Question: We recently rehabilitated a 75-year-old concrete floor in a dock area. The owner wanted to improve sanitation by eliminating the concrete surface porosity and create an easy-clean, slip-resistant surface.
First, we scarified and rebuilt the floor surface using a polyurethane-concrete slurry with a broadcast aggregate (#30 mesh quartz) to create a lightly textured or slip-resistant surface. Then, we applied a 12-mil topcoat using a two-component, 100% solids polyaspartic aliphatic polyurea floor coating. Downtime was critical, so we needed a fast-curing topcoat.
After we finished, the floor looked great and the owner was happy. But forklifts pushing wooden pallets across the floor caused scratching and gouging. Abrasion damage first appeared in the polyaspartic topcoat only on top of the broadcast aggregates that were used with the polyurethane-concrete, but the damage has become widespread. Gouges are up to 1/16-inch-deep in places.
Should we have used other materials or coating systems? Can this be repaired? What should we keep in mind for future projects?
Answer: Material options for rebuilding or resurfacing worn and damaged concrete floors primarily include epoxy- and polyurethane-concretes. For food-grade floor coatings, popular options include epoxies, polyurethanes (urethanes), and polyaspartic aliphatic polyureas (polyaspartics).
Polyaspartic Floor Coatings
Polyaspartic floor coatings have become more popular because of their unique material properties that include:
- Rapid curing from five to 120 minutes, depending on formulation;
- Application substrate temperatures from -30° F to 140° F;
- Very low viscosity (similar to water) creating excellent wetting and adhesion properties;
- High film build (up to 18 mils in one coat);
- Bubble-free surface even when applied during periods of high humidity;
- Little or no volatile organic compounds (VOCs) during application due to high solid contents;
- UV stable (never turns yellow);
- Cured coating can withstand high temperatures up to 350° F;
- Crystal clear coating (will not blush white from moisture in the concrete);
- Stain resistance, especially from oils and fats;
- High abrasion resistance (higher than epoxies and urethanes)
A polyaspartic coating was the best choice for your project because of rapid curing and high abrasion resistance. Using an epoxy or urethane coating would require a two- to eight-day cure period; a polyaspartic can be applied and cured within one day. Although polyaspartic coatings are more abrasion-resistant than epoxies or urethanes, they are still a coating. All coatings are susceptible to abrasive damage such as cuts, scratches, and gouges.
Here is one manufacturer’s warning about scratching and gouging of its polyaspartic floor coating:
CAUTION: Heavy objects dragged across the surface will scratch all floor coatings. Avoid gouging and scratching the surface. Pointed items or heavy items dropped on the floor may cause chipping or concrete pop out damage.
Because the urethane-concrete included a broadcast aggregate, it is not surprising abrasion damage started on top of the aggregate particles. Contact pressure from pushing and sliding pallets across the surface would be much higher on top of the broadcast particles. With continued exposure to sliding pallets with exposed nails, etc., abrasion damage of the polyaspartic coating is inevitable and should be expected.
Damaged polyaspartic coatings can be repaired by smoothing, roughening, and applying another coat of polyaspartic. Contact the manufacturer regarding surface preparation and application recommendations. However, if the floor’s exposure conditions do not improve, the abrasion damage will reoccur.
For future projects, discuss with the owner both the advantages and limitations of the floor coating systems being considered. Before selecting the system and materials, observe the facility’s operations. Work with the owner to develop a floor use and maintenance plan that takes everything into consideration.
The owner’s expectations for both appearance and performance of a new floor surface must be realistic. This is the key to creating a happy owner and future customer.
Kim Basham, PhD, PE, is president of KBE Engineering and specializes in concrete construction, troubleshooting, nondestructive testing, forensics, and repair. Email [email protected]