In the process employing a colloid mill, bitumen, water and emulsifier are emulsified at a high shear rate. The process is continuous, but to obtain an emulsion in which the mean diameter particle size of the bitumen is at an acceptable level, then for any given pump there is a limit on throughput in order that a sufficiently high shear rate is obtained.

Furthermore, the process is conducted at atmospheric pressure and in order for the emulsion product to emerge at a temperature of less than 100° C. then it is found in practice that bitumen cannot be fed into the emulsifier at more than 140° C. Higher temperatures for the bitumen feed require lower temperatures for the water feed.