Tack coats are thin layers of asphalt product that are used in the construction or refacing of roads and highways. This type of product is used to help the layers of asphalt laid down as part of the road building process to bond together with more efficiency. As a result, the highway or road is able to hold up under constant use for longer periods of time, making it easier to maintain the road properly.
Also known as bitumen, the tack coat itself is composed of asphalt by-products. The bitumen is sticky, an attribute that makes it ideal for use as an adhesive between layers of asphalt. Without the presence of this coat, a new layer of asphalt laid upon an existing road would deteriorate much more quickly, often creating potholes and various conditions that decrease the safety of the road.
In order to achieve the highest degree of efficiency with a tack coat, it is important to prepare the section of road properly. This means that the layer of asphalt that is already present should be dry and relatively free of dirt and other contaminants. This will help to make it easier to apply a uniform layer of the product and help the tack coat provide a greater bond with the asphalt that is applied over the adhesive.
Along with making sure the road is clean and dry, it is also necessary to address issues such as existing cracks and potholes. By filling in these defects in the road surface, the process of applying a uniform tack coat is made much easier. Some road builders even use a small amount of bitumen in the cracks and potholes before filling them with new asphalt, thus helping the plugs to bond more effectively with the bottom layer of asphalt.
The rate or pace of application is also important to the success of a tack coat. In order to achieve the desired uniformity to the coating, it is necessary to apply the bitumen at a consistent pace that ensures enough of the bonding agent is deposited, but not so slow that some areas receive more of the coat than others. Uneven distribution will often undermine the bond between the top and bottom layers of asphalt, causing the roadway to deteriorate much faster than normal.
Once the tack coat is in position, the top layer of asphalt must also be applied with care. Making sure the layer is applied evenly to the tack coat helps to increase the chances of a solid bond, effectively creating a solid road area that can hold up to heavy vehicles with relative ease. Applying the top layer of asphalt properly also helps minimize the chances of the development of more cracks and potholes, since the underlying bitumen is holding the asphalt in position, and not allowing the top layer to shift.