What is a Tack Coat?
Sometimes erroneously called a prime coat, a tack coat only ensures a good bond on the next layer. Tack is an adhesive term that relates to a sort of stickiness. In the AEMA emulsion guidelines, it is defined as “a spray application of asphalt emulsion applied to an existing asphaltic Portland cement concrete pavement prior to a new asphalt overlay, or patching to eliminate slippage planes and provide a bond between new and existing pavement layers”. The residual binder is the key to the overall tack coat performance.
SS1, which is a Slow Set asphalt cutback, is the product of choice for Ontario. Call A & A Asphalt to find out more.
How Does a Tack Coat Work?
A tack coat is a very thin surface, which is sprayed using a tack coater spray system. It should be an even coat over the entire substrate to be overlaid. The hot mixture placed on top should soften the tack coat layer, allowing it to partially fill surface voids in the hot mix and become partially interlocked with the hot mix layer.
If used before a microsurfacing, the tack coat will not be softened, but the emulsion from the microsurfacing will wet the tack coat and create an asphalt/asphalt bond.
Films of asphalt have a stability based on their cohesion versus the thickness of the layer. To act as a good tack coat, the layer must not shear sideways under traffic.
Our trucks have onboard burners that heat the tack up to 150 degrees Fahrenheit for a smooth application. All of our trucks have a computerized metering system we can adjust the flow rate for various MTO or county requirements.