Protective coatings commonly used in wastewater facilities

Protective coatings commonly used in wastewater facilities

Protective coatings commonly used in wastewater facilities

The protection of concrete tanks and basins in wastewater treatment plants is critical to the continued service of these facilities. Without adequate protection against wastewater, concrete can break down and put wastewater facilities at risk of failure that can have wide-reaching consequences.

Following are the various coating systems commonly used to protect concrete at wastewater facilities.

Protective coatings for concrete

A few things to consider when selecting the right coating include exposure time of wetness, physical conditions (temperature, flow, etc.) of the service environment, chemical conditions of the environment and the condition of the prepared substrate.

The protective coating system must also meet the wastewater facility owner’s criteria. Penetrating sealers, thin-film coating systems, thick-film coating systems or linings may be required.

  • Penetrating sealers are commonly used to penetrate the concrete substrate and seal the pores from moisture
  • Thin-film coatings commonly used with a primer have a dry film thickness (DFT) ranging from 10 – 30 mils
  • Thick-film coatings or lining systems typically have a DFT range of 40 – 120 mils

While penetrating sealers in wastewater treatment facilities are often used as primers, thin-film coating systems provide moderate chemical resistance and perform well against sulfide attack. Examples include:

  • Epoxies (typically high solids, amine-cured)
  • Polyurethanes (typically high solids, two-component)
  • Vinyl esters

While thin-film systems hold up in moderately exposed wastewater treatment facilities, a more severe environment will require a thick-film / heavy-duty lining. Severe exposures to biogenic corrosion, sulfate attack, chloride-induced corrosion and carbonation require a coating system that will not only resist these hazardous exposures, but also resist being constantly immersed in wastewater. Examples include:

  • Epoxies (typically high-build, high-performance, amine-cured)
  • Polyurethanes (Typically high build, aromatic)
  • Polyureas

Consult with coating manufacturers to learn in greater detail whether their products will stand up to the hazards on your site. Also, note that you cannot apply protective coatings at your site just once and then forget about it. The coating systems mentioned above provide the best performance given the corrosive environment, but none offers a permanent solution to deterioration in wastewater facilities.

Concrete surface preparation in wastewater facilities

Coatings only work as designed when the substrate they’re applied to is properly prepared. Skipping the surface preparation prior to applying coatings puts them at risk of premature failure that in turn exposes concrete to wastewater hazards.

For new construction, SSPC-SP 13/NACE No. 6 standard recommends concrete be left to cure for at least 28 days under favorable atmospheric conditions prior to coating. This same standard covers all surface preparation for concrete structures.

Brush-off blast cleaning is the best surface prep method. Additionally, soft or loosely bonded surfaces should be cleaned to a hard substrate via abrasive blasting.

It’s important to inspect concrete prior to applying coatings because any laitance left on a surface can result in poor adherence and lead to chipping, peeling, or flaking that wouldn’t ordinarily occur.