Stormwater Infrastructure Coatings

Stormwater infrastructure coatings are protective coatings and linings applied to structures that collect, convey, store and discharge rainwater and runoff. These include culverts, storm sewer pipes, catch basins, inlets, junction boxes, detention and retention vaults, outfall structures, channels and pump stations. Stormwater systems are often made of corrugated metal, reinforced concrete, masonry or plastic. Over time, they deteriorate from corrosion, abrasion by sediment and debris, freeze-thaw cycles and road salt exposure. Coatings are used both to protect new structures and to rehabilitate aging ones without excavation.

Deterioration mechanisms

Corrosion of metal pipe

Corrugated steel pipe and culverts are usually galvanized or aluminized. The invert, the bottom of the pipe where water flows, loses its protective layer first through abrasion and corrosion. Holes eventually form, allowing soil to wash into the pipe and creating voids above (see coating galvanized steel and corrosion science basics).

Concrete deterioration

Concrete pipes and structures can suffer from abrasion, freeze-thaw damage, chloride-induced corrosion of rebar from de-icing salts, and, in some cases, acid attack where runoff carries contaminants.

Abrasion

Sand, gravel and debris carried at high flows scour inverts and outlet aprons (see erosion and wear of coatings).

Joint failure

Leaking joints allow infiltration and exfiltration, washing soil into the pipe.

Rehabilitation approaches

• Invert paving. Concrete or coatings placed in the bottom of corroded metal pipe.
• Spray-applied coatings. Polyurea, polyurethane, epoxy and other linings sprayed onto the interior.
• Spray-applied cementitious and geopolymer linings, sometimes structural, sprayed or spun onto pipe walls (see cementitious coatings).
• Cured-in-place pipe (CIPP). Resin-saturated liners inverted and cured inside the pipe.
• Sliplining. Inserting a smaller pipe and grouting the annulus.
• Manhole and structure rehabilitation, similar to sewer practice (see sewer and manhole rehabilitation).

Selection depends on structural condition, hydraulic capacity, access and budget. Where the pipe has lost structural strength, a structural lining or replacement may be required; a coating alone protects but does not restore structure unless designed to.

Coating systems

Products should be selected for the specific flow, abrasion, temperature and chemical conditions.

Surface preparation

1. Divert or bypass flow, or schedule work in dry periods.
2. Remove sediment and debris.
3. Clean surfaces with water jetting to remove loose corrosion, scale and contamination.
4. Abrasive blast metal surfaces to the specified cleanliness where possible.
5. Repair holes and voids. Patch perforations and grout voids behind the pipe.
6. Prepare concrete to remove laitance and deteriorated material.
7. Dry surfaces as needed for the coating; some systems tolerate damp surfaces.

Application considerations

• Confined space. Pipes, vaults and inlets are typically confined spaces with atmospheric and engulfment hazards (see confined space coating).
• Weather. Rain can rapidly fill stormwater systems. Monitor forecasts and plan for rapid evacuation.
• Ventilation and access are limited in small-diameter pipes; robotic or spin-cast equipment may be used.
• Environmental protection. Prevent coating materials, blast media and wash water from entering waterways (see coating waste disposal).
• Permits. Work in waterways may require environmental permits.

Inspection

• CCTV and manned inspections document condition before and after rehabilitation.
• Thickness and holiday testing on coatings where practical (see holiday testing).
• Follow-up inspections track wear in inverts.

Asset management

Many municipalities manage stormwater systems with condition ratings and planned rehabilitation, aiming to address deterioration before failures cause sinkholes and road damage (see coating condition assessment).

In practice

In practice, stormwater rehabilitation starts with inspection, often by camera for pipes and by visual survey for basins and vaults. Engineers then decide whether coating, lining or replacement is the right choice. For coating work, flow must be diverted, the surface cleaned and repaired, and the lining applied to the required thickness. Confined space safety and environmental controls on runoff and debris are part of every job.

Key terms

• Culvert. A pipe or box that carries water under a road or embankment.
• Invert. The bottom inside surface of a pipe or channel, usually the most worn area.
• Storm drain. A pipe network carrying rainwater runoff.
• Rehabilitation. Restoring an existing structure rather than replacing it.
• Spray-applied pipe lining. A lining sprayed inside a pipe to restore protection.
• Hydraulic capacity. The amount of water a pipe can carry, which smooth linings can help preserve.
• Catch basin. A structure at street level that collects runoff and traps debris before water enters the pipe network.

Frequently asked questions

Can a coating fix a culvert with holes?

Holes must be repaired and voids filled first. Coatings protect the restored surface. Structural deterioration may require a structural lining or replacement.

Why does corrosion start at the bottom of the pipe?

Water and sediment flow along the invert, wearing away the protective layer and keeping the steel wet.

Related entries

• Sewer and manhole rehabilitation
• Water and wastewater coatings
• Pipeline coatings
• Coating galvanized steel
• Landfill and lagoon liners (new)
• Erosion and wear of coatings (new)