Which statement about tack coat and surface preparation is described for thin lift application?

• A. Tack coat is optional if surface is clean.
• B. Tack coat is the most important element, but cleaning is not necessary.
• C. Proper tack coat is vital for bonding.
• D. Tack coat can be skipped if the mix temperature is high.

Answer: (C)

Bond between the old surface and the new thin lift is what holds the pavement together. A proper tack coat provides a thin, adhesive film that promotes bonding so the new asphalt can stick to the prepared surface. This is especially important for thin lifts because there isn’t much material to create a strong interlock on its own, so a good tack coat becomes the key to preventing delamination, stripping, or raveling under traffic.

To make that bond reliable, surface preparation must ensure the substrate is clean and dry, free of dust, loose asphalt, oil, or moisture. Cleaning removes anything that could block adhesion, and drying ensures the tack coat can wet and adhere properly. Apply the tack coat uniformly at the specified rate and allow it to cure to the tacky state before placing the thin lift, so the new mix can bond instead of sliding on a dusty or dry surface. If the tack coat is skipped or poorly applied, the thin overlay is much more prone to separation, even if the mix temperature is high.

The statement is correct because bonding is the central role of the tack coat in this context, whereas simply having a clean surface or relying on mix temperature does not substitute for the adhesive film the tack coat provides.