Painting Exterior Concrete

Painting Exterior Concrete
  1. Concrete is a surface that presents a number of challenges to paint in terms of adhesion and long-term durability, especially on horizontal concrete walking surfaces.
  2. Test the concrete for porosity and moisture content. Smooth concrete with little or no porosity will not have sufficient texture for paint to gain strong adhesion.
  3. Check porosity by sprinkling a little water on the surface. If it soaks in readily, paint will likely adhere to the surface after the necessary prep work is performed. Note: Some concrete, especially in garages, is pre-finished with a glossy coating to make the surface more resistant to moisture penetration and stains. This may greatly inhibit paint adhesion if it cannot be removed.
  4. Concrete with excessive moisture will soon work to destroy the adhesion of any paint applied to it, so tape (duct tape works well) an 18-inch square piece of aluminum foil to the concrete surface and allow to remain for at least 24 hours. Remove the foil and look for condensation moisture on the side facing the concrete. If the foil is more or less dry, proceed with surface preparation and painting. If there is excessive moisture, the concrete surface is not a good candidate for painting.
  5. Any bare or previously uncoated concrete should be etched. Etching imparts some roughness and porosity to bare concrete by using a muriatic acid solution or similar product. When etching, it is extremely important to follow all label instructions regarding product usage.
  6. After etching the surface, it is very important to clean the surface of any etching residue, such as released sand or lime. Rinse the surface until rubbing the fingers over the dried surface yields no chalky powder.
  7. Apply a coat of latex or oil-based paint formulated especially for walking surfaces. Be sure to comply with all label directions regarding surface preparation and application.
  8. Note on Alkalinity: One of the ingredients in concrete is lime, which is very alkaline in nature. Alkalinity can destroy paint adhesion, so it is recommended that all newly poured concrete be cured or be exposed for a minimum of 90 days before painting.

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