Also, if the driveway does need sealcoating you must be willing to tell the homeowner to wait a few years. Sometimes this question is answered by the economical and competitive environment. However, most have painted walls and you realize that one usually does not cover fully cover the walls and two coats are needed. Two coats are what I will always recommend anytime except in the low traffic areas as mentioned in the last question. Two coats cover better and the job will last a reasonable amount of time before wearing is observed.
Additives are good tools used to modify the sealer for specialized applications.
They can build viscosity of the coating in order to hold higher sand loads, they can quicken the drying times of the coating, and they can lengthen the life of the coating by improving the tensile strength and the flexibility of the coating. However, many of the good qualities of the additive are offset if a contractor adds more water than recommended. The strength of the coating will always come from the coal tar or asphalt. Adding more water than recommended results in a thinner coating and less coal tar on the asphalt. Also testing shows that post adding latex is not as advantageous as the manufacturer incorporating the latex additive in the manufacturing process.