Q: We work on many well-known entertainment properties with lots of vehicular and pedestrian traffic. On parking structure decks, we often find battery acid spots and stains from motor oil, antifreeze, and deicing salt. What should we keep in mind when preparing the surface before applying a thick-film elastomeric coating, such as polyurea or a hybrid polyurethane-polyurea? When we start spraying, what are the pitfalls we should avoid?
A: Performance of the coating is 80% dependent on surface preparation. If the coating doesn’t stick, it isn’t going to work.
Always start with a survey to assess surface contamination, looking for such things as oils, acids, salts, and other elements that will impair the coating. Based on the survey results, follow with the correct approach to preparing the surface.
Extract grease and oil first by using a good commercial-grade degreaser or a hydrocarbon dispersant. Make sure you research local environmental compliance requirements—some cleaners and waste byproducts can’t go down a wastewater drain. Full containment and offsite disposal may be required, which adds another level of complexity.
Next is chloride and sulfate removal. Again, consider local environmental regulations when choosing the product and process. Use a widely accepted, commercially available chloride/sulfate extraction product.
The purpose of proper surface preparation is to create a profile for a good mechanical bond for the spray-applied product. Shotblast the field area and use diamond grinders for edge detailing. Both of these are dustless processes using vacuum retrieval attachments. Strive to achieve a concrete surface profile of ICRI CSP3. (For an in-depth look at surface profiles, read Kenneth A. Hooker’s “Surface Preparation: Preparing Concrete for Coatings and Overlays,” available at http://go.hw.net/cs-surface-prep.)
Before spraying, replace or repair caulking sealants and repair damaged or spalled concrete surfaces that will receive new coatings. Cracks less than 1/8 inch get routed to a 1/2-inch V-groove. Fill the prepared cracks, expansion joints, and dissimilar transitions with a urethane sealant. This step is sometimes done after spraying if someone wants to exclude it from the warranty. Use caution here when working with inexperienced spec writers or owners.
Next, install the primer, usually a 100% solids epoxy at 5 to 8 mils, followed by broadcasting #20 aggregate into the wet epoxy. The aggregate also can extend the primer recoat window, making the working time easier for the crew.
Bag off and mask the area as needed to protect against overspray. Make sure all of the fixtures and vertical surfaces are covered. In some cases, this might include using wiretape where a clean-trimmed edge is desired.
When spraying, work with the owner and manufacturer to define the end result, making sure the correct product is selected and applied based on the warranty required by the owner.
There are three major challenges when spraying. The first is overspray. This is all about common sense. Pay attention to what’s around you and how the wind is blowing. Skip this step and you can have a lot of unhappy vehicle owners.
Next are pinholes that can transfer through the base coating during the first two minutes of spraying. If this happens, stop spraying and prime again. A solution to outgassing, which directly relates to pinholes, is to apply the primer in the late afternoon when the concrete is cooling off. This creates a vacuum effect, which will pull the primer into the concrete surface pores and imperfections.
The last problem—spraying off-ratio—can create a big mess. If the equipment operator monitors carefully, he will know right away that there is a problem. Some of the newer equipment reduces the chance of these issues by incorporating data recorders and alarms that monitor heat and pressure ratios; some will shut the pump down if set that way. The fix for spraying material off-ratio can be hours of tough cleanup. Pay attention, and you will dodge that bullet.
Finally, avoid problems with plural component spray through preparation and training. Train your teams to recognize problems in their early stages. Replacing a 50-cent O-ring is much easier than tearing out and replacing 3000 square feet of bad coating.
Contributed by Don Dancey (firstname.lastname@example.org), president of Innovative Painting & Waterproofing Inc. in Brea, Calif. He is a past president of the Polyurea Development Association (PDA) and has been applying plural component coatings on jobs large and small for more than 25 years. Visit the PDA at www.pda-online.org.