August 31, 2009

Concrete Matters #2 in a series: Surface Preparation

by Kevin Morris

Concrete surface preparation is dynamic to say the least. You will need to consider several factors when selecting the method of surface preparation and the required end result. These factors could include multiple steps to achieve a satisfactory surface for proper coating performance.

The first consideration should be as to the age, previous use, and proposed use of the substrate to be coated. Old substrates, even in non-chemical or non-abrasion environments, are still corroding due to the naturally occurring CO2 in the environment. If the substrate has been exposed to a chemical environment, then the deterioration and/or contamination could be greater. The depth of contamination is something that cannot be determined with the naked eye and should be sent to a qualified laboratory to determine.

With these results in hand one can establish the depth of removal that must take place with the existing substrate for proper coating adhesion and performance. Depending on the proposed use of the substrate, it can make a difference in the surface preparation and/or finish. Contamination of oil and grease can leave contaminants that may interfere with proper coating adhesion and require the use of an industrial strength cleaner degreaser to emulsify these contaminants and prevent pounding them further into the substrate. However, it may be acceptable to an owner to see stains in a polished substrate, eliminating the need to remove this contamination and therefore providing the most cost effective surface treatment.

Areas of severe deterioration may require that the surface be built back to its original surface plane or at least one that is level.  This type of repair should be greater in profile than a surface specified to receive a thin film coating system. SSPC offers a standard for the surface preparation of concrete in SSPC SP-13. This standard should be used jointly with the International Concrete Repair Institute’s (ICRI) Technical Guideline No.03372, “Selecting and Specifying Concrete Surface Preparation for Sealers, Coatings, and Polymer Overlays”. This ICRI guide utilizes concrete surface profile numbers 1-9.

CSP Standards-3

  • CSP 1 – Sealers and Thin Film Coatings
  • CSP 2 – Sealers and Thin Film Coatings
  • CSP 3 – Sealers, Thin Film Coatings and High Build Coatings
  • CSP 4 – High Build Coatings and Self-leveling Coatings
  • CSP 5 – High Build Coatings, Self-Leveling Coatings and Polymer Overlays
  • CSP 6 – Self-Leveling Coatings and Polymer Overlays
  • CSP 7-9 – Polymer Overlays

Concrete surface preparation can contribute to long-term performance of a coating system and will provide adequate profile for mechanical adhesion. Depending on the method of preparation selected, you may exhibit a phenomenon known as “bruising”. Extreme methods of surface preparation such as scarifying, scabbing, or flame blasting can create these bruising issues that may not be evident until after coating application and cure. Curing stress of the coating can reveal areas in the substrate that may have been weakened during the preparation phase of a project and create a premature failure due to substrate failure.

Shot BlastingAcid etching when performed properly will cost significantly more than some of the other techniques available in our market. These techniques provide some of the best production rates in the market today and can included dust collection systems to minimize the amount of clean-up after surface preparation. Shot blasting or portable centrifugal wheel blasting and diamond grinding are the best options for horizontal surfaces. Abrasive, open air, blasting and water blasting (consider pressure requirements) are the best options for vertical surfaces. These options provide the required surface profile without the risks associated with the more aggressive methods of surface preparation.

As with steel substrates the profile required for proper mechanical profile will vary from applied system and manufacture. The manufacturer should always be consulted for surface profile recommendations.

Next up in the series – Concrete Repairs

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