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Credit: Tnemec Co. Inc.

The weak laitance layer—typical of acrylic modified, portland-based, and calcium aluminate-based cementitious resurfacers—should be removed prior to topcoating with high performance coatings.

Fortifying resurfacing products with acrylic polymer also increases the material's physical properties, such as improving adhesion to the underlying substrate, increasing tensile and flexural properties, and improving overall durability. However, because these resurfacers are fundamentally hydrolyzed cement, a laitance layer can still form and should then be removed before coating application.

Although cementitious resurfacing products modified with epoxy polymer are similar to other materials used to repair concrete substrates, they are unique in that the epoxy chemically co-reacts in an exothermic reaction rather than relying solely on the hydrolysis of the cement particles. This chemical co-reaction greatly improves physical properties. Consequently, the laitance layer that otherwise forms through the troweling action now is reacted with an epoxy polymer and provides sufficient tensile properties for adhesion of subsequent coating applications. It also allows for lower material thickness—down to 1/16 inch—and obviates the need for wet or membrane curing.

MANUFACTURER REQUIREMENTS

Although contractors may be tempted to lower the cost of resurfacing and coating concrete by avoiding steps required by the material manufacturer, doing so is usually a mistake. Instead, owners and engineers should enforce the manufacturer's recommendations helps to ensure a monolithic, pinhole-free coating that best protects the underlying substrate and extends the service life of the entire structure.

Key considerations when resurfacing damaged or degraded concrete include:

  • What are the coating manufacturer's requirements regarding existing substrate surface preparation?
  • What is a resurfacing material's required minimum thickness?
  • How long must the resurfacer be hydrated to achieve proper cure?
  • What is the cost to remove the laitance layer and membrane curing compound by abrasive blast or high-pressure water cleaning before coating?
  • What are the coating manufacturer's requirements regarding substrate and surface preparation?
  • The best time to avoid problems is before the work begins. Specifications should identify compatible resurfacing and coating materials and contain a material manufacturer's requirements for preparing surfaces and materials. Examine bids closely to ensure they include the necessary procedures contained in the specification. Although the finished coating may be the focus of a project, attention paid to resurfacing the substrate will ensure the longest possible life for a structure.

    — Vaughn O'Dea is a wastewater specialist with Tnemec Co. Inc., Kansas City, Mo.