Regarding the prime coat and tack coat, it can be mentioned that those who have even a passing knowledge with the road and road building sector have likely come across a variety of phrases and terminologies, some of which include chip seal, tack coat, prime coat, and seal coat, among others. The industry of road building has achieved considerable advancements in recent decades, and as a result of the development of technology and contemporary science, a variety of materials are used in this sector. It is common knowledge that bitumen is one of the most important materials used in the building of roads. In today’s world, there is a wide variety of bitumen that can be purchased, and each of the aforementioned phrases is directly connected to bitumen. The following article will provide a comprehensive analysis of the tack coat, the prime coat, and the distinctions between the two.
Text related to prime coat and tack coat

What is Prime Coat?

Prime coat (Primcoat) is essentially the process of spreading a layer of bitumen or gilsonite with a low viscosity of MC or SC type on the base layer. This is done in order to allow the bitumen or gilsonite to penetrate the pores of the base layer. The asphalt layer is then coated and adhered to the base layer in an amount of 1 to 2 kg per square meter. Prime coat bitumen helps the asphalt layer adhere to the road body in addition to consolidating the surface of sandy roads. The prime coat needs to be applied to the road surface twenty-four hours before the application of asphalt, and the machine ought to spread it out over the road surface uniformly while maintaining a certain temperature. The minimal quantity of bitumen that is ideal for a sandy surface of a road that has little porosity is equivalent to 0.8 kg per square meter. On the other hand, this amount will be equal to 2 kilogram per square meter for roads that have coarse-grained surfaces and a lot of pores.

As was previously said, there are many prime coat bitumen varieties, and the application of each of these varieties is determined by the ambient temperature. It is common practice to use RC-70 bitumen when the temperature is below freezing, MC-70 bitumen when the temperature is between freezing and hot, and SC-70 bitumen when the temperature is above hot. Primecoat bitumen requires a minimum temperature of 70 degrees Celsius for RC bitumen and 110 degrees Celsius for SC bitumen. Its typical usage is 1.2 kilograms per square meter. It is not permitted to apply Prime Coat bitumen when the weather is wet and rainy, as well as when the weather is foggy, and the weather conditions must be appropriate for its application.

What is Tack Coat?

Tack Coat involves applying a very thin coating of diluted emulsion bitumen or RCO mixed bitumen, which will be placed on top of the older asphalt layer at a rate of 0.3 to 0.6 kilogram per square meter. This will be done in order to protect the surface from further damage. The application of this bitumen layer also has specific requirements, such as the road surface needing to be absolutely free of any moisture or debris. Additionally, just like the application of Prime Coat, the application of this bitumen layer cannot take place when the weather is cloudy, humid, or rainy. For this layer to be applied to the roadway in a uniform and consistent manner, the Tack Coat spreader must also be in excellent physical condition. During the time when Prime Coat and Tack Coat are being carried out, it is imperative that all vehicular traffic be stopped, and there should be no movement of any kind on the road at any given time.

prime coat and tack coat in pavement layers figure

Related Article: road construction

The differences between Tack Coat and Prime Coat

Tack Coat and Prime Coat are used in order to both fill the voids and cover the asphalt surface, as was previously discussed. Spreading a layer of low or medium-hardness liquid bitumen over the sandy surface of the road is referred to as Prime Coating. Spreading a layer of asphalt or concrete on the surface of the road is referred to as Surface Coating or Tack Coating.

Emulsion bitumen CRS-1 and CRS-2 are the best bitumens that can be used as Tack Coat bitumen because they have a high breaking speed of the emulsion and will be available for implementation rapidly.

To apply Prime Coat, a variety of bitumens can be utilized under certain circumstances. In colder climates, RC-70 bitumen is utilized, MC-70 bitumen is used in moderate climates, and SC-70 bitumen is used in warm climates.

It is a mistake to apply Prime Coat with emulsion bitumen on closed-grained and non-porous bases, and you should avoid doing so since the bitumen will not permeate the base layer as it should and will instead stay as a thin film on the base.

Primarily, the objective of using Prime Coat is to consolidate and increase the strength of the asphalt texture, while the purpose of using Tack Coat is to create adhesion with the final asphalt layer. Both of these coats are used in the process of paving a driveway or other surface.

Tack Coat is the second layer of asphalt that is put after Prime Coat. It is able to keep the road from becoming slippery, and in certain cases, it is also employed as a sealer and a protection for the asphalt against moisture and other elements.


The manufacturing of roads makes use of several different kinds of bitumen and emulsions; some of the more frequent ones are chip seal, tack coat, prime coat, and seal coat, amongst others. Every one of these bitumens can be used to a variety of different applications. The prime coat is a very thin coating of diluted bitumen that is applied to the top of the asphalt. Its purpose is to prevent the two layers of asphalt from crawling on top of each other. It is possible for the tack coat and the prime coat to be different in terms of the type of bitumen used, the method of application, the amount of time spent applying the bitumen to the road surface, etc.; however, it is possible to say that the purpose of utilizing both of these methods is to consolidate the asphalt on the road and to keep its structure intact.


Prepared by the PetroNaft Co. research team.


Leave a Reply

Your email address will not be published. Required fields are marked *