Contractors offering milling services can support their work with a report prepared for the Washington Dept. of Transportation that supports the use of pavement milling -- even without a tack coat -- as a pavement preservation technique. Reported in the Winter edition of Centerline published by the Asphalt Pavement Association of Oregon, milled pavement surfaces had a better bond than non-milled surfaces. The study also found that when milled pavement was overlayed without a tack coat the lack of tack did not adversely affect the bond between the layers. However, the same was not found for non-milled pavement. Pavement that was not milled prior to an overlay and that did not receive a tack coat exhibited decreased bond strength -- actually no bond at all. The impact is this: Milling, with or without a tack coat, is an effective way to place a pavement overlay. If you're not milling the surface then a tack coat is essential.