Which statement is true about tack coats?

• A. They replace surface preparation
• B. They are applied to a surface that has been cleaned
• C. They are applied after final compaction
• D. They are optional on all projects

Answer: (B)

Bond between layers matters. A tack coat acts as a bonding agent—a thin layer of asphalt emulsion sprayed on the prepared surface to help the new asphalt adhere to the base. Its effectiveness depends on the surface being clean and dry, free of dust, debris, and oils. If the surface is dirty, the emulsion won’t stick well, compromising the bond and potentially leading to premature failure. The tack coat is placed before the new asphalt is laid and before final compaction; it is not a substitute for proper surface preparation, and it isn’t applied after compaction. Tack coats are typically required by contract specs on many projects to ensure adequate adhesion, rather than being optional.