Concrete surface preparation and coating selection


Concrete surface preparation and coating selection

Concrete assets are coated to protect them against harsh service environments. But a coating is only as good as the surface it’s to stick to, and it will only bond as designed if surfaces are properly prepared.

Concrete surface preparation is especially important: compared to other surfaces, it is rather variable in its composition and characteristics. This why the first step in surface prep is to conduct an inspection that addresses the following questions:

  • What existing coatings, if any, are present on the surface?
  • Is the surface contaminated with other chemicals or materials that would impact coating adhesion?
  • Is the concrete strong and sound, or is it damaged?
  • What defects --such as voids, cracks, or laitance -- are present on the surface?
  • Are there areas of potential moisture related problems?

The concrete surface preparation method on a given surface will vary based on how contaminated, damaged, or otherwise compromised it is. For instance, a surface may be in good enough shape to need relatively low-impact measures that will not alter the surface profile, such as vacuum cleaning, low-pressure water cleaning and washing or scrubbing with detergent or degreaser.

In some cases, though, a surface may be compromised to the extent that more aggressive preparation is needed to alter the surface profile. Those methods include dry or wet grinding, dry or wet abrasive blasting, vacuum shot blasting, scarifying, needle scaling, scabbling, and rotomilling.

Additional information about concrete surface preparation can be found in the standard SSPC-SP 13 / NACE 6

Consult too “Selecting and Specifying Concrete Surface Preparation for Sealers, Coatings, Polymer Overlays and Concrete Repair,” standard 310.2R from the International Concrete Repair Institute.  

Concrete coating selection

Coatings over concrete surfaces serve several purposes. As the use of concrete in industrial and municipal settings has increased, coating formulations and application systems have evolved to meet the protective and aesthetic needs in these varied environments, including:

  • To protect against deterioration from severe exposure related areas whether it be chemical, mechanical or both
  • To reduce the risk of cracking or chipping on high-traffic or impact surfaces
  • To protect against erosion of concrete due to wind- or water-driven abrasives
  • To enhance the aesthetics of indoor and outdoor facilities
  • To reflect light in indoor spaces to reduce use of electrical lighting

Many concrete coating types exist, but they’re generally broken down into thin- or thick-build formulations. Each comes with its own advantages and disadvantages.

Thin-build coatings typically achieve a dry film thickness (DFT) of 4 – 10 mils. These coatings are easier to apply than thick film coatings and are best suited for smooth, low-traffic or low-impact surfaces. However, their resistance to abrasive or mechanical stress is limited. And due to their limited film build, they reflect the surface profile of the concrete surface to which they’re applied. If aesthetics are a concern, thin-film coatings won’t do as good a job hiding surface imperfections as high-build coatings would. Depending on the formulation, thin-build coatings do provide some chemical and UV resistance. Examples of thin-build coatings include epoxies, coal tar epoxies and polyurethanes.

Thick-build coatings range in DFT from around 10 – 40 mils. These formulations are designed for service in areas with routine and severe abrasive, mechanical and chemical stress. They’re best applied to high-traffic or impact surfaces like factory floors or in immersion environments within wastewater treatment plants. However, these formulations are more expensive and can be harder to apply. Examples of thick-build coatings include polyureas, vinyl esters, and high-build epoxies.

Sealers are often used in light industrial applications or architectural applications in conjunction with the coating systems listed above. They’re designed to reduce or prevent permeability of concrete by penetrating its porous surface.

Overlays are used to repair concrete that’s been damaged or that has a rough surface profile not conducive to coating application. In some cases, they can be used alone and do not require a protective coating to be placed over them.

If you’re considering a protective coating for a concrete surface, consult coating manufacturers for more in-depth information about choosing and correctly applying the best coating for your site.