Q.: We plan to apply a coating to an industrial floor that contains fiber reinforcement. We acid etched the floor, but after the treatment was completed, fibers were sticking out of the surface. Before we apply the coating, how can we remove the fibers so they do not protrude from the floor?

A.: When fibers are used in concrete, they should be equally distributed throughout the concrete matrix or paste. Since finishing brings paste to the surface, it should be expected that fibers will be embedded close to the surface. Before coatings are applied, floor surfaces are usually shotblasted and sometimes acid etched to improve coating bond. Acid etching, however, can expose some of the fibers. The Synthetic Fiber Association and many fiber manufacturers recommend shotblasting rather than acid etching because of the safety hazards associated with using acid.

Fiber manufacturers say protruding fibers can improve coating bond through the mechanical interlocking of the coating to the concrete. However, the fibers may be visible through some coatings. If this is objectionable, you can remove the fibers by burning them with a torch before applying the coating. If the use of an open flame is not allowed, you can also remove the fibers with a high-pressure water stream or by shotblasting. Initial surface preparation by shotblasting instead of acid etching can save you from having to do this additional work.