Wastewater Coatings Glossary

This glossary provides technical definitions for terms commonly used in wastewater infrastructure protection, coating science, and corrosion engineering. Definitions are written for infrastructure managers and engineers with a technical background, prioritizing scientific accuracy over simplified language.

A

Adhesion — The force required to separate a coating from its substrate, measured in pounds per square inch (psi) by pull-off testing or in kN/m by peel testing. Adhesion in wastewater coating applications is typically specified at a minimum of 200-400 psi on properly prepared concrete.

Aliphatic polyurea — A polyurea formulation utilizing aliphatic isocyanates rather than aromatic MDI. Aliphatic polyureas exhibit significantly better UV stability and color retention than aromatic systems, making them appropriate for above-ground and exposed applications. Their higher raw material cost limits their use to topcoat applications where UV resistance justifies the premium.

Aromatic polyurea — The most common class of polyurea for infrastructure applications, based on methylene diphenyl diisocyanate (MDI) chemistry. Aromatic polyureas exhibit surface yellowing upon UV exposure but retain their protective properties in subterranean or covered applications, making them the cost-effective choice for the majority of wastewater infrastructure coatings.

B

Blistering — Dome-shaped delamination of a coating from its substrate, caused by vapor pressure accumulation at the coating-substrate interface, osmotic pressure from soluble salts in the substrate, or adhesion failure under hydrostatic pressure. Blistering in wastewater coatings typically indicates inadequate surface preparation, application over moisture-contaminated substrate, or vapor pressure buildup in sealed concrete structures.

Biogenic corrosion — Corrosion caused or accelerated by the metabolic activity of living organisms. In wastewater infrastructure, biogenic corrosion refers specifically to the destruction of concrete by sulfuric acid generated by sulfur-oxidizing bacteria as a metabolic byproduct of hydrogen sulfide oxidation. Also referred to as microbially induced corrosion (MIC).

C

Carbon nanotube — A cylindrical nanostructure composed of carbon atoms arranged in a graphitic lattice, with diameters in the nanometer range and lengths up to several millimeters. Carbon nanotubes exhibit exceptional mechanical properties (Young’s modulus approaching 1 TPa) and are being investigated as reinforcing agents in coating matrices and as membrane materials for advanced water filtration.

Chemical grout — A reactive liquid material injected into concrete cracks or voids to fill them and prevent water movement. In wastewater applications, chemical grouts are used to stop active infiltration through manhole walls before protective coating application. Polyurethane-based hydrophilic grouts, which expand upon contact with water, are the most commonly specified material for active leak control in sewer structures.

Coating thickness — The measurement of the thickness of an applied coating, expressed in mils (thousandths of an inch) or micrometers. Minimum thickness specifications for polyurea coatings in wastewater applications typically range from 80-250 mils depending on the severity of the service environment and the structural rehabilitation objectives of the project.

D

Delamination — Separation of a coating layer from its substrate or from an underlying coating layer, resulting in loss of adhesion over an area rather than at an isolated point. Delamination in wastewater coatings is typically caused by osmotic pressure, vapor pressure, hydraulic pressure, or thermal cycling beyond the coating’s elongation capacity.

Desulfovibrio — A genus of gram-negative, anaerobic bacteria that are the primary sulfate reducers in sewer biofilm communities. Desulfovibrio species are obligate anaerobes that use sulfate as a terminal electron acceptor in their energy metabolism, producing hydrogen sulfide as a byproduct. Their activity is the initiating step in the hydrogen sulfide-sulfuric acid conversion chain that causes concrete sewer corrosion.

Dry film thickness (DFT) — The thickness of a coating after solvent evaporation and cure, as distinguished from wet film thickness measured immediately after application. DFT is the specification parameter for coating performance; it is measured using magnetic induction gauges on steel substrates and electronic (eddy current) gauges on non-metallic substrates.

E

Elongation at break — The percentage increase in length of a test specimen from its unstretched length to the length at which it fractures under tensile loading. Elongation at break is the primary performance differentiator between brittle (epoxy, 1-5%) and elastomeric (polyurea, 200-500%) coating systems in terms of crack-bridging capability.

Epoxy — A thermosetting polymer formed by the reaction of an epoxide resin with a curing agent (hardener). In wastewater infrastructure, 100% solids epoxy coatings are specified for their chemical resistance and moisture barrier properties. Their brittleness (low elongation) limits their performance in dynamic substrates subject to cracking and movement.

Exfiltration — The outward movement of wastewater from sewer pipes and structures through cracks, defective joints, and porous concrete. Exfiltration poses environmental and groundwater contamination risks and represents a direct regulatory compliance concern for sewer utilities. Polyurea coating rehabilitation effectively eliminates exfiltration by creating a seamless waterproof barrier over deteriorated concrete.

F – Z

HDPE liner — High-density polyethylene liner panel systems used in wastewater structures, providing both corrosion protection and a smooth hydraulic surface. HDPE liners are typically mechanically anchored to the host structure rather than adhesively bonded, accommodating vapor pressure from the substrate without blistering.

Holiday — A pinhole or void in a protective coating that penetrates through to the substrate. Holidays are detected by low-voltage (wet sponge) or high-voltage (spark) electrical testing methods. In submerged wastewater coating applications, holidays must be repaired before service because they initiate osmotic blistering under hydrostatic pressure.

Isocyanate — The reactive chemical group (-N=C=O) that is one of the two components in polyurea and polyurethane coating chemistry. Isocyanates react with amines (to form urea) or hydroxyl groups (to form urethane). The most widely used isocyanate in coatings is methylene diphenyl diisocyanate (MDI).

Microbially induced corrosion (MIC) — See biogenic corrosion.

NASSCO MACP — National Association of Sewer Service Companies Manhole Assessment and Certification Program, providing standardized inspection protocols and defect coding for concrete sewer manholes. MACP inspection results provide the condition data foundation for risk-based manhole rehabilitation programs.

Polyurea — See the full definition article: What Is Polyurea? A Complete Technical Guide.

Shore hardness — A measure of material resistance to localized surface indentation using a standardized spring-loaded probe (durometer). Shore A hardness scale is used for softer elastomers; Shore D for harder materials. Polyurea coatings for wastewater applications typically specify hardness in the Shore A 70-90 or Shore D 40-60 range depending on the flexibility-hardness balance required for the application.

Tensile strength — The maximum stress a material sustains in tension before fracturing, expressed in psi or MPa. For polyurea coatings, tensile strength values of 2,500-4,500 psi are typical and provide the cohesive strength that prevents coating tearing under the hydrostatic, impact, and crack-bridging loads encountered in wastewater service.