulfuric acid at the concentrations found in that headspace, and has to stay bonded on a surface that is permanently damp.

Why spray polyurea for wet wells and manholes

A plural-component spray polyurea is applied hot and reacts in seconds, which in a lift station translates into three practical advantages.

Return to service in hours, not days

The lining is tack-free in seconds and can be walked on in minutes. Bypass pumping — the largest single cost on most lift station projects — runs for a day instead of a week.

A seamless membrane over a structure that moves and leaks

Wet wells have joints, pipe penetrations, benching and inflow around the frame. A spray-applied membrane goes over all of it as one continuous film, with elongation to bridge the hairline cracks that will keep opening as the structure cycles.

Thickness where the exposure is

Linings for wet wells and manholes are typically specified at 80 to 125 mils, applied heaviest in the headspace and crown where the acid attack is. A 100% solids polyurea builds that thickness in a single application with no solvent to ventilate out of a confined space.

The candid caveat: aromatic polyureas have good but not unlimited resistance to sulfuric acid, and headspace concentrations vary from station to station. For severe H₂S environments, ask the supplier for chemical resistance data for the specific product, and be prepared to specify a higher build or a purpose-formulated topcoat where the exposure warrants it. A supplier who says "it resists everything" is not one to buy from.

Surface preparation: the part that decides whether it works

Every polyurea failure in a manhole traces back to one of the steps below being skipped. None of them is optional.

1. Bypass and clean. Divert flow, pump down, and pressure-wash the structure — 3,500 psi or higher — to remove biological growth, grease and debris. Hydro-blasting at higher pressure is used where the soft layer is thick.
2. Remove all unsound concrete. Chip, scarify or blast until you reach material that rings solid. If the soft layer is deeper than the profile you can remove, it is a structural repair, not a coating job.
3. Neutralise the surface. Acid-attacked concrete carries residual acid. Test the surface pH; if it is low, neutralise and rinse until it reads near neutral, or the acid keeps working under the new lining.
4. Stop active infiltration. Water coming in through joints or pipe penetrations has to be stopped with hydraulic cement or injection grout before lining. Polyurea will not cure onto running water.
5. Rebuild the profile. Losses deeper than about a quarter inch are restored with a cementitious repair mortar so the lining goes onto a uniform surface rather than pooling in cavities.
6. Prime for the conditions. Wet wells are damp. A moisture-tolerant primer — the water-based OR E41 epoxy primer is the usual choice here — seals the substrate and gives the polyurea a consistent bond surface where a solvent primer would blister.
7. Spray, detail, terminate. Apply the membrane in passes to the specified build, detail pipe penetrations and the bench-to-wall transition, and terminate at the frame so the lining ends in a keyway, not a feather edge.

Safety: this is confined-space work

A wet well is a permit-required confined space under OSHA 29 CFR 1910.146. That means atmospheric testing before and during entry (H₂S, oxygen, LEL), continuous ventilation, a trained attendant at the top, retrieval equipment, and a rescue plan that does not consist of sending a second person down. Spraying polyurea adds isocyanate exposure to the list, so supplied-air respiratory protection is standard for the applicator. Municipal crews taking this work in-house need the confined-space program in place before the first job, not after it. Oak Ridge's applicator training covers the equipment and application; the confined-space program is a separate requirement your safety officer owns.

Acceptance testing

Write thickness verification and holiday testing into the specification. Wet-film gauging during the spray confirms the build is being reached in the crown, not just the walls; high-voltage spark testing afterward finds pinholes that will otherwise become the first point of re-attack. An adhesion pull test on a trial patch is worth doing on the first structure of a programme, because it settles the prep question before the crew has done twenty of them the same way.

Equipment for a municipal crew

A wet well lining needs a plural-component proportioner with heated hose, a spray gun, and a way to get material to the bottom of the structure. Most public works departments doing this in-house run a trailer- or truck-mounted rig with a hose long enough to reach the bench from the surface — the same rig doubles for containment areas, bridge decks and floor work. The equipment and rigs page covers the options; the municipal page covers the other jobs the same setup handles, and the parts, solvents and OR 411 cleaning agent that keep it running between stations.

Frequently asked questions

How long does a polyurea wet well lining last?

Properly prepared and applied at the specified thickness, linings in this service are expected to run for many years — but the honest answer depends on the H₂S concentration in that particular station. Inspect on a schedule; a lining that shows softening in the crown is telling you the exposure exceeds what was specified.

Can the crew line a manhole without bypass pumping?

For manholes on low-flow lines, plugging upstream and working quickly is sometimes possible. Wet wells almost always need bypass. Plan for it rather than hoping.

What about cold weather?

The material is applied hot and reacts in seconds, so ambient temperature matters less than with epoxies — but the substrate must be above the dew point and the primer must be able to cure. Heated hose and a substrate temperature check are part of the job in a Wisconsin winter.

Cementitious liner or polyurea?

Cementitious liners rebuild the structure; polyurea protects it. On badly deteriorated wells the two are used together: mortar to restore the profile, polyurea over it as the acid barrier.

Have a station that needs attention? Send the structure dimensions, the condition and any H₂S readings you have through the request form or call 800-625-9577.