15 March 2001
should be set at the proper angle (Figure 4.1.). The use of RC-70 or other cutbacks as a prime
coat must comply with local environmental regulations.
4.4. Tack Coat. The tack coat is applied to an existing pavement surface before it is overlaid
with a new ACC pavement. The tack provides a bond between the old and new pavement.
Materials which can be used for tack coats are listed as follows: cutback grades RC-70, RC-250;
emulsion grades RS-1, MS-1, SS-1, SS-1h, CSS-1, CSS-1h; or asphalt cement grades AC-2.5,
AC-5, AC-10, AR-1000, AR-2000, or AR-4000.
4.5. Procedural Steps (Tack Coat). The following steps should be conducted to apply a tack
4.5.1. Prepare the surface. The surface must be clean and dry; and free of dust, loose dirt, and
all other objectionable debris. The surface around and inside the patch should be cleaned with
brooms, air, and water.
4.5.2. Apply the tack. Tack coats for large areas require the use of a distributor. A handwand
can be used for patches and hard-to-apply areas. If a wand is not available, the tack can be
applied to patch edges with a stiff brush. The tack coat should be applied in an even and uniform
coat over the entire area. If the surface should appear that there is not enough tack -- it should
be remembered that too little tack is better than too much. No more tack material should be
applied than can be covered by the end of a working day. Application rates for tack coats range
from 0.05 to 0.15 gallons per square yard (0.23 to 0.68 liters per square meter).
4.5.3. Allow tack to cure. The tack coat shall be allowed to cure before placing the overlay or
patch material. Cure times will vary according to the type tack material used.
4.6. Problem Areas (Tack Coat).
An over application
of tack will cause bleeding and slippage;
therefore, the proper application rate should be ensured. Application rates should be tested prior